Timing Gear Shims

Information relating to the Matchless G3 or AJS Model 16 350cc Heavyweight
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Re: Timing Gear Shims

Postby nomisimon » Wed Jan 13, 2021 1:31 pm

Hi Dixter

Thanks for that...what a great way to measure the shim needed. I have plenty of solder and am sure it will be beyond the eight thou limit without the six thou shim that fell apart.

I've saved a copy of the workshop inspection standards manual.

Regards

Simon
Thank God for Southby

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Re: Timing Gear Shims

Postby Mick D » Wed Jan 13, 2021 2:30 pm

Dixter wrote:determining the required thickness of the shims is eased with a piece of wire solder as used in electrical work. Cut a short piece, trap it where the desired shim would go, replace the cover, tighten the screws and crush the solder. Measure the thickness.


Hi

I'd be very wary of using this method, especially if the clearance is small, the solder is more likely to distort the cases and give a false, (high), reading. Fine electrical solder is about 1mm in diameter, crushing this to, say, 10 thou, (0.25mm), will take some considerable force, try it with a pair of pliers.

Plastigauge is a professional product designed for these sort of applications but it's not cheap.

A small blob of modelling putty could be used and measured when cured though ;)

Regards Mick

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Re: Timing Gear Shims

Postby Pharisee » Wed Jan 13, 2021 9:32 pm

I would concur with what Mick D has said. I had the advantage that I had the complete bottom end of the engine in a stand on the bench when I shimmed my M18S. The exhaust was not problematic as I set up a dial indicator on the end of the camshaft and could measure the end float accurately. The inlet cam was not so easy. I used the fine solder wire method and placed a ring of it on the camshaft and bolted up the timing cover without a gasket. It measured 0.011" so I put in a 0.010" shim and bolted the cover on again. I couldn't rotate the crankshaft... I took the cover off again and swapped the shim for a 6 thou. Now I could rotate the crankshaft, but it still felt tighter than I thought it should. I opted for the 0.003" shim and the crank spun freely.
The bike has covered a few hundred miles since the rebuild and is as mechanically quiet as I have any right to expect.
John

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Re: Timing Gear Shims

Postby nomisimon » Wed Jan 13, 2021 11:25 pm

Thanks gentlemen

Fair comment...regular solder is quite hard, but I have some very thin, soft, low temperature stuff I was going to try.

The way the damaged shim looks, it may have been too thick at six thou; I didn't fit it. The engine had been quiet until this happened. Maybe I will fit a five thou shim which should be OK. I'll measure the exhaust valve shim and fit a similar replacement.

The book says three thou endfloat is OK but six thou is too much...maybe three thou would be better.

However...I've looked up Plastigauge...what a great and obvious (with hindsight of course) idea.

I can get a pack of ten suitable strips for £8 so have ordered one.

Thanks for the advice, I've never come across the stuff before.

Simon
Thank God for Southby

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Re: Timing Gear Shims

Postby 56G80S » Thu Jan 14, 2021 3:42 pm

I did go down the solder route, also with very thin, soft solder but would agree with Mick D now.

"The inlet bush is blanked off so no oil can exit from the crankcase into the timing chest."

Except when, as happened for me, the blanking plug came loose. I had an oily cam chest. Least of my current problems.

JohnnyB

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Re: Timing Gear Shims

Postby nomisimon » Thu Jan 14, 2021 4:19 pm

Hi JohnnyB

Sorry to hear you have problems to sort...I'm hoping this is the last of mine for a while.

The magneto packed up a few years ago and was fully refurbished (it took a while to get back on with the project due to health), the dynamo sprocket came off (the dynamo needed rebuilding and so did the gearbox as things were wrong inside, unbeknown to me), primary chain and sprockets were damaged etc...

It did feel like one step forward and two back from time to time, but I've learned a lot sorting all the problems out and had some great help from the guys on this forum.

Once the spring comes and restrictions are lifted a bit, it would be good to get out on the bike.

Cheers

Simon
Thank God for Southby

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