Corvair Forum

I've always been much chagrined that it was hard to know by looking if a valve seat was ready to come out. Sometimes you can see some erosion of the aluminum but not usually. I was much intrigued by Tom Keosabian's method of heating the head in the oven to check for loose valve seats and decided to give it a try.

When I first read about it I thought the method was to drop the head on the bench when taking it out of the oven. It turns out that was just one time when it was hot and he dropped it by accident. It's funny that when that happened, the two deep seats that had been replaced fell out and the four originals stayed in.

I wrote to Tom and asked how he does it and I hope I have it right. I'm happy to be corrected if I don't.
He says a loose seat will turn easier than it will fall out so he marks them before putting in the oven with correction fluid. He says if the seat moves you will see a crack in the "paint".
I purchased a Leontools heavy duty lock ring pliers on Ebay for the job. I'm using the 11" but I bought a set of two with a 8" as well since it was close to the same price. I had two of these tools before for internal clips in transmissions but they were not as heavy duty.

I looked for a while to find an old LP cabin size oven. I waited for cooler weather to bake my first pair. I'm glad I didn't wait for cold weather because there was a fair amount of smoke so I had to open the doors to ventilate. I didn't go hog wild with cleaning or deflash in case they failed the test.

Both of the heads I did today passed the test. I suppose I'll know more when I get one to fail.

I set the oven to 450 and put the first head in without preheating. It took about 45 minutes for the oven to get to temperature and I left it in there another 45 minutes. When I did the second head it got to 450 in a lot shorter time, maybe 15 minutes and I left it in there for an hour maybe. I bought an oven thermometer that hangs from the metal rack to monitor the temperature.

When I took a head out with leather gloves I did drop it on the bench to see if a seat would fall out before trying to rotate the seats with the pliers. After trying them once I sprayed brake cleaner on the seats to try and cool them more rapidly and tried them again. Maybe a thin stream of water would be a better choice. Maybe this extra step isn't necessary.

I'm sure some folks will think this is folly. They will say deep seats with a .007 or more interference is the only way to go. At the very least testing the seats is better than nothing. I asked on the other thread what folks are typically paying for deep seats and got no reply. I've had deep seats done and it's a good thing as long as you've got someone who can do it right. Internal Lock Ring Pliers 11" Lock Ring Pliers and Correction Fluid with brush Trying to turn the seat Line applied before baking After baking and testing

I was reading through a reply I got from Tom where he said 450 should be enough but he thought a few hours at that temperature. I probably went an hour. I've always figured an aluminum part gets to a consistent temperature throughout fairly easily.
I can certainly leave the next pair of heads in longer. I have either a 63 turbo or 140 to do next.

Interesting.

Over the years I've found the small valve and NOT turbo heads are trouble free IF they have not been over heated and the valve guides are not worn out. I look for deep grooves were the head gaskets sit that indicates the heads were overheated and loose valves as worn guides let the valves hit the seats unevenly and that seems to loosen the seats.

As for the 140HP big valve engines - the bigger valve seats seem prone to dropping even if the engine was not over heated or is not worn.

A fellow in our club has a low mileage 140HP with PG and he never abuses the engine. One day while driving in the city at about 25MPH a valve seat DROPPED out of place!!!

I do not have enough information about the turbo heads to make any observations.

Turbo heads overheat real quick if you drive them real spiritedly. As in put your foot in it and don't let up for a while.... AMHIK!

Frank DuVal wrote: ↑Wed Nov 06, 2024 8:46 pm Turbo heads overheat real quick if you drive them real spiritedly. As in put your foot in it and don't let up for a while.... AMHIK!

TRUE - Decades ago Corvair engineer Mr. Benzinger gave a great talk at the GWFBT. One of his answers to questions was about the lack of cooling on the turbocharged engine. He replied that if you held the throttle wide open for more than about a minute the engine would overheat, BUT well before a minute passed the Corvair would be at it's top speed and GM felt nobody had any business driving like that on public roads!!!! However they did install an over temperature buzzer to discourage this. If the turbo was just used to accelerate to a legal speed limit, or to pass a another vehicle the Corvair cooling system WAS ADEQUATE.

However there is a flaw in this logic as anybody who has driven the California "Grapevine" knows. In the summer if you want to keep up with traffic at 70 - 80MPH going up the loooong grade you will probably overheat a Corvair turbo engine, or have to back off the throttle! I recall somebody here posted they did that once.

I always wanted to install a water/alcohol bottle with spray jets above the cooling fan inlet to see how well it would cool under full boost - ahhhhh another "someday" project that I probably will not do.

I seem to remember that Steve Goodman said Corvairs were dropping valve seats before turbos and 140s were available so the problem applies to all engines. I believe that Doug Row had a ring around the cooling fan opening that was hooked to R12. It probably worked real well for cooling.

RexJohnson wrote: ↑Thu Nov 07, 2024 1:11 pm I seem to remember that Steve Goodman said Corvairs were dropping valve seats before turbos and 140s were available so the problem applies to all engines. I believe that Doug Row had a ring around the cooling fan opening that was hooked to R12. It probably worked real well for cooling.

True --- but the majority of posts I've seen are the 140HP engines. Not exactly a scientific conclusion.

One thing I've noticed on small valve, not turbo, heads I've looked at with dropped seats is they usually show signs at the gasket area of serious overheating.

True --- but the majority of posts I've seen are the 140HP engines. Not exactly a scientific conclusion.

Scientific conclusion requires as many data points as possible, and Steve's information adds to the data points! Seems to be a lot of discussion on small valves falling out too.

In my work over the years I have had more small valve heads repaired or replaced due to dropped seats than 140 heads. Even 80 HP and 95 HP Yes, remember these were cheap transportation and people were used to driving home or to the shop when the red light came on. Yes, these people also ruined water pumpers doing the same thing. I remember a relative who worked for the GSA (or whatever it was called then) motor pool and telling stories of the head damage in the early Corvair motor pool cars and FCs. It was a normal repair to have new heads installed.

I'm exaggerating a little perhaps but it seems like all Corvair heads have some sinking of the cylinders into the aluminum requiring flycutting of the head gasket surfaces.
I've probably got 100 cylinder heads of different years. If I put aside all of them with head gasket imperfections because I thought they had been overheated I wouldn't have many left.

This topic will become a lot more interesting if I actually find some seats that turn at 450 degrees.
I've got some turbo and 140 heads to check but don't have the time right now.

I've seen lots of head gasket depressions in heads. I just put new head gaskets in and run them.

When driving a Corvair one should allow the head temperature to come down before shutting the engine off. Don't just blast in off the freeway, down the ramp and go in the cafe, let it run a few minutes with no load.

I've got a few more heads to bake but have to wait until I can have the doors open. It gets kinda smoky in the garage if the head has oil on it but I hate to spend a lot of time cleaning one in case it fails. I get the worst of it so it doesn't bake on.

3 bots using the same picture for their user id.

Having actually tested a baseline 95 PG for temps, they are recorded and documented! The engine temps stabilized and stayed pretty consistent throughout even a full throttle blast from 60-70? MPH, maybe 75 MPH. What we did notice and didn't expect was the plenum temp shot way up at idle! Even the head temp went up at idle then started coming down!
As a qualifier, we used a thermocouple bolted to the head boss. What that means is the actual head temp is not what you are used to seeing because the probe was not 1/4" away from the combustion chamber but is still representative of what is happening.
The duct temps are almost more instantaneous than the head temps and you can see the spikes consistent with acceleration. On both charts near the end we drove normally at 45mph, when we stopped and let the engine idle you can see the temps go up then start coming down.
Yes this was for the electric fan test but still applies here. Why was the electric fan test longer? we had to consistently drive slower over the same course, I think we could only maintain 38 mph without having the overheat light come on.

So, yes, idling is good but 1000 rpm idle while cooling would be better to keep the airflow up.

As far as seats that come out? You will consistently see #5 predominantly, then #2 the most frequent. Others do come out but not as often.
My take on why, and this is a more recent reasoning, is over time the heads anneal and get soft. Soft material will not hold a press fit of anything, they just move metal and become loose. #5 is first because of the loss of air over #5 because of the fresh air outlet there. Why #2?? The oil cooler is there and taking less air away from #2.

A higher than idle speed with no load to keep air moving through for a cooldown process just feels right and it's good to know the measured data confirms it.

On Memory Lane, I remember having trouble when Ice Racing. Even with a cool down lap at the end of a race there's nothing like a below zero breeze up the tail pipe to have some temperature differences with an exhaust valve that happens to be open when the engine stops. I can distinctly remember hearing a "tink" when one fell out. I was the 12 year old little little brother so I don't remember what we did about it before the next race or if we started it to get from the grid to the paddock.