Blowing oil update: COmpress test good.

[cstreit]

Well I ran a compression test and came up with this:

#1 - 155 #4 - 152
#2 - 152 #5 - 153
#3 - 153 #6 - 153

Keep in mind I have a high lift high duration cam so I wouldn't expect really high numbers, but they are all very close!

WHAT NOW!?!?

[cstreit]

Further, I removed the case breather hose, at 3000 RPM the air coming out feels like someone blowing on your hand... Not softly, but a medium "blow" (no innuendo please!)

[dad911]

Chris, If it were mine, I would run a leakdown test for my own piece of mind. You could also cut open the filter and see if picked up any metal chunks. If that turns out ok, then fix the oil scavenging problem, and try raising or relocating the catch-can. In my 76 (stock 3.6) I had tried a catch-can in the back, but collected quite a bit of oil in a 20 minute run. I ended up relocating it to the front, and looping the vent line through the cockpit, along the passenger side roll cage. Now just the vapors make it through, the oil drains back down. But I have a front mounted oil tank in that car.

My '71 also had oil pressure problems with the stock tank, even though I have a stock 2.2. It is too small and not baffled. IMO oil sloshes away from the pickup, more so today than 30 years ago, because of our stickier tires & better/bigger brake pads. I put in a later model tank (not sure what year?) You will need to cut away some sheetmetal around the top of the tank where the oil filter mounts. And make a custom 'S' hose, as the early tank is threaded, and the latter is a 'slip-on'

If the engine tests ok, I would probably do a DE, and do an oil-analysis afterward.

[cstreit]

Last update....

THe gas coming out of the crankcase smells like gas... STRONG unbuned fuel vapor... *SIGH*

Unfortunately I think that means a cracked ring is the cause...

I can rotate the filler neck on my tank a bit, and add another 4" of rise to the vapor hose to stop some of the this, but I still think I have a snapped ring causing the problem...

The baffling should be simple enough, equal cuts on the side of the tank, slide in some steel, weld the steel and tank shut...

[dad911]

Could it be one cylinder is not firing? I would think even if it had a cracked ring, the fuel would ignite...... Try a leakdown test.

[Tim Walsh]

if it was a cracked ring would the compression be that close? Those are some darn nice compression #'s (insert evious comment here)

[emcon5]

Isn't that line supposed to have a restrictor in it? Or is that the other one.....

[Chas911]

You wouldn't have an valve seat that has settled in a little because it was new, and now you don't have any rocker arm clearance and it is hanging a valve open? Just going for optimistic ideas here.

[snowman]

Yes compression can be that close with a std compression test and a broken ring. Thats why you do a leakdown test. IT always tells all.

[J P Stein]

Those compression numbers seem low to me.
My 2.7 with 9.7:1 pistons & Solex cams has 175.

Carbs dump gas into the oil. Mine stinks too. I change it often.

[cstreit]

I'm getting a leakdown next week to be sure...

Compression numbers do seem low, but the motor is new, the cam has a lot of overlap, so I dunno...

[Joe911]

For what its worth --- I have seen compression values in the 135-145 range with several great running 2.0 911S engines so they DON'T seem so bad based in this. Whereas a Carrera can be 40-50 lbs higher because of the less overlap.

[911pcars]

I'm with Joe. I think the compression figures are commensurate with the type of cam you have. During the compression test, did you crank through about 7-8 compression strokes before recording the final pressure? Long duration cams will provide lower-than-normal readings.

You shouldn't have enough raw fuel bypassing the rings to create a fuel smell in the oil. In my earlier post (your other thread), I suggested the fuel system might be introducing excess fuel into the intake. It then finds its way past the rings and into the crankcase which ends up raising the oil level in the tank. In addition, it sounds like the amount of blowby you "feel" might be a little too much. Is there any way you can compare with a similar 911? Internally, it might be one of the compression rings hung up in a piston groove. I think you said these are new P&Cs. Did you check ring side clearance and make sure there were no burrs which could cause a ring to stick? For example, if a piston assy were dropped (shipping?), the ring groove might distort and decrease side clearance at a certain spot. Rings installed right side up? I'm just taking wild-ass educated guesses.

Sherwood
http://members.rennlist.org/911pcars

[cstreit]

THe rings were installed in the pistons when they came. Mahle's... I did check the end gap and the clearance in the ring grooves... All were perfect.

I found myself wondering after the build though, and even now, if there was a chance that I installed a ring upside down, which would probably cause what I'm seeing now... I was careful to check them, but you never know!

It might still show decent compression but have a lot of blowby...

[snowman]

YOu might be on to something. Installing the rings upside down could indeed cause the problem you are having. Rings seal because of the expanding gas pushing them out against the cylinder walls, if the rings are in upside down, the static compression test will be ok, but when real pressure is exerted on the rings and if they are in backward, they will lose seal, instead of making a better seal. Thats because of the taper or whatever other method they may be using isn't able to do its job. Under these conditions you would suck a whole lot of oil thru the system. I do not know if the leak down would find this defect or not. I suspect that it should. Leakdown should be less than 10 percent on a fresh engine, or better than 30 percent on an engine that is not broken in yet because of doing some things wrong, but not fatal flaws and will eventually get better.

By the way you should do compression test with the throttle all the way open. On my BMW M6 the compression is 155 with the thottle closed and 200 with the throttle open.