Loose Deep Valve Seats

[erco]

Famous racer Tom Keosababian mentions loose deep seats at 3:30 into his video. First bad thing I have heard about them. Those are usually touted as a must-have upgrade. https://corvaircenter.com/forum/viewtopic.php?t=1183568

[toms73novass]

It depends on the quality of the install. If done correctly, I highly doubt them coming loose, but anything is possible.

[davemotohead]

I have never had a deep seat done correctly come out. But screw in, set screwed, pin punched and peened over I have seen all come out. One thing to consider as well is the Aluminum the heads are made out of have a heat cycle life and lose hardness over time, or if the head has been severely overheated the material becomes soft and even a deep seat can fall out, the heads can be heat treated and rehardened I believe to become usable again.

[azdave]

Only Tom K. could ask $7900 for a rebuilt engine that didn't have deep seats and get away with it. Anyone other seller here would have been roasted alive for omitting that modification on an expensive, performance rebuild. Just sayin'.

I've been driving Corvairs since 1977 and have never dropped a valve seat. I've parted out dozens and dozens of engines and only ever once saw one head with a dropped seat. It's not a big deal based on my experiences and if it does happen tomorrow, I'll fix it and move on.

As for Tom's video comments, it stands to reason that if a head with a mix of both regular and deep seats was heated as a test and a deep seat fell out first, something was not done right during the seat replacement process.

Deep seats installed properly, must be better than standard depth seats right? But how many of us really need that expense for our daily drivers? Not us so far and we live in one of the hottest areas of the country. Cathy and I drive our A/C Corvairs (her 4-dr has a 140 engine) in the summer with freeway runs up and over the mountains included.

[Frank DuVal]

Oh Dave, you leave a sheltered life. Out here valve seats started falling out of heads in the late 70s. May have been earlier, but I was not repairing them then. I’ve sent out ( I do not do the repairs myself of welding the holes, etc) 95s 110s 140s 150s 180s. I had a friend drive his turboed 140 to my shop in downtown Richmond and I dropped TWO going around the block! I gave another friend who dropped one on a 3 9/16” engine sitting in his driveway.

Maybe because you have no cold air to shrink the seats after they get hot? Because that’s when they drop, after the throttle is released. Let me drive it over Afton Mountain, I can make them fall out.

[66vairguy]

Three valid points made ---

The seats have to be installed correctly.

ANY seat can come loose if the head is overheated.

The head aluminum alloy was O.K. for the era, but if you look up the specs it isn't as "robust" as today's alloys. Heat cycles (and anything over about 450F is going to be more detrimental) deteriorate the alloy strength. In theory the heads could be heat treated, but it requires knowledge of the Corvair head I have never seen presented.

I've never understood using 140HP heads for turbo applications. Yes they flow more, but doesn't a turbo overcome pumping losses of the small valve heads? The 140HP head has less material around the BIGGER valve seats and that isn't good for dissipating valve and seat heat. The other thing is a turbo boost needs HEAT to be retained in the exhaust flow and the bigger 140HP exhaust manifolds work contrary to this (larger surface area dissipates more heat). Look up boost pressured vs. exhaust heat. The more heat you loose out of the exhaust gases the lower the boost pressure.

Just my --- Feel free to disagree POLITELY.

[joelsplace]

I'll bet the extra heat radiated by the larger surface area on a 140 exhaust log isn't enough for any of us mortals to measure but the increased power from the larger valves is very noticeable. I'm sure someone here has dyno charts. I've seen them but that was on the other forum. All other things being equal you will have less boost with 140 heads because the turbo doesn't have to work as hard to fill the chamber. Less load on the turbo equals less back pressure and more power.
I can't see how having the heads heat treated would require any special Corvair knowledge outside of knowing the type of aluminum used.
140 heads will be harder to cool but everyone doing this has a Nash fan, don't they?

[Richard]

I am not an automotive machinist.
Someone told me that Ray Sedman uses a .008" interference fit for replacement seats as well as for the deep seats.
I've read that motorcycle machinists often use .003' - .005" and I think some of the Corvair machinists may do that as well.

[kmart356]

...snipped...
I've never understood using 140HP heads for turbo applications. Yes they flow more, but doesn't a turbo overcome pumping losses of the small valve heads? The 140HP head has less material around the BIGGER valve seats and that isn't good for dissipating valve and seat heat. The other thing is a turbo boost needs HEAT to be retained in the exhaust flow and the bigger 140HP exhaust manifolds work contrary to this (larger surface area dissipates more heat). Look up boost pressured vs. exhaust heat. The more heat you loose out of the exhaust gases the lower the boost pressure.

Just my --- Feel free to disagree POLITELY.

Ok, I'll politely disagree based on my recent experience installing 140heads on a turbo engine. The air flow, both intake and exhaust is increased with the big valve heads. The 140 exhaust tube modification has been done for many years (on 95hp heads mostly) to improve exhaust flow which helps the turbo spool quicker. Ceramic coating can be used on the 140 logs to minimize the minor heat loss.

@joelspace makes valid points in his reply as well. The turbo with big valve heads makes more power at the same effective boost (as measured by butt-dyno). Before big valve heads installed... 16-18psi was where the peak power hit. Now with the big valve heads, the same power is felt at 12-13psi. That's also a benefit in that less boost reduces the risk of detonation and managing AFR is easier with methanol injection.

AND... The higher compression of the 140heads contributes to the extra power and drivability off boost. Meandering around in heavy traffic is much more pleasant with that extra oomph.

[vairmech]

Well deep seats do come out! There is not a seat made that will stay in with our alloy of head material. Here is a head that is about 10 years old been in many different engines and I can't count the number of races.
The pic below is a deep seat.
Then how many of you have been around long enough to remember Moby Dick Racing? Remember their logo? "Seats guaranteed not to come out even under racing conditions." Well guess what? I had to repair one of those heads because of a dropped seat!
I can't say that I have had a street engine drop one of my deep seats.

[vairmech]

SNIP
Deep seats installed properly, must be better than standard depth seats right? But how many of us really need that expense for our daily drivers? Not us so far and we live in one of the hottest areas of the country. Cathy and I drive our A/C Corvairs (her 4-dr has a 140 engine) in the summer with freeway runs up and over the mountains included.

Believe it or not I agree with the above! As long as you have totally deflashed the head.
Most street cars don't really need the deep seats but then back in the day with stock engines I have dropped my fair share of seats. With that I don't just wholesale replace seats for my own use! I assess the condition of the head and repair as needed along with a deflash. Just because you can see through the fins doesn't mean it is good.

[jimbrandberg]

I had heads heat treated for my race car and it was a very expensive endeavor. As explained to me by the Machine Shop I was using at the time, the aluminum moves around somewhat during the process and "everything" needs to be remachined.
I believe it is absolutely the way to go because the aluminum has temper to it again. I haven't done it again because I lost access to a local guy who did the heat treating on the side and because I'm not made of money.
This all started as far as I know 25-30 years ago when racer Jon Braake had some heads heat treated at a place in California. He wrote an article for the Communique but it was a few years before it was published and the idea was largely pooh-poohed at the time. He said seat trouble on his 3-barrel Weber slant tube exhaust was cured but then he switched to a Miata a year or two after.
I know very little but my opinion is the deepest of seats won't hold if the aluminum has gone soft.
I had a machinist say once that he could tell soft aluminum by how it reacted with his cutting tools. He said a lot of things.
I cast about for Rockwell hardness testing but didn't get very far. A guy in the lab at local Flame Industries did one because he was curious but it was inconclusive and folly because the company didn't do small jobs.
The deep seat thing does have tremendous merit but I would hope the mission would be aborted if the head seemed soft when cutting the bigger seat pockets.

As I understand it, Tom Keosabian heats potential heads in the oven and inverts them on the bench to see if the seats fall out. I've been looking for an apartment size propane oven to try it on my own. Good thing to do in the Winter to help the old wood stove along. I need to get specifics from him again.

I find this topic fascinating. Just my opinions and I could be wrong so "flame on".

Jim Brandberg
Isanti, MN
CorvairRepair.com

[joelsplace]

Maybe drill radial holes in the seat and pin them?
Most modern cars have aluminum heads and I don't hear about seat issues with them. Even in ones the owners try to run air cooled.

[66vairguy]

This was a good exchange of information and ideas. Thanks for the comments on the 140 heads and turbo.

Just my , but the deep seat increases contact area with the head and IMPROVES surface tension, but has it's limits. That said it is the only COST EFFECTIVE solution with a good track record for daily drivers.

Years of comments indicate the larger 140HP valve seats are more prone to drop out and YES plenty of folks with the smaller valve seat engines never experience a valve seat drop.

I learned my lesson on buying used Corvair heads. If the head gasket ring is SUNK into the aluminum head gasket contact area, I know the head was overheated. These heads will require a lot of gasket surface machining and "most likely" the head aluminum is softer than when new - not good to retain valve seats.

Most folks DO NOT RACE their Corvairs. Over heating a head (and racing can do that) increases the possibility of dropping a valve seat.

One good comment was that after heat treating a head, ALL the machining dimensions must be checked and some will need to be corrected!!

Years ago I discussed interference fits with a buddy who is "educated" in materials and he taught me that with dissimilar materials no mater how tight the initial interference fit is, a couple of heat cycles with different expansion rates and the head material will "give" and result in the maximum surface tension between the head and valve seat. Of course the valve seat material and the aluminum alloy characteristics affect this.

I've lost the old information I had on the Corvair head alluminum alloy, but I was surprised to read that 400 - 450F was considered the point were the alloy integrity stated to decline noticeable!!!

Thanks for the information.

[jimbrandberg]

If I remember right it is 356 aluminum alloy.
Interesting point that sunken head gaskets are a sign of aluminum that has gone soft but if I threw away all the heads I have with that condition I wouldn't have many left.

[66vairguy]

If I remember right it is 356 aluminum alloy.
Interesting point that sunken head gaskets are a sign of aluminum that has gone soft but if I threw away all the heads I have with that condition I wouldn't have many left.

Yes I have had "minor" indentation heads rebuilt. You can use thicker head gaskets to help maintain valve geometry.

I recall one engine that looked like a mess externally with lots of miles and dirty inside. I pulled the heads and the gasket surface was flat and even. The shop that rebuilt them mentioned only minor machining was required.