Valve job with head gasket replacement?

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4spdcuda66

4spdcuda66

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I had a conversation about a blown head gasket with a guy who owns an auto repair shop. He told me a valve job is in order EVERY time a head gasket is blown because the head of the valve gets hot, warps, and will not seal against its seat. I've replaced head gaskets on engines that have gotten HOT, and never had any problems after the work was performed. Furthermore, a blown head gasket does not always lead to overheating. I've never heard of this before. Any merit to this?
 
No merit to it at all, I have driven a blown head gasket on a 340, blew it between #2 and #4 piston, blew a little of oil out the dip stick and smoked out the left bank, drove it for 3 t0 5 miles back in 1985, Drove it another two or three years after I changed the head gasket (hard) :burnout:
 
I don't know that I buy HIS explanation, but here's mine. If you don't at LEAST remove and lap the valves in when you go to all the trouble to remove the heads, you've missed a golden opportunity.

Sorta like payin for a "workin gal" and then just lettin her take a nap in your bed.

Bout the stupidest thing logically imaginable, IMO. No way would I do a head gasket job for myself or anyone else and not at least disassemble the heads and inspect everything. If you don't at least put a dal indicator on them in the guides, how do you know they are not warped? You don't.

While I don't necessarily agree with his reasoning, I certainly agree with his goal. What's a basic valve job gonna add to the total cost of a head gasket job? 125? 150?

Kinda stupid not to if you ask me. But then, people do stupid everyday.
 
RustyRatRod said:
I don't know that I buy HIS explanation, but here's mine. If you don't at LEAST remove and lap the valves in when you go to all the trouble to remove the heads, you've missed a golden opportunity.

Sorta like payin for a "workin gal" and then just lettin her take a nap n your bed.

Bout the stupidest thing logically imaginable, IMO. No way would I do a head gasket job for myself or anyone else and not at least disassemble the heads and insect everything. If you don't at least put a dal indicator on them in the guides, how do you know they are not warped? You don't.

While I don't necessarily agree with his reasoning, I certainly agree with his goal. What's a basic valve job gonna add to the total cost of a head gasket job? 125? 150?

Kinda stupid not to if you ask me. But then, people do stupid everyday.
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She can take a nap right after I finish. lol I agree on at least checking everything.
 
I agree 100% with Rusty. If the heads are off, freshen them up while you have them off. Make darned sure you have them checked for straightness and cracks. Why not touch up the valves and seats? tmm
 
4spdcuda66 said:
I had a conversation about a blown head gasket with a guy who owns an auto repair shop. He told me a valve job is in order EVERY time a head gasket is blown because the head of the valve gets hot, warps, and will not seal against its seat. I've replaced head gaskets on engines that have gotten HOT, and never had any problems after the work was performed. Furthermore, a blown head gasket does not always lead to overheating. I've never heard of this before. Any merit to this?
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I do not agree with his thinking. Every valve job sinks the valves, which looses power. There are a lot of parts that "mate" together. Guides, retainers, locks, springs, seals, and valves. Are you willing to replace them all? Lapping is an easy way to check seal. If it does not have a "good" valve job then it should be done, we are talking about a Performance engine. What bothers me is why did the head gasket blow? I always milled the heads flat and never had a head gasket problem after.
 
66fs said:
I do not agree with his thinking. Every valve job sinks the valves, which looses power. There are a lot of parts that "mate" together. Guides, retainers, locks, springs, seals, and valves. Are you willing to replace them all? Lapping is an easy way to check seal. If it does not have a "good" valve job then it should be done, we are talking about a Performance engine. What bothers me is why did the head gasket blow? I always milled the heads flat and never had a head gasket problem after.
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That's untrue. It's all dependent on how good the valve faces and seats are. Lots of times you can simply get by with lapping the valves back in, which removes essentially nothing. All it does is assure the there is a good seal between the valve face and seat. Even with mild pitting on the exhaust, you can lap valves back in where the seal is good without sinking them one iota.

Only when the surfaces need grinding or cutting is there any material removed and even in that instance, it can be a very light cut. I only removed what was totally 100% necessary when I was doing head work. Sometimes as little as .003", plus lapping. You will never see a reduction in power from that. We never did excessive cutting or grinding, because if they didn't clean up with a light cut, either the valves, seats or both needed replacing.

It is a fact, most people see a power increase, because now the valves are sealing again 100%, plus having the heads redone probably includes a light mill to restore a flat surface and that would negate any small amount the valves were sunk, if at all.
 
RustyRatRod said:
That's untrue. It's all dependent on how good the valve faces and seats are. Lots of times you can simply get by with lapping the valves back in, which removes essentially nothing. All it does is assure the there is a good seal between the valve face and seat. Even with mild pitting on the exhaust, you can lap valves back in where the seal is good without sinking them one iota.

Only when the surfaces need grinding or cutting is there any material removed and even in that instance, it can be a very light cut. I only removed what was totally 100% necessary when I was doing head work. Sometimes as little as .003", plus lapping. You will never see a reduction in power from that. We never did excessive cutting or grinding, because if they didn't clean up with a light cut, either the valves, seats or both needed replacing.

It is a fact, most people see a power increase, because now the valves are sealing again 100%, plus having the heads redone probably includes a light mill to restore a flat surface and that would negate and small amount the valves were sunk, if at all.
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It is true. The flow is lost from the valve sinking farther into the bowl, not up from the chamber. If you are removing material from the seat you are sinking the valve, even if it is an iota. My comments were aimed at a machinist who wanted to do a valve job no matter what, any excuse will do, to get your money. I agree with lapping and always lap a couple of each valves randomly after a valve job, since it will give you a visual of how good the seal is and the width of the seats. You give an example of how a valve job should be done and will lose almost no power, and gain a lot if the valves were not sealing. It all depends on the frequency of the valve job and how deep the seats are sunk each time.
 
66fs said:
It is true. The flow is lost from the valve sinking farther into the bowl, not up from the chamber. If you are removing material from the seat you are sinking the valve, even if it is an iota. My comments were aimed at a machinist who wanted to do a valve job no matter what, any excuse will do, to get your money. I agree with lapping and always lap a couple of each valves randomly after a valve job, since it will give you a visual of how good the seal is and the width of the seats. You give an example of how a valve job should be done and will lose almost no power, and gain a lot if the valves were not sealing. It all depends on the frequency of the valve job and how deep the seats are sunk each time.
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Depends too on the integrity of the machinist.
 
RustyRatRod said:
Depends too on the integrity of the machinist.
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Some serious truth,spoken here. Still hang around ,an actual speed/head shop. The circle track racers,usually do the "cheapest " machinist,they can find. The "cheapest" doesn't necessarily mean " best return,on investment" ,in the long run. When someone gets charged 300-400 bones ,for a knurl job, seats recut out of round,& worn valve stem valve's, with the margin cut to nothing,you end up screwed in the long run. That extra 300-600 gets you a decent product, no issues. That people still do this,just blows my mind for the work involved.
 
Abodybomber said:
Some serious truth,spoken here. Still hang around ,an actual speed/head shop. The circle track racers,usually do the "cheapest " machinist,they can find. The "cheapest" doesn't necessarily mean " best return,on investment" ,in the long run. When someone gets charged 300-400 bones ,for a knurl job, seats recut out of round,& worn valve stem valve's, with the margin cut to nothing,you end up screwed in the long run. That extra 300-600 gets you a decent product, no issues. That people still do this,just blows my mind for the work involved.
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Very true. For the cost of machine work, and for the end goal of that work, why would anyone go the "cheap" rout.
 
When I was in the business, it was std practice to mill the gasket surface of the head when doing a head gasket replacement. On the old V8s you can do this with the head assembled, and clean it with a reasonable amount of certainty that you could get all the chips out. But as part of the inspection it's not hard to see if there's a sealing problem with a valve. And the test is even easier... Flip the head chamber side up, and fill the chamber with water. If it leaks past, closer inspection is needed (as in remove the valve. Overhead cam heads you couldn't - and if it's all coming apart anyway, time for a valve job.
 
famous bob said:
quick lap all of them, will tell how wide the seats are, how far out on the valves their seating, make sure their sealing!
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I grind my own valves, so I just lap some to be sure nothing has gone wrong with my system. If I was getting a valve job the first time, from someone I did not know and trust, you are absolutely right. Of course if it is a bad valve job, you won't have to do them all to figure that out. I could tell a story or two.
 
I would agree that the valves, releated hardware and head should be checked and the guy that said that is a little oversealous about what should be done after a blown headgasket, but it's already been agreed the hell out of. :D
 
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