Tappet adjustment shims (GSF250)

[cbfb]

Now on my GSF250, the tappet clearance is 0.17-0.27mm (intake) and 0.20-0.30mm (exhaust).

Over half the valves are right on the lower limits (i.e. 0.17/0.18 on the intake and 0.20/0.21 on the exhaust).

What I can't seem to find out though is:

1. At what stage do I need to adjust them? They are still within the correct range but instinct tells me it's best to adjust them now before something nasty happens and also cause I've got the engine apart anyway.

2. When adjusting the shims, what clearance should I be aiming for? Instinct says to go for halfway between the extremes, i.e. 0.22mm for intake and 0.25mm for exhaust. Is this correct?

[clint640]

If you've got the engine apart already it makes sense to reset the clearances to the middle of the range IMHO.

If you want max performance it is better to run at the tight end of the range, but check them frequently to make sure they don't go too far under. If you can't be arsed adjusting the valves all the time running them at the loose end of the spec will mean less adjustments but maybe a tiny tiny bit less grunt.

Cheers
Clint

[cbfb]

If you've got the engine apart already it makes sense to reset the clearances to the middle of the range IMHO.

If you want max performance it is better to run at the tight end of the range, but check them frequently to make sure they don't go too far under. If you can't be arsed adjusting the valves all the time running them at the loose end of the spec will mean less adjustments but maybe a tiny tiny bit less grunt.

Cheers
Clint

Cheers Clint. When you say the tight end, I'm guessing you mean the lowest clearance (i.e. what they're on now)? From what I've read it's worse if they go off this end of the scale than if they get too loose. And no I can't be arsed checking them more than for its annual service!

[ducatilover]

Personally I would adjust them to the clearance that will give you the most margin for wear. Either way it should be done at routine intervals and chances are you won't have to do them again. As long as you are withing spec I wouldn't worry, but, do them since you have it apart just for a peace of mind.

[cbfb]

Personally I would adjust them to the clearance that will give you the most margin for wear. Either way it should be done at routine intervals and chances are you won't have to do them again. As long as you are withing spec I wouldn't worry, but, do them since you have it apart just for a peace of mind.

Right-o, will go for the middle of the recommended range then, that should sort it out. Yeah I plan to flick the bike on in a year or so anyway so hopefully be the last time I have to do it.

[Jonno.]

Put them in the middle and you probably won't have to look at them again.

[marsheng]

If it is for racing, the smallest gap is the best. For the road, within limits is fine. At $16 each or so I would not change them. My Honda's clearance is .06 and .08 so anything over .1 is fine.

[Jonno.]

If they're shims and not adjustable tappets then you can probably get away with measuring every one and the clearance, swapping a few and replacing only one or two and have good clearances all-round.

[marsheng]

Basically you don't need any clearance when hot as long as the valve closes. The clearance is to take up wear. As the valve wears and sinks into the valve seat, the clearance gets taken up. My guess is that .2 mm clearance is so the bike will run for 100k with no adjustment required.

[ducatilover]

Basically you don't need any clearance when hot as long as the valve closes. The clearance is to take up wear. As the valve wears and sinks into the valve seat, the clearance gets taken up. My guess is that .2 mm clearance is so the bike will run for 100k with no adjustment required.

You need clearances when hot. Many motors require the engine to be hot for the clearances to be done.

[cbfb]

You need clearances when hot. Many motors require the engine to be hot for the clearances to be done.

Second that, can do quite a bit of damage with insufficent clearance.

Suprised about the engine having to be hot though, my bike's service manual specifically says cold.

[ducatilover]

Second that, can do quite a bit of damage with insufficent clearance.

Suprised about the engine having to be hot though, my bike's service manual specifically says cold.

It varies between cars. Have to set clearances in the straight 8 Buicks when hot. I've had a few cars that needed to be done when hot, and the other way around too.
Have fun with the clearances

[cbfb]

It varies between cars. Have to set clearances in the straight 8 Buicks when hot. I've had a few cars that needed to be done when hot, and the other way around too.
Have fun with the clearances

Interesting, wouldn't like to have to do that with the bike, would be a bit of a race getting it all stripped down, rad off etc before it cooled.

Cheers all for your advice.