1963 Corvair Engine detonation

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edherba
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Re: 1963 Corvair Engine detonation

Post by edherba »

Yes, 255F is oil temp.
I did not machine the head where the gasket seats. But over the past 50 years, maybe someone else did. How do I know? Can I measure the head gasket seat depth? What should it be?
edherba
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Re: 1963 Corvair Engine detonation

Post by edherba »

From Clarks Corvair page 7: "Solid copper head gaskets, reuseable for standard bore thru 3½” (a must on +.030 or larger bores to avoid gasket “hang-over”). Can also be used to adjust for cylinder head resurfacing and lowering compression for running on regular gas. Stock thickness is approximately .032 (so .042 gains .010 and .052 gains .020). 2 Big Bore gaskets can be stacked to adjust for resurfacing. The stock distance from the head surface to the head gasket surface is approximately 0.570-0.580. CHECK TO SEE IF YOURS HAS BEEN RESURFACED".
These head gasket thicknesses are before they are compressed?
edherba
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Re: 1963 Corvair Engine detonation

Post by edherba »

I bought some octane booster and put the whole bottle in a full tank of gas. The detonation was greatly reduced and would only be heard slightly when accelerating hard from stop. Oil temp is still a concern at around 255F after 15 minutes of driving in town. I may try swapping the carb jets from #51 to #53. See if that cools it down a bit. Plugs looked normal with the #51. I am on the verge of taking the heads off and installing the copper 0.052" head gaskets. My current compression varies between 160 and 180 depending on cylinder. Should I put the thicker gaskets?
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flat6_musik
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Re: 1963 Corvair Engine detonation

Post by flat6_musik »

That one thing that concerns me is that you mentioned the oil puddling in one of the cylinders, also the deposits around the outer circle of the spark plugs. I hope this motor doesn't have any oil consumption issues, because that will be an instant path to increased detonation, guaranteed.

Have you noticed oil consumption that's above normal?
edherba
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Re: 1963 Corvair Engine detonation

Post by edherba »

No oil consumption issues that I noticed. Puddling in cyl 5 is because car is parked on a floor with a slope towards the floor drain and that cyl is the lowest point. I'll keep an eye on that though.
edherba
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Re: 1963 Corvair Engine detonation

Post by edherba »

So I redid the compression test with another compression gauge just to eliminate the possibility that my gauge is wrong. It showed compression between 170 and 185 psi. When I checked again with my tester I got 175-190psi. This is done cold. So I guess it confirms that my compression is definitely high. How thick of a head gasket should I use to get the compression down to around 150psi ? Should I go straight away with the 0.052" (0.020" thicker than stock).
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terribleted
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Re: 1963 Corvair Engine detonation

Post by terribleted »

You should measure to see what thickness is needed to return to stock dimensions.
Corvair guy since 1982. I have personally restored at least 20 Vairs, many of them restored ground up.
Currently working full time repairing Corvairs and restoring old cars.
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edherba
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Re: 1963 Corvair Engine detonation

Post by edherba »

To follow up on my high compression issue (180-190 psi).I removed the RHS head and measured the depth from cylinder head surface to the head gasket surface and it is between 0.563 and .569". Clarks says stock distance should be 0.570-0.580. Therefore the head gasket surface does not seem to have been machined in the past and the head is not the problem. My next step is to measure the cylinder barrel height from gasket surface on block side to gasket surface on head side. What is that height supposed to be? For a 102HP engine.
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terribleted
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Re: 1963 Corvair Engine detonation

Post by terribleted »

What does the head gasket surface look like? Is it totally flat? The stock head has a raised area around the outside of the opening where the cylinder goes. The head gasket sits on top of this little raised area. This step measures almost 50 thousandths of an inch. The top of the cylinder (the part that inserts into the head) should measure about .560 inches (height of the machined area above the fins to where the cylinder sits against the head gasket). If the step is gone from where the head gasket sits (no step) and the cylinder top measures stock then a head gasket thickness approaching .080 would be needed to be back at stock. If the cylinder has been topped (machined shorter on the head end then compensation would be needed for that as well. Here is a photo of an uncut 140 head. the step is all there. This head needs to have the head gasket step machined to be flat for new head gaskets as you can see the groove impressed into the head by the head gasket. The silver scratch is along the base of the raised step. Came from me scraping carbon off to show the step.

The length of the cylinder would not be that relevant overall. If they are Corvair cylinders the height from where they seat against the block to the top of the fins should be fine. The thickness of base gasket is very relevant. Are there cylinder base gaskets installed under the cylinders? How thick are they? The height of the top part of the cylinder above the fins is also very relevant since if this measurement is short the piston will sit closer to the head than designed.
IMG_4373[1].JPG
Corvair guy since 1982. I have personally restored at least 20 Vairs, many of them restored ground up.
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66vairguy
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Re: 1963 Corvair Engine detonation

Post by 66vairguy »

USUALLY when the head gasket area is machined the head is ALSO machined to prevent interference between the head and cylinders!! So - measuring from the head surface to the gasket surface is meaningless to determine compression. It will only tell you the head will fit over the cylinder without an issue.

The best way to determine a compression ratio is to "CC" the head chamber area (use a fluid and plate with measuring device to see how much fluid fills the head chamber up to the gasket surface. There are formulas for the bore and stroke that allow you to change the gasket depth to find a correct compression ratio. If the a gasket thickness that is excessive is needed to make the numbers work, then you have to have the head chambers machined to increase volume to lower compression (don't machine the piston tops as that can create a weak piston). I don't have the info for which Corvair books have the formulas, but I bet Brad does.

Sometime I find a heads has been "over machined" and I junk them since welding up the gasket surface and machining it again is expensive vs. just finding a good used head. Just me.
edherba
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Re: 1963 Corvair Engine detonation

Post by edherba »

I measured the cylinder portion which inserts into the head at is is 0.560". The cylinder head has a raised portion for the head gasket as shown in the pictures. There is a cylinder steel base gasket (stock size) which I installed when I rebuilt the engine. The piston seems to come right to the top of the cylinder. Is that normal? See picture.
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terribleted
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Re: 1963 Corvair Engine detonation

Post by terribleted »

I have an engine here with no heads on it and stock cylinder base gaskets. I measured the piston at TDC to be .020 or maybe just a hair less below flush (used a feeler gauge0. Your pistons look to be protruding from the cylinder. I have built a number of engines and the pistons are never dead flush to or protruding from the cylinders. Is the head gasket still in the head in these photos? What I am seeing looks like a cylinder base gasket not a head gasket. Stock base gaskets are flat with a little ridge in the center. Head gaskets are a rolled steel ring with a flat side and the other side has a triple layer of steel rolled over flat on it. If this is a base gasket in the head it would not give the proper thickness as stock base gaskets are only .015 and stock head gaskets are .032.

On my personal powerglide cars and some I many I have built for customers. I add an additional .010 or .020 head gasket thickness to decompress just a little to avoid detonation with todays crappy fuel I always run 92 octane. I have run both in personal cars and can really not tell any difference in performance with the butt dyno.

Here is a photo of base and head gaskets side by side. The head gasket is on the left the base gasket on the right. the flat side (down in the photo goes against the head). The ridge on the base gasket goes against the cylinder.

IMG_4375.JPG
Corvair guy since 1982. I have personally restored at least 20 Vairs, many of them restored ground up.
Currently working full time repairing Corvairs and restoring old cars.
https://www.facebook.com/tedsautorestoration/

Located in Snellville, Georgia
edherba
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Re: 1963 Corvair Engine detonation

Post by edherba »

The photos I posted are without the head gaskets. I was aware of the difference between the base gasket and head gaskets when I built the engine and was careful to install them as correctly. I will measure the distance between the piston top and the cylinder end. If mine protrudes then a thicker base gasket might solve the issue. However a copper base gasket is only 0.020" which only 0.005" thicker than stock. Not sure that will be enough.
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terribleted
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Re: 1963 Corvair Engine detonation

Post by terribleted »

That is good that head gaskets were it the heads😀. Was hard to tell in the photo as the head gasket seat has what looks like a base gasket sitting in there or a fine line impressed in it (looked like the thin line in a base gasket). Clark’s lists a .032 base gasket also.
Last edited by terribleted on Thu Dec 31, 2020 9:47 am, edited 1 time in total.
Corvair guy since 1982. I have personally restored at least 20 Vairs, many of them restored ground up.
Currently working full time repairing Corvairs and restoring old cars.
https://www.facebook.com/tedsautorestoration/

Located in Snellville, Georgia
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flat6_musik
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Re: 1963 Corvair Engine detonation

Post by flat6_musik »

I would think that the thicker head gasket could cure this, and to worry about adding a thicker base gasket is a waste of time. Same outcome, but way simpler to just do the head gasket.

I would also work towards getting that oil temp down as well. Any way you can pull heat out of this motor will be a plus. Remote oversize oil cooler with a fan; if mine, that's what I'd do.
66vairguy
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Re: 1963 Corvair Engine detonation

Post by 66vairguy »

AFAIK -- cylinder to block gaskets and head gaskets are a different diameter. Can't mix them up.

Your cylinder gasket area is VERY smooth and shiny, not typical of a used cylinder. Someone may have cut the top cylinder gasket area to make it even and smooth AND that lowers the height of the cylinder - just guessing that is your problem. Maybe Ted can measure a good used cylinder and get you the numbers. As Ted said, the piston should NOT PROTRUDE above the cylinder edge, although it's normally close - spec. in in the shop manual. NOTE: new cylinder base gaskets do have a bump in them that compresses after the head is torqued down. BTW - Did you check to see if the base gaskets are in place???

If your cylinders are a little short - then a thicker base gasket can be used. A thicker head gasket could work, but the bigger the gasket gap, the greater the detonation issues IMHO.

If your oil cooler is good don't worry about your oil temperature, not out of range for an air cooled engine. Except for racing an external oil cooler is NOT required for a stock engine. If you don't have the fine fin 8 plate oil cooler, then installing one would be a good change. Fits without modifications.

Good luck.
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