Trying to do some research here, and I'm getting mixed answers. Per this (http://datsunzgarage.com/heads/), the N47 was the first head to have hardened valve seats. I've heard conflicting information though, that early '75 cars came with Brass-N42 heads, while the later '75 and '76 cars had hardened seats in their N42 heads.

Can anyone shed light on this? Did all N42's come with brass seats, or did Nissan swap over at some point during the N42 run?

Thanks,

Bill

Hi Bill,

I have not seen a N42 in original state with steel valve seats. You often come across them with steel seats these days because the machine shops change them over when rebuilding or repairing the heads.

They are pre-unleaded fuel heads and dont have the liners in the exhaust like the N47 and P79. For the rest they are one of the more popular heads with the P90 probably being the most desired of them all.

I run a N47 on a N42 block (original egine) in a 77 280z. These heads cop a lot of bad reviews because of liners in the (diamond shaped) exhaust ports and poor squench design. It works fine imo, but I dont race it so Im not pushing to the limit.

Hope this helps

Chas

Hi Bill,

I have not seen a N42 in original state with steel valve seats. You often come across them with steel seats these days because the machine shops change them over when rebuilding or repairing the heads.

They are pre-unleaded fuel heads and dont have the liners in the exhaust like the N47 and P79. For the rest they are one of the more popular heads with the P90 probably being the most desired of them all.

I run a N47 on a N42 block (original egine) in a 77 280z. These heads cop a lot of bad reviews because of liners in the (diamond shaped) exhaust ports and poor squench design. It works fine imo, but I dont race it so Im not pushing to the limit.

Hope this helps

Chas

Or, in my case, the E31, big-valved and ported and polished by BC Gerolomy. It works fine... Way fine.

This 1976 Service Bulletin sheds a little light - http://www.xenons30.com/files/Datsun280Z_1976Supp.pdf -, page 8.

There was either an intermediate, more durable, material used before the N47 intake seats or the change happened sooner than thought. Or maybe the the intake valve was changed before they got to the exhaust valve. They don't really say what the new material is.