Blowing Oil update: Final Chapter, FIXED!
 

History: Race engine broken in through 100 miles of street driving varying load and RPM throughout the rev range with natural oil. Getting serious blowby, enough to continually fill oil catch tank with oil, practically emptying oil tank.

First thread (the problem analysis): http://forums.pelicanparts.com/911-engine-rebuilding-forum/111257-oil-tank-blowing-oil-cracked-ring.html

Second thread (the speculation): http://forums.pelicanparts.com/911-engine-rebuilding-forum/112382-blowing-oil-update-3-no-broken-rings.html

Analysis: Compression test showed perfect numbers of 152-153 across the board, teardown found no broken rings.

Fix: Rebuilt engine with same rings, oriented them 180 degrees lined up with the wristpin. Broke in motor on the racetrack this time by shortshifting and applying heavy load to motor for about 35 miles, added smaller cam line oil orfices and raised the oil overflow hose 2-3".

The motor now has NO blowby. Last race I got 1 qt of oil in the catch tank per session, now, I got 1 tsp of oil the entire weekend in the catch tank!

I'm convinced the rings just hadn't seated, reorienting them and going through a much more agressive break-in session properly seated them and eliminated the blowby! WAHOO!

Thanks to everyone for their help, comments, and suggestions, and to Souk for coming over to help rebuild and Ray911s for the muscle!

No thanks required....maybe just more Guinness!!

Yippeeee!!!
Congratulations, Chris. Enjoy the ride.

Looking forward to more videos. Best of luck.

So glad to hear it, Chris. I am just about to break-in my motor, it's going to be ND oil and heavy accel/decel under load, three or more good sessions within first 50-60 miles. The race track can be a great place to do it, sounds like you found the recipe! :cool:

Cool - lesson learned: don't tear your engine back down until at least 1000 miles...

-Wayne

Wayne,

Would re-orienting the rings make them have to re-seat, or was it the driving style?

I ask because I had 400+ miles on the motor with no break-in, but then after re-orienting the rings (which presumably causes the need for a "reseat") they then seated in 50 miles.

So the question is, if I had left the motor alone and driven it this way, would they have seated, or did I have to turn them a bit, then drive the motor harder immediately to get them to seat?

Whatever the reason, I'm thrilled.

So for what it's worth, the first time I tried to break in the motor, I did use full throttle, etc... However this time I feel that I was on the edge of "lugging" the motor by short shifting outside the power band and then running it up.

Would a more restrictive case vent help to reseat the rings? hmm..

Hmmm Indeed... You know, it would force more pressure against the back side of the rings...

damn, my crystal ball won't boot up!

Do you need more pressure in the crankcase? Nah, don't think so. The lower the pressure the better. More pressure taxes the gaskets and creates more oil leaks. It's also a pumping loss as the pistons must overcome crankcase pressure as they move downward. In fact, some big block engines rig a vacuum pump to evacuate the pressure from the crankcase area.

The compression rings derive a lot of their sealing power from the combustion pressure, not crankcase pressure. I also don't think increasing crankcase pressure is going to do anything for seating the rings. This is a function of ring and cylinder wall compatibility, engine oil and the proper break-in routine.

I'm glad you found the solution.

Sherwood

Sherwood, I get the idea behind low to no pressure in the case, and it's advantages on power. What I really wonder is how the rings seat? And if a little case pressure would help?

Can someone beat into to my dense skull the theory behind setting pistion rings? I understand valve seating, but when trying to seat piston rings, are we trying to keep the rings from rotating by allowing them to score the the pistons and piston grooves in which they ride in?

Perhaps I wouldn't ask so many questions if I knew how the rings seat! I use to drive my Calculus teacher NUTTY! Poor bastard probably gave me a passing grade so he didn't have to see me on a repeat!

This is what know about it:
The ring and cylinder wall surfaces must wear a compatible pattern into each other. Brand new (or otherwise not mated), the metal surface of each component, when observed microscopically, is shaped like so many peaks and valleys. During break in, the peaks and valleys rub away, or at least conform to the shape of its rubbing counterpart, and along with lubricating oil, create a closer "metal-to-metal" seal. In addition, increased engine vacuum created during deceleration, pulls up additional oil onto the cylinder walls to help wash away metal particles from the surfaces.

Combustion pressure (via ring and/or piston design) forces the compression rings outward to increase the cylinder wall seal. The oil rings help scrape excess oil from the cylinder walls.

Sherwood

Chris,

Just saw the post. Fanastic job man, FANTASTIC JOB!!!

http://www.mototuneusa.com/break_in_secrets.htm

Any questions?

Sort of what I recommend in my book - getting the gasses in front and behind the rings.

Snowman had a good point earlier - the rings do rotate in the piston grooves. If you didn't align them properly at assembly, it may have contributed to the longer break-in. Eventually, they should have rotated apart though...

-Wayne

Hey Chris, Glad you got it straightened out!

This has probably been one of the best recent threads on this board due to this info on the breakin and rings and how you solved your problems.

Now with those good tires, you should really be cooking!!!http://www.pelicanparts.com/support/smileys/wat6.gif

Thanks Dennis and Grosbeck... (Oops, it looks like Esther has logged me off... )

Big load off the old noodle. I'm sure it was just rings seating, because the crankcase ventilation has changed dramatically, the other changes I made are probably just helping incrementally at best.

Why did they seat better? Not entirely sure, perhaps revving the engine isn't enough, but applying more load to the engine helped?

My best guess is that because I had to do the 20 minute/2000 RPM cam break in, that this was not condusive to the rings seating properly right way, then re-orienting them forced them to reseat.

Okay, that's better....

Chris,

I'm glad you found the problem and you also brought up a good point.

What does the 20 min, 2K RPM initial cam break in run do for ring seating? I know there is limited load on the rings during this period, but the rings do have a softer outer coating the helps promote ring seating during the initial run. I'm guessing that the 20 minute run will help remove this coating and correct ring seating will take longer than if the cam break in procedure was not used/needed......Is this correct thinking?