oil blow-by question and question for rotary expert.
 

What can cause this on a rotary? I can understand on a piston engine where pressure from the piston ring can leak but on a rotary?

Reason i am asking is because i swaped an engine (rebuilt) in a car with a rebuilt turbo at the same time (apex seal went through). When we first started the car, it would smoke like crazy. I removed the downpipe and there was a shit load of oil in it, and i mean A LOT. I thought well the turbo is leaking, bad rebuilt. Made sure it wasn't coming from the engine as there was no oil in the manifold and spark plugs were perfect. Engine seemed to run great.

So i get the turbo back from the rebuilder again, reinstall and bam, same thing happened. I said to the guy bring him the car and make sure he has it running before it comes out of his shop, i don't want to swap turbo until he is sure he did it right, it was the second time i was swapping it. The shop owner said it wasn't the turbo, he said it was just the line that goes from the filler neck to the oil catch can that was pinched. So blow-by would pressurize the oil return line in the turbo and oil wouldn't come out of the turbo, thus, leaking through the exhaust side.

Do any of you guys beleive that? Can there be so much blow-by that the oil in the turbo wouldn't come down well to the oil pan? The problem is that he charged us 360$ for that and i have a hard time beleiving him.

Thanks for any input.

Rotaries can have oil blowby issues, though not on the scale you're talking about. It sounds to me like the turbo needs a restrictor pill in the oil feed line, somewhere in the 0.050-0.060" range, especially if you are running higher than stock oil pressure. You may also check the drain tube for obstructions, or if it's an aftermarket drain tube you might consider rerouting or enlarging it for better flow.

To be absolutely sure it isn't the turbo causing the smoke...block or reroute the oil feed line temporarily, run it into the oil drain fitting or the oil filler neck. use vise grips (carefully!) on the compressor wheel nut on the turbo to as not to allow it to spin any, and put your airflow meter after the turbo somewhere temporarily using some extra couplers or pipes. Now start the car and let all the oil burn off until the smoke stops. Shut it off, leave it overnight, and try this again the next day. If it still smokes, the turbo is NOT the culprit. If the smoke stops, the issue is with teh turbo. You can also do this test by removing the turbo from the engine altogether and running it open-manifold.

You could also be pressurizing the crankcase if you have blocked off all the ventilation nipples on the oil filler neck, so be sure there is an oil catch can or a vent line of some sort for pressure to escape from.

that's what the guy said because the oil catch can which is on one of those nipple was pinched so there was no ventilation at all.

How can crankcase pressure raise with this, i just don't understand how it can, care to explain, some sort of rotary specific. From where in the engine, can the pressure raise?

The side, corner and oil seals do not completely seal combustion pressure. If you're " crankcase" has no vent, as described the turbo will smoke.

ok, i am not very familiar with the internal of the engine but that would mean that pressure would build around the e-shaft and go to the oil pan through the oil return?

All engines can build crankcase pressure.

1) compression is never 100% divided from the oiling system. IN a piston engine you have a small amount of ring gap that allows blowby. IN a rotary you have a slightly greater amount of gap between the joints of the side/corner seals, and the oil scraper rings are not a perfect seal either.

2) as oil heats up it expands and pressure is generated. This is why all engines have a PCV valve (positive crankcase ventilation) to relieve the pressure.

You don't even have to understand what we are saying, just do it. :D

well thanks but i do want to understand lol. I know a rotary can build crankcase pressure, i just didn't know how it could.

So you guys think that a sealed filler neck with no way in the oiling system to release pressure would be enough for the turbo to leak oil, i mean a lot of oil?

what would cause this, rising of oil pressure in the oil feed line to the turbo or problem returning oil in the pan because of the pressure that is in it?

By the way, car didn't have that problem for 4000 miles before we did an other rebuilt so the oil feed line and oil return line are adequate. (back when the oil catch can hose wasn't squeezed.