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Re: dropped valve seats?
Posted by: jcorvair ()
Date: November 24, 2019 03:42PM

I lost one on one side in a 140, put a good used head on and got 30 miles down the road and dropped one on the other side. With respect to original valve seats, there are two kinds. Those that have dropped and those that will.

James
West Kelowna, BC

1965 Corvair, Corsa, Convertible 180/4 - Artesian Turquoise w/ white interior
1966 Corvair Corsa Coupe, 140/4 - Aztec Bronze w/ black interior
2013 Hyundai Santa Fe Turbo
2016 Dodge 3500 Crew Cab 4x4 (for hauling cars, trailers, fifth wheels, quads, etc.)
2013 Victory Car Hauler (enclosed)
2019 Express Car Hauler (Aluminum, Enclosed)
2015 Polaris 570 EPS
2016 Polaris 570 SP
2017 Corvette Z06 Convertible

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Re: dropped valve seats?
Posted by: Ron62 ()
Date: November 24, 2019 04:31PM

This is becoming a bit scary now. My 67 has 56000 original miles on it. Runs great but now im getting nervous about driving it any distance. Perhaps I should start looking for a spare set of 110 heads that I can have rebuilt with deep seats .

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Re: dropped valve seats?
Posted by: 63turbo ()
Date: November 24, 2019 05:45PM

Here's the deal- The 2 main reasons that valve seats fall out are valve float/bad valve control and excessive head temperatures and total time at excessive temperature. These factors are why 140's are famous for dropping valve seats because they have a really high red line compared to the other engines, and probably, owners of 140' are more prone to test the redline more frequently smiling smiley- I know I liked to do it!!. One of the GM cams was prone to multiple valve bounces, and I suspect this cam was used on the 140. Multiple valve bounces are not true valve float, but do fall into the category of "bad valve control". When the valve bounces and comes off its seat it is not transferring heat, so removing excessive bounces from the valve improves its heat transfer and helps the heads live longer.
The other thing is that 140's tend to run hot at freeway speeds when its hot out. Every time the heads go beyond 350, the heads begin softening and loose some interference on the valve seats. Its pretty normal for a stock 140 to get to 400f! Also, the valve seats didn't have enough interference anyways!
Add the temps, valve bounce/valve float, lack of sufficient interference on the seats, this would be why the 140's tend to drop seats much more frequently than the small valve heads do.
If you know for a fact that your heads have never gone past 350F, and haven't tested the rev limits of the engine, chances are good that you have a lot of miles left in your heads! In any case, when you get a chance to remove the top shroud, deflash the heads!
Yes, though deep seats are a great idea for any Corvair engine, and I would add to that, to add 10 lbs extra valve spring preload, to reduce valve bounce,
and seal the shroud, as there are numerous small leak spots. It all helps!
Of course... theres a really trick, cool fan that will be coming out soon....
smiling smiley

------------------------------------

Kevin Nash
Friday Harbor Washington
63 Spyder, Daily driver, EFI read about my project here: [corvaircenter.com]
first test start on EFI here:[www.youtube.com]
first official EFI boost test here:[www.youtube.com]
My new fan! [corvaircenter.com]
engine less 62 Spyder
Canadian 64 Monza Parts car



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Re: dropped valve seats?
Posted by: JimBrandberg ()
Date: November 25, 2019 04:51AM

It's cost and risk.
It's hard to get Corvair people to spend $1800 or more on just the cylinder heads. Despite all the hyperbole you can't absolutely guarantee that there's not going to be another failure some day with 50 year old aluminum and other parts.
When a seat comes out it's often just a "smile" in the piston top that you might be able to live with. Sometimes they shatter into small bits that go all over the place.

I had my racecar 140 heads heat treated. You have to take EVERYTHING out of the heads. Then with the stresses of heating almost to melting and quenching the casting all moves around a little so skilled machining is required when putting everything back in. Racer Jon Brakke thought heat treating was the best way to go. He spent a lot of money racing a Corvair for 20 years at the SCCA National level.
I've had several deep seat jobs done by various providers and have not had a deep seat come out. I do wonder if it will happen if the aluminum casting is still somewhat soft.

I have been unsuccessful with coming up with an easy test for assessing overall temper condition of a cylinder head. I took one to a heat treating lab where they did a Rockwell Test but it was inconclusive. Questions like "where do you shoot the ball" come up and "what do you compare it to". The lab guys did it as a courtesy and something interesting but can't do it on a regular basis and/or spend a lot of company time on a one shot deal.
I had an old machinist tell me once my heads were soft based on the chips coming off his tools. This was an offhand remark when I was picking up the heads already done rather than an assessment before "going in". I haven't had occasion to track how those heads held up.

Heat treating Corvair heads is a nifty thing but not many people are on board. The pair I had done were by a guy that worked at a heat treating facility and snuck them in on the side. He no longer works there. Jon Brakke had them done in California but that's been about 20 years ago now.

Just some opinions from a guy who is not a machinist and I'd like to read more.

"They are all going to come out" is an opinion as well. I'm not saying it's a bad opinion, just saying...

Jim Brandberg
Isanti, MN
CorvairRepair.com



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Re: dropped valve seats?
Posted by: JerryM ()
Date: November 25, 2019 06:18AM

What's the rationale behind heat treating to remedy dropped seats?
I've never seen any documented evidence heat treating aluminum changes it's coefficient of linear thermal expansion.

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Re: dropped valve seats?
Posted by: mtmouse ()
Date: November 25, 2019 06:30AM

The statement was made that the "140's" are notorious and the main culprit with dropped seats. Does this same "higher" risk follow into the 180 turbo? It is my understanding that the 180 has a different cam and some improved internals.Not sure yet about that and not sure how that would effect the valve seats.
Right out of the box I would assume the intake air would be hotter on overrun than with a 140. I would also assume the turbo would have a different camshaft with different lift and duration spec's than a 140.
So is the dropped valve guides issue on a 180 more or less or bout the same as on a 140?
Joe

Joe in South Ga
1965 Corsa 2 dr Coupe Turbo 4sp because I love the looks
18ft Chaparral 180 Sport because I live on a lake, seemed like the thing to do
Chevy Pickup to tow boat and tote things
Chevy Cavalier because they drive like a go-cart

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Re: dropped valve seats?
Posted by: MtnVairMike ()
Date: November 25, 2019 09:24AM

JerryM Wrote:
-------------------------------------------------------
> What's the rationale behind heat treating to remedy dropped seats?
> I've never seen any documented evidence heat treating aluminum changes it's coefficient of linear thermal expansion.


Lots of good reading in this post from several years ago. From what I understand excursions above 400F over time soften the hardness of the T356 alloy. This I think leads to less ability to grip the steel valve seat, not change the aluminum thermal expansion rate.

Thanks,

Mike

1966 Monza Convertible, 140HP-4 speed, Ermine White

Others in the menagerie...
72 Corvette Stingray, 58K miles, owned since 86
72 MGB, 112K miles, bought from original owner in 09
78 Chevy pickup, 124K miles, bought new in 78
93 Corvette, LT1/6spd, 210K miles, daily driver since 96

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Re: dropped valve seats?
Posted by: Jonathan Knapp ()
Date: November 25, 2019 10:27PM

Quote
Kevin Nash
"The other thing is that 140's tend to run hot at freeway speeds when its hot out. Every time the heads go beyond 350, the heads begin softening and loose some interference on the valve seats. Its pretty normal for a stock 140 to get to 400f!"

After I deflashed my heads, caulked all of the air leaks in the sheet metal and brought the lip of the air inlet on the top shroud down to less than 1/8" off the fan, I could never get my head temp above 325, even autocrossing on a 90 degree day. On 40 degree days I couldn't get the head temp above 225 and the oil temp would stay around 170. The shroud doors would never fully open, they would just crack a little bit. 75 degree day on the freeway at 70 mph they would run (temp gauges on both heads) at just over 250, oil temp around 190. The oil temp would actually heat up when I pulled off the freeway and idled. The engine was slightly heat-soaked and the lack of air-flow over the Otto Parts pan and over the valve covers made the oil temp go up for a while. Get back up to speed for a while on the freeway and the head and oil temp would go back down.

Jonathan Knapp
Now in Martins Ferry, OH
'66 Corsa Autocrosser

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Re: dropped valve seats?
Posted by: mtmouse ()
Date: November 26, 2019 12:26PM

Not sure I would call this scary. Nobody ever posts about how their valve seats stayed in place all day today.
Normally discussion forums have more negative mentions than positive.
Maybe I am the fool here but I believe Chevrolet spent more time and money in development and testing than we did. I "Assume" that in stock form and for intended use the majority of valve seats stay just where they were placed. Of course you will have the certain percentage of failures, but.
I have no doubt that in racing applications corvair engines will drop a valve seat. They were not designed to be race engines. I have no doubt that dropped valve seats are more common on modified engines. Modify the intake system and more so on a 140 than any other engine you have removed an air filter that makes air flow two feet from engine bay ambient through warm metal intake duct to valve seat. With pod filters on a 140 you have reduced that distance from ambient air temp to valve seat to about 3 or 4 inches. Add high vacuum and idle circuit fuel evaporation during overrun and you can easily have inlet air temps at the valve seat that are lower than engine bay ambient. Modifying or failing to maintain the factory designed cooling system could possibly be an accelerant of dropped valve seats.In some cases the factory engineers made the correct decisions. Chevrolet made millions of corvairs, not everyone has dropped a valve seat. How many people have dropped valve seats on dead stock well maintained engines?
Just my 2c
Joe
Ron62 Wrote:
-------------------------------------------------------
> This is becoming a bit scary now. My 67 has 56000 original miles on it. Runs great but now im getting nervous about driving it any distance. Perhaps I should start looking for a spare set of 110 heads that I can have rebuilt with deep seats .

Joe in South Ga
1965 Corsa 2 dr Coupe Turbo 4sp because I love the looks
18ft Chaparral 180 Sport because I live on a lake, seemed like the thing to do
Chevy Pickup to tow boat and tote things
Chevy Cavalier because they drive like a go-cart

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Re: dropped valve seats?
Posted by: MtnVairMike ()
Date: November 26, 2019 12:50PM

MtnVairMike Wrote:
-------------------------------------------------------
> JerryM Wrote:
> -------------------------------------------------------
> > What's the rationale behind heat treating to remedy dropped seats?
> > I've never seen any documented evidence heat treating aluminum changes it's coefficient of linear thermal expansion.
>
>
> Lots of good reading in this post from several years ago. From what I understand excursions above 400F over time soften the hardness of the T356 alloy. This I think leads to less ability to grip the steel valve seat, not change the aluminum thermal expansion rate.
>
> Thanks,
>
> Mike


Sorry to quote myself but I forgot the links I mentioned.

[www.corvairs.org]

[corvaircenter.com]

1966 Monza Convertible, 140HP-4 speed, Ermine White

Others in the menagerie...
72 Corvette Stingray, 58K miles, owned since 86
72 MGB, 112K miles, bought from original owner in 09
78 Chevy pickup, 124K miles, bought new in 78
93 Corvette, LT1/6spd, 210K miles, daily driver since 96

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Re: dropped valve seats?
Posted by: Spectre ()
Date: November 26, 2019 12:54PM

Good info there Mike.

David Clamp


1965 Corsa convertible - 140 4spd/3.55/AM-FM

2013 Mustang GT convertible - 5.0, 6spd auto, Procharger i-1

2003 Miata SE - 6spd manual (wife's toy)

"Victory is mine!" - SG

Norman, OK

<a href="[www.wunderground.com] src="[weathersticker.wunderground.com]; alt="Click for Norman, Oklahoma Forecast" height="90" width="160"></a>

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Re: dropped valve seats?
Posted by: alan_smithee ()
Date: November 26, 2019 01:15PM

kept em big so you could see how the gasoline gods spared me from piston head damage




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Re: dropped valve seats?
Posted by: aircooledairhead ()
Date: November 26, 2019 06:21PM

In my years in the Long Island Corvair Association (1974-80) the club was huge (over 60 members) and I can only recall 2 dropped valve seats. Both were in 140's and both were driven hard.

I drove over 200,000 miles in a 65 140 Corsa. Never dropped a valve seat, but did have to rebuild after missing a 2-3 shift, causing a piston to crack at the oil control ring above the slots and bury itself into the head. Bent pushrods but no head damage. Went .30 over with forged TRW pistons and no further problems. Of course, these cars were only 8-15 years old when I had them.

I had many, many Corvair misadventures, but they were the more fun to drive than anything else I've owned. My son just picked up one and I'm helping him get it squared away.

I'll work on my signature.

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Re: dropped valve seats?
Posted by: 63turbo ()
Date: November 26, 2019 06:30PM

mtmouse Wrote:
-------------------------------------------------------
> Not sure I would call this scary. Nobody ever posts about how their valve seats stayed in place all day today.
> Normally discussion forums have more negative mentions than positive.
> Maybe I am the fool here but I believe Chevrolet spent more time and money in development and testing than we did. I "Assume" that in stock form and for intended use the majority of valve seats stay just where they were placed. Of course you will have the certain percentage of failures, but.
> I have no doubt that in racing applications corvair engines will drop a valve seat. They were not designed to be race engines. I have no doubt that dropped valve seats are more common on modified engines. Modify the intake system and more so on a 140 than any other engine you have removed an air filter that makes air flow two feet from engine bay ambient through warm metal intake duct to valve seat. With pod filters on a 140 you have reduced that distance from ambient air temp to valve seat to about 3 or 4 inches. Add high vacuum and idle circuit fuel evaporation during overrun and you can easily have inlet air temps at the valve seat that are lower than engine bay ambient. Modifying or failing to maintain the factory designed cooling system could possibly be an accelerant of dropped valve seats.In some cases the factory engineers made the correct decisions. Chevrolet made millions of corvairs, not everyone has dropped a valve seat. How many people have dropped valve seats on dead stock well maintained engines?
>


No matter what modifications are made to the engine air inlet, gasoline and air enters the engine well above ambient. On my engine I have an "engine temp" sensor that is used to gauge how well the engine is warmed up or not, and it
is actually checking the temperature of the intake port on the #1 cylinder. Closed loop comes on when the engine temp sensor hits 100 degrees, and when the head temperature gauge reads 250 or so, the engine temp sensor is reading 155, and the air temperature sensor, in the cross over manifold (turbo car) will be reading around 115-120 without ever going into boost!
Part of the issue with dropped valve seats has to do with what Chevy thought were "acceptable" head temps. On the original 80hp 1960, the heads would go to around 375f when going 60 miles an hour, and hit 400 at around 75 miles an hour
when it was 100 degrees out. This is already "over the line" and is most definitely NOT racing speeds or rpms. Either Chevy didn't know this was going to cause the seats to fall out at some point or they didn't care, as warranty standards were a lot different then.
The big reason that many know that they dodged a bullet is when the shop that rebuilds their heads tells them that half the valve seats were ready to fall out!! It is less common on the small valve heads for the seats to fall out but it does happen.

------------------------------------

Kevin Nash
Friday Harbor Washington
63 Spyder, Daily driver, EFI read about my project here: [corvaircenter.com]
first test start on EFI here:[www.youtube.com]
first official EFI boost test here:[www.youtube.com]
My new fan! [corvaircenter.com]
engine less 62 Spyder
Canadian 64 Monza Parts car



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Re: dropped valve seats?
Posted by: CorvairHaven ()
Date: November 26, 2019 06:59PM

alan_smithee Wrote:
-------------------------------------------------------
> kept em big so you could see how the gasoline gods spared me from piston head damage



What pictures? Just see circles with a hyphen in it.

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Re: dropped valve seats?
Posted by: MattNall ()
Date: November 26, 2019 07:34PM

> mtmouse Wrote:
> -------------------------------------------------------
> > Not sure I would call this scary. Nobody ever posts about how their valve seats stayed in place all day today.
> > Normally discussion forums have more negative mentions than positive.
> > Maybe I am the fool here but I believe Chevrolet spent more time and money in development and testing than we did.
===================================================

But the parts are now 50-60 years old... Who knows what has changed with the Aluminum's "makeup / Characteristics"

MODERATOR
Sea Mountain, between Charleston Harbor and Coos Bay! SW Oregon Coast
Click HERE for My Website...Click HERE for My TechPages!
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Re: dropped valve seats?
Posted by: 66vairman ()
Date: November 26, 2019 07:58PM

mtmouse Wrote:
-------------------------------------------------------
> The statement was made that the "140's" are notorious and the main culprit with dropped seats. Does this same "higher" risk follow into the 180 turbo? It is my understanding that the 180 has a different cam and some improved internals.Not sure yet about that and not sure how that would effect the valve seats.
> Right out of the box I would assume the intake air would be hotter on overrun than with a 140. I would also assume the turbo would have a different camshaft with different lift and duration spec's than a 140.
> So is the dropped valve guides issue on a 180 more or less or bout the same as on a 140?
> Joe

The general consensus is the 140HP engines are more prone to dropping factory valve seats than the other Corvair engines. The 140HP is fine with the deep seats if NOT overheated. So what's the difference - the main difference is the 140HP valves and seats are BIGGER. Less head material around the seats and a bigger seat (ring) expands more. The difference is not that great and why using a deeper seat (more contact with the head material) works.

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Re: dropped valve seats?
Posted by: REM654DPG ()
Date: November 26, 2019 08:47PM

140s have less cooling fin area than the small valve heads which probably adds to them running a little hotter.

And the stock seats besides being very shallow are made out of some cheap crap. If you've ever Tig welded a set to remove them the exhaust seats weld okay but the intakes weld like their made out of some kind of subgum recycled crap. The replacement seats we use now days are made from very high quality steel - plus they are deeper.

Then there's the debate between a 5/16 vs 3/8 deep seat and as most know I favor the 3/8.

And have a Great Thanksgiving Everyone!

Regan Metcalf
Portland, OR

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Re: dropped valve seats?
Posted by: joelsplace ()
Date: November 26, 2019 08:58PM

I realize all the reasons given contribute to the problem but the only seat I've lost was on a well maintained good condition 80hp in a Greenbrier just cruising along about 45mph. I have an 84hp ragged engine that I've put a lot of full throttle miles on that still runs so I would say it's also bad luck.

Joel
Northlake, TX
5 Ultravans, Lost count at 100 Corvairs...

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Re: dropped valve seats?
Posted by: joelsplace ()
Date: November 26, 2019 09:00PM

Who would debate against 3/8"?

Joel
Northlake, TX
5 Ultravans, Lost count at 100 Corvairs...

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