Crank Case Pressure again

[xupkid2]

Hey guys

I posted this question a little bit ago but just did a new test that really concerns me so figured I'd se what you guys have to say about it.

The new test I did was at the J-boot, unhook the crank case breather hose. When the engine is running I found that the hose is sucking air instead of releasing air. I dont understand why this would be?

Previous info/question

This past winter I rebuilt my engine replacing all seals, o-rings, piston rings & bearings. Now I am having a problem with my crankcase pressure. When running my cars my oil dip stick will pop out because of crankcase pressure. I checked all the hoses for the breather all the way through including pulling off the oil fill neck and they were free and clear. I did find a very small amount of oil residue in my j-boot, no pooling of oil though. I also did not find much oil residue past there into the intake. When running the car idles around 900 RPM, if I pull out the dip stick or take off the oil cap the RPM's drop a little bit.

I also compression tested my cylinders thinking it might be the piston rings not seating correctly and each was within less than 5% of each other at around 165 according to my compression tester.

The last thing I am finding is that around 1 certain turn at the track, a constant radius left hander, I will shift gears and I get a puff of smoke out my exhaust. No where else does this happen and it only happens around 6K RPM's. I have added a oil pan baffle so not sure if that makes a difference.

Im now stumped as to what could be the cause of the crank case pressure and why it isnt being relieved. I just ran my car for a 3 day track event and it ran like a champ but this problem concerns me. Any thing else I can check to try and identify the problem?

Thanks
Brian

[Techno Duck]

Did you ever check the oil pressure relief valve? Generally they stick open causing low pressure, maybe yours is stuck closed.

[944 boy]

Hey, I have the same thing. I rebuilt the motor in the summer (still winter here --> snowing today<-- ) and the dipstick has been popping out ever since. Funny enough its also on an 88. I have not checked the vent hoses, but when I remove the oil cap the RPMs drop by about 50. I also have a high idle as well. I'm going to go check compression now that you have me worried. I have redone the OPRV but that could always be a possibility. Le me know if you find out what it is.

[944 boy]

Compression on a 35 deg. day was 180 even across all 4. Intereting note, with the cap off the oil filler, there is a high pitched whining. Ona side note, do you have a crank scraper? I added one and that was about the only change I did when I rebuilt it.

[xupkid2]

I just realized after I posted this that I was checking the wrong hose on the J boot. I did check the correct hose and it was flowing the correct way. While the motor was running I put a piece of tissue in front of it and it was blowing so it was releiving the pressure.

I then went and ran my car with the hose undone from the j-boot thinking maybe my airbox pressure was more than the pressure from the crankcase and was reversing the flow. Well that didnt fix the problem either.

I now have no clue. I am going to check the OPRV but Im unsure how that would effect the crankcase pressure but its worth a shot.

I am going to do a leak down test in the coming week, hoping that the test comes out ok. I really hope it isnt an issue with my piston rings.

If there are any other ideas anyone has to check please throw them my way as I can't come up with anything else

Thanks
Brian

[Razorback1980]

Put a pressure gauge on the oil dipstick housing and on the tube coming from the oas and see if that pressure is the same. You might even be able to tell with your finger. If not, then you need to look at the oas and see why it's not relieving the pressure. Take it off and make sure there are not blockages in the block where it goes in. Did you use sealant when you put it on? Maybe you blocked the holes with sealant or there is an old oring stuck in there. Put an air pressure hose on the oas and see if it is blocking pressure from being released. If the oas is not the problem, then you'll need to look at the oil passage inside the engine. I am not sure where the oas picks up the pressure but I would guess that if the oas is not the problem, then the scraper you put in probably blocked the holes going to the oas. Since both of you put the scraper in and both of you are experiencing the same problem, ...maybe that was the issue, but I am not sure where it bolts and where the oas picks up the vent. I don't know the oil passage ways of the 944, but i would hope the venting of the crankcase doesn't go through the oil passage way so I would put off the OPRV until last.

[badjones]

Not really sure where this is going. The oil pressure from what I understand from your description of the fault is not at all related to the problem, and oil pressure is not related to the oil air seperator. The oil air seperator is just a vent from the lower crankcase which gives any oil mist in the motor a chance to become liquid before being sucked into the inlet tract by the partial vacuum created by the positive crankcase ventilation sustem. This is no magical thing happening in the oas, its all pretty basic. What it cannot do is seperate the oil from the air when there is excess compression gasses being forced past the rings by the process of compression and combustion. Generally excess blowby is a result of ring or cylinder wear, or in the case of these motors, possibly the result of honing the cylinders during a rebuild. Both reports are after a rebuild which makes me wonder if the cylinders were honed in the process. Interesting to know if the one corner you have trouble with is a sharp right hander.

[xupkid2]

The motor is a recent rebuild with all new rings, seals and bearings. I did not hone out the cylinders and just washed them down with soap and water before the rebuild so I did not damage the walls. Im just stumped at this point.

[badjones]

Did you measure the conicity and out of round in the bore to check and see if it is in spec. Its a fairly large bore and any out of round will be hard for a new ring to seal. I will think some more about it.

[Razorback1980]

The out of round theory is true, but is the question "how much compression is going by the rings" or is the question "why isn't the pressure escaping back through the hole in the block/oas back into the j boot"?

[xupkid2]

I think the question is more about "why isnt the pressure escaping back through the hole in the block/OAS" The reason I am heading down this path is because of the compression test. Each cylinder tested out even so therefore if there was a leak it would have to be on each cylinder the same exact amount. Also if there was a leak during the compression test the crankcase would have pressurized and the dip stick would have popped out with 180psi. When I run my engine at idle for 30 min or so nothing happens to the dip stick so I believe it is only when it is at 3K or higher for a few min that it pressurizes. I am wondering if the Lindsey Racing oil pan baffle is causing the oil level to be very high near the OAS, since the trap door is on the opposite side of the OAS, and at higher rpms the oil level in that part of the pan blocks the OAS hole and therefore the pressure builds up and has to escape somewhere and the dipstick is the weakest point. I wonder if I reduce my oil level if that will help. I just dont want to have another #2 journal failure.

Any thoughts?

I plan on doing the leakdown test this weekend to make sure my piston rings are sealing well but Im trying to develop other theories in the meantime so I can test more and more things. It isnt like this is a huge problem cause I ran the car for 3 days at the track and it was ok so this doesnt stop me from track days. Its just annoying and I sense the more pressure in the crankcase the more pressure on the pistons which would mean it looses efficiency and therefore HP.

[jwade944]

I run the Lindsey oil pan baffle in my '88 motor and I have not had this problem. (2 race weekends since I installed the baffle.) It seems like there are only two possible problems. One is blow-by and if you have new rings, they may just not be seated yet. The second is a vacuum leak as the oil-air separator uses vacuum from the intake to vent the crankcase. If everything is working normally, the crankcase should be under a slight vacuum. (That why you hear the idle change if you loosen the oil cap.) I would recheck all of your vacuum lines and j-boot for cracks, kinks, etc. If everything is tight, maybe just wait and see if the rings seat after a few more hours on the engine. I doubt there is a measurable loss of HP or efficiency. (It's a 944. We have no HP.)

[xupkid2]

Checking the vaccum and j boot is a good idea. I just replaced all my vaccum lines and followed the diagrams so I think they are ok. When I checked the breather hose it was releasing air and did not have suction which I believe should be the case.

Additionally I've put about 1000 miles on the engine since it was rebuilt along with 3 full track days, about 10hrs. I would think the rings would have seated but maybe not. Ill double check the vaccum and j boot again tonight and make sure I have it all hooked up right.

Thanks for the advice.

[Razorback1980]

I'm with you xupkid....if it's blowing the dipstick out, then something isn't right and needs to be fixed. Having pressure on the bottom side of the pistons is not a good thing and it makes it hard to get the engine run correctly. This can't be too difficult of a problem to find though. There are only three parts to the whole system...the holes in the block, the oas and the line running to the j boot. I haven't seen an actual scraper install so I'm not sure where it bolts or if you can put it on incorrectly so I really can't comment on any issues it may cause intelligently. But unless it bolts toward the back of the engine, I'm not sure how it could block the oas hole but that certainly is a possibility. I would call Lindsey racing and see if they have ever heard of this issue. I would think one of the techs would know where it bolted and how it worked. Never a bad thing to educate yourself from people who know.

Please do not run your oil low...that is NEVER a good solution to any problem. Fix the real problem and do not jeopordize your engine because you can't find what's really wrong. Make educated decisions and keep working with the parts that are relevant, you'll find it. Check your o rings on the oas, check the vacuum at the j boot, inspect the holes in the block for a left over o ring and take a compressor and blow air through them to make sure they are open. Do the same to the oas...a little diligence will pay off.

[xupkid2]

So I talked to Lindsey today and they were stumped. Never heard of the problem. I went and checked all my vacuum lines and they are all correct. The thing Im not understanding now is I pulled out the dipstick at idle and there is a suction on the dipstick. It seems to me that when I drive the car that pressure reverses and blows out the dipstick. Anyone know how that would happen? Im at a loss now because I'm just about out of things to check.

[badjones]

Just as a matter of interest what oil did you use to run the motor in after the rebuild.