Don Terrill’s Speed-Talk

Please help. Some time ago, after really bad experiences with local shops, I decided to do my own valve jobs. I bought Neway cutters, a seat indicator and started cutting. As I recall, I managed to get concentrically to with in .002 and really good sealing, about two percent leakage with my leakdown set up, which only measures valve leakage, (v. the seven percent I was getting from the pros)
The problem is: one of my exhaust valves was sunken pretty deep I was OK re. installed height but it was pretty deep. I've run this head in six races ( it's in a road racer) and it's been great, really good compression, leakdown, and power, but now, I've been told that I'm risking disaster and a broken valve on that sunken valve. True? or am I OK.
This is a 16v, 1.6 Miata.

What's the reason your risking disaster? Did you ask the person to quanitfy their remarks?

If it lasted 6 races already, then you probably answered your own question. You never know, but it will probably last a full season or even a full 10 seasons. I've seen alot of junk motors that had alot more problems hold together in my life. Back in my kid days, we'd take a nearly stock motor and run tons of NOS through it. Somehow just about all of them stayed together, minus a few head gaskets.

davidb wrote:Please help. Some time ago, after really bad experiences with local shops, I decided to do my own valve jobs. I bought Neway cutters, a seat indicator and started cutting. As I recall, I managed to get concentrically to with in .002 and really good sealing, about two percent leakage with my leakdown set up, which only measures valve leakage, (v. the seven percent I was getting from the pros)
The problem is: one of my exhaust valves was sunken pretty deep I was OK re. installed height but it was pretty deep. I've run this head in six races ( it's in a road racer) and it's been great, really good compression, leakdown, and power, but now, I've been told that I'm risking disaster and a broken valve on that sunken valve. True? or am I OK.
This is a 16v, 1.6 Miata.

How deep?? Deep has nothing to do with breaking a valve.

The Guru who predicted a broken valve now tells me that the valve will become "tulipped." No explanation just that the valve will "tulippe. What is this?"

Assuming you are okay with the stem height not bottoming the hydro lifter, not sure what problem it could cause
I don't see how a sunken seat can tulip a valve

Your Guru may be assuming the valve is sunk mostly because the valve head is thin from too many grinds. I get the impression that's not so? A valve should have a discernable margin- maybe 0.020" or so, not a razor edge. A thin valve head will indeed overheat and 'tulip', just before the edge burns up or the head pops off, especially if the motor is intended to turn mucho rpms or has stiff springs. But besides a thin valve, removeable valve seats can pound into a casting and "sink a valve", or be over-ground and not cause problems beyond a little port flow inefficiency. My 2¢-
J DeRyke (no guru but also have a valve grinder for cars & bikes in the garage)

Not to get off topic but, how do you like the Neway system? Which one did you buy?

Bobqzzi: Thanks, and thanks for the spelling help too.

jsgarage; That's what I expected; I'm using stainless valves with thicker heads; I'm beginning to think that the "guru is B.S.ing me.
Thanks to this discussion, I'm beginning to sleep better at night.

tflow: I simply bought the required carbide cutters, and a cocentricity indicator, and,importantly, a bottle of red layout dye.
I also have an old Souix valve grinder with a collet, but valves are so cheap that I don't bother with it.

I think the cutters are capable of producing a really good seat, that seals pretty well, but, man is it time consuming!

They seem to tear the seat material if too much pressure is used.

I'm convinced that my problem with sunken seats has more to do with trying to correct a professional valve job that was previously done with a CNC mill, than with my cutters.

After the CNC screwing, I took the head to a shop with a Serdi and they made it even worse (10% leakage).

Now do yourself a favor and buy a Souix seat grinder off of Ebay. It will do a much better job than the Neway carbide cutters.

davidb wrote:Bobqzzi: Thanks, and thanks for the spelling help too.

jsgarage; That's what I expected; I'm using stainless valves with thicker heads; I'm beginning to think that the "guru is B.S.ing me.
Thanks to this discussion, I'm beginning to sleep better at night.

tflow: I simply bought the required carbide cutters, and a cocentricity indicator, and,importantly, a bottle of red layout dye.
I also have an old Souix valve grinder with a collet, but valves are so cheap that I don't bother with it.

I think the cutters are capable of producing a really good seat, that seals pretty well, but, man is it time consuming!

They seem to tear the seat material if too much pressure is used.

I'm convinced that my problem with sunken seats has more to do with trying to correct a professional valve job that was previously done with a CNC mill, than with my cutters.

After the CNC screwing, I took the head to a shop with a Serdi and they made it even worse (10% leakage).

You never have said how much deeper that valve is? Did you measure?

It's hard to take a lot off with neway cutters. I have a set and don't use them too often, but find them useful for quick touch-ups on small seats.

What's the best way to measure that? Installed height v. stock?