BJ8 Choke Woes

One of the problems I had with my MkIII (BJ8) was that the choke control kept coming loose in the dash. BJ8’s came through the shop on a fairly regular basis and at least half of those would arrive with the same problem. This fault did nothing to enhance the driver’s ability to adjust the engine’s fuel mixture requirements when the engine was cold and when they are correctly tuned BJ8s need a good choke to get them started in cold weather. Unfortunately this is not a repair to which the Workshop Manual devotes much space.

The choke control features a friction lock, the idea of which is that when a satisfactory setting is achieved the choke control can be held in position by merely rotating the handle a little to lock it. The locking mechanism, although very simple, is quite ingenious.
The choke control shaft has a groove along its length. The choke body has an axial hole up near the dashboard end and inside this hole resides a ball bearing. Over the outside of the hole and pressing the ball against the shaft of the control is a spring steel ring. The parts can be seen in this exploded view.

exploded-small.jpg

If the choke control is rotated relative to the body in either direction the ball rides out of the groove and is forced to move up the axial hole against the pressure of the spring ring.  This pressure creates friction between the shaft of the choke control and the body which locks the choke in position. Turn the control back so that the ball drops into the groove and the lock is released.
This is what the whole thing looks like when assembled.

close-up-small.jpg

Pretty tricky but, when used in a BJ8, there is a problem.
A nut and washer fit onto the thread on the body to secure the choke body into the veneered plywood dash. The plywood is clamped between the nut and the flange on the choke body. This arrangement works fine when first assembled but after a few of these knob rotating operations the nut has a tendency to work loose. When the body is not firmly secured into the dash it rotates readily in the dash rather than the control shaft rotating within the choke body and it becomes impossible to lock the choke.
Just to make the correction of this situation a little more difficult the back side of the dash is counterbored, probably so that a standard choke control could be used rather than having one with a longer body especially developed. This counterbore makes it impossible to fit a normal box spanner (wrench) onto the nut to rectify the aforementioned looseness. THIS IS QUICKLY BECOMING A VERY FRUSTRATING EXERCISE.
The only way I have been able to correct the problem is to start by disconnecting the choke cable from the splitter on the bulkhead.

splitter.JPG

Then I thread 5/8” spark plug socket over the cable and up to the dash where, using a spanner on the hex on the top of the plug socket, I can tighten the nut on the choke control again. To prevent the control coming loose again I then fit a 5/8” UNC Palnut.

palnut0051.jpg

These are stamped out of spring steel and they really serve to lock that sucker in there. I’M NOT GOING TO GO THROUGH THIS AGAIN.!!!!!
The most difficult part of the operation can be reinstalling the choke cable to the splitter. This is most easily achieved by removing the two 10/32 screws which secure the splitter to the bulkhead and then threading the cable end through the hole in the bulkhead and into position in the splitter before resecuring the splitter to the bulkhead.

Alan has commented that his original BJ8 choke control was of this type which has a round knob with picture somewhat like a fan on it:

 

choke-1.jpg

 

I was of the opinion that this is a later version of the locking choke mechanism but could be wrong. The one pictured is from of my 1970 UK Market MGBGT. The original BJ8 choke knob was round and fairly flat with a white circle close to the outside edge and the word “CHOKE” across the center.

A couple of point that I have remembered about this operation which may be of help to anyone working on the choke control of their BJ8.

1. When the handle is pulled completely out of the body the inside of the body will acceptan Allen key which is of great help when tightening things up.

2. It is a lot easier to work on the choke control whith the tachometer removed.

Comments welcomed.

About Michael

Who is this guy? Born in New Zealand some time back. Went to Maori Hill Primary School then Kaikorai Valley High before joining the RNZAF and an Airman Cadet in 1968. Graduated 1972 with an NZCE in Aeronautical Engineering. Then embarked on the typical Kiwis "Big Trip Overseas". Got to see quite a few places, and spent a while in the U.K. "home" as it was refered to by many New Zealanders in those days, before travelling on to New York and then to Canada by bus!! This trip is presently on hold (has been for the last 34 years). Met my dear wife Judy not long after arriving in Ontario and we have been happily married since 1976. After travelling around New Zealand and the pacific in 1979 I started Precision Sportscar andfor the next 23 years grew the business and helped raise 2 boys Drew and Robin.
This entry was posted in BJ8 Restoration Information. Bookmark the permalink.

6 Responses to BJ8 Choke Woes

  1. Alan says:

    Michael –

    My factory original BJ8 cable had a little woodruff style half moon key under the spring ring rather than the ball. I’m quite sure this was factory original because it was on the car when I bought it in 1984 – BJ8 style replacements weren’t available then.

    I replaced it with a repro cable, but it works on friction alone, rather than the friction lock method which I prefer. Maybe I need to reinstall my old original BJ8 cable… if I can find it in my stuff!!

    Cheers,

    Alan

  2. Mike Owen says:

    I have had the very same choke cable trouble. I made a wrench by bending a strip of heavy gauge sheet metal around the retaining nut leaving a slot wide enough to pass the outer cable through. I then brazed a one inch long screw to the strip to give a handle to use. I have used this tool many times over the years.

    Mike Owen

  3. Michael says:

    Mike that sounds like a great idea. Send me a picture and I’ll post it on the blog.

  4. tom mitchell says:

    I replace my cable, although I liked the old one (cosmetically) better.
    Unfortunately the old cable has a strand that had unravelled causing it to bind, yet worked. In retrospect, if I had to do it again, I’d leave it alone.
    I also replaced both choke cables. They were frayed and once I removed the holding nut, I couldn’t get them back on.

    BTW I had to drill out the little connecting block as I found the heads on the new cables were a little larger in diameter.

  5. John Fautz says:

    My choke cable is attached to the dash securely and does not rotate. I can twist the knob but it won’t lock into position. My cables to the carbs are sheathed in rubber/plastic so there is no way I can lubricate them from the outside. I’ll bet they’er replacements? No slot anywhere on the shaft. I guess I’ll have to give Moss another handful of cash and buy all new cables. The choke/jet arm of one of the carbs raises much easer than the other. The culprit may be that little brass cylinder on the left side of the carb. I’ve noticed resistance there.
    Do I really need to remove that carburetor to track down that issue? (I know the answer to that question.) I would love to hear any other suggestions.

  6. Petter Moen says:

    Hi Michael

    I am looking for windshield pillars and glas frames, early 3000.

    Regards
    Petter Moen

Leave a Reply

Your email address will not be published. Required fields are marked *