New valves in not-new heads - Vintage Mustang Forums
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post #1 of 9 (permalink) Old 05-20-2019, 01:11 PM Thread Starter
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New valves in not-new heads

Bit of history here. Back some 20 years ago, I bought a set of rebuilt heads from eBay. They cam assembled, and everything looked really good. I bolted them to my engine, and thought nothing of it. Since then I have probably 15-16k miles on these heads. No issues. These are 1971 351-2V heads (not my originals obviously).

Fast forward to today. I am rebuilding these heads with all new components - new single piece stainless valves with single groove locks, new retainers, and new springs. I have taken these heads apart to find a) the guides have been replaced, and they are in great shape, and b) the valve seats all look great. I have checked the install height for the springs, and I am finding that all the install heights are at 1.795-1.800", exactly where I want them, and very consistent, meaning (hopefully) that all seats were ground to the same depth. My plan was to blue the valves, and if minor lapping was needed, lap them in, and leave it at that.

Now, someone has asked me why I dont have the heads machined and the valves lightly ground to ensure a quality seal. My response is, because as far as I can see they don't need it. My position is that if the blue and lapping proves to show a good seal, that I dont need to worry about machining the seats, that the valves will seal just fine. Since the guides are nice and tight, and all the valves were in like new condition (save some carbon build up), nothing points me towards thinking I need to do any machine work.

But I kick the question to a larger audience... in this scenario, is lapping the valves in a good option (meaning a reasonable life span of normal performance)? This is a street machine with under 5000 miles annually. No racing, just spirited stupid driving.
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post #2 of 9 (permalink) Old 05-20-2019, 05:05 PM
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An engine builder told me that lapping valves leaves residue from the lapping compound. If there's a problem with the valve sealing, get the seats recut. I don't think lapping is the best choice for the long haul.
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post #3 of 9 (permalink) Old 05-20-2019, 05:32 PM
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If the seats don't need to be re-ground, the valves are in good shape and the heads have not seen a lot of run time, I see no problem with lapping the valves. Just look at all the seat patterns very closely to make sure nothing odd has happened and that the seats and valves were ground properly before. My opinion on this will not likely be a very popular one on here.
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post #4 of 9 (permalink) Old 05-20-2019, 07:08 PM
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I would lap the valves. No question about it.
I would also take the time to index the spark plugs.
Maybe even do some light port work. Especially on the exhaust side.
And port match the intake manifold.

Basically, do all the cheap little things you can while the heads are off. Every little bit counts.

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post #5 of 9 (permalink) Old 05-20-2019, 10:52 PM
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Do the new valves have chrome plated stems? If not, I'd double-check your guide material. If the guides are cast iron it won't be a question of IF the valve(s) seize in the guide(s) but when.

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post #6 of 9 (permalink) Old 05-20-2019, 10:56 PM
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I like yr plan blue, if clean even seat, put it together and go driving
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post #7 of 9 (permalink) Old 05-21-2019, 01:54 AM
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Generally, you clean things up after you lap the valves, so there isn't residue...

It does make a difference in seal, and really tells you if they are true while you're at it. A worthwhile thing to do, IMHO!
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post #8 of 9 (permalink) Old 05-21-2019, 10:40 AM
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To check the seal, reassemble the heads and fill the ports with lacquer thinner.
If it leaks out, lap or re-grind the valves.
If it doesn't leak out, move forward.
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post #9 of 9 (permalink) Old 05-21-2019, 02:15 PM Thread Starter
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Quote:
Originally Posted by Woodchuck View Post
Do the new valves have chrome plated stems? If not, I'd double-check your guide material. If the guides are cast iron it won't be a question of IF the valve(s) seize in the guide(s) but when.
Yes, new valves have chrome plated stems... AND I think the new guides in the heads are in fact bronze. They are spiral-type.
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