Austin Healey 100 Crank Failures.

“Cumulative Fatigue Failure for Dummies”

I broke a crankshaft while racing my 100S and that experience always haunted me because original 100S engine blocks are extremely rare and I knew that I had been very lucky not to have destroyed mine with that “blow up”.

Over the years I had encountered many cases of 100 crankshaft failures and it was the fear of another in the “S” that caused me to study the issue. The conclusions arrived at and described below prompted me to build a very special competition engine for the car which you can read about here.



The Austin Healey 100 engine was actually developed from a 1929 Chevrolet design and several aspects of the design contribute to the crankshaft failure problem, these include:

  1. The engine size which at 2660 c.c., is around the upper limit of what is optimal in an automotive 4 cylinder unit.
  2. The relatively spindly forged steel crankshaft which has no “pin overlap” and is only supported in 3 main bearings
  3. The extremely big and heavy flywheel necessitated by the engine design.

To understand why these 3 aspects of the design are major issues it is first important to understand some less than common engineering terms and concepts.


Referred to in this article as CRSO simply refers to the changes in the speed of rotation of the crankshaft that occur during each revolution.

The real cause of CRSO is not, as one might initially conclude, the firing pulses of the engine, but more a function of the kinetic energy of the reciprocating parts of the engine, i.e. the pistons and connecting rods.

As the engine runs the mass of each piston and wrist pin and a portion of that of the connecting rod is accelerated to a substantial velocity then decelerated back to stationary twice a revolution. The forces required to do all this work are applied directly to the crankshaft and they result in significant changes in its speed of rotation during each rotation. CRSO is particularly exaggerated in four cylinder engines because those forces, which are proportional to the square of the engine’s RPM, occur at all four crank throws at the same time.


Interestingly the largest force from the “power stroke” of each cylinder occurs exactly whilst the crankshaft is attempting to accelerate the reciprocating parts so actually serves to decrease CRSO but that combustion force is pretty small when compared to the peak torque of around 2400 lb ft that CRSO produces.



One way to think of torsional vibration is to consider a long spring steel rod supported in bearings with one end rigidly fixed and a weight on the other. Turning the weight a little, i.e. twisting the rod, and releasing it will cause the weight to oscillate back and forth under the influence of the spring action of the rod much like the escapement in a clock.

This oscillation will have a set “frequency” regardless of its amplitude (size), or for that matter the speed of rotation of the assembly, and is termed the critical frequency of the assembly.

A very small force applied regularly and in phase with those oscillations can rapidly increase the amplitude of the oscillation much like a series of small pushes on a child’s swing, keep doing it long enough and junior will either fly off into space or wrap round the top bar!!.

In the case of a crankshaft the flywheel acts somewhat like the fixed end of the rod and the CRSO somewhat like the small applied force.

Testing by The University of Southampton’s Institute of Sound and Vibration Research has shown that the 100 crankshaft is very susceptible to torsional vibration particularly over 4500 R.P.M which is not at all surprising considering its “spindly” design.



Fatigue failure is defined as “The tendency of a material to fracture by means of progressive brittle cracking under repeated alternating or cyclic stresses of an intensity considerably below the normal yield strength of the material and is a function of the magnitude of the fluctuating stress.” You may be able to tell that I didn’t write that mouthful!!


Engine designers use flywheels to dampen CRSO and make their designs run more smoothly, particularly at lower speeds. By dampening the CRSO the flywheel also serves to protect the transmission. The flywheel cannot totally remove the crankshaft’s speed oscillations and the elimination of most the remaining is achieved by installing torsional coil springs into the clutch disc.


Unfortunately the problem with using a heavy flywheel, like that in the 100 engine, is that the crankshaft must absorb the oscillations by “flexing” or twisting somewhere near the flywheel causing torsional vibration which in turn produces metal fatigue and ultimately fatigue failure of the crankshaft usually somewhere around the #4 throw. (Refer to pic above…..nasty!).


As mentioned above the forces that generate the CRSO increase dramatically with R.P.M. and metal fatigue increases as a function of the magnitude and duration of this fluctuating stress.

All crankshafts have a critical frequency but in general terms with “spindly” crankshafts the critical frequency is lower, at a guess, probably somewhere around 160Hz in the case of the 100 engine.

This is all very bad news for those of us who like to drive our sports cars the way that they were intended to be driven.


I think the reality is that if you have an Austin Healey 100 with an original equipment crankshaft and flywheel, which you drive it at all spiritedly, sooner or later the crankshaft is going to break somewhere around the rear cylinder.  You can take some solace in the fact that usually such a break does not completely destroy the engine but you certainly are not going to be able to gently drive the car home!!!


In no particular order here are some measures that may be considered.

Limit Maximum R.P.M.

Probably the best option, particularly as the 100 engine is a real torque producer and even with an “M” cam will pull strongly from under 1500 R.P.M. however, with a standard diff ratio and 28% overdrive, the engine is usually running between 3000 and 3500 R.P.M at highway speeds which is not good. Changing to a 3.66/1 (spiral bevel) or 3.54/1 (hypoid) differential ratio certainly helps keep engine speeds down as would the very rare 32% overdrive however, eventually the crankshaft will probably exceed its so called “fatigue life” and break.

Replacement Crankshaft.

The first things that most people consider when they have a broken crank is where can I get a stronger replacement and what will it cost?

There are lots of folks out there flogging “steel” or “competition” cranks but there isn’t a lot of information about what these cranks actually are. The debates about the merits of the various manufacturing methods rage on but there is no question that the material used is very important. Top of the line cranks these days are made from EN40B chromium molybdenum or 4340 nickel, chromium, molybdenum or some similar alloy steel so if you could acquire a good quality forged or billet crank made from that it would probably last a long time. Unfortunately just replacing the crank with one of similar dimensions will not do much to minimize the affects CRSO or change the critical frequency because those properties are inherent in the engine and crankshaft design.

Nitriding or “Tuftriding” the Crankshaft.

Nitriding is a process which does not modify the properties of the base material from which the crankshaft is manufactured but it does produce a very hard and durable surface some few thousandths of an inch thick. Whether or not nitriding increases the fatigue life of a crankshaft is however not a “slam-dunk” and is very dependent upon the parent material and the process used. Nitriding however requires that the parent material contains some aluminum, chromium, molybdenum or titanium which apparently a standard 100 crank does not. The original 100S crankshaft was made from EN40B alloy steel which is very strong and ideal for nitriding.

Tuftriding produces a much thinner hardened surface but does not require the specialized parent material.

Lightened Flywheel.

This option will almost certainly decrease the magnitude of the torsional vibration and increase the life of your crankshaft BUT over time the rotational speed oscillations will probably be more than the clutch plate springs can withstand resulting in their failure and, furthermore, the elimination of flywheel inertia will result in the transmission being subject to potentially destructive vibrations. Let’s say that “the jury is still out” on that one.

Crankshaft Harmonic Damper

To quote Wikipedia “To minimize torsional vibration, a harmonic balancer is attached to the front part of the crankshaft. The damper is composed of two elements: a mass and an energy dissipating element. The mass resists the acceleration of the vibration and the energy dissipating (rubber/clutch/fluid) element absorbs the vibrations.”

The Austin Healey 100 engine was designed in the days before crankshaft dampers were in common use. The design of such dampers is a complex process as the damper’s natural frequency is critical and unique to the particular application. Installing a damper of the incorrect type can be worse than not having one at all. Before installing one I would want to be very sure that it was correctly designed specifically for the 100 engine. Additionally it should be borne in mind that a damper will do little if anything to minimize CRSO.

A good article on dampers can be found here.


Lightened Rods and Pistons.

Another expensive option which would almost certainly have definite but limited benefits.

Improved Crankshaft Design.

This is only an option for the “serious money” crowd. The much heavier and stronger EN40B nitrided crankshaft from an FX3 Austin Diesel taxi engine can be installed in the 100 block.


To accommodate the much heavier webs the center main bearing is narrower which necessitates some creative machining of the block and the addition of a substantial “strap” to reinforce the narrowed bearing cap. Custom connecting rods and different pistons are required to accommodate the 0.250” increase in the crank pin diameter and 3/8” shorter stroke of this crankshaft. Because of its increased mass a substantially lighter flywheel can be used. This radical modification addresses the inherent design issues with the 100 engine and has proven to produce the basis for a powerful and reliable engine however, the crankshafts are now very hard to find. A custom made billet crank of similar dimensions could be produced.

As they say……”Pick Your Poison”.





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New and Used British Sports Car Parts

Below are links to lists of new parts available for purchase:

I also have a large number of used parts:


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MG TD TF Cluster Gears $350.00 Exchange (Free Shipping)


In the early days of the last century one of the major considerations in British motor engineering design was to manufacture at MINIMUM COST and this principle was evident in almost everything that they produced.

One area where this was most notable was in the design of the 4 speed gearboxes fitted to almost every British car. In order to avoid the necessity of adding an extra set of gear teeth to the cluster gear (laygear) with the attendant requirements of additional overall length, extra gear cutting etc., etc. they universally selected not to make the 1st gear a “constant mesh” type but opted instead to use a straight cut (spur) gear so that that gear could also be used as part of the reverse gear train. The inevitable result was the dreaded “non-syncro” 1st gear.

rapierI have a Drivers Handbook for a Sunbeam Rapier MkII within which the writers refer to what is actually 1st gear as “emergency low gear”.

“The use of emergency low gear is recommended when starting on a hill or when the car is fully loaded. It is also desirable, during the running in period, to make full use of all four gears, to ensure that all new parts in the gearbox become bedded in as the process of running in proceeds. Thereafter, low gear may be used for moving off on level ground.

My bet is that when an owner showed up with a ruined gearbox during the warranty period the service manager could confidently point out this paragraph to deny coverage.

As a consequence of this economizing measure the vast majority of these early 4 speed gearboxes failed prematurely as a result of drivers “grinding” them into 1st gear while the car was still moving. When this was done the little chips of hardened steel knocked off the 1st and cluster gears eventually made their way into the roller bearings in the gearbox and destroyed the bearings and the shafts that they ran on.

The “sports car” gearboxes seemed to be more vulnerable to this than the more sedately driven family cars, probably as a consequence of the way they were driven, and this resulted in many premature gearbox failures.

While new replacement parts were available repairing this damage was a fairly straightforward gearbox rebuild but, when the supplies of new gears ran out, this became a serious problem as setting up to manufacture new gears, and in particular new cluster gears, was a very expensive process.

Fortunately some years ago a brilliant and unnamed individual came with the idea of just replacing the 1st gear on the cluster gear and we started purchasing these and installing them in customer’s gearboxes in the ‘90’s.

Of course there is always someone around who can produce a less expensive and lower quality part and after a few years we started to encounter problems with the new gears on the rebuilt cluster gears wearing prematurely.

Testing revealed that the replacement gears that had been failing prematurely were substantially softer than the other gears on the cluster or the original 1st gears so, after some research, we have developed a process that produces a re-manufactured cluster gear of superior quality using modern materials and a high speed welding process that avoids overheating the gear next to the weld.


Re-manufactured MG TD/TF Cluster Gear Available From Stock

I can now offer a limited number of these re-manufactured MG TD, TD MkII, TF and TF 1500 for  gears for sale:

Outright $US395.00

With a rebuildable core $US350.00 exchange.

Prices include shipping to  the US lower 48 or Canada.

Contact info above…..


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BN1 Gearbox Front Seal Replacement

BN1 gearboxes are somewhat renowned for their ability to leave pools of oil on the ground.  One of the most annoying of these leaks occurs when the car is parked facing downhill. This particular leak is inherent in the design.

bn1-gearboxThe BN1  Gearbox and Overdrive Unit

Rather than having a lip type seal this gearbox has a “scroll” seal between the input shaft and the housing. Scroll seals are actually a clearance seal in that there is a small gap between the shaft and the housing and, to prevent the oil from working its way through this gap, one surface, in this case that of the housing, has a thread cut into it which serves to “wind” the oil back into the gearbox.

Scroll seals actually work reasonably well in most situations but when the oil level in the case is higher than the seal and the shaft is not turning they don’t work at all!!!

The normal oil level in the BN1 gearbox is about 1 ½” below the bottom of the front shaft so as long as the car is parked on a relatively level surface all is well however, when the car is parked facing downhill, the oil level at the front of the box can rise sufficiently to submerge the area where the front shaft enters the box with the result that oil can easily leak through the scroll seal and either run down the input shaft and soak the clutch plate linings or just run out the bottom of the bellhousing.

When this gearbox was used in the vehicles for which it was originally designed it did not have an overdrive unit on the back of it. Adding the overdrive unit increased oil capacity and aggravated the “downhill facing” leakage issues.

I was asked to see if there was any way that I could correct this problem on the 100 that I’m presently restoring and after making some measurements determined that it was possible to modify the front seal housing of the gearbox to incorporate a lip seal.

The front housing is a die cast cover which integrates the scroll seal and locks the input front bearing in position.

The first job was to increase the inside diameter of the housing in the area where the scroll seal was originally located by 7/16”. To achieve this I had to figure out a way to center the hole in the face plate of my lathe. After experimenting with a dial gauge for way too long I decided to take a different approach.


Custom Machined Centering Arbor

I turned up an arbor that used the female #1 Morse taper of the headstock spindle as the center and extended forward at the inside diameter of the scroll seal.

centering-castingUsing Arbor to Position Housing

With the housing centered using the arbor it was possible to mark out the centers for 3 holes in the faceplate which were then drilled and tapped with ¼” UNF threads which in turn accommodated hex head screws that were used to secure the housing to the faceplate.

mounted-on-faceplate3 Hex Head Screws Used to Secure Housing to the Faceplate

Once the housing was accurately located on center this way I simply removed the faceplate, extracted the arbor then reinstalled the faceplate with the housing now accurately positioned for machining.

finished-to-size-and-faced-offThe Housing Accurately Machined to Size

The housing was carefully machined to the correct size for the seal and lightly faced off.seal-installedThe Selected Seal was Carefully Inserted

The selected seal was then pressed into place using Locktite to ensure that it stayed in position.

 installed-sealThe Modified Housing Reinstalled

Once the housing was reinstalled into the bellhousing the result looked just great.

I realize that this modification is probably beyond the abilities of the average home restoration so if anyone needs it done I would be happy to modify their gearbox’s front housing and install a seal using the setup I have built, just contact me.

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Tire Truing (A Home Solution)

  • After the concours inspections at Enclave 2015 in Gettysburg, PA I managed to catch the last few minutes of a tech session presented by Ken Beck of K & T Vintage Sports Cars of Allentown, PA  on the dreaded “Scuttle Shake” so common to Austin Healeys.
    The solution proposed in this presentation was to shave the tread of mounted tires to eliminate radial run out. It turns out that this procedure is very effective on our older wire wheels because they are inclined to be somewhat out of round.
    I have encountered scuttle shake many times in Healeys and had found that it was very pronounced on my 100 particularly when running the original “flat center” 48 spoke wire wheels. These wheels are correct for the very earliest of 100s but were replaced by a stronger version early in production.
    Service J

The change to stronger wheels is detailed in the above Service Journal.

When I checked the run out of my wheels I found that they were as much as 0.100″ out of round ….no wonder I had scuttle shake.

Having been unable to find anyone offering the service locally I looked into the idea of shipping my wheels and tires off to PA or NC to have them shaved and trued but the cost of doing that from Canada was more than the wheels were worth!!!

I got to thinking about how might I develop a home remedy for this problem and thought that I could probably achieve the same result with the equipment I have and a little “Kiwi Ingenuity”.


Here’s what I did  …   fortunately we don’t get a lot of OSHA inspections around here.

I have a newly sharpened 60 tooth carbide ripping blade in the saw and you will notice a short length of 2″ x 2″ lumber behind the tire that is forming a rigid strut between the saw bench and the rear axle housing. To avoid damaging the blade I had to be sure to dig all the little stones out of the tread before starting.

Four cuts were required to shave the entire surface of each tire and during each cut the blade was gradually raised, using the blade height adjustment of the table saw, until it was apparent that the blade was contacting the tire throughout its full rotation. The blade was positioned ahead of the wheel center with the wheel rotating in reverse to prevent the possibility of the blade “digging in”. This particular car has a limited slip differential so both wheels rotate in the same direction when they are in the air. Without a limited slip diff it would probably be necessary to lock the brake on the other rear wheel.

After the cutting was finished the surface of the tire tread was a little fuzzy but that loose rubber wore off entirely within a few miles of driving.

The end result was a total transformation. At 60 MPH, the speed where it was previously most pronounced, the car has no scuttle shake at all and that is on a set of wheels that have never been balanced!!!









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Lucas 17L Tar-Top Battery Solution

During the final weeks of the restoration of my early Austin Healey 100 it became apparent that acquisition of original style batteries was going to become a major problem.

The only “acceptable” batteries for a concours car are original “Lucas” 6 volt 17L “tar-top” batteries.

BN1 Batteries

BN1/2 Battery Installation

I had acquired a pair of originals with a view to having them rebuilt but, when I made inquiries about having this done, it quickly became obvious that this was just not going to happen as the only re-builders that I could find worked exclusively on large industrial batteries and had neither the parts nor any interest in tackling such a small job.

I had had a pair of reproductions on order for some months but calls to the supplier were not encouraging and the chances of getting them before Enclave 2015 were virtually nil!

I decided that an alternate plan was called for.

Ballistic in Mini

Ballistic in Mini Race Car

I had seen several track racing minis equipped with Ballistic Lithium Ferrous Phosphate batteries and, having had some experience with starting highly tuned competition engines, I felt sure that if one of these batteries could start a race mini it could probably start a Healey 100 engine with a compression ratio of only 7.5:1. When one of the mini racers mentioned that his Ballistic battery had provided good service for 3 seasons I was convinced.

The problem is of course that this modern battery really did not look much like the old “tar-top” Lucas relic from 1953!!

Ballistic EVO2 16 Cell

Ballistic EVO2 16 Cell

However, upon further investigation, it became apparent that the tiny size of these modern batteries meant that one with sufficient cranking capacity for a Healey would easily fit inside the case of the original Lucas battery.

Here is how it is done.

Of course to start you have to have a pair of original or reproduction tar-top batteries to modify.

First remove the fill caps and drain all the old electrolyte out of the original batteries. Be sure to use rubber gloves and wear goggles while working with the battery. Also see if you can safely recycle the acid and not run it down the drain. Do rinse the case over and over before you start cutting and pulling stuff out. You may also want to wear a mask as acid fumes are nasty. (Thanks Ira).

The next task is a bit brutal.

Battery Top Cut Off

Battery Top Cut Off

Using a large band saw or similar implement of destruction cut the tops off the original batteries. Cut straight across all the way just below the bottom of the hold down lugs then pull out all the lead plates and dispose of them safely.

Removal of Lead Plates

Removal of Lead Plates

The next task is to remove the 2 dividing partitions from the case of one of your 2 batteries. These need to be cut out right down until they are level with the grid in the bottom of the case. A multi-purpose oscillating tool works quite well for this but I’m sure there are plenty of other methods.

Partitions Removed

Partitions Removed

Note: With the second battery it is only necessary to cut some small “V”s out of the top of the partitions but we didn’t figure that out until all the work had been done to remove them entirely.

Battery Lid Guide

Battery Lid Guide

To ensure that the lid will index accurately when replaced on the case we installed some plastic guides on the underside of the lid.

Once this is done you will find that your new Ballistic EVO2 16 Cell battery will easily fit right inside the case.

Ballistic Battery in Lucas Case

Ballistic Battery in Lucas Case

I used some strips of Styrofoam insulation to “nest” the Ballistic battery and ensure that it wouldn’t rattle around inside the case.

The next task is to connect the Ballistic battery to the +ve and –ve posts molded into the lid of your original battery. These connections and the cables will have to carry the full load of the starter so they have to be fairly substantial.

Jumper Cables Connecting Ballistic Battery to Original Posts

Jumper Cables Connecting Ballistic Battery to Original Posts

I used sections of some old heavy duty booster cables to make up short jumpers for this. It was necessary to drill and tap the undersides of the posts to secure the terminals that I had soldered onto the ends of my jumpers. Be sure to make the jumpers long enough that you can attach the Ballistic battery terminals to them as you install the lid.

Drill and Tap The Undersides of Both Posts on Both Battery Lids

Drill and Tap The Undersides of Both Posts on Both Battery Lids

With the second battery it is only necessary to make up a jumper, again heavy duty, to link the +ve and -ve terminals. That is why some small “V”s in the partitions on the second battery are all that is required.

Jumper Connecting Posts Inside 2nd Battery

Jumper Connecting Posts Inside 2nd Battery Lid

It is not necessary to glue the top back in position as the as the original battery securing rods will hold it in place..


The Modified Battery is Indistinguishable from the Original

Now install the batteries into the car and you are almost finished.

Once Installed the now Acid Free Batteries Look Totally Authentic

Once Installed the now “Acid Free” Batteries Look Totally Authentic

One last thing and this is very important if you want your expensive lithium ferrous phosphate batteries to last a long long time.

The instructions that come with the Ballistic battery emphasize that over charging will permanently damage the battery so it is essential that you adjust the regulated output of your generator to ensure that the maximum voltage that it can produce is 13.6 volts.

I found this very simple to achieve and procedure is clearly explained in section O/13 of the Factory Workshop Manual. It is the regulator adjustment that needs to be adjusted as this is normally set to something around 15.5 volts for a lead/acid battery.

Use a digital voltmeter to get it right and make sure that you drive the car while checking the revised output voltage just to ensure that it is correct.

I would recommend leaving a note inside the cover of the regulator indicating that it will require readjustment if lead acid batteries are installed in the car at some later time because an output setting of 13.6 volts will decrease the storage capacity of such batteries.

A couple of other things that are important to remember are:

  1. Just like a lead acid battery your Ballistic battery will be permanently damaged if allowed to completely discharge so be sure to turn off your master switch when you are storing the car for more than a few days.
  2. A regular battery charger is capable of delivering more than 13.6 volts… Be sure to use one that will not overcharge your Ballistic battery
Posted in Healey Stuff, Restoration Techniques, The Restoration of Healey #174 | Tagged , | 4 Comments

Smiths and Jaegar Fuel Gauge Solution

This gallery contains 2 photos.

After having all the original Smith’s instruments in my latest Austin Healey restoration entirely rebuilt I was rather disappointed to discover that the fuel gauge reading was so erratic that it was difficult to know just how much fuel I … Continue reading

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Low Mileage Austin Healey 100. A Rare Opportunity to Look Back.

Recently Bob Yule of Autofarm Ltd was kind enough to allow me to take a close look at a very early 1954 Austin Healey 100, with only 5300 miles on it from new, that he had in his shop for service.

One does not often get the chance to examine such an original car close up so I am very grateful to Bob, Tom and the owner of the car for this opportunity.

Having just completed the restoration of my own BN1 I had a number of details that I was very keen to check and during the course of the inspection I photographed several interesting and little known details about these early cars.

The car in question is C. BN1L 151405 body number 1267 and the engine number is 1B205529.

Car LH front

The car’s original paint is a very unusual “Gunmetal Grey” colour. Records have been found for around 6 cars painted this colour at around the same time so it is thought that this was a “trial balloon” to see if it was a seller.

The interior is bright red (persimmon), which is also original.

Although the car is in outstanding condition for a 60 year old vehicle a couple of small “additions” have been made to the electrical system and unfortunately the engine and gearbox have at some stage been out and reputedly rebuilt. Whoever did the engine rebuild did a good job but some details of the re-installation have been done a little carelessly meaning that those areas affected by this work are somewhat suspect insofar as originality is concerned.

The following are some very interesting details that I noted on the car which were previously unknown to me although I’m sure some at least are well known to others.

 Generator terminal phenolic separator plate.

Plate on generator terminalsI suspect that the paint was applied after the engine rebuild. I believe that this was an original, but often discarded part, as it can be seen in the in Fig.8 on page O/7 of the factory workshop manual.

Small tag on wiring harness.

Wiring harness tag

Handbrake lever finish.

Handbrake plating and tunnel paint. Handbrake polish

Shift knob lock nut.

Shift knob lock nut

The vent duct material.

Good shot of the original fresh air ductingMost restorers use “Kopex” tubing in this location but that is definitely not what was used originally. I think it may also have been used in early Sprites. If anyone can tell me where to get some of this I would be very grateful.

Horn rim securing screws.

Horn screwsI had always thought that these screws were painted with the horn but on these horns they most definitely were not. What is strange is that overspray of the horn paint is often seen on the black spring disc under the sounding disc..

Low tension connection at distributor.

Distributor low tension leadOf note here is the unpainted engine number plate. I suspect that this is one of the things done incorrectly during the engine rebuild. It is pretty well confirmed that these were painted engine colour.

I should also mention that the rubber sleeve was used on most connectors on these early cars other than grounding points.

Notch in bottom on RH inner sill. (this one really surprised me)

Fender and inner sill knotch On the right side there is less than 4″ between the inner sill and the pedal shaft support bracket. On the left side there is 7″. There was no sign of this notch on body #174.

My guess is that someone didn’t check the build sheet and installed the pedal shaft on the wrong side on this car and, after the engine was installed, the only way to get it out and move it to the correct side was to cut this notch in the sill.

The bonnet latch parts appear to have been plated.

Bonnet catch striker pin and cap finish

Bonnet latch sliding plate finishI have pointed these finishes out because there are errors on this point in the 2015 Concours Guidelines

Fuel line in trunk painted black.

Fuel line in trunk

Seat runner reinforcement plates under floor.

Seat runner reinforcement plates

Tonneau cover and windshield spring parking posts on scuttle.

Scuttle posts left Scuttle posts rightI believe that the windshield springs are meant to be “parked” on the inner post. There was no reason to believe that these posts had ever been changed so I have no idea why they are different side to side. On later cars a “Lift The Dot” post was used for the springs but on earlier cars all 4 were Tenax posts.

Bumper splash pan securing screws.

Splash pan outer screwsBy installing these 10/32 screws with the nut forward only the head was visible inside the fender which looked tidier. This is common to all 100s other than on very early BN1’s where  self tapping screws were used here again with the head visible inside the fender.

 Harness clip secures cables at gearbox cover adaptor plate.Cable clip at tunnel adaptor plateAgain common to all 100s and sometimes hand painted black.

Poor panel alignment.

Door alignmentThe panel alignment is really quite poorly done with the crease line on the drivers door being almost 1/4″ above that of the fender.

Boot lid seal is installed in the shroud gutter not on the lid.

Lower right corner Lower right side Right side Top left side Top right side Upper left cornerThis is something that I have been pretty sure of for some time so it is nice to have it confirmed. With the aluminium boot lid it would have been very difficult to install the seal on the lid because of various obstructions. The seal itself appears to be very similar in section to that used on the steel lids but it has a strange “mesh” surface texture.

The parts book refers to this seal being 4 pieces but on this car it was definitely a single piece of foam rubber.

There are several other interesting details on this car that were new to me so more later.


Posted in Healey Concours Information, Healey Stuff, The Restoration of Healey #174 | 2 Comments

BN1 Gearbox. A Plethora of Threads

Back in the days when I was a really poor British sports car mechanic I managed to pick up a Suzuki LJ80V all-wheel drive van with a badly slipping clutch to use for winter transportation.

Suzuki LJ80V

Suzuki LJ80V

It was a horrible little thing but great in the snow and all I could afford at the time. Before I could use it I had to replace that clutch and in doing that job my opinion of Japanese design improved immeasurably. The only tool required to change the clutch, which required that a gearbox with a 4WD transfer case be removed, was one 13 millimeter wrench. ONE!!!



For a guy who was accustomed to using almost every tool in his 15 drawer tool cabinet and a few borrowed ones just to change a fan belt in an MGB this was a revelation and made me realize just how far the British motor industry had to go in 1953 when they started producing the Austin Healey 100.

From the manufacturers perspective such simplicity can produce extensive benefits because not only is the vehicle easier to construct and service but the parts inventory required both for construction and after sales service is dramatically reduced.


The Austin Healey 100

The Austin Healey 100

1952/3 must have been interesting and challenging times for the Austin engineers as the Longbridge factory was geared up to produce the new Austin Healey 100. Britain was desperate for overseas sales but their factories were old and funds for new machinery and imported materials were just not available.

Unfortunately as a result of the shortages the new car had to use an old power train. The engine, with two cylinders lopped off, was a copy of a pre-war six cylinder Bedford lorry power unit which had been adapted from a 1929 Chevrolet design. There was no time or money to “modernize” the engineering so it was still being produced with outdated British Standard threads, British Standard Fine (B.S.F) and British Standard Whitworth (B.S.W) at a time when all new designs were being produced using the modern SAE thread system of Unified National Fine (U.N.F) and Unified National Course (U.N.C.). This was not ideal situation but there really weren’t any viable alternatives.

However, if the engine was not exactly “start of the art”, the gearbox was even less suitable for the latest in sporty motoring vehicles. Adapted from a column change saloon car “cog box” it was never designed to handle even the modest 144 lbs. ft. of torque delivered by the lump ahead of it but, again, it was all that was available within the budget so it had to be used. I suspect another factor was that Len Lord the president of the newly formed British Motor Corporation had hundreds of them lying around as a result of the Austin Atlantic disaster.

The BN1 Gearbox

The BN1 Gearbox and Overdrive Unit

Studying the threads used in this gearbox gives us an idea of the lengths the engineers at Austin needed to go to in their efforts to get those Healeys out the door.

The starting point was a 4 speed box designed to be used in vehicles like the Austin 16, a staid family car with barely enough power to “pull the skin off a rice pudding” as my Dad used to put it. The first job was to come up with an inexpensive way to produce a floor shift as no self-respecting “sports car” could have anything resembling the “three on the tree” gear change that the gearbox was designed around. This was achieved with a nifty adaptation of the original gearbox side cover and the addition of an Austin Taxi “change speed control box body” upon which a gear lever could be pivoted.

The Change Speed Control Box Body

The Change Speed Control Box Body

Everything worked out just fine but the threads… oh my, the threads.

Change Speed Box Cover Stud

The interesting thing about this “change speed control box body” is that within the design of this small cast part 3 different threads were used and that is just the beginning!

Two Different Threads in Very Close Proximity

Two Different Threads in Very Close Proximity

It was found that because of the 4.125/1 Austin Healey differential ratio (another saloon car legacy) 1st gear in the four speed box was useless and reputedly produced “nothing but wheel spin with anything like a spirited take off.” (See note below). The solution was that the 1st gear in the box would need to be blanked off producing a three speed gearbox.

One can only imagine the wails of anguish from the marketing department as no sports car of the day could be sold with a three speed gearbox even if it was all synchromesh … an overdrive unit was required. Fortunately the Laycock-de Normanville unit selected was a modern design which used U.N.F. and U.N.C. threads.

Speedometer Pinion Bearing Locking Screw

Speedometer Pinion Bearing Locking Screw

This clever addition appeased the marketing department but really complicated the thread issue as it required an adaptor plate with BS threads on one side and SAE threads on the other; not a design achievement that any engineer could be very proud of.

Joseph Lucas’s Switch

As a further complication the overdrive unit required a plunger switch on the side of the gearbox to prevent the overdrive being engaged when the gearbox was in reverse as doing so would destroy the overdrive unit. Enter Joseph Lucas. Now Joe was a very traditional guy and, apparently, a big fan of BS threads which the Lucas Company stuck with right through into the 1970’s so the switch he supplied used yet another thread form namely British Association (B.A.).



So now we have five different threads in this unit; B.S.F., B.S.W., U.N.F., U.N.C., and B.A….but wait… there’s more! We have to consider the drain plug for the gearbox.

The Tapered B.S.P. Threaded Drain Plug

The Tapered B.S.P. Threaded Drain Plug

Rather than use a standard parallel thread screw with a soft washer under its head the gearbox incorporated yet another thread system British Standard Pipe (B.S.P), which is tapered, in order to stop the oil from leaking out and to save the cost of a sealing washer.

Surely at this stage the engineers must have been tearing their hair out; six different thread standards in one gearbox unit but we aren’t finished yet.


As a grand finale the box incorporated this 1 7/16” LEFT HAND THREADED nut with fourteen threads per inch to lock the front bearing of the gearbox onto its shaft. As far as I can figure there is no “standard” for this gem.

The Front Bearing Nut

The Front Bearing Nut

Seven different thread forms in one gearbox unit that’s quite an achievement. You can see why I was so impressed by the Suzuki.


I have a theory about why the 4.125/1 rear axle ratio was used in the 100.

Geoffrey Healey states in “The Healey Story” that ”Austin did not have a high* enough gear ratio for the A90 rear axle” but that is not strictly correct. The Austin Atlantic convertible used a much better 3.66/1 ratio which, incidentally, was even offered as an option on the 100 and a 2.92/1 and even a 2.69/1 ratio became available in the 100S and those cars used the same rear axle housing .

Conventional wisdom has it that the 1st gear in the BN1 gearbox was too low and produced excessive wheel spin but I think that is a marketing myth. Donald Healey in “My World of Cars” states “The only disappointing part of the A90 was its gearbox, which was not man enough for the job in a sports car”.

My bet is that it was discovered early on that the torque of the engine was just too much for the gearbox and “The New Austin Healey 100 with enough torque to rip the teeth right off its 1st gear” didn’t sound like a winning slogan. The decision was made to stick with the lower diff ratio, which meant that 2nd gear starts were satisfactory, and “block off” 1st gear in the interests of reliability. Unfortunately that limited the top speed to 90MPH at maximum RPM, a problem solved by fitting an overdrive unit.

* A “high ratio” differential has a low ratio number whereas a “low ratio” has a high rati0 number.

Posted in Healey Concours Information, Healey Stuff | 1 Comment

Laycock-de Normanville Overdrive Installation Tool

Many years ago I made up a little tool which has proved invaluable when attaching an “A” type Laycock-De Normanville overdrive unit to a gearbox.

For those not familiar with this operation a little explanation will help. If you have “been there, done that” skip this part down to the picture with the tape measure in it.

The rear shaft of the gearbox mated to these overdrive units has to be aligned with three individual splines while compressing an oil pump spring and 8 clutch springs as the two units are joined together.

One of the splines is located on the inside of the oil pump cam.

Oil Pump Cam With internal Spline

Oil Pump Cam With internal Spline

The other 2 sets of splines are away down in the middle of the overdrive unit, one in the clutch sliding member and the other in the unidirectional clutch.

8 Springs, 3 Splines, Big Problem

8 Springs, 3 Splines, Big Problem

As can be seen in the above picture when the pump cam is positioned on the pump plunger roller the plunger spring holds the cam out of alignment with the rest of the bore of the unit.

Conversely when the cam is fitted on the partially installed gearbox shaft the pump plunger roller protrudes below the cam and will not allow the cam to slip by into its correct position against the overdrive centre bushing.

The Pump Roller Blocks the Pump Cam

The Pump Roller Blocks the Pump Cam

The factory workshop manual for the Austin Healey 100 illustrates the “recommended” method of installing the overdrive. They suggest “placing the oil pump cam in position on top of the center bushing (as in the photo above) then carefully threading the mainshaft through the oil pump cam and into the center bushing.”

Try Holding a Gearbox at Arms Length Like This for a Few Minutes

Try Holding a Gearbox at Arms Length Like This for a Few Minutes

What they don’t mention is that the gearbox weighs in at some 25 kg so holding it with one hand as illustrated while attempting to align the various components with the other is just a little difficult.

They also add as a NOTE: ”the gearbox mainshaft should enter the overdrive easily provided that the lining up procedure previously described is carried out and the unit is not disturbed.”

Well, if I know of one sure way to become “disturbed”, it is to try to mate the gearbox to the overdrive the way that they describe!

This is where the little tool mentioned above can help you maintain your sanity.

The Tape Measure is For Scale. (In Case You Didn't Guess)

The Tape Measure is For Scale. (In Case You Didn’t Guess)

This very inexpensive “Special Tool” is made from a piece of coat hanger wire. After you find out how well it works you may want to get it chrome of even gold plated!

So…How does it work?

In the filter cavity of the overdrive unit there is a conveniently located hole.

Tool in Place Viewed From Below

Tool in Place Viewed From Below

The “Special Tool” is inserted through this hole and up the side of the pump plunger.

Tool in Place Before Installing Springs

When the pump plunger is pushed down against its spring the hooked end of the “Special Tool” engages into the plunger just below the roller and holds the plunger in the down position. It is easiest to install the “Special Tool” before placing the clutch springs in position.

The shape of the little hook on the top of the “Special Tool” is very important but not difficult to form.

Again..Pencil Tip is for Scale

Again..Pencil Tip is for Scale

Now when the cam is placed in its correct position there is plenty of clearance between the lower section of the cam and the plunger roller allowing the cam, while installed on the gearbox shaft, to pass into position against the overdrive centre bushing without contacting the pump roller.

No More Interference Problems

No More Interference Problems

Now the installation procedure is much easier.

Use a little heavy grease to hold the pump cam in place on the gearbox shaft with the high part of the cam uppermost.

Position the overdrive unit with the drive shaft flange on the ground.

If You Can't Find Anyone to old the Overdrive Bolting The Flange to a Piece of Wood Works.

If You Can’t Find Anyone to old the Overdrive Bolting The Flange to a Piece of Wood Works.

Use a dummy shaft to check the alignment of the internal splines and then ensure that all the clutch springs are correctly installed (short ones innermost).

Put the gearbox into 1st gear then carefully lower the gearbox down onto the overdrive unit. You may have to turn the gearbox input shaft to align the splines inside the overdrive. When the gap is down to about 1/2″ peer in using a flashlight to ensure that the clutch springs are all correctly positioned at the top.

The gearbox and overdrive should pull together easily.

Don’t forget to extract and save your “Special Tool”.

Posted in Restoration Techniques | 5 Comments