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Message started by Hiko on 11/12/21 at 00:13:16

Title: The eternal cam chain tensioner
Post by Hiko on 11/12/21 at 00:13:16

Anyone who has read these pages knows that the cam chain tensioner is an issue on these bikes.
I could well be totally wrong but I would like some discussion on this
The tensioner is there to keep the chain from going slack ?
The cylinder heats up and expands tightening the chain against the guide which is held in position by the pawl
The chain tension pushes against the guide and either wears or bends it
The bike cools down chain relaxes and the spring pushes the guide again to take up the slack
Pawl takes up new position and the cycle starts over

Some on here I believe have removed the pawl
Does this stop the excessive wear or bending of the guide ?
Does the chain flutter then against the guide without the rigid support of the pawl?
I am not familiar with the tensioners used on other bikes
What do they use ?
Do they have issues?

Title: Re: The eternal cam chain tensioner
Post by Dave on 11/12/21 at 02:26:32

I removed the pawl and installed a spacer that prevents the tensioner shaft from going back too far into the housing. I installed a new cam chain and them assembled it with the stock spring in the tensioner - then machined a spacer that installed inside the tensioner and allowed the plunger to move 2mm back into the housing as the engine warmed up.

Does it work better? I don't know as I have only put a few thousand miles on it since then and I have not yet had it apart. I can't hear or feel any difference in the way it operates.

I will have the cover off this winter so I can do the DragBikeMike DR650 clutch improvement.....I will get a chance to look at it then.

Title: Re: The eternal cam chain tensioner
Post by DragBikeMike on 11/12/21 at 09:18:06

I did some tests and inspections on cam chains. The cylinder grows on the order of .025". My observation is that the chains don't wear out, the rear guides lose their arc. I am fond of a jack-bolt to buck up the rear guide. The Verslavy mod is an inexpensive and easy solution.

This post has some good info.

http://suzukisavage.com/cgi-bin/YaBB.pl?num=1593671973/0#14

Title: Re: The eternal cam chain tensioner
Post by Hiko on 11/12/21 at 14:03:49

My apologies to all This ground has been well plowed over before
I should have done more searching before posting.
I was well aware of the Versy mod to prevent catastrophic failure and have addressed that but was thinking about why the darn thing gets out that far in the first place.

Title: Re: The eternal cam chain tensioner
Post by ohiomoto on 11/12/21 at 14:49:38

I always wondered how our chains stretched so much until DragBikeMike more or less proved that they didn't. :)

Title: Re: The eternal cam chain tensioner
Post by Hiko on 11/13/21 at 18:21:28

Possibly a chain of events ;) ?
Idle speed too slow
lack of oil to chain
wearing and bending of chain guide
tensioner plunger extending too far and falling out
tensioner spilling its innards into gears in case
Expensive damage

Title: Re: The eternal cam chain tensioner
Post by justin_o_guy2 on 11/14/21 at 10:18:38

Mike is quite the mechanic and has accomplished some cool stuff, but I measured my first chain and it was longer. And, yes, the guide had lost some of its curvature. The pawl locking the tensioner is a problem. There are a couple of ways to solve that. I have a spring stashed that, if I ever put one on the road again, that I intend to install in the end of the tensioner where it mounts on the engine. I described it some years ago, don't remember if anyone actually got it, but I think a spring stronger than the tensioner spring with a small ball bearing pressing against the arm the tensioner slips on, with a bearing in the end of it, and a slightly expanded hole in the tensioner will do it. That way when the pawl locks the tensioner and the expansion of the jug starts pulling on the chain that spring will compress and protect the chain from undue tension. Hafta drill a pocket for the spring and lengthen the hole, but it's not much.
I saw someone had measured the change in the distance from cam to crank when the engine is up to temperature..
Aaand, I forgot how big of a difference it is.

I'd really like to know that. I Will write it down this time.

Title: Re: The eternal cam chain tensioner
Post by DragBikeMike on 11/14/21 at 16:04:01

It's .025" (0.64mm).

Title: Re: The eternal cam chain tensioner
Post by justin_o_guy2 on 11/14/21 at 22:09:22

Thanks! I'm no mathematical whiz,,but I'm betting .025 isn't gonna translate directly into the amount of deflection in the chain to allow for that change. One thing is obvious, A chain with a bit of a bend in it getting pulled .025" isn't gonna lose a lot of the bend.
I still think it will work.