G80s '54 - dynamo chain/ primary chain clearances

Information relating to the Matchless G80 or AJS Model 18 500cc Heavyweight.
StephenG80
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G80s '54 - dynamo chain/ primary chain clearances

Post by StephenG80 »

Just replaced the primary and dynamo chains on my bike. I know when under tension they will run straight but I was still suprised how litter horizontal clearance there is between the two just before the dyamo sprocket. With both adjusted spot on for "uppy downy movement", the lateral movement means they can touch -just! - presume this is normal, can't see it can't be.
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Re: G80s '54 - dynamo chain/ primary chain clearances

Post by SPRIDDLER »

The dynamo chain should not be able to touch the primary chain under any circumstances. A special nut, lock washer and circlip is used to secure the dynamo sprocket since clashing chains can be pretty (very) disastrous.
I guess you know that you can move the dynamo in and out (i.e. laterally) to adjust the clearance between chains? It can be moved inwards (away from you) to increase the clearance so long as the dynamo chain run remains sympathetically in line with the engine and dynamo sprockets.
If yours has a 'Stop plate' on the dynamo to indicate correct alignment (none of mine ever have so I mark the dynamo body for future reference when correctly aligned before refitting the outer chaincase) perhaps it is incorrect or incorrectly fitted. You can of course remove it if it's 'in the way' of achieving correct alignment.
If you have checked all the above there's a remote possibility that one of the chains is too wide.............?
The dynamo chain should be endless and the primary chain will have a joining link.
I've always found that when finally tightening the dynamo clamp it changes the previously O.K. chain tension. I usually have to set the chain a bit tight or a bit slack (can't remember which) so that it ends up 'just right' after the clamp has been fully tightened.

Later...
If you have removed the dynamo sprocket is it replaced fully home on the dynamo's tapered armature shaft and Woodruff key?
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Which taken at the flood............'
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Rob Harknett
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Re: G80s '54 - dynamo chain/ primary chain clearances

Post by Rob Harknett »

I believe it is....... if you set the dynamo chain tension correct, it will tighten. How much will depend on how loose and how far forward the dynamo is before you start to tighten. As you tighten the dynamo strap the dynamo will tighten up moving back, tightening the chain tension
Like Spridler I do not have any plates on my dynamo's. If you have a plate it should be set correct to line up sprockets. You say your chains touch. Look again and you will see they will not touch if the dynamo is in the correct position. Where to look? Look at the engine sprocket. With both primary and dynamo chains fitted. At this point you surely must see there is a gap between the two. If the dynamo is set correctly, so both sprockets line up, that same size gap should be seen along the chain runs.
StephenG80
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Re: G80s '54 - dynamo chain/ primary chain clearances

Post by StephenG80 »

Thanks Gents - there was nothing on this in any my manuals so glad I posted. Yes, sprocket is on taper with new key, all snug. Special nut, lock washer, circlip all used. Re chain thickness - both chains are from club spares -so I hope not!! (also looked the same as the ones I took off). Yes - played the game of "guess the end point tension"with the dyno chain tensioning up as the retaining strap is tensioned.

By eye, although it cannot be viewed directly square on because the lip of the inner primary gets in the way, the space between the chains is the same as when on the duel sprocket at the front but if side ways pressure is put on the correctly tensioned primary chain (3/8"?), they could technically rub. I know in normal operation there is not going to be any lateral force but I was susprised at how close they are.

For peace of mind I'll slacken off the strap and pull the dyno out (towards RH of bike (as in when riding)) as far as possible to maximise the distance whilst not causing it to the hit on the inner primary or be overtly out f line with from sprocket.

Thanks for the heads up.
Andy51
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Re: G80s '54 - dynamo chain/ primary chain clearances

Post by Andy51 »

Hi Stephen, I wrote a short article for the Jampot a while ago on setting the Dynamo position, complete with photo. In essence you clamp a short steel bar or similar to the Outer, primary sprocket (make sure it it doesn't overlap the chain or it will go wrong) and use a vernier calliper to measure distance from bar to Dynamo chain close to sprocket. Then measure distance from bar to Dynamo chain near Dynamo sprocket, and push Dynamo sideways until you get same measurement near both Dynamo chain sprockets. With a little effort you can get the difference down to under 5 thou, better than any stop plate. Andy
StephenG80
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Re: G80s '54 - dynamo chain/ primary chain clearances

Post by StephenG80 »

Hi Andy - could you please post a link to your article. Thanks
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clive
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Re: G80s '54 - dynamo chain/ primary chain clearances

Post by clive »

But you can only use this method with the chaincase cover off. Like Spriddler I have never had a stop plate on my dynamos. Once it's set up with the chaincase off, I stand in front of the bike and line up the edge of the dynamo with the engine plate and Mark it with a permanent market. When subsequently changing the dynamo chain tension I can then check the spacing when I have finished without removing the primary cover.
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StephenG80
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Re: G80s '54 - dynamo chain/ primary chain clearances

Post by StephenG80 »

Well, my outer chain case is off at the moment, so I'll use Andy's system tomorrow and then, once set, find that permanent marker :-)
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Re: G80s '54 - dynamo chain/ primary chain clearances

Post by Triumph-Legend »

In this months Jampot magazine there is a very good picture of the damage to the crank case that can be caused by using incorrect or omission of the crankshaft sprocket spacer. Surprisingly common and not cheap to repair as the chain can cut right through the crank case bearing support boss. I think that one of the problems with these old machines is that they are simple and tough enough to stand an awful lot of ham fisted abuse and still keep on running. Seemingly fine, until somebody comes along with greater knowledge or experience who then has to rectify years of abuse.
StephenG80
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Re: G80s '54 - dynamo chain/ primary chain clearances

Post by StephenG80 »

Ok - just measured the outside, inside run, of the dynamo chain (ie the side closest to the inner primary) and at the centre I have 2mm plus clearance between that edge and the inner primary. I have 3 mm plus between the primary chain (outside link at rivet end) and the dynamo chain (rivet end). With lateral force on the primary chain (quite a lot) the chain can still, technically, just touch the dynamo chain, but under load this is not going to happen. With only 2mm on the dynamo chain/inner case I don't have any wriggle room to increase the primary/dynamo chain clearance. Do these measurements sound about right or have I rebuilt something completely wrong? ( I don't see how I could have done though). I appear to have a "stop" lug (is this the "plate" referred to???) on my dynamo - if I turn the dynamo a lot, the lug will pass through a gap (in the dynamo/gearbox plates) allowing the dynamo to move towards the chain case. But in normal rotation for dynamo chain tension, this tab stops the dynamo going further into the chain case. So I am presuming as the lug on dynamo is snug up against the plate (dynamo/gearbox plates) then this is factory preset and my distances above are standard. Does this sound right?

Another wee question - re the engine sprocket nut (which hold the spring loaded engine dampener in place) - how tight should that be? as presumable the spring should not be over compressed or you lose its purpose.

Thanks for all the advice so far-its bit critical I get this right! :roll:
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