Effects of incorrectly shimed valves?

[Drumagician]

Hi all,
Just purchased my 1st xs1100 about 3 weeks ago. I have done a complete tune up except for reshimming the vlaves. I have checked clearances and they all seem to be tight ( approx. 0.05 - 0.1mm). I am curious as to the long/short term affects of this. Do I need to reshim now or is there no real hurry? How much performance can be gained from properly clearanced valves?
Thanks.

[natemoen]

If the clearances are too loose then the valves will not open properly and you will not get enough air/fuel mix or the exhaust will not be able to exit properly. If the valves are too tight then they may not shut completely and then loosing compression.

So you do stand to gain/ loose a lot if they are not correct. If you have it open check them and set them to the proper clearances.

[Drumagician]

Makes sense. My compression check came back with all 4 being around 155-160psi. I think these numbers are about as good as it can get right? So I think that my valves are closing completely. As long as this holds true, I would think that leaving them with the current tight tolerances would be best. Please correct me if I'm wrong.

[natemoen]

The clearance get smaller as the valves ware on these bikes. So if you are at the bottom end of the clearance already you are going to have to fix it very soon anyways. So again I say if you have it open check it and set them. If its not open and its not clicking and clacking and rattling your ok for now.

[Drumagician]

Well, no clicking noises of any sort so I will leave them be for now. I am curious as to what exactly is happening to make these noises in this scenario. Also, i would like to know if it is possible to have the valves open so much (tight clearance) to the point where it would negatively effect performance (intaking and exausting too much).

[dbeardslee]

Being open too far isn't the problem - it's not fully closing that gets you. These things are noisy on top to begin with, and after shimming they often make more noise - probably due to the lobes slapping the top of the valve buckets. The other thing that makes noise on top is your cam chain - supposed to be retensioned every 1k miles. That will make a big difference in how noisy the top is.

[Drumagician]

Got it. Thanks for the replys guys.

[Incubus]

Steel expands as it heats up. If your valves are too tight they may not close properly when the engine gets hot. That's why you set valve clearance to begin with. To allow for heat expansion.

Patrick

[Drumagician]

Ah, I should have guessed. I suppose I will re-shim based on that.

[DGXSER]

Note that the clearances given in the manual are for a cool engine, not a warm or hot engine. I doubt nayone is going to be reaching and feeling around in there much when its hot, but just to be clear on the issue.

Another note worthy point, the valve clearances for the 80 and newer engines is different than the older ones. The Clymer manual has a separate chapter in the back for the changes in the newer models.

[Drumagician]

Good point.

[DenyP]

Too tight and they will float at high RPMs causing the engine to cut out.

Deny

[Crazcnuk]

Not likely. Float will happen at a set speed no matter how they are set.

However, too tight will cause your valve(s) to burn over time. Once one or more valves can't close all the way the combustion temps will start to burn the valve.

[DenyP]

Not likely. Float will happen at a set speed no matter how they are set.

I disagree. The point where float happens when dealing with solid lifters is based upon a number of factors and setting them too tight is one of them. However, you are entitled to your opinion.

Deny

[Crazcnuk]

Actually 'float' is determined by the valve springs. When the valve springs can no longer close the valves fast enough to complete the cycle properly, due to over reving, you are suffering from valve float.

Feels like a rev limiter, if the rest of the engine holds up. Many engines are designed to do this on purpose, it's a cheap way to limit engine speed. This is why it is recommended to change valve springs when you put in a performance cam.

Small block Dodge engines were easily capable of turning 8000rpm, but the factory springs usually only allowed 5500-6000rpm.

If your valve(s) are too tight, you will experience compression loss at all engine speeds once the engine is up to temperature because the valves will open sooner and close later than they are supposed to.

Too loose settings cause the valves to open late and close too soon, also cutting into performance.

The trade off is to set them according to how often you want to check the valves. For optimum performance you set them at the minimum clearance and check often, or for convenience you can set them loose and check less often.