Not enough Exhaust valve adjustment

scharny61

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Hi all
I've been adjusting my valve clearances and come across an exhaust valve that won't open enough to get a .15mm feeler guage in. Does anybody know what could be wrong? Sticking valve maybe?
The valve appears to go in and out OK, new timing chain adjusted OK. Other valves adjusting OK.
I did do a valve grind when I had the engine out and could possibly ground off too much?

1980 stock.
thanks in advance.
 
It would be unusual for a valve to be stretched that much, I would think. Seat grind may be too deep. If the valve was sticking, it would tend to be a wider gap. Since it is too tight, the valve is coming too far up in the head or is over length. Did you check your valve overall length?

Double check and make sure you are at TDC, compression stroke, and the correct cylinder marks.
 
It would be unusual for a valve to be stretched that much, I would think. Seat grind may be too deep. If the valve was sticking, it would tend to be a wider gap. Since it is too tight, the valve is coming too far up in the head or is over length. Did you check your valve overall length?

Double check and make sure you are at TDC, compression stroke, and the correct cylinder marks.

Thanks, the seat didn't look like it had been ground before but the engines history is unknown. I agree with you about the sticking valve. I did put a donor cam in; does anybody know if there was a difference in the cams between models or engine types. I have the 447 motor. I'm going to take the head off and double check everything.
thanks again
 
You may be onto something with the donor cam. I think I read something about centers being 1.5 MM different? May be talking out my ass (wouldn't be the first time) but something to look at.
 
I don't think the earlier "256" cam will swap in because the sprockets are a different number of teeth. To use one, you need to change the sprocket to the later "447" one. Usually, you're able to back off the adjusters so there's like near 1/4" of clearance between them and the valve stem top. I don't think you could over-grind a valve seat that much but maybe I'm wrong. Did you hand lap the valves or spin them with a drill? Spinning with a drill is not recommended because you can lap them too much that way.

The only other thing that comes to mind is maybe the collets that retain the washers on top of the springs are not installed correctly and the springs are sitting too high. Correctly assembled, the washer and springs should sit just below the valve stem top .....

ValveKeepers.jpg
 
mmm, how many teeth are there on the 256 cam as opposed to the 447? I am also wondering if I set the cam chain one tooth out? could account for the lack of adjustment because even the inlet valve doesn't have that much adjustment room. I thought I did it as per the manual though. The collett looks normal, I tried that first.
As for the valves, they were done on the proper machine at work and I didn't touch the seats at all.
thanks guys
:banghead:
 
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