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Message started by Dave on 07/16/12 at 12:56:59

Title: Manual Cam Chain Tensioner
Post by Dave on 07/16/12 at 12:56:59

Things seem a little quiet around here today.....maybe this will be similar to an oil thread...but hopefully not. It is not my intent to "stir stuff up", but I have never owned a motorcycle with a manual chain adjustment and don't know if they even exist. American v-8 engines used to go for years with a similar cam chain that had no adjustment at all.

The spring and pawl chain tensioner on our bikes seems to decide the proper chain tension on a cold engine - but cannot compensate when the engine becomes hot. The result is that the chain gets stretched a bit on each heat cycle, and replacement is more required by the number of heat cycles than by duration and mileage.

Would it be possible to replace the existing spring/pawl automatic tensioner by one that is manually adjusted? A threaded stud with two lock nuts could be made that fit into the existing aluminum piece and limited the movement of the chain - and a spring could still be used behind this stud to place tension on the chain ramp while the engine is warming up. At some interval it would probably become necessary to make an adjustment - but it might extend the life of the chain by eliminating the constant "over" tightening of the chain by the pawl arrangement.

Title: Re: Manual Cam Chain Tensioner
Post by Oldfeller on 07/16/12 at 14:13:33

Yes, back when we were fighting through the cam chain wars we doped up a manual threaded system that came out of the back side of the barrel chain channel and was adjusted by hand periodically. It had issues with resealing an "O" ring against a threaded shaft, so it was never considered fool proof.

Problem is the Slavy fix is so durn cheap & easy that even the inventors of that system (and a hydraulic system that was dreamed up at the same time) each went with the Slavy fix. Both persons realized that the Slavy was just too good and just too cheap and easy to argue with.

Not that trials weren't done on other systems that were even easier and cheaper than the Slavy fix weren't done. I've got a motor sitting waiting for my current motor to die that has an "inelegant stick" fix/method in it.

;)

Title: Re: Manual Cam Chain Tensioner
Post by 360k+ on 07/16/12 at 14:13:48

I have had a bike with a manual chain adjuster. It was an old Yammy that had dual overhead cams with a single cam chain. It was a 500cc side by side twin with the cam chain in the middle between the cylinders. I believe it was every other maintenance interval you loosened a bolt at the back of the cylinders which allowed an internal spring to push a sprocket against the chain. The adjuster had a smooth rod that stuck out between cylinders 1/2 inch or so with little etched marks on it to measure the service limits. You first had to manually turn the crank to an orientation where the valves were all closed, relieving any pressure on the cam lobes. I had the bike 35 years ago, but I do remember the adjuster rod hardly moved when I loosened it, and I never replaced the chain or adjuster.

Title: Re: Manual Cam Chain Tensioner
Post by verslagen1 on 07/16/12 at 14:42:46

The problem with this type of adjuster is access.
And even though there is a way that is can be done, the average savagittian can't do it w/o taking it to a machine chop.
So while it's a solution, only 1% are going to do it.

Title: Re: Manual Cam Chain Tensioner
Post by SALB on 07/16/12 at 15:25:50

Although incredibly hard to engineer, I think a direct gear drive eliminating the chain would be cool. ;) :D

Title: Re: Manual Cam Chain Tensioner
Post by rfw2003 on 07/16/12 at 15:33:19

What about eliminating the ratchet claws in the verslay and just letting the spring do all the work? Since the verslay has the pin to keep it from over extending it wouldn't have the issue of falling apart plus with just the spring keeping the tension it wouldn't have the issue with making the chain to tight from the heat cold cycles possibly catching the next claw on the ratchet.

R.F.

Title: Re: Manual Cam Chain Tensioner
Post by ralfyguy on 07/16/12 at 15:35:46

How are other engine's tensioners designed? Do they have a pawl and spring as well? How do they not abuse the chain to stretch it out as fast as on the Savage?

Title: Re: Manual Cam Chain Tensioner
Post by ralfyguy on 07/16/12 at 15:37:35

22362762606063500 wrote:

I believe the problem with that would be oscillation, making the chain slap around on different rpm. The pawl keeps it steady.

Title: Re: Manual Cam Chain Tensioner
Post by bobert on 07/16/12 at 16:19:23

"I think a direct gear drive eliminating the chain would be cool."

Hard to retrofit, yes. I always liked the the Ducati bevel drive design. It was trouble-free on my Ducati 250 back in high school.

Title: Re: Manual Cam Chain Tensioner
Post by justin_o_guy2 on 07/16/12 at 16:47:54

The cure is worse than the disease, after the Versy mod, next step is someone smoothing out some teeth on the tube. The chain is just part of it, making it less of a pain,, thats for us to do,

Title: Re: Manual Cam Chain Tensioner
Post by Dave on 07/16/12 at 17:46:21

I wasn't thinking about accessing the manual adjustment from outside the clutch cover, I was thinking that the clutch cover would have to be removed to make the adjustment. That could be a reasonable approach if adjustment intervals were long enough. It probably would not operate any differently than the current tensioner when it is adjusted to the same tension - but it would not be self adjusting. I really don't have any idea what kind of interval would be adequate between service.....and I guess the onset of a noisey chain would be the first clue.

I believe the problem with the spring only approach, is that the cam chain does get some hard pulls in both directions at low speed - especially at start up or shut down. When the cam lobe is opening a valve the tension in the cam chain is normal - but at the point where the valve reaches maximum lift and the cam starts down the ramp of the lobe - the valve will be pushing on the cam in the other direction and it will try to remove the slack in the back side of the chain and move it to the front side. This probably won't happen when the exhaust valve is opened as the intake valve immediately starts to open at that point and they will cancel each other out - but when the intake valve cam lobe reaches maximum lift - the opposite direction tug on the cam chain will begin.

Title: Re: Manual Cam Chain Tensioner
Post by 360k+ on 07/16/12 at 18:49:35

On the Savage in particular, the two sprockets are too far apart for a clean gear drive solution. You'd need 3 or 4 gears to get from the case to the top end, and that probably brings a whole set of different problems. A gear driven cam with push rods, however, would work, because the cam could be kept in the case. The downside of a push rod solution is that the extra parts add mass inertia to the valve train, but the Savage isn't a high RPM motor anyway, so you're not likely to have valve float problems. If designed right, it may also be possible to implement hydraulic lifters.

Title: Re: Manual Cam Chain Tensioner
Post by justin_o_guy2 on 07/16/12 at 21:01:56

I remember someone really, REALLY trying to get heard in a " Im having trouble bleeding the brake" thread.. empathy is the first word that comes to mind.