cylinder head numbers

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Jim in Wis.
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cylinder head numbers

Unread post by Jim in Wis. » Fri Nov 03, 2017 2:44 pm

In getting ready to order parts, we printed out a "engine worksheet" from Clark's Corvairs. One of the lines to fill in was a seven digit number on the heads. They only seem to be asking for one number, so I figured the heads would both have the same one, but they don't. One head has 3883863 and the other has 3856759. This motor has other mixmaster stuff, like pistons and valves - did someone also switch heads? What is the correct head number? Am I right in thinking the heads are the same right and left? Or is it me that all mixed up?
This is a 65 Monza 110 hp 4 speed (at least that what it's supposed to be).
Thanks
Jim S.

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terribleted
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Re: cylinder head numbers

Unread post by terribleted » Fri Nov 03, 2017 3:22 pm

Both those heads call out to be 65- 67 110HP heads from the reference chart in Clark's catalog. 66 and later heads would have 3/8x 16 holes all along both sides holding on the top shroud. 65 heads would have a couple 3/8x16 bolts on one end and 1/4x20 holes across the rest of the side. They are not a matched pair but as long as the combustion chambers are shaped the same and they are machined and assembled properly they should work fine. Factory assembled motors almost always, if not always, had matching head casting numbers.
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Jim in Wis.
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Re: cylinder head numbers

Unread post by Jim in Wis. » Fri Nov 03, 2017 4:09 pm

Thanks Ted, now we have one less thing to worry about. The combustion chambers do appear to be the same.

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terribleted
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Re: cylinder head numbers

Unread post by terribleted » Fri Nov 03, 2017 5:25 pm

Pay attention to headgasket surface machining. If it is not even (one head has less step under the headgasket than the other), you may want to compensate by using thicker headgaskets on the side that is short.
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: cylinder head numbers

Unread post by 66vairguy » Fri Nov 03, 2017 11:16 pm

The CORSA guide says the 3883863 is a casting number for a 110HP engine for 1965. The 3856759 is the casting number used in both 1964 and 1965 for the 110HP, BUT that may be erroneous since the 64 engine used the narrower cylinder outer diameter vs. the 1965 and later heads. It's possible there were too different machining numbers assigned to the same casting number, but the CORSA guide does not indicate that.

Both heads have the same combustion chamber size.

The 3856759 could be on 65 cylinders, or maybe someone used 64 cylinders on one side of the engine. Only a physical inspection will determine what you've got.

Jim in Wis.
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Re: cylinder head numbers

Unread post by Jim in Wis. » Sat Nov 04, 2017 3:46 pm

I'll measure those cylinder diameters - we'll need to replace at least one, probably two anyway. We're negotiating for another motor for parts - it's just the block, cylinders, heads, crank, pistons, cam, and it's stuck tight like ours was. Maybe between the two we can come up with 6 useable matched cylinders. This motor has the four carb type heads, unfortunately one carb mounting block is broken.
Nobody said this was going to be easy!

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Re: cylinder head numbers

Unread post by 66vairguy » Sun Nov 05, 2017 9:11 am

A broken head mount may be worth repairing IF the 140HP dual carb head is worth it.

I sold a 140HP head that was beyond an affordable rebuild (ruined by an incompetent machine shop) to a club member that had it cut up to repair a broken carb mount on an otherwise very good 140HP head he had. In this case he found a shop that specializes in aluminum engine/head welding.

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Re: cylinder head numbers

Unread post by terribleted » Sun Nov 05, 2017 10:54 am

Hold the boat!! You say the heads you listed above have 2 carb pads on each (so 4 carb engine)? If this is the case they are fully custom as the only 4 carb engine heads made by GM are 140HP which would not bear the casting numbers you stated. 140 heads would also sport a very large intake valves. A number of heads over the years have been modified for 4 carbs with heli-arced on secondary pads. If you intend to use these you are pretty much locked in to finding a way to repair the broken pad as finding a replacement head that was modified the same way (or the parts to modify a head ) could prove to be difficult. I am sure someone has some of these items laying around, but, not many. You need to look closely for other modifications as well and pay very particular attention to cylinder to piston clearances if the chambers have been machined where the head gasket step has been eliminated or machine a lot shorter. Thicker head gaskets can be used to compensate. Clark's sell a few diff thicknesses in their copper "big bore" head gaskets.
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Re: cylinder head numbers

Unread post by bbodie52 » Sun Nov 05, 2017 2:00 pm

The chart I am looking at (attached below) states 3856759 is a 1965 110 hp engine (single carburetor on each side).

3883863 is not listed on the CORSA tech chart. 3883862 is a 1966-69 110 hp head, and 3883863 is skipped, with 3883864 being a 1966 140 hp large valve 4x1 carburetor head. On the Clark's Catalog Page (below), 3883863 is listed as a 1965-1967 110 hp head.

Image

I have also included several detailed photographs of the 140 hp cylinder heads. In addition to the additional carburetors, special linkage and fuel line arrangement, the exhaust manifolds also have a larger cross-section for improved exhaust breathing. A photograph of the 110 hp cylinder head combustion chamber is shown below for comparison…

Image

Image

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110 hp Engine
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Attachments
CORSA Corvair Technical Guide 1+2 - Corvair Code Numbers.PDF
CORSA Corvair Technical Guide 1+2 - Corvair Code Numbers
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Brad Bodie
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Image 1966 Corvair Corsa Convertible

Jim in Wis.
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Joined: Wed Oct 11, 2017 4:09 pm
Location: Sheboygan Falls, Wis

Re: cylinder head numbers

Unread post by Jim in Wis. » Sun Nov 05, 2017 3:58 pm

Ted - The engine we have has the 2 carb cylinder heads with the numbers I posted. Our engine has the RD code
Someone we know has the other partial engine with the four carb heads. This is the one with the broken carb mount on one of them. I don't know what numbers are on heads or block.
The chart and pictures are great - thanks.
My friend (who owns the car) would sort of like to convert to 140. This might not work out though.
He just got back from the SEMA show in Vegas and showed me pictures of a fancy green Corvair that was on exhibit.
Jim S.

66vairguy
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Re: cylinder head numbers

Unread post by 66vairguy » Sun Nov 05, 2017 4:22 pm

There are two types of 4 carb 140 heads. Easily identified from the top by the small vs. big holes mentioned before by Ted.

Note the 66-69 140HP heads were revised to support the "heavy" A/C compressor. In 65 A/C was NOT available on 140HP engines.

If A/C is not a consideration, then the 65 style heads work fine.

There is some conflict among the various Corvair books on 140HP casting numbers. The general consensus is:
65 only casting #3856728
66-69 casting #3878570

Machining numbers vary (that number was not stamped on the heads) to accommodate changes for emissions equipment. Combustion chambers stayed the same, regardless of emissions requirements. The myth of the "open chamber" 140HP head persists, but none have ever been documented as coming from the factory.

As with ALL 140HP heads, they should be rebuilt with the newer DEEP seats to prevent a seat drop out - common on high mileage 140HP stock heads.

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