Dropped exhaust valve seat again.....

Anything Corvair related
User avatar
855r
Posts: 66
Joined: Thu Nov 08, 2012 9:43 pm

Dropped exhaust valve seat again.....

Post by 855r »

This is still part of the fun right? well after the recent turbo upgrade, clutch and flywheel upgrade, front disk brake conversion, new wheels and tires the Spyder showed me she has some fangs. Yesterday I noticed a tiny unfamiliar pop out the exhaust while idling but the car drove great so I didn't get too concerned about it I actually thought it was ignition related. This afternoon just cruising down the road all of a sudden it felt rough, like a dead cylinder. I gently drove the couple miles to my house and parked it. This evening I compression tested and sure enough #2 at 0psi again. I pulled the valve cover hook up my remote started and turned the engine over. All the valves open and close but #2 exhaust didn't look right to me so I removed the rockers and the exhaust valve spring stays about 1/4 compressed :doh: I guess there's a slim chance of a stuck valve but it fully opens just fine it just wont seat completely.

Having had the engine/transaxel out like a month ago it should go a lot faster. I'll keep this post updated with findings and pictures when I get the head off and find some hard evidence.
notched
Posts: 674
Joined: Wed Jul 25, 2012 8:13 pm
Location: Southern New Jersey

Re: Dropped exhaust valve seat again.....

Post by notched »

Did you have the valve seats replaced? These cars are 47+ years old now. Its one of the small detail items that people neglect until something fail. Since having seats drop on other Corvair engines I now make seat replacement part of the rebuild process and have done so on 3 sets of heads.
1966 Corsa turbo
1969 Monza convertible
1987 Buick Grand National
miniman82
Posts: 1216
Joined: Wed Jan 20, 2010 2:40 pm
Location: Great Mills, MD
Contact:

Re: Dropped exhaust valve seat again.....

Post by miniman82 »

Sucks when it happens, but unfortunately I know all about it being a VW guy as well as a Corvair guy. I had to pay bookoo bucks to have a set of Porsche 914 heads redone with better seats, bronze guides and stainless valves, they cost as much as a set of Corvair heads. When my 180 heads got done, the guy advised me to only do the exhaust seats since he said the intake rarely fall out. So I did, and never had any problems. As I understand it 140's are more at risk than any other because of the size of the seats, they experience rapid cooling on decel which causes them to shrink right out of the head.
Image
Click it!
66vairguy
Posts: 4531
Joined: Tue Dec 21, 2010 3:44 pm

Re: Dropped exhaust valve seat again.....

Post by 66vairguy »

Notched is correct - replacing the seats with a "deeper" seat is standard practice for a proper engine rebuild.

Over the years many schemes have been tried to prevent factory valve seat drop out, especially on the 140HP engines. None have worked well. The issue is a mechanical one. The seats and heads have different expansion rates so no matter how "tight" you try to get the head to seat clearance, eventually expansion causes the aluminum to shift after a number of temperature cycles and the interference fit loosens up. The only reliable fix is a deeper seat that provides more contact area between the seat and head.

There is a shop in L.A. that's been doing aluminum heads for decades with the deeper seats. So far not one of the 140HP heads has dropped a valve after a rebuild.
notched
Posts: 674
Joined: Wed Jul 25, 2012 8:13 pm
Location: Southern New Jersey

Re: Dropped exhaust valve seat again.....

Post by notched »

The big problem is that the heat treat was inconsistent on these heads and IF the engine overheated at any point you lose the heat treat making the aluminum very soft which makes it even harder to retain a seat. A VW buddy of mine makes it a point to have heads that he rebuilds retreated. I have a set of heads I have been putting together that I am planning to have retreated.
1966 Corsa turbo
1969 Monza convertible
1987 Buick Grand National
66vairguy
Posts: 4531
Joined: Tue Dec 21, 2010 3:44 pm

Re: Dropped exhaust valve seat again.....

Post by 66vairguy »

Heat treating of aluminum has really advanced in just the last four decades and certainly worth a try, especially for engines that will be raced. How about getting a hardness test done before and after the head treatment?

The Corvair is about 50 years old and even when new the heads were soft relative to today's aluminum alloys used for engines.
User avatar
flat6_musik
Posts: 2659
Joined: Sun Apr 04, 2010 10:03 am
Location: Hesperia, CA

Re: Dropped exhaust valve seat again.....

Post by flat6_musik »

Edelbrock needs to step up to the plate with some fresh offerings! (I can dream, can't I? )

"Would you like those push rod or overhead cam, sir?"
66vairguy
Posts: 4531
Joined: Tue Dec 21, 2010 3:44 pm

Re: Dropped exhaust valve seat again.....

Post by 66vairguy »

New heads have been speculated about for years. What it comes down to is COST. There are still enough rebuildable heads at a cost that deters anyone from trying to develop new, and more expensive, replacement heads.

A properly rebuilt Corvair head is usually trouble free for normal use and even the racer types get by fine with modified stock heads.
User avatar
855r
Posts: 66
Joined: Thu Nov 08, 2012 9:43 pm

Re: Dropped exhaust valve seat again.....

Post by 855r »

Thanks for all the replies guy's, I did get my proof over the weekend. These heads were gone through about 2 years ago with this cylinder having been repaired at that time from a dropped exhaust seat from before. I had given instruction to do "whatever it takes" to make these heads into top shape when I took them both to get refreashed. A deeper seat was never suggested and in my ignorance at the time it did not get done. It will now though. So I'm only going to have this one head fixed as I managed to pull it off with out removing the engine from the car it wasn't so bad and saved me a ton of time.

The plan is to get this head fixed proper with deep seats installed on the exhaust valves at a minimum and possibly the intake too. reinstall it and just get the car driving again for as little money out lay as possible while getting it done correctly. This is why I'm only doing the one side that is off for now and I'm not going to use the same place again for repairs. I'll de-shim my wastegate to lower my boost a few pounds in an attempt to de-stress the engine to try and get some more reliability out of it. I'll just enjoys the car for what it is, a fun cruiser. Then in a month or two I'll start the process of gathering parts with the idea of building a completely different engine over time that will be my fire breathing monster. This way my car will be drivable and I won't feel the need to drive it hard because I'll be building a engine especially for that reason.
Attachments
20160423_155337.jpg
20160423_155337.jpg (72.53 KiB) Viewed 1574 times
20160423_155347.jpg
20160423_155347.jpg (53.21 KiB) Viewed 1574 times
20160423_165650.jpg
20160423_165650.jpg (51.95 KiB) Viewed 1574 times
User avatar
thewolfe
Corvair of the Month
Corvair of the Month
Posts: 229
Joined: Thu Feb 27, 2014 4:01 pm
Location: Portland, OR

Re: Dropped exhaust valve seat again.....

Post by thewolfe »

Have all the seats done deeper. You'll wish that you had later and now is the time if you're having the other ones done. I've been in the same boat - drop a valve seat, get it replaced then the next year the same one dropped again. I had a total of 4 dropped seats on my stock turbo heads in the few years after buying my car before I wised up and had a set of performance 95 heads built with all deep seats. And the 4 that dropped were all intake valves, not exhaust.
Nate Wolfe
65 Corsa 180
61 Lakewood 140
66vairguy
Posts: 4531
Joined: Tue Dec 21, 2010 3:44 pm

Re: Dropped exhaust valve seat again.....

Post by 66vairguy »

Part of the old car hobby is learning and having those "I wish I had known that before" moments.

Years ago I called around and all the machine shops said "Oh sure we can do Corvair heads", but when I got into specifics I realized most shops did not have a good understanding of the Corvair head, or were just going to lap the valves and knurl the guides to freshen up the heads, not a real rebuild.

Finally one honest machine shop said "Take you Corvair heads to the machine shop that does them for the Corvair repair shops around here". I got the information and confirmed it. The shop spent about half an hour explaining what they would do and why one set of heads I had were not worth the cost to rebuild since finding a better set would be less expensive to rebuild and they showed me what to avoid in used heads.
User avatar
855r
Posts: 66
Joined: Thu Nov 08, 2012 9:43 pm

Re: Dropped exhaust valve seat again.....

Post by 855r »

Just as an update I had all the valve seats removed yesterday and the head is now at the tig welders shop to have the damage repaired. Once I get it back hopefully this week or Monday I'll return it to the machine shop to have the deeper seats cut and installed at all the valve locations.
User avatar
855r
Posts: 66
Joined: Thu Nov 08, 2012 9:43 pm

Re: Dropped exhaust valve seat again.....

Post by 855r »

Well I'm back in business. Picked up the cylinder head from the machine shop this morning. in my excitement I neglected to get a picture of the welded up valve seat pockets showing the flowed aluminum repairing the gouged valve seat area. Take my word for it, it was done right and looked really good. This head now has 5/16" valve seats intake and exhaust. So here are the final cylinder head repaired shots. I'll work on it the rest of this weeks at night and hopefully be driving on Saturday.
Attachments
20160510_134520.jpg
20160510_134520.jpg (79.19 KiB) Viewed 1356 times
20160510_134507.jpg
20160510_134507.jpg (98.08 KiB) Viewed 1356 times
User avatar
cad-kid
Posts: 2569
Joined: Thu Sep 09, 2010 4:29 pm
Location: Kronenwetter, WI
Contact:

Re: Dropped exhaust valve seat again.....

Post by cad-kid »

:tu:
Jeremy (cad-kid)
Kronenwetter, WI (Central Wisconsin)
SOLD 9-2016 65 Monza 4spd/140
My 65 Monza thread
:soapbox: My YouTube page
User avatar
855r
Posts: 66
Joined: Thu Nov 08, 2012 9:43 pm

Re: Dropped exhaust valve seat again.....

Post by 855r »

Pulled a late night off and got it back together. Test drove to work and it ran great. The only thing that had me concerned was the amount of time #2 cylinder took to pump up the lifters, lots of clatter. Probably has to do with the fact that I disabled it and moved the car before I pulled the head so it just bled down completely I think. After about 5-6mins of idle time it quieted down and the car drives good so it's fine. I did pull a few shims out of my wastegate so boost is limited to a solid 10lbs in a effort to not put so much stress on the engine and hopefully lengthen the run time between parts failures. obligatory parked at work picture.
Attachments
20160513_081101.jpg
20160513_081101.jpg (45.97 KiB) Viewed 1312 times
User avatar
cad-kid
Posts: 2569
Joined: Thu Sep 09, 2010 4:29 pm
Location: Kronenwetter, WI
Contact:

Re: Dropped exhaust valve seat again.....

Post by cad-kid »

:goodpost:
Jeremy (cad-kid)
Kronenwetter, WI (Central Wisconsin)
SOLD 9-2016 65 Monza 4spd/140
My 65 Monza thread
:soapbox: My YouTube page
Post Reply

Return to “Corvair Talk”