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High valve clearance on #1 exhaust cylinder - cause for low compression?

The Jimbonaut

The Jimbonaut
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I did a valve clearance check today, the numbers looked like this (from left to right, sitting on the bike) -

Exhaust - 0.004, 0.009, 0.002. 0.002, 0.003, 0.003, 0.004, 0.003
Intake - 0.004, 0.004, 0.004, 0.005, 0.004, 0.003, 0.006, 0.004

The compression test I ran the other day gave these numbers (from left to right, sitting on the bike) -

125, 150, 145, 150

So, am I right in thinking the low compression on #1 cylinder could be caused by the high clearance on one of #1 cylinder's exhaust valves?

Are the other valve clearances ok (0.005 is I believe a good number to aim for) - would my numbers be considered within the boundaries of "healthy valve clearances"?

Cheers,

- J
 
All you can do is attempt to bring that .009" down and see what happens. Flog bike a bit after setting it and see if anything changes. Valve may be toast. So are the .002" if left alone long enough-commonly those will be an issue real quick and I don't leave .003" alone either.

I have personally burned valves that carefully checked and rechecked at .002". In fact the first brand new one of these ('80 750F) I owned, in less than 5K miles, I thought I was within the book spec (and indeed I was) and I burned 5 valves to varying degrees.

The numbers are not real, I assume remove a couple of thou off any one you measure and closer to the real number running then.

Why I say use .005" as the go to number, they make virtually no extra tappet noise there. .004"-.006" as the range.
 
Thanks amc (again!), I really appreciate the help. I'll do that (I'll try pouring a little oil into the cylinder as well to check if it's the piston/bore that might be the problem).

By the way, when I took off the valve cover, there was so much oil in the cylinder head that it overflowed when I turned the crankshaft. How much oil in there is too much? I had to wick some out in order to be able to see where to put the feeler gauges!
 
Strange you should mention that about the #2 exhaust clearance.
As we already discussed, all my valve clearances would appear to be 'too tight as well (less than .034mm), except for that one cam which is at .06mm.
I'm now really curious to see if my compression test matches yours....
 
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The head has lots of oil in it and normal, the cams have to have it to live. Bunch of pockets to hold it for startup lube before oil pump comes online. ALWAYS suggested if new/rebuilt head to fill those back up with oil before an engine light up.

I've never checked exact valve positions for repeat inaccuracies but entirely possible there may be one spot where the cams moving around move to show the most valve clearance one can have just like burying it the other way.

I'd also be looking close at that cam lobe for wear, when valve clearance drops to zero it also begins to wipe all the oil off lobe and then lobe dies.
 
Thanks for the oil info, good to know that's situation normal =)

Just ran another compression test across all cylinders, #'s 2-4 all at 150psi, #1 at 130psi. Poured a teaspoon of oil in and whammo - psi went up to 180+. That means piston rings situation in that cylinder and not valves, right?
 
Depends on how much oil is put in. It's a false statement that says the engine has bad rings if the oil can even think about getting to the valve seat too, it can seal there just as much as at the rings. Whirling around to check compression will also throw some into the exhaust tract too.

So, while the answer is yes, it's not a qualified yes. Probably works there.

That one valve at .009" is telling you something...............not normal to be off that much.
 
The Clymers manual indicates that pouring a teaspoon of oil into the cylinder (and getting a higher compression psi reading) means a piston ring problem, not valves. But I've also been told that this test is far from black and white - a leak down test is the correct procedure.

When you say "probably works there" do you mean that in my particular case the oil-in-the-cylinder test works, and gives a good indication that it is piston rings? Not sure I totally understand what you mean there.

Do you have any idea what may have caused the 0.009" clearance in that one valve? Would that be indicative of something or could it be a number of things? I hope you don't mind all these questions - I'm new to all this and really appreciate you guys taking the time to help a brother out
 
The amount of oil put in as well as the angle of engine (actual piston assembly, and valve package in relation to it) have much to do with that. Personally I never put any emphasis on which one, it's low meaning it comes apart anyway to me.

Valve bent slightly to not close, guide seized up at a certain point, greatly eroded seat or valve seat ring on valve itself, Somebody tried and used incorrect shim there, tappet sticking from somebody moving engine around with no shim in tappet, it tears up tappet edge then tappet sticks, dead worn cam lobe. Look close at the lobe, common to wear it out when the clearance goes to zero, once lobe begins to wear there is no stopping it. You can turn lobe sideways in head and measure it from the side across the tallest point and compare to the others.
 
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