Valve Cover Gasket

[TamSV]

I've got the covers off for valve clearance check. Mr Haynes tells me the gasket should come off "glued" to the cover. Half right.

The gaskets were stuck in the half moons - I got them freed off without damage but now have half the gasket stuck to the cover and other half not.

I know I have to put some sealant on the half moons when I reassemble but should I be putting some in the groove on the cover too?

TIA

[Sid Squid]

No, it shouldn't need it if it's in good condition.
Only the semi circles should have sealant, but it isn't commonly renewed when the cover comes off, often with no ill effect.

[TamSV]

Thanks for the quick reply Sid. I was asking in the firm belief that I'd be tightening it all back down tonight. However, measurements are;

Front Left Right
In 0.11 0.14
Ex 0.20 0.20

Rear Left Right
In 0.11 0.10
Ex 0.20 0.18

These were quadruple checked in that "I don't want this to be true" kind of way. First thing I'll be doing is borrowing another feeler gauge to check again.

Assuming I get the same result, one exhaust valve is out of spec and several are right on the edge. Should I be changing shim on just the one or should I do the others just now while I'm in there?

The clearances were checked by a bike garage at 17,000 miles and the bike is now at 25,000. This seems like a hell of a lot of adjustment for 8,000 miles but maybe someone can put me right. Looking more closely at the paperwork this bike might have more mileage on it than has been presented but that's worthy of another thread which will be started forthwith.

On a positive note, I wasn't going to check the clearances for another 5,000 miles. Do I wish I'd checked when the engine was out a few months back? You betcha.

[fastdruid]

FWIW when I checked mine at ~16500 none of them needed touching.

Doesn't mean that its happened in this case but it wouldn't be the first time someone has charged and not done the work knowing it unlikely that they'll actually need doing...

Druid

[Sid Squid]

Seeing as you're doing it and it's apart now I'd take everything that's on the edge out as far as it can go, that means it will be the longest possible time until it needs doing again.

[TamSV]

Cheers, I'll take that approach.

Suitable shims and tensioner gaskets then.

And while I'm in there...pointy cam swap perhaps.

[TamSV]

Originally Posted by Sid Squid

I'd take everything that's on the edge out as far as it can go.

I'll be digging the shims out at the weekend to see what I need.

The table in the service manual suggests I drop down .05 to get back into the middle of the range. Just so I'm clear, are you recommending I drop 0.10 to bump them to the top of the clearance range i.e. they're only going to continue to tighten up?

[TamSV]

As you were.

On removing them, I've noted the factory shims are odd sizes so it becomes clearer which replacement I need to get into a good part of the acceptable range.

[Sid Squid]

Originally Posted by TamSV

Just so I'm clear, are you recommending I drop 0.10 to bump them to the top of the clearance range i.e. they're only going to continue to tighten up?

Yes, as long as it's in the acceptable clearance, the widest clearance, particularly for the exhaust as they have the hardest time, means the longest time until it will need to be changed again.

What happens to your exhaust valve and why the clearance closes up:

Originally Posted by Me!

Every time the inlet valve opens it receives a nice cooling rush of incoming gas, and when it's closed it dissapates heat through the valve seat, even though that's a small area for conducting away heat - every little helps - in short the valve itself has an easy life, and thus wear in the opening mechanism commonly outweighs the wear to the valve - thus the clearance often opens up a bit. Exhaust valves however don't have such an easy time, they get and stay very very hot, their primary way to dissapate heat is the thin ring of the valve seat, and a little up the stem, everytime the long suffering exhaust valve opens it gets fried with gas at/near combustion temperature - typically 300-700C - thus in the case of the exhaust, the valve tends to wear more than the opening mechanism, hence the clearance reducing.

Also we have a nasty Catch 22 - if the clearance becomes significantly reduced, (or worse still if there's no clearance and the valve never fully closes), the valve spends less of the already small amount of time that it should do closed, thus it never disspates the heat it should do and can literally melt, this is called burning a valve, no surprise there, and you really don't want to get into that.

A round of applause for your exhaust valves please - the hardest working bit of your bike, full stop.

[fastdruid]

I've found it worth while noting what *all* the shims are, sometimes you can move them round so that you only need one or two shims.

Druid