JPCorvetteC3

Hello.

I took some pictures of the GM part numbers and date codes stamped on the cylinder heads for my 1971 LT-1. I have checked the GM part number and it is the correct number, however I am not certain if the valves are the right size when compared to the base 350.

I have figured out that the dates read like this: H220 - August, 22nd day, 1970
C261 - March, 26th day, 1971 - the 6 could be a 5?

My car is a June build in 1971, do these date codes seem correct? I don't have much history on the car, and I know for a fact that some of the engine components aren't original (intake manifold, carb, etc.)

Any idea what the stamped 15 stands for?

Thanks so much.




Drivers Side * a random number?


Drivers side GM Part # - 3973487 Date Code - H220


Passengers side GM Part # - 3973487 Date Code - C261

Easy Mike

Casting dates are okay for your car, although dates can often be closer to the engine assembly date. What is the engine assembly date? All part dates must precede the engine assembly date.

It's cast, not stamped, and is probably the casting mold number.

JPCorvetteC3

[QUOTE=Easy Mike;1597782333]Casting dates are okay for your car, although dates can often be closer to the engine assembly date. What is the engine assembly date? All part dates must precede the engine assembly date.

Hi Mike,

The only number I have for the engine is this: V0331CGZ - I'm reading that as a March 31 production

If that is right, then the date codes seen on the heads will work.

Does it make any sense that a head was used from August 1970? That's 8 months it would've been sitting there for.

This isn't the end of the world, I'm just trying to make sense of things.

JPCorvetteC3

It's cast, not stamped, and is probably the casting mold number.

That's good to know. Thanks.

stingr69

The engine has been apart and heads pulled off at least once based on the over spray on the bolts No way to tell if the valve sizes are right without a tear down. Should have screw in studs and push-rod guide plates. Not real critical either way but if you just have to know more you will need to pull the heads off again. Small valve heads can be converted to big valve but not everyone does the chamber wall machining like the factory did.

Easy Mike

Correct. Engine assembled March 31 at Flint (V) for an LT-1 Corvette (CGZ). The time build code for your car must be after 3/31/71. You say June. That works.

Yep.

Flint assembled about 5500 small block engines of all types on a daily basis. They were usually pretty good at keeping up with raw stock, but anomalies have been reported.

JPCorvetteC3

It looks like there are push rod guide plates installed. I'm not familiar with the screw in rocker arm studs, do you have a picture? Would the screw in type be more correct to an LT-1 engine or is it correct for all 350 engines?

JPCorvetteC3

I've read stories of things like that happening, maybe that's the case here? At any rate, the car drives just fine. It's always nice to know.

Cheers!

stingr69

The guide plates are retained by screw in studs so you do have them both. The special push rods required are heat treated to prevent excessive wear against the guide plates. Screw in studs and guide plates were used on GM factory optional HP engines only as base V8s do not have them. They were used beginning in 1970 and up. Also a common owner added modification during service.

EarlyC34me

EarlyC34me

JPCorvetteC3

Thanks for all of the responses to my questions, I've learned a lot.