engine and drivetrain Oil Consumption On A New Motor - How Much Is Too Much?

[kaptanoglu]

Howdy all -

 

It looks as if my KFish issues are well on their way to being resolved (pump was rebuilt, but not rebuilt correctly), and now it is time to tackle the next thing on the list.

 

Since I picked up the car ~3,000 miles ago, Sputter has been consuming about 1 quart of Castrol GTX 20-50 per tankful of gas (or a little less).  I reasonably careful inspection on a lift did not show any hemorrhages, though I have asked the Werk Shop to give it a careful look after running it hard to see if it only occurs at temp.

 

It was running very lean at higher RPM/WOT (hence the KFish rerebuild) and when I picked it up and had too much advance dialed in.  As a result it was knocking at around 4,200 RPM.  I am a little concerned that detonation could be a culprit as well.

 

Compression was tested when I got back to Houston and was 160# across all cylinders and leak down at 2%.

 

So here are the questions:

 

1) What is typical oil consumption on a fresh motor?  Build details below:

• Pistons are 2 mm overbore (91 mm) with 10:1 compression, gapless rings and forged rods
• 284 cam
• Head ported and polished, stock sized valves
• 1.5" header
• Pictures of the build - http://www.flickr.com/photos/tep_icp/sets/72157634053646253/

2) If it is leaking, where could it be leaking that might be hard to spot?

 

3) If it is burning oil, what are the most likely culprits (on a new motor)?  Where can I inspect to get a better sense of the cause?

 

4) How critical is this to fix right away?

 

My sinking suspicion is that bad ring seating/knock broke/misseated a ring, and I need to pull the bottom end of the engine out and re-ring the pistons.  If it will survive (happily) as long as I keep oil in it, I can wait until the spring when I have a driveway.  Otherwise, it is writing more checks.

 

TIA for the help,

 

John "kaptanoglu" Jones

[KFunk]

Keep in mind in a rebuild all gaskets that seal in oil were replaced, and the bolts that hold them may or may not have been secured with loc-tite.  You might want to check how snug all the little bolts are (oil pan, timing cover, dizzy housing, etc.).  Things could be seeping a tiny bit in lots of places.

 

My rebuild had some oil 'consumption' for the first few thousand miles, and I re-tightened a lot of things.  It may have just been due to break-in too, I dunno.  I don't have that much experience with rebuilds.  Mine seems to be holding tight now at 7K+ miles on it, though. 

Edited October 2, 2014 by KFunk

[jimk]

That's a lot of  oil, qt per tank of fuel.   As you  say a new engine, was break-in oil used?   I'd say that's an unacceptable build.  My build started at a qt/3500mi. and settled in at a qt/4500 mi. and on 10W-40 oil too.  My current S14 started out with 300 mi using break-in oil and now uses a qt in about 6000mi. on 15w-40 (didn't have 10W40 in stock and had to get to the MidAm02Fest)..  Next change will be 10W-40.

[Preyupy]

If you are burning a quart every 200 miles (1 tank of gas) that is WAY TO HIGH of consumption.  If you are Leaking that much you will see it under the car.  The worst I have seen on a healthy engine during break in is 1 Qt every 1000-1200 mi.  The rings should have seated within the first hour of running, if you are going through that much oil you need to talk to the engine builder immediately, go on record with them right now!

[kaptanoglu]

Thanks for the comments on this.

 

I am surprised to see such good compression/leak down given the consumption (if, in fact, it is consumption).  It would be great if I could narrow down what might be wrong, as that might inform what I do to fix it.  Sending the motor back to the builder would be a PITA, but may be the only option.

 

J

[Preyupy]

do you get a lot of smoke on Decel? It might be valve guides and seals which would not show up on the compression and leak down tests

[kaptanoglu]

It was first noticed by someone driving behind me, who was seeing puffs when I shifted (so lifting off of throttle).  It hasn't been billowing smoke by any stretch, leading me to initially suspect that there was a leak that only exhibited itself with hot oil when running (so not puddles).

 

Bad valve guides would be surprising on a freshly rebuilt head, though bad rings are equally surprising.

 

J

[jgerock]

Sometimes it is the way you treat a rebuilt engine in the first +/- 2500 miles that determines how well it will last.  I had several very helpful conversations with Rob Torres of 2002Haus when I redid my tii engine (using some parts I purchased from Rob). 

 

Did you keep the revs below 5K and alternate the engine load gradually using the transmission as a "brake" to help seat the rings?  I notice you mentioned gapless rings.  Do you know what brand they are?  Do you know the brand/type of pistons the shop installed?  Was oil with ZDDP additive used during the break-in period?

 

What brand of camshaft was used? Some manufacturers have specific break-in instructions - others don't say anything (like Schrick!).

 

What type of valve springs were used?  Were they OEM BMW or aftermarket?

 

Did the valve stem seals get upgraded to the E30 type or did the shop use the std. M10 seals that come in the gasket kit?

 

Did the Werk Shop do the engine work or did they farm it out?

[percy]

I tend to agree with others that your consumption is atypical.  Although I have not done any full rebuilds recently, the last one consumed about one quart of oil per 1.000 miles for the first 2,000 miles.  For the next 80,000 miles, consumption has been negligible between 3,500 mile oil changes.  I also think that the greater-than-normal consumption should evidence itself either externally or internally (unless you are syphoning oil in your sleep).

Leaks should be easy to detect by parking over a clean "oil free" area or placing some clean paper or drip pan under the engine and transmission.  If the engine is burning the oil, I would expect you would find some evidence of this by examining your spark plugs.  Another telltale might be your exhaust and that includes what comes out the tail pipe and any residue left in the pipe.  I just read where you suspect bad valve guides or seals because of deceleration exhaust.  This should be easy enough to detect on your plugs and tail pipe.  While '02s are notorious for bad valve seals followed by guides, on a new engine, I would look for other areas that might inadvertently introduce oil into the intake side of the engine, including the valve cover breather.

Your build pictures suggest that things were installed with care and cleanliness yet that is no guarantee of mechanical perfection.  Even the prettiest piston rings can be have installation problems.  Occasionally, “hard” chrome plated rings take a long time to seat, especially if the cylinder wall finish is too smooth.  Sometimes even a fool can goof up the "foolproof" installation of a multi-piece oil control piston rings, or cylinder bores can look straight but have a measurable taper.  You mentioned a "knocking at around 4,200 RPM"  which I hope was more "pinging" or "preignition", rather than "knocking."  Hopefully, the noise is no longer present.  IF the engine was knocking, I wonder if you could have had any interference issues with pistons and cylinder head.  I refer to your pictures where you appear to have started with "piano top" pistons and ended up installing a modified bathtub style piston.  It looks as though there should not be any interference issues but I merely raise the remote possibility.    To repeat, I am not saying you have any of these specific problems. 

Rather than jump to conclusions, try to exclude the possibility of a simple leak, e.g., a rear main seal, front crank seal, or a compromised oil pan gasket.  I would expect that your engine builder would ask this.  I am sure others will offer opinions on any spark plug pictures you care to post.   If you have identified the source of the consumption as valve-related, as you probably know, replacement of guides and seals typically means "off with the head."

Your concern reminds me of an '02, purchased new.  It had an "unscheduled" and "premature"  valve job because of bad valve seals.  If I recall correctly,  the seals were not seated on the guides or they were too "hard" to properly fit over each guide.  Whatever the specific seal issue,  to address it, the head was removed.  Conventional wisdom prefers the so-called "newer" style valve seals over the "earlier" style viton seals.  Strangely enough, I have used both style seals for decades, and it occurs to me that I have not experienced any problems with either style seal used in both M10 and M30 engines.

[TobyB]

It could be something as easy as a valve stem seal that's popped back off.

 

The total seal rings give great static leakdown numbers, but a botched oil ring would do it,

and might not show up in leakdown.

 

Both would be seen mostly on decel.

 

Other than a mistake or a defect, there's no reason for consumption that high.

 

If it was leaking that much, you'd see a puddle everywhere you stopped.

I botched a rope rear mainseal once, and a quart every 500 miles

left a saucer- sized puddle every where I parked it.

[kaptanoglu]

Thanks again for all of the feedback.  It will be interesting to see what turns up when I open it up.

 

J

[oldguy]

• , gapless rings

found your problem

 

There is no HP in an m10 to be gained by utilizing these and they require specific cylinder wall roughnesses.  This is especially true if you're utilizing a gapless second ring.  If so throw it away and reinstall the piston with a plain jane cast iron ring.  your problems will be solved.

[TobyB]

I disagree that it will solve the problem.

 

I've run a gapless second, and I've run a motor that

was built with a gapless top.  Neither had oil consumption issues.

 

Both had standard oil control rings.

 

Neither made any more power than with standard rings,

THAT we agree upon.

Had great static leakdown numbers, but that seemed to be

the only tangible benefit.  

 

Didn't suck, though.

 

t

[oldguy]

I've experienced endless problems with people hell bent and determined to utilize a total seal gapless top and gapless second only because leakdown numbers win races to encounter oil control/seating issues because the gasses get between the two rings and flutter the second and the angle cut in the second does not allow proper oil control as in a conventional napier style or torsional style ring thus solving a problem that does not exist. 

 

The basic m10 ring package with a moly top.  cast second and practically any style oil control ring will break in and seal acceptably on almost any hone surface unless you've broken out some exotic stone for like nicasil line bores.  The basic M10 ring package does not need to be examined and replaced unless you're building a specialized race motor.

[TobyB]

Oh, you're totally right, there. I've never run BOTH a top and middle gapless.

 

... Because I'd heard, from more than a few racers, that the gapless upper 

caused them problems.  It worked for me, in an engine I bought-

but again, that motor only had one, not two.

 

So yeah, it very well MAY be the double gapless setup, given that the

gapless leakdown's so low...

 

t