Chicagoland MG Club: Driveline August 2015
Technical Stuff
Fix It With Steve...

Hi Folks,

July has been a busy month -- and with the CMGC Project Car in the wings, August will also be busy.

Early in the month Bob Simon’s engine and transmission were reunited with their body. That went fine but there is a lot of work to complete the reconnection of all the ancillary items and Bob will be working at it for a bit to come. Later, Steve LaFond brought his B over. As is becoming a habit, his car provided a tough challenge in troubleshooting. We removed and replaced all the gaskets between the cylinder head and the carburettors, adjusted the rocker arm clearances and checked the ignition timing, but the engine persisted in backfiring under acceleration. It seems the carburettors need a thorough overhaul and that is what’s planned. Interestingly once the air filter were put back on, the engine smoothed out and ran fine. So this looks like two problems combining to solve each other!! Carbs running weak (the plugs had white tips on the electrodes) getting fixed by restricted air filters getting the mixture somewhat back into the correct territory

I started work on a 1974 TR6 that’s been stored for some time. The objective was to fix the brakes and get it running. The brake pipes need replacing and we got the front pretty much done. We also looked over the car and found some other things needing attention — cracked rear brake hoses for instance — front wheel bearings with too much play in them and a clutch slave cylinder in dire need of a decent burial.

A host of things got attended to on the TR until we got stopped — first by a broken ground wire in the distributor. By the time I had soldered it together again it was too short to fit, so a new one has to be ordered. It’s made of a special fine wire so it can take all the flexing of the vacuum advance mechanism. If you use regular wire it won’t last very long before it breaks. The second show stopper for the day was a broken thermostat housing. The cause was the thermostat itself. It hadn’t been put in its housing properly and was sitting ‘proud’. So when the housing covering it was tightened down, it was pivoted on the stat and the casting just snapped. Not very good for holding water! So more parts to order.

With work on the TR stopped I changed to rebuilding a pair of HIF carburettors off an MGB. Again I got stuck with only one completed! The SU HIF is more complicated than the


earlier HS type. The first problem I found was the spring on the top of one of the needles was missing. On the HS the needle is rigidly mounted to the piston, but in the HIF it’s spring loaded. Without the spring the needle is loose and can flop around; so the mixture setting will be hit and miss at best, probably mostly miss.

The other carb was in far worse shape. The bimetallic temperature compensator that holds the jet didn’t have the correct spring so that was all over the place. The jet itself was seized in its housing and probably because of that, the carburettor body where the mixture adjustment screw is fitted was stripped. Effectively the rear carburettor body is trash --a big problem. By the way just to add to the ‘fun’, the carbs are handed, front and back, so the bodies are not interchangeable.

Later in the month with all the things mentioned previously getting finished on the TR6 – brakes, clutch bled, etc. – it came the time to try and get it started — after two hours of frustration we quit for the day. No luck.

Returning the next day with fresh heads it all got fixed and she started and ran well. There are a couple of things to mention. It does help to read the instructions! Or at least remember that the TR6, like later MGB’s, has a ballasted resistor in the 12V feed to the coil. You need to connect the Petronix Ignition to a clean 12V supply and not to the coil after the resistor. That was my ‘oops’. Secondly, though we were getting a good spark it helps to take the distributor cap off and check that all is well. You’ll find the broken rotor arm a lot quicker that way.

Finally finishing the last of the TR6 projects the task now was to check out the wiring and get it all working. The issue was grounds. Nine times out of ten, funky electrical issues turn out to be grounding related and the TR was no exception. Doing that got the rear lights, turn signals and brake lights sorted. Even the heater fan previously not working turned out to be a loose ground. I rest my case! The car has now returned home to continue its restoration.

-- Steve Skegg

Auto Appraisal Group British Wiring
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