Valve Clearances

[Diddums]

Yep. It'll go bang in a big way. If you're realy unlucky it'll seize up at speed, locking the rear wheel, which could cause a horrible off if you don't get to the clutch in time. Better still, it could seize and throw the chain, which could wind itself around the hub / sprocket / whatever and lock up the wheel, except that this time the clutch won't save you.

I'm not trying to scare you and the odds of it happening are fairly slim but the damage it could do both to he bike and you are fairly considerable.

 

[Teabag_Terry2]

Well I had a brand new 2 stroke enduro bike I paid 7 grand for lunch its engine and gearbox at around 60mph. The oil pump failed and the engine had no oil. Woke up in hospital, not pleasant.

Better put my R1 in for the valve clearances I suppose.

Bloody annoying paying that much though.

 

[unKle]

I'm interested to know how an engine can possibly destroy itself if valve clearance adjustments are neglected? My understanding is that camshaft/lobes/shim buckets/valve stems wear which leads to the valves not opening/closing when they're supposed to, altering the valve timing and effecting the performance of an engine, i.e. running like a bag of crap.

The worst outcome is burnt out valves which would not destroy an engine. Costly repairs, but certainly not a seizure.

I'm not saying you shouldn't have valve clearances checked, as you say it's ridiculous that you have to pay out a lot of cash for a vehicle that's not worth a great deal, but that's how it is, have to swallow it or risk a possible expensive repair!

Borrowed from Vstrom forum;

"For every four stroke cycle, the valves are accelerated from rest to fully open by the cam, stop, then are accelerated to fully closed by the valve springs. The wear that takes place as the valves smack into the valve seats slowly closes up the clearance between the cam & cam follower (bucket). The exhaust valves have to endure the same conditions and deal with erosive combustion gases as well, while not having the benefit of cooling from the intake mixture. This is why the exhaust clearances usually close up quicker than the intake.

 

[Dogbreath]

I'm interested to know how an engine can possibly destroy itself if valve clearance adjustments are neglected? My understanding is that camshaft/lobes/shim buckets/valve stems wear which leads to the valves not opening/closing when they're supposed to, altering the valve timing and effecting the performance of an engine, i.e. running like a bag of crap.

The worst outcome is burnt out valves which would not destroy an engine. Costly repairs, but certainly not a seizure.

Pretty much this. As clearances tighten you start losing performance because the valve starts being opened (slowly) by the acceleration ramp on the cam, which is there purely to take up the clearances at a sensible rate. When the wear is sufficient that the valve doesn't fully close when hot, you start losing compression and even more performance and at some point a burnt valve is inevitable. If you limp along long enough without burning out a valve/seat then the valve will stop closing fully even with a cold engine, and then it will become very difficult to start.

 

[TripleT]

Pretty much what my mechanic said too, I've not bothered as the bike is worth sub £2k and I'm doing 50miles a day on it so running it in to the ground.

 

[TripleT]

Following my cam cover gasket leaking my mechanic replaced the seal and whilst in there checked the clearances for no extra cost. Sitting at 23k miles now, they were due to be checked at 18k but I didn't due to cost and surprise surprise they're fine.

So great for peace of mind I guess but I wouldn't have bothered if I didn't have too.

The mechanic said the same as a different garage, he can only remember having to adjust 2 or 3.