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Message started by DangRider on 07/05/12 at 11:50:12

Title: Stretched cam chain - affects timing?
Post by DangRider on 07/05/12 at 11:50:12

I've read through many of the posts regarding the cam chain and tensioner.

Verslagen's tensioner can take up more slack, increasing the usable life of the chain, but how much do the stretched links affect the timing of the valves? Is there power loss, valve fouling because the timing is a little retarded?

I don't mean any offense. I'm pretty new to motorcycles/engines in general and trying to get edu-ma-cated.

Thanks.

Title: Re: Stretched cam chain - affects timing?
Post by 360k+ on 07/05/12 at 12:03:32

Good question. My guess is a miniscule amount. You'd actually have to measure overall chain length on a new chain vs a stretched chain. The difference divided 2 (chain is a loop) would probably be proportional to the % of valve offset. It seems like one thread in here did mention the amount of stretch you could expect to get on a worn out chain.

Title: Re: Stretched cam chain - affects timing?
Post by Routy on 07/05/12 at 12:16:32

You are correct about timing, but I'd bet it is not much more than theory,........or at least I have never noticed an increase in performance after changing any chain or belt in other applications,......even tho we know that in theroy there had to be some.

Kinda like, if your perfectly flat kitchen table is level in the middle, its impossible to be level nearer the edges :o

Title: Re: Stretched cam chain - affects timing?
Post by Cavi Mike on 07/05/12 at 12:31:07

Maybe a degree but not enough to matter.

Title: Re: Stretched cam chain - affects timing?
Post by Oldfeller on 07/05/12 at 12:35:28

It has been calculated out at 5-6 degrees retarded when the chain is totally shot on the second life (hitting itself in the middle).

It is what it is, no one around here has ever suggested replacing a hundred+ dollar cam chain to regain that little bit of performance.

Title: Re: Stretched cam chain - affects timing?
Post by verslagen1 on 07/05/12 at 12:58:41

You're allowed about .060" chain stretch.
for each .010" you get about 1° of cam retard.
if you were racing, it might matter.
otherwise, I don't think it matters.

Title: Re: Stretched cam chain - affects timing?
Post by DangRider on 07/05/12 at 13:30:09

Thanks for the information. I'll plan on getting a Verslavy this winter when the snow flies! (I've been told snow and two wheels is too much excitement :-/ )

Title: Re: Stretched cam chain - affects timing?
Post by justin_o_guy2 on 07/05/12 at 15:45:02

Naaah, snow is okay, its that blasted Ice ya get into,, BUT,, with some outriggers & an arm off the back of the frame with a spike & some cable & an explosive charge so you can "Drop Anchor" in an emergency, I dont see any reason to park it,, Well,, except for the occasional car skidding across the road or thru a stop lite,, hey,, I can picture riding thru the winter in Idaho.. suuure I can,, Im not really able to picture surviving it,, but, hey, how will ya know if ya dont at least try, right?

Title: Re: Stretched cam chain - affects timing?
Post by 360k+ on 07/05/12 at 19:14:56

544750514E4345474C13220 wrote:

You're allowed about .060" chain stretch.
for each .010" you get about 1° of cam retard.
if you were racing, it might matter.
otherwise, I don't think it matters.

I think I remember seeing that spec (actually .070), but measured over just 5 inches of chain (or 20 pin spacing). So .070 of stretch would be about 1.4% and constitute a "worn out" chain. IDK how long the chain is overall, but if measuring the entire length, of course, the stretch spec would be much higher. I don't remember where I saw it, but I'll see if I can find the spec again.

Title: Re: Stretched cam chain - affects timing?
Post by verslagen1 on 07/05/12 at 19:32:18

that might have been taken into consideration, might not have.
it's been a couple of years since I've done it.

Title: Re: Stretched cam chain - affects timing?
Post by justin_o_guy2 on 07/05/12 at 19:39:27

Whatever change in length the cam change has in it, considerable less than half of that is between the spot on the cam gear where the chain comes free & the spot on the crank gear where it stops being free. The rest of the difference is taken up in the teeth on the gears & the tensioner,
Yer not gonna lose Hoot in performance,

Title: Re: Stretched cam chain - affects timing?
Post by 360k+ on 07/07/12 at 09:17:30

At 65, I still have a memory like a steel trap, snap shotting virtually everything I see ...ummm, except WHERE I saw it! ;D

Zuk's service manual...

CAM DRIVE CHAIN 20·PITCH
LENGTH
Pull the chain tight to remove any slack, then using
vernier calipers, measure the 20-pitch (21 pins)
length of chain. If it measures more than the limit,
replace the chain.
Service Limit 128.9 mm or 5.070 (.070 over)

The 20 chain links measured is almost exactly 5 inches in length on a new chain, from the front of pin 1 to the front of pin 21. The .070 stretch limit is 1.4% which equates to just over 5 angular degrees of lag on the cam sprocket (1.4 X 360 = 5.04). So make sure you are NOT measuring the entire length of the chain when checking service limit. For instance, lets say the overall chain length was 25 inches. In that case, the service limit when measuring the ENTIRE chain would .350 inches of stretch (.070 X 5).

Title: Re: Stretched cam chain - affects timing?
Post by justin_o_guy2 on 07/07/12 at 10:17:53

I think the cam drive gear diameter is necesary to calculate this.

Title: Re: Stretched cam chain - affects timing?
Post by 360k+ on 07/07/12 at 10:54:02

726D6B6C71764777477F6D612A180 wrote:

I think the cam drive gear diameter is necesary to calculate this.

Hmmm, I don't think so, but now you've got me curious? My thinking is that the 1.4% is absolute length increase, no matter whether you measure the whole chain or one link. As such, it corresponds to the rotational angle difference (lag) between the driving gear and the driven gear. I wish I had better sim tools (or the brain I used to have before all the drugs, drinking, fast women, and other debauchery of my youth).

In any case, the point was that the .070 service limit was over just 5 inches of chain, not the entire length. I didn't want members to be throwing out chains that had only .070 on the whole length, which would probably be garnered in the first few thousand miles.

Title: Re: Stretched cam chain - affects timing?
Post by justin_o_guy2 on 07/07/12 at 11:46:40

Well,, heres my thinking,, If a gear is a foot across & I move the perimeter an inch, the # of degrees the center turns will be one number.
If I have a gear only 6 inches across & I move the gear an inch, the # of degrees the center rotates will be quite different,. &
if I have a gear only one inch around the perimeter & I move IT an inch, it will be a full 360, so, diameter matters.,

Title: Re: Stretched cam chain - affects timing?
Post by verslagen1 on 07/07/12 at 11:54:45

here's some info...
http://suzukisavage.com/cgi-bin/YaBB.pl?num=1296202131

Title: Re: Stretched cam chain - affects timing?
Post by 360k+ on 07/07/12 at 13:14:18

607F797E63645565556D7F73380A0 wrote:

When you say "1 foot across" I'm not sure if you mean 1 foot in diameter? Because the rotation of an inch along the circumference is based on pi. In any case, for this discussion, the .070 is constant, but would rotate each gear a variable amount (degrees) depending on its size. I dunno and probably don't amount to much anyway, but interesting to think about tho.

One of the things that I have noticed is why the extreme (premature?) wear on the Savage chain in the first place? To me, it constitutes a "problem" that should have been fixed years ago, given the bike's longevity. I've had other bikes that used chain tensioners, and they didn't wear out nearly as easily. Some had "automatic" tensioners and on others you losen a bolt and let an internal spring set the proper tension. My Harley even had a monster tensioner on the primary drive between the crank and the tranny. It provided drive for the whole bike, but lasted longer than the Savage cam chain???

Title: Re: Stretched cam chain - affects timing?
Post by justin_o_guy2 on 07/07/12 at 13:28:09

When the jug gets hot, it gets taller, then, when it cools, the tensioner may catch a new tooth with the ratchet pawl, then the next Heat Up cycle pulls the chain tite again, If a guy would only fire it up & keep it at operating temps for 100 mile stretches ( yea,, I used stretches in a cam chain stretching thread) then the chain would last 40 or 50 thousand miles maybe,, I think the answer is to smooth out every other tooth on the tube that extends, If I was keeping mine, Id give it a shot,.
A dremel & some cut off disks & some careful work & I think I could do it,

& yea, for the sake of getting the idea across, I was talking about a foot diameter in the first example,

Title: Re: Stretched cam chain - affects timing?
Post by Dave on 07/09/12 at 12:08:09

213E383F22251424142C3E32794B0 wrote:

,, I think the answer is to smooth out every other tooth on the tube that extends

I agree that making the system a little more forgiving and able to compensate for the heating/cooling cycle would be good. I don't think just grinding off a every other tooth on the plunger will actually work. if I remember correctly the pawl has multiple teeth and it locks into several teeth on the slider. It may be possible that a single tooth is not strong enough by itself to handle the loads imposed on the plunger when the engine is running and up to temperature.

I have two thoughts about this:
One would be to go back in time and actually replace the automatic tensioner with a manual one. If you replaced the spring plunger with a threaded one and had to adjust it manually - how often to you think you would have to make an adjustment?
Second would be to install a second spring on the other side of the plunger that would cushion the excess tension caused when the engine is hot. It would only compress as the engine wamed and tightened the chain - and it would not affect the operation of the pawl ratchet or tensioner spring (It would only relieve the excess tension when then engine gets hot).

Title: Re: Stretched cam chain - affects timing?
Post by justin_o_guy2 on 07/09/12 at 12:29:53

I wouldnt be afraid to smooth the pawl out some if that what it took, Ive seen what a tiny piece of metal can hold, if the chain is being pulled so hard that deflecting it from 90* is so difficult that one tooth on a ratchet wont hold it, it NEEds to let go, You have considered the power required to deflect a rope or chain sideways?