hornetball

iTrader: (4)

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!!

Godless Commie

iTrader: (2)

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

curly

iTrader: (25)

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?

Godless Commie

iTrader: (2)

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

hornetball

iTrader: (4)

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.

rleete

iTrader: (21)

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.

hornetball

iTrader: (4)

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.

jpreston

iTrader: (4)

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.

hornetball

iTrader: (4)

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??

hornetball

iTrader: (4)

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

18psi

iTrader: (76)

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

jpreston

iTrader: (4)

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.

k24madness

iTrader: (6)

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.

emilio700

iTrader: (3)

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

Savington

iTrader: (31)

No


Yes

guttedmiata

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.

hornetball

iTrader: (4)

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?

aidandj

iTrader: (5)

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

hornetball

iTrader: (4)

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).

Godless Commie

iTrader: (2)

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