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Old 07-08-2007, 07:15 PM
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Cylinder Head Help

I have a real puzzler that I cant figure out. My brother bought a set of RHS cylinder heads 12301 cast iron 180 cc runners and 74cc chamber. .202 and .160 valves we put .100 long valves and a set of springs for his camshaft which is a comp cams 280h. He put the heads on his 383, flat top pistons, 780 vacuum sec Holley carb, GM HEI. The car started up and ran fine He set the timing carb, etc and took it for a drive, he made it about 5 blocks and it started to miss and a small knock. He shut it off pulled it home pulled the valve covers and saw #8 exhaust valve stock open. Pulled the head and found the valve gaulded(sp). Took it to the machine shop. They replaced the valve and ran a .343 reamer through the guide. put it back on and started it up and it ran for about 10 or 15 minutes and started to miss and knock.. Pulled the valve covers and found #3 exhaust valve open.. Pulled both heads and took to the shop and replaced all the valves and ran the .343 reamer throught each guide. Put the heads back on and guess what.. about 15 minutes it started to miss and knock.. I only know of 3 things that will cause a valve to gauld Heat, being thight, and lack of lubracation. I measured all the valves and all the guides had a "new" .343 reamer ran throught them. I personally lubed each valve stem and installed each valve.. I cant figure out why this is happening.. Any help???

Thanks guys..

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Old 07-08-2007, 07:54 PM
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Since all of your troubles are with the exhaust valves MAYBE the valve guide is sticking out into the exhaust air flow too much. If the guides are pressed in maybe they were driven in too far to begin with or maybe the retainer is hitting them in when the larger lift cam opens the valve?

Just my thoughts.

Good Luck
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Old 07-08-2007, 09:44 PM
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This is a good example of why you can't just buy a set of heads and just bolt them on. I have seen serious issues with almost EVERYBODY'S "ready to bolt on" heads.

I have said it many times here. When you get some new or reworked heads from somebody you don't know personally, HAVE THEM CHECKED by a good machine shop with a good reputation.

What it would cost you (I generally have to do a valve job and mill them, especially NEW aluminum head assemblies), you have probably aready spent in gaskets, materials, and machine work. You can't take anything for granted.

Having said that, I would make sure the timing isn't retarded. That will make the exhaust valves run hot, making them stick in the guides.

But a lot of the "big name" shops like to brag about how tight they make the valve-to-guide clearance (too damn tight in my opinon). THEN they use a positive valve seal on that too-tight of a guide.

If the valve seals have a garter or tension spring on the top of the seal (making it tight on the valve, not the guide), it wouldn't be a bad idea to remove it from the exhaust seal.

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