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Discussion Starter #1
I am prepping a 94 roller 351 for my 68 mustang. I got a set of gt40 heads for $75. I am considering a rebuild on heads. New guides probably. Question is, do you replace all valves during a rebuild? I have surface grinder and spin fixtures to properly grind valves, i just don't know if it is acceptable to reuse them. Are they usually magnafluxed? I also have seat grinder. A light clean up isn't going to go through the induction hardened seat? I have seen guides diameter of .502. If i ream with a .500, is the .002 interference fit enough? Or do i need a .499 or small reamer? Lastly, valve springs. If they check out fine do most people reuse? (Straight, correct pressues at heights). Is there a source for quality stock replacements, i am just using a .444 ho cam with 1.7 rollers(.472 adjusted lift) and clearly not going to be a screamer, hoping strong till 5500, although that might be optimistic, gt40s aren't the best...thoughts? Not really trying to replace valves or pop for the trick flow kit with better valve springs(i think stock springs can handle 5500 rpm provided they are in good condition as i used to run my 5.0 till 6000 plus with no float), but at same time trying to get something together to last a few years till i can do a proper build.
Any experience would be appreciated, i am looking forward to doing my heads, i made a face mill to mill heads, i bought a tilting table for my Bridgeport to do guides,got a spring compressor, bought carbide burrs for porting and was given the seat grinding tool. I just want say i did them, but saying i did it is no fun if I mess it up
 

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So many questions.... GT-40 or GT-40P?

a. Replacing valves. I only replace ones that are damaged (bent, scored, tip wear, etc.) or where insufficient margin (< 1/32") is left after grinding, or if you plan on installing larger valves then, of course, you'd replace them all. I don't think I'd bother with magnafluxing them.

b. Seat grinding? Even re-grinding the seats for a larger valve isn't going to "go through" the induction hardening so go for it.

c. Interference fit of your valve guides? .0010-.0015" when installing into cast iron heads. I would lean toward the .0015" end...better to be too tight than too loose, right? LOL.

d. Valve Springs? For me, a lot would depend on how many miles are on the springs and how the engine was run. Valve springs break from fatigue so maybe better to be safe than sorry? If you have GT-40P's then replacing the springs is a certainty as they are barely adequate for "truck" use.

:)
 

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Discussion Starter #3
Thanks Wood chuck. Forgot to mention, 3 bar gt40 not the p. You have confirmed everything i thought. Any idea where to get quality replacement springs?
 
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