Camshaft drive chain worn out early

[Roles]

Camshaft drive chain worn out early

About a month ago I took my Trophy for a ride and I noticed it sounded like a dieselengine in the lower RPM when it was cold and at idle speed. After warming up the sound nearly dissappeared. After a few rides the sound remained more noticable at low RPM. I tried Forte I and II, maybe it was a fuel problem? Alas, that didn’t work!
So I began to think about a possible cause and concluded that it had to be in the camshaft chain area. A month before my holiday I adjusted the valve clearance, so that couldn’t be the problem and the engine sounded good after that job.
At first I took off the tensioner for inspection, but there was no real wear to be seen at the plunger, the spring was not broken, so it was OK.
That was the easy part! To look any further I had to take off the cover, the tank, airbox and valve cover again ;-( But it had to be done!
After stripping the bike I could see the chain and the tensioner. By turning the crankshaft via the hexnut I could hear a rattling noise from the tensioner when the cams where all in a more or less upright position. There was no tension on the chain via the cams and all slack of the chain had to be compensated by the tensioner. But the plunger of tensioner was already in the outmost position, so there was a gap. When that gap was closed, the plunger was driven to its rest position against the resitorspring. That caused the rattlesound! Excessive wear of the chain made the plunger rattle against its rest position. That’s how the dieselsound was produced…

Now I knew what to replace in this camchain system: the chain, the guideblades, the tensioner.
Then, when I turned the crank once more to be sure, the allenbolt that secured the hexnut broke off!!! Half of the bolt was inside the crank... Now what to do???

How could this happen in an engine that just turned a 105.000 km?? Anyway, I was so glad that this happened when the engine was NOT running! And when I was NOT driving it at a highway for instance. You can imagine what could have happen....

But how could such an important bolt just break off? I guess that there is a tiny movement / wobble of the chain sprocket while the engine is running. That could make the allenbolt shake a little since there is a length of 5mm free thread after it leaves the thread of the crank. Anyway, the bolt broke exactly at the point where the thread of the crank stops. I strongly recommend to renew this bolt every second valve clearance jobs, so after each 64.000 km! I also recommend to check the cam chain wear and the length of the plunger of the tensioner at these intervals.

To drill out the part of the allen bolt in the crank, I took another allen bolt of 8mm and drilled a hole of 3 mm exactly in the middle. This (very short 5mm) bolt I used to guide the 3 mm drill in the middel of the remaining piece of bolt. It worked! When I had a hole of 7mm I could use a left tap to screw it out of the crack.

The rest was building up the machine again… ;-)

I include some pictures and later on a separate file with just the length of the plungers. And some pics of the wear of the guidance blades.

[Roles]

Plunger length

[Roles]

Wear of the blades

[earthman]

I can't say that I noticed any play around that crankshaft sprocket and that bolt when I done the 20K service on mine, not that I were looking for any to be honest. Surely that's all meant to be tight/have no play? The keyway is the main component that's taking the strain/force here but I would have thought that bolt were meant to hold the sprocket firmly in line/place?? 

[earthman]

Anyone else noticed any play around that bolt/crankshaft sprocket?

Has for the wear of the cam chain blades, that does concern me but what you can you do?...get an old Honda VFR with gear driven camshafts or maybe a 2 stroke engine.

[Roles]

Maybe play isn’t the right word because you can’t feel it. But there could be a minor pressure change in the bolt, right where the thread of the crank starts. From that location on there’s a bit of space between the rest of the bolt and the surrounding crank. Anyway, it broke exact at the place where the thread starts. That made me think of a possible cause... a two stroke trophy would be nice ;-)

[earthman]

Do you know if a torque figure is mentioned by any chance, when installing this bolt from the factory for example??

[Roles]

What do you mean by torque figure? The servicemanual says 27 Nm. Not very tight for a bolt with 12.9 strength..