Help!! My Intake Valves Keep Wearing Out!
 

Red car.

Engine:
'95 BP Block
'01 Pistons
'99 Head, mildly ported
BP5A Intake Cam, '99 Exhaust Cam

History:

8/9: Rebuilt Engine put into service. Mazda OEM valves and springs.

9/13 ~1500 street miles + ~18 track hours. Head pulled due to loss of compression. Found extreme wear (concave surfaces) on the faces of all intake valves. Head rebuilt with all Supertech valvetrain including valves, dual valve springs and Ti retainers.

9/29 Engine with freshened head put into service.

12/28 ~500 street miles + ~22 track hours. Noticed slight miss at idle. Leakdown shows loss of compression through valves. Intake valve lash has closed up again.

Soooo . . . WTF?!? Is this normal? How long should I be able to go on a valvetrain before reshimming? If not normal, any ideas on what's causing the valve face wear? I wouldn't expect weak valve springs to be an issue with the dual Supertechs. In all cases, the head work was professionally done by a local machine shop.

Help!! :vash:

Join the club...
https://www.miataturbo.net/engine-pe...en-warm-82232/

If anything you made it worse with the super techs, which is evident in your shortened life span after rebuild. Were the seats replaced at any time?

I think the seats are the culprit in both cases.
I mean, the way they were machined.

I got more track hours with the Supertechs than with the OEM valves. By the time I pulled the head with the OEM valves, the car would not idle. I'm catching the failure much earlier this time.

I don't know about the seats. Given that the machine shop has already rebuilt this head twice (the second time under warranty with me furnishing some parts), I'm "assuming" that they've checked/replaced/machined the seats as required.

Dang, I said that word again . . . "assume." A problem with the seats is really the only reasonable explanation I can come up with.

2 heads, similar problems. Only commonality is the ST valves.

I suspect that there is a problem with them. Maybe not stress relieved, and the stems are bending? I dunno, it just sounds like too much of a co-inky-dink to me.

Uhhh . . . 1 head, 2 sets of valves (1 set OEM, 1 set ST). There is something in common here, but it's not the ST valves.

Is it possible that you were sold a 94-97 intake cam instead of a BP5A? Using a hydraulic lifter cam with solid lifters can damage the valves and seats.

The intake cam is prominently cast with "BP" and "5A." I have heard of at least 2 cases of a camshaft being mispackaged by Mazda. But I haven't heard of any with incorrect casting marks. Still, when I pull this head, I'll compare the lobe shapes to the original camshaft. Maybe??

Thanks for the link. I think these snippets from Andrew are likely to be my issue:

so find out what angle leaves the fattest footprint and request then re-cut specifically that way?

Seems unlikely, but it's getting close to 20 years since BP05 cams were in production, and the BP5A is the most recent non-VVT cam casting. I could believe that racers have bought all the old BP05 stock and mazda is now having to grind BP05 profiles onto BP5A castings.

Either way, the quotes from Andrew sound like the more likely answer.

What kinda revs are you seeing? Make sure the shop used the factory shims under the supertech valve spring seats. If still running heavy factory shim over buckets I would bump valve pressure a bit. All in all I suspect the problem is too little spring pressure for RPM's/Cam.

Stock width valve seats and stock fuel cut with fresh seats should last 100+ hrs.

What rev limit?
Any money shifts?
Downshift too soon when entering corners? This is the most common BP killer that I see (and hear in videos).

NB1 valve springs are weakest. Run NA8 at minimum but ideally ST singles for stock RPM and ST light doubles if venturing to 8k

No


Yes

Have the springs pressure tested. Wouldn't be the first time I've heard of ST double springs losing strength in a short period of time.

AWESOME. Props. Thanks guys.

With the MS, Soft Cut (reduced timing to 10*BTDC) is 7000RPM and Hard Cut (Fuel) is 7200RPM. I noticed that my factory tach seems to read higher than the MS by about 200RPM, which I "think" is pretty normal. As I've been getting faster, I'm hitting hard cut regularly at the end of some short straights.

See above for rev limits.

No money shifts from me on this set of valves/springs, but I've had less experienced codrivers at some events, so . . . .

I have been guilty of early downshifts but am improving a lot there. This has been minimal from me on this set . . . but don't know about the codrivers.

Springs are ST light doubles (bought them from an outfit called 949). ;)

Good thought.

I'm getting pretty darn fast at pulling the head (sigh). Compiling my list.

For Machine Shop:
1. (Most likely) Check and triple check the darn valve seats. In my mind, the fact that in both instances we've had abnormal intake valve wear with normal exhaust valve wear points to a machining issue or other problem with the intake valve seats.
2. (Probable and SOP) Double check valve spring seat pressures, make sure they are properly shimmed and the springs are in spec.
3. (Unlikely, but just in case) Inspect the cam lobes. Make sure they have a mechanical lifter profile.

For Driver:
No money shifts and no early downshifts. Reconsider this codriver thing.

I'm still wondering about the discrepancy between the MS RPM and the factory tach. Anybody else have a factory tach that seems to read ~200RPM low at the top end?

Normally the tach reads high by about 200 is what I've read. Is your tach driven by the MS or the coils?

Coils (I think). Whatever the OEM setup for a '95 is. Car has an MSPNP Gen. 1, but the ignition system is otherwise stock (no COPs).

Using a digital timing light would be an easy way to verify who's lying.

https://www.miataturbo.net/attachmen...ine=1420384479

Your MS rpm is correct to within an extremely small error. It needs to be in order to correctly time ignition events ;)

If running light doubles and not critically money shifted (8500+), then it's the seats. No installed or cut correctly. I've posted this before but BP heads don't flow much regardless of what you do so there is no sense in getting agro with teensy drag style valve seats that destroy valves in 10 hrs. The seats themselves need to be the correct hardened type as well. We lost a head a few years ago that had the wrong seats installed, also ate it's valves in short order.

Test the valve springs if you like but we have not encountered any losses in spring rate in any of our ST valve spring sets. Every set that goes into or comes out of one of our engines in is checked.

Great info. This particular head had been "ported" prior to my ownership, so there is a distinct possibility that there is something funky with the seats.

Not gonna get into a pissing match with a vendor, but my previous statement is from tested springs, not just theory. Might not be every set, but I will never put ST springs in my engine.

My tach reads 2-300 RPM high at the hgh end as compared to what the ECU reports to the scanguage. I think it's a deliberate Mazda "feature."

Its not metalurgically (did I make that up?) possible for a spring NOT to lose pressure once it's broken in. Valve springs are a wear item in a race motor and should be treated as such....valves shouldn't be wearing out before the springs do though.

I have personally seen popular name brand valve springs lose as much as 20% of their seat pressure after 200 autox runs.

Hmmmm . . . . 200 runs x 1.5 minutes ~ 300 track minutes ~ 5 track hours.

good info in this thread. thanks for posting everyone. I don't have anything to add other than my tach is the exception to the rule and it reads dead nuts accurate up to about 7500 rpm... I wish I didn't know that and I wish i didn't have the MS logs to prove it.

Yeah . . . but you have one of them fancy NB cars . . . .

(Oooops, I guess Mobius does too).

I think either of these guys could help you out with your valve issues :)


K Miata Home

NA/B 90-2005 - LFX products - V8 Roadsters

:rofl:

Inching closer . . . .

It would be curious to see the percentage of time spent at the upper RPM range in that time period.

I would say on National Level courses 75% of the time on course is spent above 5000. But that's just a WAG

I would guess the same based on my experience in a CSP car.

Head's pulled. I'm getting damn quick at it. Going to someone I trust tomorrow. My instructions will be simple . . . (valve face support) > ("flow")

Please take some close up pics of the valves and seats.
We can post and compare our cases when I get a chance to pull my head.
(Will at least be a couple days before this snow storm goes away)

Here's what my last set of valves looked like (the ones that were removed in September):

Intake Valve (trashed):
https://www.miataturbo.net/attachmen...1&d=1420517945

Exhaust Valve (normal):
https://www.miataturbo.net/attachmen...1&d=1420517945

Closeup of that Intake Valve:
https://www.miataturbo.net/attachmen...1&d=1420517945

I expect this set to look similar. They are very recessed into the head.

I'm expecting to see my intake valves look the same. I'm hoping otherwise. My intake valves all tightened up, builder (trackspeed) recommended reshimming and checking it more often. And I hope its just normal wear. If it opens up another .001 in the first 2 auto-x's the heads coming off and I know that this will the problem. I dont know why no one here is using the manley valves they cost $10 more per set of 8 and use a higher quality stainless. You arent even close to the first one to see intake valves exactly like that, it was the plague of a certain west coast csp car. I think he adjusted his machinist adjusted his valve job to compensate or something.

Add me to the list of people hearing about other people's ST springs loosing seat pressure. Those super cheap BC springs in bogous svo's thread seem better and better.

Do you ever read your own posts? You bitch about the valves, talk about a CSP car having the same issue, and then admit that the machinist adjusted the width of the fucking valve seat to fix the issue.

Cognitive dissonance at its finest. Jesus fucking christ.

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.

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

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

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

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

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.

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?

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

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

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?

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).

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.

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.

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

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.

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...

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. :x:

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.

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.

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.

This

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.