Bronze valve seats?

[Eddy67]

I have a E31 head that is is excellent shape and I noticed that it has the bronze valve seats in it, they are also in excellent shape, do I need these replaced with steal ones, or should I not worry about it?

[Diseazd]

Replace 'em.....w/o lead additives, they'll be pounded out shortly. IMO

[rcb280z]

Iv'e always heard to replace them.

[Eddy67]

Can I bore the old ones out an simply press fit the new ones in? I am a machinist, just don't know what the tolerances are like on this stuff

[Walter Moore]

When I had my head redone the shop told me that the old seats had to be cut out, and that as a result they had to be replaced with larger seats and intake valves. So I bought the 280Z intake valves and seats. (44mm I think)

This shop pretty much exclusively worked on aluminum cylinder heads. They had big ovens to heat them up so they could remove and install the seats, guides, and other steel parts. The machinist told me that if you get the head hot enough and give it a solid tap, all the steel parts will just fall out. ( He may have been exaggerating. )

[Jeff G 78]

My bronze seats failed in my race car and I had them replaced with steel. It was only about $200 to replace the 6 intake seats and do a valve job. They did not have to cut them out.

[Zed Head]

Can I bore the old ones out an simply press fit the new ones in? I am a machinist, just don't know what the tolerances are like on this stuff

The replacement procedure is described in the Service Manual. It doesn't look too complex. They recommend boring them out, heating the head and pressing in the new ones. No tolerances given but maybe there's only one size and the hole is assumed to be untouched. After they're installed though they need to be ground to fit the valve. That's the part that takes the skill and is most important. If you're not going to grind them too you might as well have a shop do the whole job.

You said you're a machinist so may know that but just in case...

[Eddy67]

I have a spare head that I just put in the oven at 380f, I will see if the old valve seats come out easily, if not I will keep turning it up.

[Eddy67]

What are your thoughts on this head?

[Eddy67]

Is it too far gone?

[Jeff G 78]

Eddy67,

Anything can be repaired, but unless the head is a full race head and that's the only damage, it's scrap and you should look for a new one.

[Eddy67]

Its a shame, this one has never been machine down, still lots of thickness to it, and its straight