Hi all. My A12 blew its head gasket yesterday. I have a rebuilt H891 head off an A15 to go on. I am not sure if I should use an A12 or A15 gasket. The head is going on to an old style A12 (dizzy at front. I'm not sure at this stage why it blew. In the past I have had corroded water galleries on a few occasions with the older style heads especially. I know the oval port head isn't the best option for a relatively stock engine. But it is most likely in better condition than the one that is on there. Any advice appreciated. Cheers

Oval port head is a fine head for a stock A12. If you rev it up it will make more power than stock.

Use an A12 gasket, as the A12 block has smaller-diameter pistons than an A14/A15.

Thanks mate. My main concern was the chamber on the H89 being bigger than the A12 head. Most of my driving is on the free way so power up top is good. The head has been decked. Not sure how much. I am also running a 32/36, Hei and some Hi Teck 4 into ones. Bit more fuel up top and should be good for 10's Baaah..

Don't forget to check the oil path to the head. The later heads don't have the oil passage in the head like the 1200's do. In the later models the oil passage into the middle head bolt is in the block instead of the head.

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I doubt if the chamber is larger. A-series tend to control compression by the piston dish, and Datsun used the same heads A12, A14 and A15. Yes, in USA, they fitted the same heads to A12 and A15. The pistons have a different dish.

I'm pretty sure this is the case as I once had that hole welded up on a head I had done up. It was so long ago I cant remember the specifics. So this poses a new question. Can I even fit my H89 to an older style A12 block?? mmmm. It got real hot so wouldn't be surprised if I bent the head that's on there..

chambers can be different, heart shape/kidney shape/open chamber. best to cc the heads, check if any differences,(just to be sure) also you can drill oil hole into h89 on a angle into head bolt hole.(if needed).

My head is has the kidney shaped chambers. It's also been shaved to about 72.5- 73.

is that the h89 shaved 72.5mm(approx cc would be 27cc roughly)do the two chambers(a12 to a15) look different. put up pics.thickness of a12 as well.

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Sure, it bolts right on. Just need to modify the oil passage or the rockers won't get lubricated.

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You will need to ... unless it has already been done. See Oil Passage in the head