Leafy

iTrader: (1)

It just seemed odd that adding supertech springs and valves only slightly increased his motors life, even if his machinist got a little to happy with the valve seat cutter. And I was pointing out that a total of $20 more spent buys you valves with a noticeably better stainless alloy.

hornetball

iTrader: (4)

Actually, this is consistent with the issue being a too-narrow seat rather than valve float.

shlammed

iTrader: (8)

Adding a high flow fuel pump wont increase the size of your injectors.

Stiffer valve springs don't help an improper valve job.

Savington

iTrader: (31)

No, it doesn't seem odd at all. I don't think you understand how engines work.

sixshooter

iTrader: (12)

If the valve seat was the problem with the first valves then it would still be the problem with the second set of valves if the same machinist had them set up the same way.

Think of it like being divorced three times. Sometimes it's you that's the common problem.

Mobius

iTrader: (2)

If I'm understanding you correctly, you are bringing up the Manley valves because you believe their better alloy will wear less/survive longer with inadequate seat support?

Savington

iTrader: (31)

Asking good valves to endure shitty valve seats is like asking good pistons to endure detonation.

NiklasFalk

iTrader: (1)

And treating thin seats with harder springs is like curing detonation with more boost.

hornetball

iTrader: (4)

Talked to the machine shop about the valves. He said after the first set got destroyed, he made sure to cut the intake valve seat (the portion at 45*) extra wide. He mentioned .060" off the top of his head

Problem is, this guy's shop is so busy and he rotates so many employees . . . so??

Took the head to my normal guy who has just completed his new shop. He's a solo operation -- does everything himself. Should know the real story soon.

What are the recommended "fat" ex/int valve seat widths?

DNMakinson

iTrader: (3)

Props for asking the right question. Take it 1 step further. Sixshooter showed you all kinds of pictures explaining what could be done, and to show definitions. Now you want a successful user *Savington, hint - hint* to suggest the total seat profiles that have been proven to work well (all angles and land widths).

hornetball

iTrader: (4)

More info:

Head is torn down and the intake valves are cupped beyond repair.

Machinist stated the valve seats were cut wide. Original shop also reported that, according to their notes, the intake valve seats were cut to a width of .060". That seems ample.

So . . . WTF? Anyway, I had a spare used head, and we're going to rebuild that one instead. Really wish I knew what the failure mechanism was here.

Leafy

iTrader: (1)

So they're moving like inside out umbrellas and its not like theres a sharp lip in the sealing surface (like you'd expect to see from a valve seat cut too narrow), just like your other valves.

EO2K

iTrader: (37)

Change something this time around. Definition of insanity and all that.

jmann

Sorry to hear Rick that widening the seats didn't fix the issue. I have had the same issue with ST intake valves and narrow seats. We widened the seats and went to double springs. Well keep a close eye on the lash adjustment when I get back on the track. If this doesn't work I am going back to stock intake valves with inconel exhaust. Never had an issue with stock valves with stock seats and several money shifts with a six speed.

mr_hyde

iTrader: (4)

I'm seriously considering ST springs on OEM valves. On a bone stock BP4W head, I have bent intake valves twice (money shifts) but the seats always look fine. The stock exhaust valves look pretty darn great after 50+ track hours at 15psi. The tune is great so I'm not burning them so why mess with the seats using harder metal? Big boy springs should help the intake float when I grab 3rd instead of 5th at ~110mph or 4th instead of 6th at ~125mph...

hornetball

iTrader: (4)

That's our current plan. Start with the bone-stock used head. Refresh. Swap in the BP5A intake cam, ST light doubles and ST Ti retainers. Keep the OEM valves. Carefully shim for correct seat pressures. Give it a shot.

Once again, only the intakes. Exhaust valves are fine. Makes me wonder about the cam. It definitely has a mechanical lifter profile, so it really is a BP5A just like the casting marks say.

hornetball

iTrader: (4)

No. They were worn just like the others. When I said cupped, I meant that the valve face was excessively worn and had a "cupped" shape and almost no margin left. But the valve is not otherwise bent or misshaped.

k24madness

iTrader: (6)

I'll say again..... make sure the factory shims are installed under the supertech spring seats. It's easy to think it's not needed (my builder did).

Both Supertech and the new head builder felt the valve cupping was due to light spring pressure. The proper way to install springs is to check yours before install and know what you want to run for spring pressures.

Read SVO's spring thread. https://www.miataturbo.net/engine-pe...ng-info-70450/

He likes to run a bit more pressure than most. It's kinda the opposite of what you think. More spring pressure does not hurt the seats, too little does due to bounce. Valves don't just slam home once they bounce 1-3 times before resting on the seats.

I ended up running a bit more spring pressure on the intakes than exhaust. I did the math and calculated the extra force from boost on the valve and then added that back in. Even without boost the intakes are heavier than exhaust. That MSM/BP5A cam may need a bit more. Whatever pressure you choose 56,60,74 etc have your guy check em.

emilio700

iTrader: (3)

This

hornetball

iTrader: (4)

More info from the original machine shop. Double checking their machine settings, the intake valve seat width was machined to .048". OEM specification is .031-.055". So, not super-fat, but not overly thin either.

I've asked the new machine shop to be super----- about seat pressures and shoot for 74 pounds. They've already pulled and tested the springs and they were found to be within spec.

I'm confused about your statement re: factory shims. I was always under the impression that you shim as required to achieve a seat pressure (which is what I think BogusSVO was showing). Shims are shims. Is there something special about the OEM shims? Or are you saying to make darn sure it is checked and adjusted as needed? I can see how a machine shop would be tempted to skip this step on a vanilla rebuild.