Plan is to use GX head on A15 block. GX head came from A12 engine which has oil passage opening. Do I need to send the A15 back to the machine shop to drill this out?

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A pre-1974 cylinder head (like a genuine GX head) will bolt onto any engine block, with no modification required

Early heads have the oil passage in the head face. Late heads are missing it (instead the late block has been modified)



1974-up blocks have this hole plugged at the factory. Instead oil flow through the head bolt hole. So late blocks can work with either old or new heads

Thanks DD. So the GX head will have proper oil circulation for the rocker assembly? If this oil passage is not being used then this passageway is not used at all and remains dry?

You will have no problem using the early GX head on the later A15 block. The oil will come up the center spark plug side head bolt over to the rocker tower.

Use the A15 head bolts with the "13" on them and remember that the middle spark plug side bolt is longer than all of the others. Use the FelPro 21199PT-1 head gasket.

Yes no problems. The passage will not be dry but will back fill from the head bolt hole




* Yes, use the '13' bolts -- because they are strong Chromoly V steel (can be torqued to 54 lb ft, unlike lesser head bolts which can only be torqued to 36 lb ft)

Fel-Pro 21199PT-1 head gasket will work. Is there some advantage to it over other brands?

Dave take it f what it's worth but the only head gasket I've had fail in and of itself was a non Fel-Pro.

The most recent one was due to the motor overheating royally.

I had one other failure because somehow I got on head bolt wrong (I think I used to short of a special bolt in the oil hole which partially blocked the flow to the rocker shaft as well as not torquing properly. I was in a hurry to get car put together fro an event......broke my golden rule of being ready no less than one week in advance.

I have had this felpro gasket set for a while now. HS 21199 PT-4. Any difference between this and the HS21199 PT-1?

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-4 is a "head set" while -1 is the head gasket only. The Head Set contains the same head gasket as well as the manifold gaskets, rocker cover gasket, and some other small seals and gaskets

The only Datsun head gasket I had fail of itself was a Fel-Pro PS (Printo Seal) -- it leaked coolant. That was some years ago and the new ones are PT with PS overlays. 21199 PT-1 is much better looking to my eyes. The A12 photo above looks to have the older-style Fel-Pro Printo-Seal

Ok thanks so I am in good shape then. That A12 motor is my spare and was the engine that came with the GX head, GX manifold and Hitachi carbs all of which will go on my A15. I think you mentioned I can use the timing chain and gears from that for my A15. Might do that if there is an advantage. But will save that for another thread when I get to that point of my rebuild.