Alright so,
I have a built BP4W in a 99' NB and ever sense I built the engine its been burning oil. Because of the symptoms of the smoking I assumed it was oil coming from the head via the valve stem seals. (symptoms like smoking after sitting and smoking after idling and clearing up after driving) So I took the head off and had the valve stem seals replaced with OEM units. So I put everything back together and its still doing it, maybe even worse now that I have my turbo kit setup. I did not replace the valve guides when I replaced the valve stems seals.

Here are some details about the engine build that may apply to oil consumption. -Wesco low compression forged pistons with a 3.5 thousandths piston to wall clearance. -Wesco rings with 21 and 23 thousandths top and bottom ring gap. -Kraken low mount turbo kit with BW EFR 6258 turbo. -Using 5w-40 mobile 1 oil. -Engine was overheated before engine build and the head was warped 7 thousandths and decked back to flat. -Crank case is vented to atmosphere.

here are some diagnostics that I've done so far to figure this out.
-Oil noted on top of all pistons via bore scope. -Car smokes only after warming up and siting at idle and clears up after driving. -engine compression numbers are 1=175psi 2=170psi 3=155psi 4=165psi
-Leak down test results are 1=7% leak down, air coming out of crank case 2=7% leak down, air coming out of crank case 3=12% leak down, air coming from intake manifold and crankcase 4=4% leak down, air coming from crank case.

So, anyone have any experience with an issue like this? Anyone think this could be the valve guides? (if that would even cause a problem like this) Any help is very appreciated!

 

I went through this on me semi-built (rods only) build. The machine shop inspected the valve guides and said they were in spec, and we went together with Supermiata valve stem seals on the head refresh.

The car has always had a puff of smoke here and there, on long decel, after idling, etc. After checking with a boroscope it's clearly coming from the stem seals in my case, you can see where the oil gets on the top of the pistons after sitting (and of course under high vac scenarios).

Long story short after some reading on the forums I came across several posts from some of the gurus (maybe Emilio? Can't remember) that said you should ALWAYS replace valve guides while in there or else your stem seals will leak, so I always assumed that was my mistake.

Personally it's not a huge deal for me, what's a puff or two from a BP every now and again. The car still uses nearly no oil between changes, including lots of track time, so I've been OK with it. I could do without the smell on my catless car though to be honest.

If it makes you feel any better my 78k mile nb1 does the same thing, all stock motor and unopened. It always surprised me that such a low mi motor would do it, but again even that car is ******* 25 years old so I guess that explains it.

TL;DR: replace the valve guides anytime you have a head refreshed, or expect puffage. I've rarely seen a BP that doesn't do this.

 

If the head was warped .007 what did you do to fix the cam bearing alignment? The head should have been straightened, pressured checked and then surfaced.

 

Thanks for sharing, I think my setup is probably burning more oil then in your experience though. When I was running the car prior to replacing the valve stem seals it was burning like half a dip sick every 200 miles or so. I haven't driven the car enough to know how much oil I'm burning after I got the head back on the second time, at least it hasn't had any noticeable effect on the dipstick in about 30 miles of driving so far. Also at idle it smokes A LOT like I'm almost concerned its also burning coolant, but I did a pressure check and I didn't find any pressure loss from the cooling system over time although I need to do more diagnostics for this as well.

 

To my knowledge nothing has been done to fix the cam bearing alignment, the machine shop I went through didn't even bring it up. I also don't know if it was pressure checked, but I know it was at least straightened.

 

What are your leak down and compression numbers? Half a dipstick in 200 miles is your entire oil capacity in 1600 miles, I’d be tearing down the engine personally.

 

I posted leak down and compression numbers in my original post, and they don't seem too bad. Around 7% leakdown and 170psi compression across the board.

 

I would tear it down and inspect the ring assemblies. Make sure they’re installed correctly.

It sounds like there are issues with head. Straightening is not the same as, decking, milling or surfacing. The head is warmed while being mounted to a surface plate with shims to bend it. Then pressure tested and milled (cut).

The straightness can be checked across the top vac rails and the spark plug bosses with a precision straight edge. If the guides are worn it will burn oil. Although in my experience replacing the valve stem seals will usually stop it for a short period when the guides are worn.

 

Ah I see it now. #3 has me a little concerned as leak down and compression are both lower.

I'll post my own experience, I've put dozens of refreshed heads on BPs, none of them with new guides, and none of them have smoking issues.

Was the oil restrictor in the block modified?

 

Well thats not encouraging for an easy fix. And as far as I know the oil restrictor wasn't modified, but the engine was built by a machine shop so they may have done something undesirable. I'll try and find a picture of the block before it went together.

 

Ah, so yah I definitely don't think the head was properly straightened. I think it was just decked back to flat on the mating surface.
Also I don't have a ton of experience with engine building and if I was going to rebuild the whole engine my miata experience would be finished for this summer unfortunately. (up here in upstate NY we have summer for like 3 months lol)