Author Topic: Head question  (Read 528 times)

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Offline geraldt52

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Re: Head question
« Reply #15 on: September 11, 2017, 11:55:05 am »
geraldt52,
        It is common for '69 and later heads to have "sunken" exhaust seats on brand new heads.  In the '70s when my friends raced stock eliminator, they would order 10 heads at a time and keep the ones with the highest exhaust seats. We couldn't add false seats ( as we called them then) per NHRA rules. There were MANY heads with low seats to start. I'm not saying that is your case , but it is a fact.  68.5's were machined so virtually the entire valve was above the chamber. Mine still are that way.
   Randy
Mine are "68.5", Randy, an April build KR.  There's no way to know when it happened between 1968 and 2012, because the engine was never apart, but I strongly suspect most or all of it occurred sometime after leaded premium disappeared mid-80s.  This car never "sat", been on the road continuously since '68, while so many have had long periods of hibernation, especially since leaded premium disappeared.  Valves can't recede when the heads are laying on a shelf somewhere, or driven 50 miles every couple of years  :D.

You bring up a good point that I've never been able to confirm. I've heard that the heads "work" better the higher that the seats are. Is there any truth to that story?
Well for one thing, the higher the valve is, the lower the chamber volume is, the higher the compression ratio is.  I couldn't tell you how it might affect flow, all other things being equal.

Offline Armond

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Re: Head question
« Reply #16 on: September 11, 2017, 12:55:15 pm »
I took a look at the heads this weekend and I don't see any signs of them having seats installed.  I will have the guy's who are assembling it for me check them anyway.
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Offline 161854

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Re: Head question
« Reply #17 on: September 11, 2017, 04:38:51 pm »
  Valves that are "sunk" , hurt flow because the valve is shrouded by the "wall" surrounding the valve.  It certainly is possible there was some seat migration in the '72-75 era when the unleaded gas formulation was being "fussed with". A friend of mine ( rip) was a chemist at Conoco back then . He recounted that they did allot of "testing" on gas formulations in the begining without the public's knowledge. They had no idea of the long term affects . Some stuff burned really "hot" was one of his comments. He was there until the current E10 stuff was developed. He didn't believe in the addition of alcohol but said it was a cheap and easy way to help with tail pipe emissions.
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Offline b--r30

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Re: Head question
« Reply #18 on: September 13, 2017, 10:12:51 am »
Armond,I see that you said that the heads were done. It is true that seats become "work hardened" after extended use and will normally be no problem if still in decent orig shape. Obviously,big spring pressure would be a problem. Unfortunately,done heads usually means the seats were ground which removes most of the work hardened material.What I do with good orig seats is get new valves or really good reconditioned used and lightly lap the seats.If the contact area is decent and they pass the leak test,they are good to go. The ship might have sailed for this deal in your case but....

Offline redscj

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Re: Head question
« Reply #19 on: September 13, 2017, 11:47:04 am »
Armond,I see that you said that the heads were done. It is true that seats become "work hardened" after extended use and will normally be no problem if still in decent orig shape. Obviously,big spring pressure would be a problem. Unfortunately,done heads usually means the seats were ground which removes most of the work hardened material.What I do with good orig seats is get new valves or really good reconditioned used and lightly lap the seats.If the contact area is decent and they pass the leak test,they are good to go. The ship might have sailed for this deal in your case but....
     Once upon a time I bought some hard seats that were specifically designed to work harden in the first few hours of use. Nice thing was that grinding them was a breeze. Most hard seats don't have any of the seat cut into them. Because they are already hard, you wear the stones out fast. Then you need to keep sharpening the stones in order to get flat seats. Talk about a pain. These seats already had part of the seat cut in them & since they were in the "soft" state they ground really well.
     As for seats in original heads "work hardening". I'm a bit too skeptical to count on it. True, I'll give you that some might. Maybe even many or most might. But the fact that at least some heads don't harden leaves me to conclude that it is not a sure thing. If you have had an exhaust seat recede in a head. Then I'd be thinking that all of the exhaust seats in that head are in danger of receding. Others may disagree & that's ok with me. If I had a seat recede in a head, I'd replace the other seats in that head at the same time.
     One of the iron valve guide builders used to advertise that they used a better grade of iron in their guides than what most heads are cast of. I've never worked on a head that had one bad original guide that all of the guides weren't bad. Same on valve stems. If one valve stem was worn under, the whole set were worn under. It's a brutal environment in a cylinder head.
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Offline rhynerj

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Re: Head question
« Reply #20 on: September 13, 2017, 08:05:48 pm »
When I bought the R code coupe back in 1990, the Motor was machined and heads were done etc, but un assembled.  I plan on having the heads and block etc checked and assembled by a shop I have in mind.  My question is, can you tell just looking at the valves, if the heads had hardened seat cut in already?  Maybe it is a dumb question to some, but I hate grease and these things I leave it to professionals. I would like to know before I take them in.  Thanks for any input.
I'm having trouble believing that you've had an engine unassembled for 27 years... just amazing patience there.
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Offline Armond

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Re: Head question
« Reply #21 on: September 13, 2017, 11:10:27 pm »
Well everyone else's car seems to have come first. So yes it has been that long unfortunately.  I did do the 69 Boss 302 for myself back in 2005/2006, that car became my priority for a number of years.  I will have the Engine builder look at the heads and hopefully get some good advice.  Thanks again for all the feedback!
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Offline RoyceP

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Re: Head question
« Reply #22 on: September 15, 2017, 09:07:43 am »
On the flow bench it's easy to prove that the valves work best if they are about halfway proud of the seat, in other words the valve seats are flush with the surface of the head.

geraldt52,
        It is common for '69 and later heads to have "sunken" exhaust seats on brand new heads.  In the '70s when my friends raced stock eliminator, they would order 10 heads at a time and keep the ones with the highest exhaust seats. We couldn't add false seats ( as we called them then) per NHRA rules. There were MANY heads with low seats to start. I'm not saying that is your case , but it is a fact.  68.5's were machined so virtually the entire valve was above the chamber. Mine still are that way.
   Randy
     You bring up a good point that I've never been able to confirm. I've heard that the heads "work" better the higher that the seats are. Is there any truth to that story?
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