had to put new exhaust seats in 401-425 heads.my machine shop said I needed new exhaust seats, I said you cant put new seats in a nailhead. he said why not if your care full and don't go down to deep. they came out just fine.
Well,,, pard that was a mistake.....but ,,, you may get away with it....the best way to rebuild the seats on a nailhead is to build them up with weld and then recut....and that takes special tech and talent.... If you start hearing noises , shut down immediately and dont restart untill you check it out completely.....
My machinest has told me a couple times he can and has done the seat replacement on nailheads. I have not run a set of heads that had them done but if I had a set of heads that the choice was junk heads or new seat, I know what I would be trying:TU:
My buddy Marty had a set of heads done with thin seat inserts. He was about to fire the engine for the first time when he found one of the cylinders filled with coolant..... want to guess where it came from? It's probably hit-or-miss on whether it works depending on the particular castings amount of metal in that area.
I agree with Doc. Even if you "get away with it", The cast iron under those new seats is paper thin. I wish you all the best, and I really hope it works out for you, but I wouldn't do it - nor would I install those heads on my engine.
They say the same thing about Big Block Chevies. Not enough material under the seat, causes coolant leaks. Install the CORRECT seat with correct press-fit, using a heavy-duty Loctite anerobic sealer. Sometimes need to pressure-seal the head/seat joint using an industrial pressure or vacuum machine, and additional chemical compound. Done. Not even horribly expensive. (beyond the ordinary and expected cost of installing and then cutting the hardened seat inserts.) If your machinist can't install exhaust seats, you need a new machinist.
my machinst puts them in big block chevys all time, even in the 409 chevy engine. if they leak, then we know the only cracked head is the one holding the steering wheel, for messing around with engines and trying to go fast.ou:
got the heads on, was turning over made a noise then would not crank over. you know what I was thinking. it cranked by hand so it had to be the starter. it kick back while cranking timing was off. it was a mini starter a had for 3-4 years. called Tom T. Monday wanted to try his starter this time. he said he had one right at the shop here and it was his newer design, he was going to lunch as I called and said he would take it with him to the post office and mail it right out and send a check out Tuesday that was great really wanted to get it running as soon as I could. its running now the seats seem to be fine so far. thanks Tom for sending it right out, I like this starter better than the one I had.
Dont know how the job is done now... but back when :Brow: they first came out with those, I watched a guy install some one day... What he did was to pack the hard seat in dry ice... and after a certain amount of time, like 1 hour... he measured the od and put it back on ice and while it was cooling back down, he cut the hole in the head 1 thousanth smaller than the od of the seat... ( the head was heated in hot water) Then he took the seat out and very quickly drove it into the cut in the head.... it made a squealing sound as both temps came toward each other.... The problem aint the seat or the system,,, the problem is people that dont know how to do the job right but think that they do.....:Brow: then the thing fails and tears your engine up..... :af:
Carmen Faso, who knows Nailheads very well, did a set of heads for me with oversize valves and seat inserts...no problems. As most have stated, it probably boils down to who is doing the work...but then, again, doesnt it always? Tom Mooney