Question about Valve Seat Machining

[pjmoreland]

I recently had a set of heads machined at a local shop. I noticed that on some of the valve seats, there is a lip at the edge of the seat where it meets the unmachined cast surface of the combustion chamber. It seems to me that ideally this would be a smooth transition instead of a lip. Is having a lip there normal and acceptable?

[tj1970cst]

I would be concerned that the installed height of the valves is the same. I think the ridge is an unfortunate thing that would happen when the seat is cut deeper. That would be difficult to remove.

[Bigdav160]

Hopefully the tips of the valves are cut and the shims for the springs available. I agree, those seats are cut pretty deep.

[BigBird05]

How old are those heads? They don't look like they have the hardened valve seats in them. The valve job won't last long with todays gas if the seats aren't hardened.

[BASE]

They do look deeper than what I'm used to seeing. I wouldn't want to leave that. All of mine have always had 3 or 4 angle valve jobs, which transition into the seat angle. The same thing could be done to yours to get rid of that ridge (I think). Probably just a 75 deg cut would do it.

Seems like it would be crappy for flow, and would likely be a hot spot in there as well.

[BASE]

Originally Posted by BigBird05

How old are those heads? They don't look like they have the hardened valve seats in them. The valve job won't last long with todays gas if the seats aren't hardened.

I had an interesting conversation with an engine builder last weekend on that. He all but refuses to put them in race and boat engines, and strongly urged me not to put them in my truck engine. He had a box of pistons that were all beat up from seats coming loose, and a few heads that were wrecked as well. He recommended taking the heads off at 70-80k and getting a valve job and not worrying about the seats beyond that.

I'm guessing his experience with HO engines might not be perfectly representative of what a typical auto engine goes through, but he does have me reconsidering my stance on hardened seats. I'd be curious to know what experience others have had with or without hardened seats.

[pjmoreland]

Originally Posted by BigBird05

How old are those heads? They don't look like they have the hardened valve seats in them. The valve job won't last long with todays gas if the seats aren't hardened.

They are out of a 1997 Tahoe that had 130,000 miles on it.

[geunther]

This could certainly be one of those back and forths, to install seats or not. As long as you are prepared for valve jobs.

I agree those look a skosh deep. At a min, I would clean up that lip. Keep any power tools away from the machined surface, but some emery cloth just to get rid of any burrs. Might be important depending on compression.

These were some that I purchased from GM that were heat treated and without inserts. But I have not heard of shops with this capability and I can't intelligently speak to its effectiveness. The engine had strong springs, solid lifters and high compression and I never had an issue.

[pjmoreland]

From what I've read, these heads have induction hardened exhaust seats. I see vehicles in wrecking yards regularly with 300,000+ miles on this type of head.

[pjmoreland]

I took these heads to another shop to get their opinion, and the guy there pointed out that the lip around the seats is not shiny, so it was machined that way by the manufacturer.