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Primary chain tension AMC 20T

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Primary chain tension AMC 20T

Post  rob spence on Sat Oct 28, 2017 10:11 am

When I re assemble my 20T engine (which will be soon) I need to address the tension of the primary chain. How is this achieved and/or is a primary chain tensioner available for this engine? When I dissasembled the engine their was a very thin metal shim gasket in between the engine and gearbox. The current chain has a spring link fitted and is not endless.

rob spence

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primary chain tension

Post  Bigjim on Sat Oct 28, 2017 10:52 am

rob spence wrote:When I reassemble my 20T engine (which will be soon) I need to address the tension of the primary chain. How is this achieved and/or is a primary chain tensioner available for this engine? When I dissasembled the engine their was a very thin metal shim gasket in between the engine and gearbox. The current chain has a spring link fitted and is not endless.

If it's like the villiers, a slack chainmeans a worn chain. Sometimes people put extra gaskets/shims twixt box & cases. Generally a new chain fixes the problem.
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Chain

Post  kerabo on Sat Oct 28, 2017 6:49 pm

The 20T uses shims to tension the chain. You will be supprised how much difference even a thin shim makes. Take this opertunity to get it correct.
Don't shim it with and old chain or worn sprockets or you won't be able to fit a new chain afterwards without removing the engine.
It's hard to join the split link with a tensioned chain so best put it round the sprockets and feed it on.
I do mine an a mockup without fitting the inner case and assemble when correct.

Regards Ken
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Re: Primary chain tension AMC 20T

Post  Ted Snook on Sat Oct 28, 2017 9:10 pm

The correct chain is endless and has no spring link. Needs to be put on both clutch chain wheel and engine sprocket simultaneously by sliding the chain and sprockets, assembled, on the respective shafts together. I got mine from Villiers Services.
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Re: Primary chain tension AMC 20T

Post  rob spence on Mon Oct 30, 2017 12:22 pm

Thanks all...to shim the engine/gearbox mating faces does it have to be metal shimming ( as in the original), if so are they available or do you have to cut your own.Or are paper or cardboard ones ok?

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Shims

Post  kerabo on Mon Oct 30, 2017 1:59 pm

You can't really use anything but metal as it will crush. Buy some 5 and 10 thou shim steel or brass and either draw round an old shim or the gearbox end face.
You can cut with good snips. On mine the edges I cleaned up with a Dremel once clamped together. Remember to use some sealant.
Don't remove every bit of play as I would imagine as the cases expand when hot it would put a fraction more tension on it.

Ken
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Re: Primary chain tension AMC 20T

Post  rob spence on Mon Oct 30, 2017 2:18 pm

Thanks Ken.

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Re: Primary chain tension AMC 20T

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