69 corvette L36 engine cylinder heads

[Mark B.]

I bought a 69 BB car with a L36. Its a numbers matching car except the usual everyday parts wear the was changed to replacement parts. I have a question as I replaced the valve covers, I noticed that the casting number on the cylinder heads are different then what they should be. I have casting numbers 3964290 which says 69-70. My corvette was a late production built in Nov25 69.

My question, The owner said that that were original and that the cylinders heads were not replaced. Could GM started using them at that time? Did they run out of the what should of been?

Mark

[Michael J.]

Re: 69 corvette L36 engine cylinder heads

What are the casting dates for the heads? This tread may help:
https://www.forums.ncrs.org/showthre...97-69-BB-Heads

[Terry M.]

Re: 69 corvette L36 engine cylinder heads

I bought a 69 BB car with a L36. Its a numbers matching car except the usual everyday parts wear the was changed to replacement parts. I have a question as I replaced the valve covers, I noticed that the casting number on the cylinder heads are different then what they should be. I have casting numbers 3964290 which says 69-70. My corvette was a late production built in Nov25 69.

My question, The owner said that that were original and that the cylinders heads were not replaced. Could GM started using them at that time? Did they run out of the what should of been?

Mark

Mark
They likely didn't run out of anything. It is common in the automotive industry to "pull forward" parts scheduled for the next model year in order to get all the old parts out of the system before the new model year. That assumes there are no interference issues using both new and old parts. So in some cases old parts will "run long" into the next model year; and in other cases the new part will be pulled forward. Your cylinder case is another example of a "pulled forward" part.

An additional complication for the 1969 model year for Corvette and Camaro is their model year ran into what ordinarily would have been the 1970 model year. The 1970 model year for all Chevrolet models except Corvette and Camaro began in August 1969; so 1970 model year engines, transmissions, differentials, alternators and so on were being built on the very same assembly lines as 1969 parts for Corvette & Camaro. Keeping all this organized must have been a real challenge to both workers and management at the time.

The real determinate for the originality of your cylinder heads is the casting date. Is it compatible with casting dates on other engine parts (cylinder case, intake manifold, water pump, exhaust manifolds)/ Comparing all these casting dates, some of which are not routinely judged, will tell you more than the casting numbers given the late model year build of your Corvette.

[Mark B.]

Re: 69 corvette L36 engine cylinder heads

J22- 8 10T is that correct? where would they be ?

[Terry M.]

Re: 69 corvette L36 engine cylinder heads

J22- 8 10T is that correct? where would they be ?

I would bet it is J 22 9 = October 22, 1969 Which would fit well with your November build. Is the November date the stamped engine assembly code (T1125xx), or the car's build date from the trim tag (P25)?
It is very hard to distinguish 8, 9, 6 & 0. when the casting mold fills with sand the differences in these numerals is often obscured.

[Mark B.]

Re: 69 corvette L36 engine cylinder heads

the november date is off the tag on the driver side

[Edward B.]

Re: 69 corvette L36 engine cylinder heads

My October 21st, 1969 built L36 Roadster has a 3963512 block dated I-8-9 (September 8th, 1969) and the heads are both 3964290 dated J-8-69 and J-11-69 (October 8th and 11th, 1969).

Ed

[Mark B.]

Re: 69 corvette L36 engine cylinder heads

same block casting # but only see GM . Where is that I-8-9 located on the block?

[Edward B.]

Re: 69 corvette L36 engine cylinder heads

On a mid 1969 3963512 block (and later), the date code is opposite the casting number on the rear pad where the bell housing attaches. Earlier 1969 (and prior) 3963512 blocks had the date code on the passenger side of the block under the number two core plug.

Ed

[Michael J.]

Re: 69 corvette L36 engine cylinder heads

J22- 8 10T is that correct? where would they be ?

Finally found the HEAD date casting from my '67 L71 BB head, it is here:

[Mark B.]

Re: 69 corvette L36 engine cylinder heads

Mine reads J 28 - (8) i think on the passenger side

[Mark B.]

Re: 69 corvette L36 engine cylinder heads

ED mine read J-28 but didn't see 69 in the casting. It was a little dirty

[Edward B.]

Re: 69 corvette L36 engine cylinder heads

Sometimes the date code can be VERY difficult to make out. Try cleaning it with a little carb cleaner on a rag and see if you can take a picture and post it.

Ed

[Michael J.]

Re: 69 corvette L36 engine cylinder heads

Mine reads J 28 - (8) i think on the passenger side

Is that the BLOCK casting date, or a HEAD casting date?

[Joe L.]

Re: 69 corvette L36 engine cylinder heads

I would bet it is J 22 9 = October 22, 1969 Which would fit well with your November build. Is the November date the stamped engine assembly code (T1125xx), or the car's build date from the trim tag (P25)?
It is very hard to distinguish 8, 9, 6 & 0. when the casting mold fills with sand the differences in these numerals is often obscured.

Terry and Mark-----

It has to be 1969 (or, 1970). The 3964290 cylinder heads were not being produced as early as October, 1968. I have no doubt these heads are original to the car.