Adjusting Andys Primary Chain

Been giving some thought about adjusting, or tensioning, the primary drive chain(s) and I have come to the conclusion that the 'tensioner' is not a tensioner at all!
If you observe the chain coming off a MotoGP bike (or any other for that matter) you'll notice that under acceleration the inertia of the chain causes it to try to follow the countershaft sprocket until it is pulled down towards the rear sprocket. Where this happens on the primary drive on our Laverdas seems to be exactly where the 'tensioner' is located.
If the bike only accelerates or is at constant load, the follower (or tensioner) would not be needed. HOWEVER, when backing off, and the rear wheel tries to drive the engine (engine braking) the loads are reversed. During this transition, any slack in the chain will cause it to snatch, increasing the load on the chain thus shortening it's service life.
In my view, the tensioner should be adjusted to it is just not touching the chain under load but reduces the amount of slack in the chain when backing off.
Anyway, that's my two bob's worth ;)
Don't forget, all hipsters must hang.
 
Legs said:
Been giving some thought about adjusting, or tensioning, the primary drive chain(s) and I have come to the conclusion that the 'tensioner' is not a tensioner at all!

Don't forget, all hipsters must hang.
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Ah fuck Terry, that opens up a can o worms.

BTW: I’m sure I saw Putin in a flannel shirt and cords.
 
Dellortoman said:
Do you stick your finger through the window with the engine running or static?
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Very good question, static is the logical answer.

However, if you are the type of person that contemplates checking the tension of a chainsaw chain whilst in operation, you may well think the ‘running’ option to be feasible.

Frankly, I prefer the stethoscope method.
 
chrisk said:
Very good question, static is the logical answer.

However, if you are the type of person that contemplates checking the tension of a chainsaw chain whilst in operation, you may well think the ‘running’ option to be feasible.

Frankly, I prefer the stethoscope method.
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Don’t use a good stethoscope, the chain wears them out.
 
Legs said:
Been giving some thought about adjusting, or tensioning, the primary drive chain(s) and I have come to the conclusion that the 'tensioner' is not a tensioner at all! <snip>
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(I'm sure we've been here before ... :rolleyes:)

Jean-Louis said pretty much the same a long time back. Here are his thoughts on the subject, translated from the original:

"The tensioner is not a "tensioner" at all!

It is only there to limit the flexing of the chain, not to put tension on it.

If there is any tension on the chain, the adjustment is wrong. It will pull on the bearings, on the chain itself, on the needle bushes in the housing and it will eat into the rubber of the tensioner.

The factory triple machines for example did not have a tensioner, just two fixed pads to limit the flexing without ever touching the chain itself at rest.

When adjusting, no tension should be applied to the chain.

The adjusting screw is gently screwed in and, as soon as resistance is felt, is loosened by about one turn, until the tensioner is completely free".
 
Yeah well! never saw Jean-Louis' post.
Just used basic engineering common-sense as to why the workshop manual said to rev the engine to 3 thou rpm and back off the adjuster till the noise has just gone.
 
Ventodue said:
(I'm sure we've been here before ... :rolleyes:)

Jean-Louis said pretty much the same a long time back. Here are his thoughts on the subject, translated from the original:

"The tensioner is not a "tensioner" at all!

It is only there to limit the flexing of the chain, not to put tension on it.

If there is any tension on the chain, the adjustment is wrong. It will pull on the bearings, on the chain itself, on the needle bushes in the housing and it will eat into the rubber of the tensioner.

The factory triple machines for example did not have a tensioner, just two fixed pads to limit the flexing without ever touching the chain itself at rest.

When adjusting, no tension should be applied to the chain.

The adjusting screw is gently screwed in and, as soon as resistance is felt, is loosened by about one turn, until the tensioner is completely free".
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Jean-Louis wasn't the only one to make that comment, several of us did.
The early factory twins didn't have a tensioner only two guide blades. The primary chain was changed mid race in the long races. The top blade was carried over into production on the early twins.

Paul
 
Paul Marx said:
The early factory twins didn't have a tensioner only two guide blades. The primary chain was changed mid race in the long races. The top blade was carried over into production on the early twins.

Paul
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Early twins had a roller tensioner with the roller made of rubber. They were soon followed by a nylon roller, indeed with a small guide above the chain on the S. Then the slipper tensioner came. Chain guides with the two blades came in the 1973 works SFC racers. The space frame triples with their 4 row primary chain had such a chain guide too.

Swapping a primary chain during the race is news to me, but usually the 73 racers had thrown a rod before that time.. 😉

Marnix
 
Changing a primary chain during a 24 hour race??? Just how fragile are the bloody things?? For the time it would take you could probably ride baby the motor and ride 30% slower per lap and still be ahead of swapping out the primary, resetting the points etc etc!!
 
piranha-bro2 said:
Changing a primary chain during a 24 hour race??? Just how fragile are the bloody things?? For the time it would take you could probably ride baby the motor and ride 30% slower per lap and still be ahead of swapping out the primary, resetting the points etc etc!!
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Fragility aside, having just put on a pair of Jason’s Merc primary chains, I reckon a speedy mechanic could do the swap in less than 15 minutes using the cush rubber removal method leaving the Jesus Christ nut in place and assuming they are using a Witt system or similar that doesn’t need re-timing.
 
piranha-bro2 said:
Changing a primary chain during a 24 hour race??? Just how fragile are the bloody things?? For the time it would take you could probably ride baby the motor and ride 30% slower per lap and still be ahead of swapping out the primary, resetting the points etc etc!!
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I never heard about this and I think I can say that I would have heard about it if they did. I have many reports that mention the repairs they did in detail. Such a chain swap surely would have been mentioned.
The triplex Reginas at the time were virtually indestructible and you rarely see damage caused by a broken primary chain when you open an SFC engine with racing history. Regina chains breaking happened relatively recent when they started to make chains with bigger diameter pins. Those are to be avoided at all time.

Marnix
 
Well, I'm sure that I read somewhere about the preventive primary chain swap. Maybe a private team, maybe just once or twice?

Otherwise, major mechanical work during an early 70s 24 hour race was quite common. And you could still finish, and in the points table. It's quite possible that the rules didn't allow crankcase changes but a lot of the rest was allowed, and done. The pace over 24 hours wasn't what it is now, and changing a primary chain on a Laverda isn't a big deal.

Laverda must have had doubts about the primary chains to have gone for a 4 row chain on some works triples.

Paul
 
I don’t doubt that you read it somewhere and also agree that in endurance racing everything is possible, and it is still the case today. However, if a Laverda team was one of the contenders for victory they wouldn’t swap a primary chain halfway the race as a matter of precaution.

They clearly had doubts about the triple being too strong for the triplex chain, never saw one mounted on an SFC.

Marnix
 
I make the point because race strategy would calculate exactly how costly in terms of lost laps such a primary chain replacement would be. Is racing an SFC as hard on a primary chain as hammering an SF for 30,000km ... over crap roads, corrugated, potholed dirt for hundreds of km, stop-start traffic on cities day after day - it's just never been a weak link in that motor. And SFCs back then didn't have Witt ignition - they had points; remove the primary cover and you are bound to reset the points - if you didn't your race chances would be taking a far greater risk of self-immolation than leaving the primary chain in situ for 24 hours!!
 
I remember Slaters removing an SFC cylinder head during an endurance race, it was probably a UK one and maybe Brands Hatch, 24 hour races never realy caught on here, nor did 500 milers over much either, I remember doing a VERY VERY long race on my Monty in 1980, it was at Snetterton circuit and was called "the anual fifty miler" and was part of the Bantam racing clubs programme, normally races were about 20% of that. I finished but didnt change my primary chain.
CLEM
 
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