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Discussion Starter #1
I took this valve out of my 1996 Bronco 5.8L... these valves were ground a couple years ago, and the car never quite ran right. Loud tappets, and a weird knock once per cam rev (instead of crank). Didn't blow smoke, but I always thought the compression could have been better. I think the compression values were about 145 per cylinder. All the intake valves look like this one! It's as if... the tool my machinist used was ... not right? I didn't do these valves myself, I had them done by a machine shop.

see picture included...
 

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Did you just take the valves, or the whole head? If they did just the valves, did you seat them?
 

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Discussion Starter #4
prior, I took in the heads and the valves and he did both. I took it to a different machine shop today, the first guy is highly suspect... he said, "these valves were misground, there is no WAY this pattern could have been caused by chatter or loose valves, or by any other means, his grinding stone wasn't properly maintained, and he caused you to have to take out your engine again. No WONDER it didn't run right."

He's re-cutting the head valve seats, and the new valves I bought. damn.
 

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Did he say why the inlet valves are only affected ? and how that pattern could have been caused by grinding stone ? Be very interested in his conclusions as never seen that caused on any machined valves before .
 

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Discussion Starter #6
he said that as the valve turns in the chuck, if it's turned fairly rapidly, and the stone is oblong, even *slightly*, it will "beat a pattern" into the valve. Though this pattern does seem way, way too symmetrical for that. But then, if it was caused by the valve clacking around loose in its guide, why would it be this symmetrical? The only answer is for it to be harmonically stabilized bouncing around in its seat, due to some crazy just-right circumstances, OR it makes sense it was ground wrong. since the grinding chuck always turns the same frequency, and the stone is the same amount of out of round, it makes sense that all the intake valves have exactly the same pattern... weird that the exhaust valves don't show this pattern.
 

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Not really a viable explanation , too many ifs or buts , backtracking and no reason why the exhaust valves were not the same . Bit disappointing as myself and another retired garage owner who I had shared the picture of the valve with were hoping for an answer to something we had never seen before .He especially as he had also spent many years in a machine engineering shop .Well guess we will never know for sure , hope everything goes well after rebuild . Keep us informed ?
 

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Discussion Starter #8
Nope, you're right, he said it's the CHUCK that was out of round on the valve grinder, not the grinding wheel, I misunderstood him. That makes sense. And there is no guarantee that the machine shop ground the exhaust valves the first time, I didn't check up on them after he gave the heads back. My exhaust valves were really cruddy when I took them out this time. The new machine shop guy said he'll clean them up and look for the same pattern.

The new machine shop guy also said the valve seats were "WAY OFF" and he had to really pay attention to get them back into flat + round. He said it was a wonder the car even drove...
 
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BroncoBuck
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