Intake/Exhaust valve adj and compression?

[TOKFLA]

I spent quite a length of time finding valve shims (25mm) for my 1.6L 4AFE Corolla and have finally gotten them in. I do not claim to be an expert on this and since shims were 13.30$ from Toyota I got some std sizes and specifics for about $6 ea. The car has about 77,000 miles on it now and the last time I checked the compression it was about 145 or so uniform on each cyl. Today it was running 132 to 140. 3 of the exhaust valves are down to .007 where they should be .008"-.012". What risks am I running at this clearance? With the valve clearances tighter will the compression be lowered? The motor does not smoke or the like. Seems to run better with the closer clearances and I did not intend to get the .007" exhaust valves so tight but getting the proper shims is a pain and I did not want to put them back to what they were.

[SCT]

The shims basically increases/decreases the opening when the valves open up; Not increase cylinder compression. The only time compression is related with valves are when the valves are not closing completely, like from carbon build-ups or damaged valves.

When you put in a bigger shim on the exhaust, more exhaust can exit out the chamber. Bigger shims on the intake, more air/fuel in the chambers.

Shims do wear over time which decreases the performance of the engine. If you're replacing them, I recommend only replacing them with the original size shims or close to it. It does effect fuel economy, I think.

[TOKFLA]

Thanks for the input. I agree with your logic. What I was concerned about was possibly having burned a valve from too tight clearance on the exhaust. I thought the tolerance specs were to allow for heat expansion.

[SCT]

I don't think tighter clearances can cause a burned valve but may lead to it from normal wear and tear with the given 'new' spec shims.

Even though the shims can be changed out, it doesn't effect the size of the valve. When the valves were designed and manufactured, heat expansion is considered so the valves can seal close to perfect at normal running temps. Changing shims will not effect a valves heat expansion.

Also, with more air/fuel going in and depending on the mixture settings, you could be increasing the temperature which would also take it's own toll on the valves. Things get hotter thus expands more... then it slowly gets worse from there...

[MR2Jedi]

Originally Posted by TOKFLA

I spent quite a length of time finding valve shims (25mm) for my 1.6L 4AFE Corolla and have finally gotten them in. I do not claim to be an expert on this and since shims were 13.30$ from Toyota I got some std sizes and specifics for about $6 ea. The car has about 77,000 miles on it now and the last time I checked the compression it was about 145 or so uniform on each cyl. Today it was running 132 to 140. 3 of the exhaust valves are down to .007 where they should be .008"-.012". What risks am I running at this clearance? With the valve clearances tighter will the compression be lowered? The motor does not smoke or the like. Seems to run better with the closer clearances and I did not intend to get the .007" exhaust valves so tight but getting the proper shims is a pain and I did not want to put them back to what they were.

You run the risk of the lifter hitting the camshaft.

I guess you mean 2.5 mm. (25mm is close to an inch)
What made you decide to buy that thickness shim? If your clearance has gotten smaller, it probably means the valve seat is worn. You need a thinner shim to achieve the proper clearance.
If the shim were worn, you would have larger clearance.

This is the proper way to figure the new adjusting shim thickness.
T..........Thickness of used shim
A..........Measured Valve Clearance
N..........Thickness of New Shim
N = T + (A - optimum specified valve clearnce )

[TOKFLA]

No I meant the shims are 25mm dia shim and they are the same as some Honda Motorcycles. The last ones I bought were 3.00 and 3.10 mm and I had measured previous but these could only be bough in 5x's the earlier 4 were exact. What a job doing this! The clearance was larger previous to changing them and that is why I did that. I did all the calculations you mentioned. The clearance I was talking about was between the shims and the camshaft.
What a race car you've got there.
I am out of here for a while.

[MR2Jedi]

Yes it is and you're welcome.

[verlaryder]

Why don't you want to set the clearances within the factory specs? How would you feel if a dealership mechanic did that to your engine? And are you using motorcycle shims instead of Toyota shims?

If the exhaust clearances were originally between .008-.012 then you should not have installed any new shims to tighten the clearance to begin with. It's rare for the clearances to get out of spec on the 4A-FE, even after 300,000 miles.

Slightly tight clearances will not likely hurt anything and the engine will sound smooth, but it will also tight and reluctant to spin at high rpm.

To get the .007" valves back to .009 or .010 you will need to install a shim that is one size thinner. The shims CAN be purchased individually for something like $4-6 bucks each at online discount Toyota dealerships like www.1sttoyota.com

You are also not following proper procedures for checking the compression because the correct compression is up around 190 PSI on all cylinders and 77,000 miles is not enough miles to cause a drop in compression

[Flashmn]

Tighter clearances will lessen the time the valve is on the seat and the valve will run hotter, it might eventually become a problem.

[TOKFLA]

I could not get the exact sizes. The Honda shims are identical. $13.30 per shim was too much following the first 4. I told you they were beyond specs- over .012 etc. I appreciate your criticism but the car had sat for 4 years in the southern humid sun and started out really quiet but following 2000 mile drive on fresh valvoline in place of synthetic the valves were starting to make noise. They were above the specs. I am at 4700 feet and that changes compression=10Lb/1000 feet. I will check out www.1sttoyota.com as I have not heard of them. I know I need slightly thicker shims.
Thanks

[MR2Jedi]

What year is your Corolla?

[verlaryder]

Originally Posted by TOKFLA

I could not get the exact sizes. The Honda shims are identical. $13.30 per shim was too much following the first 4. I told you they were beyond specs- over .012 etc.

It sounds to me like you attempted this job without reading or understanding the Toyota factory repair manual.

The manual would tell you that if the measured clearance of an exhaust valve is .013" (slightly too loose) then you the installed shim and measure its thickess using a micrometer. If the measured thinkness is, say 2.70mm, then the manual tells you a shim that size = a shim number 10 size shim and that the next available thicker size shim is a number 12 shim (2.75 mm). So you call a Toyota dealer and ask when you could pick up a number 12 shim for a 4A-FE Corolla. Then when you install the number 12 shim the clearance will decrease down to about .011", which puts the clearance on that valve back to within specs.

Do this procedure for all 16 valves.

Honda shims might have a different metalurgy that could result in heavily wear to either the shim or the camshaft lobe. A Honda shim might not even fit perfectly right. If a shim should pop out of the bucket valve lifter on it's own for any reason (such as not being a perfect fit or shape), your camshaft would be instantly destroyed.

[TOKFLA]

You might have a point about the metallurgy but my experience I have never seen these sort of shims wear as they are the hardest stuff I have ever seen. (Tried grinding down some yamaha shims at one point-almost impossible). They could be harder on the camshaft but fit at a perfect 25mm. The wear would be in the future and not immediate. I did the measurement correctly but it was an extended period buying all shims and getting them in and I had to approximate as I said.

"They were above the specs. I am at 4700 feet and that changes compression=10Lb/1000 feet. I will check out www.1sttoyota.com as I have not heard of them. I know I need slightly thicker shims.
Thanks" - Sorry, I meant thinner shims.

The corolla is 1992.