What's happening to my cam sprockets?

[ianralph]

The plastic part bonded to the cam sprockets that has the timing arrows etc appears to be breaking down. On the inlet cam a chunk has broken off and on the exhaust the cam chain is beginning to make indents.

See

http://ls1.sceggs.nsw.edu.au/~ian/cams/inlet.jpg

and

http://ls1.sceggs.nsw.edu.au/~ian/cams/exhaust.jpg

The cam chain has fewer than 10,000Km - the bike '79 GS1000SN has over 100,000km.

Is this just something that happens with age? Has anyone else had this problem? What to do - replace the sprockets - replace the chain or both?

[silverhorse47]

I really have no clear idea, but if this were my engine I would be looking at:
timing chain way too tight for some reason
engine not cooling timing chain for some reason (plugged oil canals)
wrong or totally burned out oil
way overheated engine in which case.......check the mains, big and little ends as well

[Steve]

In the few engines where I have seen the cams, I don't remember ever seeing anything but metal on the cams.

It appears that the sprocket might be wearing a bit, much like the sprockets on the drive chain. Try pulling the chain away from the sprocket. If it is noticeably loose, there has been some wear. You say the chain is relatively new, so it's probably the sprockets, but measure the chain stretch anyway.

.

[Nessism]

Did you use a Suzuki cam chain? Almost looks like it's contacting that plastic piece because the profile of the chain is different or maybe the sprockets are worn to the point where the chain is sunk down?

[flyingace]

I'm guessing that plastic wrapper was a way to place the cam timing marks on the sprocket in early models. I have a 79-80 spare 850 engine, and there is no plastic on these sprockets. I would further speculate that you are seeing the reason they stopped using plastic.

So I gather that this is a bike with high mileage on the cam sprockets on which you placed a new cam chain. My guess is that in the same way you should buy new sprockets for a new final drive chain, you should buy new cam sprockets for a new cam chain. If one is worn out, so is the other. A new chain will acclerate the wear of an old sprocket.

I'm just throwing out this second thought as a possibility to see what others think. I'm not sure if you should replace the sprockets and chain at the same time or not.

[trippivot]

the plastic when it was new was designed as a sound dampener . just like the side gears on the clutch/ crank.

industrial "copy" of the older kawasaki engine with improvements.= gs1000
quieter and more power.

when the plastic gets old it gets brittle. loose camchain slap has removed a chunk. probably a no load rev and release or sustained rough idle( chunka chunka chunka- you know the rough low idle engine noise )

it will just go down into the lower oil pan . won't hurt any thing . the strainer is elevated .

drop the oil and drop the pan clean it out put it back together and ride it.

[ianralph]

Thanks for your replies. I'll drop the pan and see if I can find the bit of plastic that broke off.

I suspect that this was what was making the intermittent clicking sound that I reported in an earlier post -

http://www.thegsresources.com/_forum/showthread.php?t=135085

The noise may have come either as the plastic was in the process of breaking off or after it came off.

[ianralph]

After closer inspection I found that the plastic was starting to come off the exhaust cam sprocket too.

I took the sump pan off and found quite a bit (about ½ teaspoon full) of ground up plastic and one larger, still recognisable piece of plastic, from the sprockets in the pan. I suspect that the bits that fell off were ground up after falling down the cam chain tunnel and being caught between the cam chain crankshaft sprocket and the cam chain - after which the product of this process ended up in the sump pan.

I'm going to remove the rest of the plastic from both cam shaft sprockets, clean out the sump pan and oil-strainer gauze, replace the oil filter and ride it.

[Suzuki_Don]

IAN do you plan to re-mark the sprockets with the existing timing marks for future reference when you remove the rest of the plastic bits that are left.