Topic: Broken camchain

[eigenvector]

I'm working on one of the CB550 engines that I bought today and I'm seeing a pattern that I don't like.

This would be the 3rd engine that I've worked on, and I notice that it too has a broken camchain.  The break is clean right at the roller, like it snapped suddenly.  The follower is pretty torn up, the tensioner looks well used.  I see no evidence that the camshaft or camshaft sprocket are damaged - look pretty good really.  I see no evidence of damage in the crankcase itself.

My paranoid mind is wondering a few things and I'm hoping I'm wrong.

Is a broken camchain generally a sign of a siezed engine?  I'm afraid I haven't tried to test that theory because the engine isn't in a position for me to turn the crankshaft (crowded workshop).  The engine oil is still in the bike, inexplicably they didn't drain it before storage - and the oil is VERY black, smells like smoke.  I see no particles in it though.

Believe it or not that's my positive assumption, my negative assumption is that the guy I bought it from disabled the engine purposefully (perhaps required in order to sell it as a junk engine - I don't know just guessing).

Just how common is a snapped camchain and just how long do those followers last - this engine can't have more than 30k on it.

[MoMo]

the rubber roller can deteriorate from many factors-gas in the oil, not adjusted properly, normal rubber rot.  I just had a 350 cam chain break-roller guide was totally shot and the chain broke bending one valve, not bad damage all things considered...Larry

[HondaMan]

The 500/550 is one of those engines that feels like it can wind up forever. I've seen quite a few that got would a little TOO far forever, and the long intake runners will fuel that thirst just fine to about 12k RPM if you're not careful. After enough collisions between valve and piston, it can stop one short and the resulting bottom-end momentum parts the cam chain. If the bike was run a long time with 10w40 oils, the chain pins wear a lot, helping this process along.

[Tempast]

I've got 10-40 in my '77 right now, as the dipstick says. What should I be running instead? I live in BC, Canada so we have mild temps. Usually summer is 15c in the morning and up to 28 during the day.

[dave500]

oil aint the cause of snapped cam chains,downshifting too hard is,if the oil is #$%* enough to cause a chain to wear to the point of snapping the bearings will have turned themselves inside out first,only a mechanical jam up will snap a cam chain,or a poorly fitted peened over replacement link or clip type dislodged,even with a sloppy worn/out of adjustment tensioner the cam chain wont snap,itll be noisey though.