Austin Healey 100 Heater Valve Stem Repair.

The Smiths heater used in the Austin Healey 100 is controlled by a valve mounted on the engine cylinder head.There were 3 versions of this valve but all have an inherent weakness in that the stem is easily broken just below the handle when too much “enthusiasm” is used to shut off the valve.

The handle is secured to a squared section of the stem of the valve with a very fine thread  brass nut.

As is to be expected spare parts for these 60 year old valves are not available, in fact original valves are difficult to find at all however all is not lost as the stem can be repaired.

Making an entire replacement stem, which has a “floating cap” on the end, would require a lot of machining.

This is the process that I use for the repair however ,be advised, that this involves a lathe and some machining skills.

I start by facing off the broken end of the stem and drilling out to 11/64″ to a depth of 0.4″.

Because the jaws of my lathe are too deep to hold the stem such that the end protrudes to permit facing off I have made a special collet to hold the stem in the chuck.

The next step is to make a steel insert to fit into the hole drilled in the stem. This has a  11/64″ diameter stem on one end which is 0.4″ long stepping up to a 17/64″ diameter section 0.200″ long and then down to 3/16″ diameter 0.250 inches long.

I have been unable to identify the original thread used for the nut on these stems, let alone purchase a die to cut it so I cut a 10/32 thread on the insert. I then hand file the 17/64′ diameter section down to a square to fit into the original handle. (NOTE … Thanks to Bob Haskell who has identified the thread 3/16″ x 40 T.P.I. is a Model Engineers thread.)

After ensuring that the 11/64″ section of the insert will fit neatly into the drilled out stem

I then carefully “tin” both the insert and the drilled hole in the stem and solder the insert into the stem. (Sorry about the focus on this pic)

The finished repair of the stem looks like this.

and the handle can then be secured with a brass 10/32″ nut.

In reassembling the valve I use greased hemp to replace the original packing

and the valve is ready to reinstall.

A sharp eye would notice that the top of the stem is now steel rather than the original brass but, as this valve is painted engine colour on a concours car this cannot be seen.

I’m confident that this repair is at least as strong as the original brass stem but caution all 100 owners to be gentle when operating this valve as it only needs to be turned until one can feel resistance CRANKING IT HARD DOWN WILL NOT SERVE ANY USEFUL PURPOSE AND CAN EASILY BREAK THE STEM.

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.
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