High compression 205 psi average on all cylinders

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WinginEngineer
Posts: 150
Joined: Sat Sep 03, 2016 3:31 pm

Re: High compression 205 psi average on all cylinders

Post by WinginEngineer »

That looks like a key sheared/shattered and took a piece of the gear keyway with it. And that would certainly retard your cam timing.

If your keyway looks like that, even if the keys is good, your timing is off...
Kevin - Phoenix/Mesa, AZ
1962 Corvair 700
notched
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Location: Southern New Jersey

Re: High compression 205 psi average on all cylinders

Post by notched »

The key was intact. I suspect that the original owner reused the cam gear OR broached it by cold pressing it. It fell off when the cam was removed.
1966 Corsa turbo
1969 Monza convertible
1987 Buick Grand National
notched
Posts: 674
Joined: Wed Jul 25, 2012 8:13 pm
Location: Southern New Jersey

Re: High compression 205 psi average on all cylinders

Post by notched »

Also, if it is a GM camshaft many times it will have the GM part number in between the lobes (almost exact center of the shaft). Some of the NOS GM cams had it stamped in the end of the shaft.
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1966 Corsa turbo
1969 Monza convertible
1987 Buick Grand National
tom becker
Posts: 53
Joined: Wed Jul 19, 2017 6:25 pm

Re: High compression 205 psi average on all cylinders

Post by tom becker »

Here is the latest, kind of good news. I went to a new oil filled certified gauge. Left side #2-195--#4-187--#5-190. Going to tear down, will talk pictures of cam gear to crank. This compression check is with two .032 head gaskets. This should offset the 40 over pistons a little. Thanks for the pictures of the cam numbers, I will look for them. TOM
tom becker
Posts: 53
Joined: Wed Jul 19, 2017 6:25 pm

Re: High compression 205 psi average on all cylinders

Post by tom becker »

The block is split, I may have been one tooth off to the left. I indicated cam lobes. The intake from 0 to .203 high and exhaust is .228 high. The only ID on the cam is GM 5. TOM
WinginEngineer
Posts: 150
Joined: Sat Sep 03, 2016 3:31 pm

Re: High compression 205 psi average on all cylinders

Post by WinginEngineer »

Congratulations! You may have just found your problem. That one tooth would do it like I said earlier.

Someone expert will have to help you with the cam because i don't want to split my other block and I don't have a pare cam for comparison.

But I'm glad you found your bug!
Kevin - Phoenix/Mesa, AZ
1962 Corvair 700
notched
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Joined: Wed Jul 25, 2012 8:13 pm
Location: Southern New Jersey

Re: High compression 205 psi average on all cylinders

Post by notched »

:tu:
1966 Corsa turbo
1969 Monza convertible
1987 Buick Grand National
tom becker
Posts: 53
Joined: Wed Jul 19, 2017 6:25 pm

Re: High compression 205 psi average on all cylinders

Post by tom becker »

I'm back with an update on the engine compression. I got my compression lowered to 145# average by adding a thicker head gasket. I also replaced the cam with a Iskenderian 270-HL-HYD grind cam. I got a degree wheel and using .050 lobe lift got the cam on the mark. The engine vacuum is down to 11 inches and steady, I was told with that cam, the vacuum would be lower, but not sure it should be that much. Now to driving. the engine idles good. starting out in low its ok, but when I give it full throttle, the acceleration seems poor as if not getting enough gas. The same for drive, runs ok until you step into it, and some times it cuts out. It just seam it not getting enough fuel. The fuel pump is new and pressure and gas flow was checked out and ok. Do I need to get larger main jets? Not sure what's in there now, but after your comments I will remove the cabs and check them out. Thanks for any help, TOM
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GasDaddy140
Posts: 327
Joined: Tue Aug 19, 2014 1:57 pm

Re: High compression 205 psi average on all cylinders

Post by GasDaddy140 »

Wow! You got that compression down a good chunk! I like your modifications. Re-jet for sure. Are your carbs healthy?
Last edited by GasDaddy140 on Tue Aug 22, 2017 6:38 am, edited 2 times in total.
Alan Duquette
Rohnert Park, CA
"When in doubt...Hit the gas!" A.J. Foyt.

1965 Corvair Corsa (field find) Project
1971 Dodge Sportsman "shorty" 318 van
2015 Nissan Juke S
64powerglide
Posts: 1604
Joined: Tue Mar 25, 2014 9:18 pm
Location: Kalamazoo Mi..

Re: High compression 205 psi average on all cylinders

Post by 64powerglide »

What does the timing light say??
64Powerglide, Jeff Phillips

Kalamazoo, Mi..
tom becker
Posts: 53
Joined: Wed Jul 19, 2017 6:25 pm

Re: High compression 205 psi average on all cylinders

Post by tom becker »

Hi All; the carbs are rebuilt, and the timing is set at 16 BTDC. I called Isky cam about the low vacuum and they said that is about normal. They also said to up-size the jets one or two from factory specs. Not sure what is in there now, I ordered two sets above specs. When I get new jets I will install them and see what happens. Good question on the timing. With that size cam not sure what the timing should be. When the parts get here, I will let you know what happens, Thanks TOM
64powerglide
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Re: High compression 205 psi average on all cylinders

Post by 64powerglide »

My 64 110 is at 14, I started at 16 but got spark knock with hard acceleration so I backed it off to 14, running 87 octane. You should try it a bit lower & see how it responds. I had a 62 102 HP & it ran best at 18 advanced, no spark knock.
64Powerglide, Jeff Phillips

Kalamazoo, Mi..
tom becker
Posts: 53
Joined: Wed Jul 19, 2017 6:25 pm

Re: High compression 205 psi average on all cylinders

Post by tom becker »

When I step into it I get no ping or knock. With that longer duration and higher cam lift (.293 or .036 more from factory spec.) not sure if the timing should be advanced more or less???? When I get the new jets in I will try both ways. Thanks TOM
Wagon Master
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Re: High compression 205 psi average on all cylinders

Post by Wagon Master »

I time mine to just barely ping when lugged on the cheapest gas I can find, then run mid or premium grade. After finding what you thought was the root cause of your high compression in the cam timing.......I'm not sure I would have still lowered the compression with thicker head gaskets.......but that ship has sailed. :dontknow:
tom becker
Posts: 53
Joined: Wed Jul 19, 2017 6:25 pm

Re: High compression 205 psi average on all cylinders

Post by tom becker »

Update on the project. Put #53 jets in the carbs, factory says #50 but with the new cam I went larger. Runs great and no cutting out up to 60 mph. I may drop the jets down to #52 and see how it runs from there. Will keep you updated on what happens. Thanks all of you for the help you have given me.
TOM
tom becker
Posts: 53
Joined: Wed Jul 19, 2017 6:25 pm

high compression 205 psi up date

Post by tom becker »

First I would like to thank Corvair Forum and all that those who helped giving me advice on my engine problems. Most of the poorly running engine was do to the distributor. Someone at sometime worked on the distributor, and installed the advance weights and cam assembly in backwards. After correcting the problem the vacuum went from 10" up to about 15" steady, not bad for that 270 cam. I took it for a test drive and WOW it ran great. Thanks to all of you. TOM
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