[ejrempel]

Where should my machine shop set the valve guide to valve clearance on my #781's? The old shop had them at 7 to 9 thou, and my new guru said that it would promote fairly rapid wear of the bronze K-liners that loose. So he charged me 480 bucks to redo the heads and put a complete new guide in one hole. He hasn't told me where he set them.

 

[Wolfplace]

Originally posted by ejrempel:
Where should my machine shop set the valve guide to valve clearance on my #781's? The old shop had them at 7 to 9 thou, and my new guru said that it would promote fairly rapid wear of the bronze K-liners that loose. So he charged me 480 bucks to redo the heads and put a complete new guide in one hole. He hasn't told me where he set them.

I hope you mean 7-9 tenths
7-9 thou is WAY TO LOOSE
It depends on what kind of guide but for liners or bronze we use .0008-.0012 intake & about 0015 for exhaust.

 

[camcojb]

7 to 9 thousandths is very loose. 7/10 to 9/10 of a thou is more normal (.0007 to .0009) Mine have always been in the 9/10 to 1 thou range (.0009 to .001)

Jody

 

[von]

A few years ago mine were set at .001 (supposedly) with new cast iron guides and new valves. With about 70 miles on it an intake valve seized in the guide. What could've been the problem?

 

[ejrempel]

Von, the clearances could have been too tight. This is what my old shop says about my new shop: that valves are always hanging open on him, thereby causing great grief and destruction.

 

[camcojb]

Yeah, my .001" recommendation above would be on an intake; exhaust like to be a little looser, .0015" is a good number. I'm guessing that they probably weren't checked and were just too tight.

Jody

 

[Wolfplace]

Originally posted by von:
A few years ago mine were set at .001 (supposedly) with new cast iron guides and new valves. With about 70 miles on it an intake valve seized in the guide. What could've been the problem?

In my opinion .001 is a little tight for cast iron. It is fine for bronze but I prefer .0015 min for cast especially with positive seals.

 

[von]

When I took it back (others were OK but a couple were starting to gall), they opened them up to .002. I now have bronze liners from another shop. It was the #5 intake. For some reason that cyl seems to run hotter than others (396). It welded the valve to the guide in the open position, piston hit the valve and bent it, but no other damage. Thank the forged pistons for that.

 

[ejrempel]

I asked my new shop how he measures his valve to guide clearance, and he uses a dial indicator at the head of the valve, gets his measurement, and divides by two. So, 6 to 9 thou is really 3.5 to 4.5 thou. Still, way to loose. He set them up at 2 thou, and widened the valve seats to 90 thou, from the extremely narrow values I had going in. He said that with my spring pressures at 575 to 600 lbs open that a wider seat on the street would live longer. The cuts were 30, 45 and 60 degrees. Two of the seats were difficult to obtain due to the radical removal of metal in the throat area during porting by 'experts'. They sit a hair lower. Another $385 bucks, bringing the total to $865 for this round of repairs to the heads.