Rocker arm adjusting screw

I finally received my new heads gaskets. Figured I’d purchase two so as to have a spare. Got the head on and torqued down, then proceeded to attach the rocker arm assembly. While adjusting the rocker arms, I found that one adjuster had the nut severely rounded and the adjusting screw had thread damage. I finally got the nut off the top but when trying to rotate the screw down and out, one side of the slot broke off……and of course, the piece went down the push rod hole! :face_with_symbols_over_mouth:
I’m going to have to use vice grips to rotate it down enough to grab the ball with vise grips to turn it then cut off at the bad thread area so I can get it out.
Does anyone here know what thread these are? Does any one have an extra one? Seems like this engine is fighting me at ever turn!

Hi Wayne, my memory is the screw threads are British Cycle. The threads are hardened and chip easily. I will check threads and my possible extra stock and post further info.

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Thanks Roger. Any help will be greatly appreciated!

C.561 Ball-Pin (Adjustable) in Rockers Plate H.62 has 5/16x26 BSCY threads on the hardened threads. It is easy to damage the threads on the Ball-Pin and also on
C.437 Rocker No. 1 and C.438 Rocker No. 2.

I can supply an extra Ball-Pin with C.379 Nut, Lock, for Ball-pins. If you wish one from me, please send me a private message.

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This is a post from Ed Nantes from a few years back.
OK tappet adjusting screws. The originals had a design weakness. The BSC thread is very fine and the screws were case hardened. Unfortunately the depth of hardening from both sides of the thread meant they were ,in effect, through hardened. And, so brittle. And often there broke pieces off in situ and jammed. Sometimes one could not wind them through[ the normal way to remove them] but sometimes it worked to cut the ball off with an angle grinder and try to wind the thread out backwards.
A few years ago i had a batch made, but being cuning , I had the thread masked off during the heat treatment… easy to do. Which meant the ball was hard but the thread was just tough and retained tensile strength.
These all worked well and I had hundreds made. I though I might still have some, but from memory i sold the remainder to Simon Whitworth at Worcester classic Spares. So he would be the best bet. I do have a handful of the half nuts , new , if anyone needs a few.

Reading about the loose screw in Helmuts tappet, I suspect someone has used an MG TC as a replacement. When I did the batch an SSowner who also worked on TCs said" waste of time, you can use MG TC’ as though MG TC screws were lying round everywhere[ and for 4 cylinders too] But checking the MG doesn’t have exactly the same thread. . From memory 1 TPI difference and fractionally smaller. { Probably metric as MG got a deal on cheap metric threads around the time of the TB/ TC. But this meant all the load was on just one turn of the tread… And I know from making pushrods, MG are an odd size ball.

Really the whole rocker gear needs to be dismantled and cleaned and checked and new wicks put in and the shaft condition checked. And one would like to see lots of oil running down the pushrods when idling.
Sorry I can’t help with replacements.

You might try a stick magnet tool.
I remember it was British Cycle thread. I’d never heard of it until that topic came up here. Probably a legacy from Standard.

A cautionary note when considering using MG threads. They are metric fine (with Whitworth hexagons) up to the end of the T series in 1955 for engines. This is a legacy from the end of WWI when Morris resumed car manufacture using the French Hotchkiss tooling transferred to them by the French to avoid German capture.

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I was able to screw the tapper adjuster out without too much problem. A member here is sending me a replacement. As for the little broken piece of tapper, I didn’t see which hole it went down if it actually found a hole and didn’t arc over the edge of the head. I’ll keep trying to find it with my tiniest stick magnet until the replacement tappet arrives.

The adjuster came last week and I installed it today. Thank you very much!!!


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