Changing timing chain at valve adjustment

[ballisticexchris]

Bought a new tensioner from a member here, and i figure that if i have it that far apart, why not replace the chain, set the timing, and be done with it.

Hi there I highly discourage replacing just the timing the chain on this bike. The timing chain, camshaft sprocket, and crankshaft sprocket wear together and are required to be replaced as a set as per service spec. This is a pretty big job. You would need to split cases and replace both timing gear and crankshaft. It's over 1000 bucks in parts and at least a day or two downtime in labor. I'm pretty sure the sprocket has nowhere close to 1/4 tooth of wear. Still would not be a bad idea to check and monitor though.

View attachment 50651

 

[RCinNC]

I don't think it's specified anywhere that the timing chain even needs to be replaced. Now of course, it is metal, so eventually it's going to wear out, but even on my Toyota Camry that also has a timing chain, there's no replacement interval. My guess is that the engineers figure that the projected lifespan of the timing chain and camshaft and crankshaft is beyond that of the projected lifespan of the engine. I don't think I've ever heard of a cam chain failing on a Super Tenere (or any other bike, for that matter); a tensioner, yes, but never a chain itself.

Cam chains and the camshaft and crankcase gears aren't under nearly the same load as a drive chain; I suspect their lifespans are magnitudes longer than a drive chain and gears.

 

[blitz11]

Thanks for your post, but why would you discourage it if the system is apart? It's my business. Moreover, you are assuming that chains and sprockets wear in the same way. I assert that they do not - please let me explain.

Consider the surface area on a sprocket tooth, and how it engages the chain (be it a conventional roller chain or a "hy-vo" chain as used by the super 10 cam chain). The contact area between the sprocket tooth face and the face (hy-vo) or chain roller (roller chain) is significantly larger than the contact area between the pin and the chain plates (be it the hy-vo chain or a roller chain). The weak link? The diameter of the pin.

The engineering stress on the PIN is much higher than the engineering stress on the plates. Moreover, the plates ROTATE on the pin, whereas the plates or rollers DO NOT move with respect to the tooth face of the sprocket (when everything is new - as things wear, you have a bit of sliding as contact is made, but once contact is made, they don't move with respect to one another.) The rotation of the plates on the pin is what causes the chain wear. As the pin wears, the pitch length of the chain increases, and this increase in pitch length requires that the sprocket wear to accommodate the increase in pitch length. This happens because the tension of the chain is not evenly distributed along the circumference of the sprocket, so a few teeth take significantly higher loads with a worn chain than do teeth take with a new chain.

When I was in graduate school, i was VERY poor, and trying to race bicycles. I did the math, and if i replaced chains every 1K miles, I could have my freewheel and chainrings last about 7K miles. If i just went with one chain, my life would be about 4K miles. Chains then were $5, so it was much cheaper for me to replace chains at that interval than it was to replace the driveline (this was in the age of freewheels, not cassettes).

That all being said, RCinNC's observation about everything being well designed, and if this runs in clean oil probably makes my argument moot. If i wasn't going to replace the tensioner, i wouldn't replace the chain. BUT, for $23 additional, i can put a new chain in. I have thing apart already, and the chain is ~$7 more than the gasket! At the very least, it will buy me 25K more miles than if i didn't replace it, which comes to $0.10 per mile for that 25K miles. (I would argue that the loading on the timing system is less than the driveline, but loading doesn't matter as much as the engineering stress on the components.)

Thanks for reading.

 

[RonH]

Even an engine with 1/2 million miles will never show any wear on the cam sprockets. It doesn't work the same way as the drive chain. On those motorcycles that use a chain, the sprockets always wear because they are out in the elements in dirt, water, and no one ever lubes near often enough. Cam chain in oil will eventually wear, but the sprockets will never show wear. Just my experience. Has anyone actually ever seen a worn sprocket on a camshaft or crankshaft?

 

[OldRider]

I've seen a lot of roller chain cam/crank sprockets wore away to nothing, BUT it was because the chain was stretched out, loose and riding over the top of the sprocket teeth. Same as drive sprockets wear.

Although it has probably happened, I've never seen HyVo sprockets wore out. If the chain gets real loose it will jump time and make things go boom!! A bunch of Honda 250 atv's went to their grave with wore out HyVo chains and perfect looking sprockets.

Putting a new chain in will do no harm and at that price I'll probably do it at the next valve check.

25K miles @ .10 cents would be $2500.00. $25.00 spread out over 25K miles would .001/mile.

 

[ballisticexchris]

Thanks for your post, but why would you discourage it if the system is apart? It's my business. Moreover, you are assuming that chains and sprockets wear in the same way. I assert that they do not Thanks for reading.

Fair enough, do as you choose.

 

[BWC]

I did choose to change out my timing chain at 81,000 km on my 12 when the valves required a clearance adjust on a few of the valves. Also weighed the cost, around $25.00 for the chain, $16.00 for the clutch cover gasket and its ease of replacement at the same time the cams are removed as the Teneres timing chain runs down the side of the engine instead of the center as on many other bikes which useually requires splitting the cases to replace it. Big job.
The idea being with no wear showing on the cam chain drive and driven sprockets it would be easy and somewhat beneficial to replace the chain at that time. The CCT was upgraded to the 14+ version at 50,000 km.
I tried to compare the new and old chains and there was some noticeable wear, but very minimal. It would have likely gone double the mileage or more without issue.


Old chain on right

Old chain on top

Cam sprocket