sbrian2

iTrader: (12)

A little history on the whole situation. I got a junkyard pull from a wrecked 97 M-edition w/ 78K mile last summer. I tore the motor apart down to the short block. With the pan and head off I inspected everything on the bottom end and saw no need in going further since everything looked great. I ported the head, lapped the valves, replaced the valve seals with OE mazda parts. I re-assembled the head and did a leak down once the head was bolted to the engine. Leak down numbers were all just under 1%.

Once the engine was in the car, non turbo for now, it started on the second crank. I had some pulley wobble, but that turned out to be a bad dampener and has been resolved. The car runs great and pulls strong, but it smokes a bit close to red line and quite a bit between shifts. I have a new PCV valve and have routed it as stock as well as straight to a catch can and the smoke is still present. I also did a compression check and the numbers were 196, 195, 193, 195 dry. I have also done a 24 hour soak of the combustion chamber with Marvel Mystery Oil in case it may be a stuck oil ring, but that showed no improvement. I am consuming around 1/2 qt. of oil between fill ups right now and there is a sooty deposit on my back bumper and the tailpipes are black, black, black.

My question is what is left? I am leaning toward valve seals, even though they are new. I can replace those without removal of the head and have thought about going with the Viton seals that MiataRoadster sells. Is there anything else I could be missing? With the compression and leak down numbers that I have and the visual inspection of the cylinder walls, I have a hard time believeing it could be rings, but I guess it could be?

I have a BEGi S5 manifold and DP on the way and a T3/T4 ready to go in, but I want this issue resolved before installation. Help!

rleete

iTrader: (21)

Rings, no doubt. How do the plugs look?

sbrian2

iTrader: (12)

Surprisingly good

y8s

iTrader: (8)

the 190s numbers are dry compression or wet?

sbrian2

iTrader: (12)

Dry, that is why I have a hard time suspecting rings.

Braineack

iTrader: (62)

I'd run the leakdown tester again....

y8s

iTrader: (8)

leakdown tester will at least tell you what's leaking. the ol "sssss" out the intake or exhaust is telling.

you could also put in a transparent hose for the PCV

rleete

iTrader: (21)

Well, I have bad seals in mine. It smokes a bit on startup, but once that clears it's okay. So, I'd have to say I don't think it's seals. That leaves head gasket or rings as most likely.

If you're planning on redoing the seals anyway, you might as well try to re-torque the head bolts.

sbrian2

iTrader: (12)

I am going to re-do the leak down, but if that shows good then it must be valve seals, right? Leakdown will only tell you that the valve seats are sealing, not the oil seals. The PCV is currently routed to a clear Dasani water bottle, AKA catch can. I haven't driven it enough like this to see if any oil is accumulating.

sbrian2

iTrader: (12)

I guess I should re-state when the smoking occurs. If I sit there and rev the car with no load, then it smokes, especially on start up. If I take it to red line and speed shift, I see almost no smoke. If I shift normal, then a pretty big wisp of smoke. It seems like high vacuum in the manifold creates the problem, which would lead me to believe it is pulling oil past the valve seals. The engine has very strong vacuum numbers and is reading around 28-30 KPa at idle or 20-21 in/hg. There is no oil in the coolant or coolant in the oil, so the head gasket is not the culprit.

rleete

iTrader: (21)

Did you do the seals yourself? I remember a similar post on m.net a while back, and he swore it couldn't be seals because he had them replaced recently.

Upon opening it up, it was discovered that the garage had charged him, but not touched the seals at all.

y8s

iTrader: (8)

leakdown test compression test

chucker

iTrader: (4)

Man, this is so true...

OP, Definitely redo your leakdown test. Less than 1% seems erroneously good. It may seem strange that you would burn so much oil with great compression numbers but I think the oil control rings could be worn which would permit leftover oil on the compression rings, keeping them sealed even though they’re toast. And I’m starting to think compression tests are nearly pointless unless you’re simply attempting to confirm that the motor hasn’t grenaded. “Bad” rings can still produce good compression numbers. I had a similar situation: compression numbers were in the high 180’s but the leakdown was a mess. The leakage past the rings was so bad, I couldn’t even confirm valve sealing. 1 qt was burned in about 400 miles, soot on the bumper, all that ****. I turbo’d it anyway, and while it did “work”, it was a spyhunter smokescreen anytime I hit upper RPMs (I had the breather and PCV lines vta). Barely a trace of oil came out of PCV. Plus, the A/F numbers were unreliable due to the high oil content so fine-tuning my map was pointless. Vacuum was 19-20”, btw. Also, I used a can of engine restore and it worked supremely well… for about 200 miles, then the same smokescreen bullshit came back.

Braineack

iTrader: (62)

hell i still had great compression when i had a failed headgasket....leakdown showed like 20% loss on #3.

As a rule of thumb, if you miata is averaging over 190 across, then all four probably have some liquid sealing the rings and masking a problem....

Arkmage

iTrader: (3)

If you re-used the stock head bolts last time the head was removed replace them with ARP studs before you waste a year trying to find the problem. I had very similar symptoms and it turned out to be a leaking head gasket due to stretching head bolts at higher RPMs.

sbrian2

iTrader: (12)

OK, so I came home and did a leakdown test and re-did the compression test since I noticed the o-ring on my compression tester was pretty ratty looking (picked a new one up at the hardware store on the way home). I did the leakdown first and photgraphed the results:

#1


#2


#3


#4


All great and less than 2%, most closer to 1%.

Compression numbers were a steady 200 psi across the board with the new o-ring on the tester. If it is the rings, then I would think it could only be the oil control rings at this point with numbers like that. I also have no oil in my makeshift catch can that you can see in the pictures. It is just the PCV line run to a water bottle and the manifold port is capped. Oh, and another data point is the emissions test I had done last week. The CO was 0.00 of an allowable 1.20 and the HC was 5 of an allowable 220. It runs great and pulls extremely strong for a n/a motor, but the smoke and oil comsumption is a *****. Any guesses now as to why this bitch is smoking and burning oil?

Braineack

iTrader: (62)

whats the compression wet? 200 across to me says that are saturated in oil....

y8s

iTrader: (8)

oil sealing the rings and leaking past?

or did you plumb an injector with the oil feed maybe?

sn95

iTrader: (2)

It's starting to sound like a combination of valve seals and possibly too much oil being "trapped" on top of the cylinder head. Are your valve seals the stock umbrella type? These don't create a true positive seal (thus the reason some people use the Teflon/Viton type that are press-fit on top of the valve guide) and can sometimes get stuck up on the valve stem and fail to seal the top of the guide. This, combined with slightly clogged oil drainback holes in the head can result in a lot of oil getting sucked in through the intake guide. Have you tried to see how much standing oil you have on top of the head at idle (peer through the oil filler if possible). Also, are you running right at the top of "full" on the dipstick?? If so,trying running 1/4-1/3 qt down from full and see if that helps oil consumption.

rleete

iTrader: (21)

+1 Something ain't kosher.