cws1807 Posted April 18, 2011 Share Posted April 18, 2011 Hey guys, I've got a stock N42 head that I'm gonna put on my 78 280z. Some people have told me that the N42 heads do not have hardened valve seats because they were designed to be run on leaded fuel. Its a pretty expensive machining job to have new ones pressed in and every machine shop I've talked to says they already have hardened seats, but some guys in my local club say they do not. I've been searching on here and other forums and talking to other people and I'm getting different answers. Thanks for the help Quote Link to comment Share on other sites More sharing options...
NewZed Posted April 18, 2011 Share Posted April 18, 2011 I have heard the same. But I have a PDF copy of a 1976 Service Bulletin (Vol. 23) that says "Cylinder Head Intake Valve Seats - The material has been changed to increase endurance reliability." There might have been more improvements after that but I've not seen it documented. If the head is off of a 76 at least you'll have "increased endurance reliability." I've never read a report anywhere about excess wear or galling on the valve seats from someone running today's unleaded through an old engine. It's an interesting factoid but not much backing to it. Quote Link to comment Share on other sites More sharing options...
cws1807 Posted April 18, 2011 Author Share Posted April 18, 2011 Ok thanks for the reply, I pulled this head several years ago off of a junk car so I cannot remember the year model. Are there any casting numbers or anything that would tell me if it is a '76? Quote Link to comment Share on other sites More sharing options...
BluDestiny Posted April 18, 2011 Share Posted April 18, 2011 Found this, should help. "- The larger valve N42 came on the 1975-76 280Z. 48 state U.S. 280Zs didn't use a catalytic converter until 1977, so the head came with softer brass valve seats for use with leaded gas. Many people like these for performance because of it's square exhaust ports. And as a easy mod, putting it on a flattop L28 motor puts compression in the mid 10's. It uses an external oil spray bar." from: http://datsunzgarage.com/heads/ Quote Link to comment Share on other sites More sharing options...
cws1807 Posted April 19, 2011 Author Share Posted April 19, 2011 Hey thanks BluDestiny it'll be easy enough to check if they are brass. If they are will it harm the head or valves to run on unleaded fuel? Quote Link to comment Share on other sites More sharing options...
BluDestiny Posted April 19, 2011 Share Posted April 19, 2011 Wouldn't know, never ran a head with brass seats. Are you building a performance head? Quote Link to comment Share on other sites More sharing options...
cws1807 Posted April 19, 2011 Author Share Posted April 19, 2011 No just a temporary fix until I do a turbo swap, old N47 head had a broken exhaust stud and the N42 was laying around. I'm gonna spend the money for a good coated header and since the N42 flows a little better it just makes sense to do a valve job and drop it in. Quote Link to comment Share on other sites More sharing options...
cws1807 Posted April 19, 2011 Author Share Posted April 19, 2011 Anyone out there running a stock 75-76 head with stock valve seats? If so are you having any problems? Quote Link to comment Share on other sites More sharing options...
Xnke Posted April 19, 2011 Share Posted April 19, 2011 Yes, USDM N42's were OE with bronze seats. They are yellow in color and if you look at your head, you should be able to see that. If it's too dirty to tell, it's too dirty to go back on the engine. That said, the JDM ran the N42 for a LOT longer than we did here, and those heads (and Nissan replacement heads) came OE with hardened steel seats. Also, a lot of these heads have been worked before, and had the seats replaced then, too. Chances are pretty even that you've got a bronze seat head, so I'd check it to be sure. Even if you do, a lot of folks don't have problems with them...that they know of. I have three bronze-seat heads here that have serious valve recession, ostensibly from running unleaded gasoline. It's all in the composition of the gas you run, the seat material, the duty cycle, and a host of other factors as to if you're going to have problems with the bronze seats. Quote Link to comment Share on other sites More sharing options...
cws1807 Posted April 20, 2011 Author Share Posted April 20, 2011 Ok thanks Xnke thats exactly what I needed to know Quote Link to comment Share on other sites More sharing options...
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