View Full Version : How to Reduce Crank Case Pressure.....

07-05-2006, 09:04 PM
I am blowing oil out of my rear crank seal, I think. When I push the car really hard and finally come to a stop and shut the engine down, I am getting a white smoke coming from beneath my engine from the area of the transmission. I posted this question before and I have all the components for a new seal, ring gear (missing a tooth), clutch and TO bearing. My question is, when the engine is pushed hard, does crank pressure build? I don't think I have enough vacuum on my crank. The only thing that is pulling on the valve cover is the 3 ZS carbs, and this goes through an oil separator. On normal driving, this oily smoke doesn't appear as apparent. I am very tempted to use that extra little nossle (now blocked off) on my intake, the other operating my brake booster. How could I hook up that vacuum outlet, maybe through a PCV valve, and still be able to use the carbs vacuums. Make sense? GoodParts markets a PCV valve that I think works in conjunction with the trips setup, frankly haven't bothered to call him. Any ideas out there.


07-05-2006, 09:22 PM
Bill, if the crankcase is properly vented, as I'm sure yours is, then you should have no blow by problems unless you "might" have worn rings.

I say might because it is only a guess. Try taking a "wet" and "dry" compression reading from each cylinder with a known good compression gauge. A cylinder leak down test can also be performed to further the testing process.

You can have good compression and secondary rings, but have a problem with the oil control set. Worn or sticking rings and expanders can cause a lot of problems depending on how the car is driven. For example, worn oil control rings (or the scraper rings as they are sometimes called) will allow excess oil to remain on the cylinder walls and cause light smoke even under normal throttle. But if those rings are not really worn too bad but the expander ring in behind them is stuck from carbon buildup, a condition such as yours may occur under hard acceleration, but not show up in day to day driving. It will remain that way at least for the time being, but it will eventually begin to show all of the time.

I'd try the compression and leak down test(s) mentioned above if you've exhausted all breathing issues. (No pun intended.)

07-05-2006, 09:37 PM
I dunno, Paul. I have fairly new Deves stainless steel rings and my compression is even all the way across, about 160. I think that there is a rear main seal leak causing this. I also think that I have a Speedi Sleeve on the back of the crank from the jerk that originally built my short block. I am waiting till after the VTR convention to push the tranny back out and pull the seal. My real concern was am I building more pressure at high rpm's and thus trying to really blow the seal. Do you have a PCV valve on your setup? And if so, how did you plumb it? Yes, I do have the Gunst bearing sitting in my office, along with a B&B clutch. No, I have not finally decided if this is what I am going to install. The jury is still out for me on this. I have had no problems with the Sachs clutch and Koyo bearing, may just go back to that. I have been told that the Luk and the B&B are now one and the same. Not trying to raise that issue again, just doing a lot more research before I pull it again.


07-05-2006, 10:12 PM
I experienced something similar to that Bill. What I found though was rather suprising. The plug for the oil gallery on the rear of the engine had started to work loose. I am positive that it was tightened upon assembly. Never the less, it was loose and leaking. My rear main was just fine. You have to pull the flywheel for either. I thought that I would have to pull the rear engine plate as well but as luck would have it, there is a hole in the plate specifically for that plug.

The speedi sleeve on the crank could also be the problem though. Good luck and, other than yanking the trans and flywheel, may it be an easy fix for you.


07-05-2006, 10:13 PM
The Triumph-designed engine in my 1500 Spridget is closely related to your six and has the same underachiever rear seal.
I tried a simple road draft tube at first and pumped oil out all the time. I'd lose a half quart in a 15 minute race.
Then I set up the design below and eliminated the problem completely. I've run in 4-hour enduros with no oil loss.
I do not have a PCV valve in the system and I depend on the suction of the carb to increase as the enigne speeds up. The spacer is a piece of 2" PVC pipe. I tried without the spacer, plumbing the vent pipe into the air filter and it didn't work so good. I think the pipe has to be right near the intake of the carb to have a good effect. You don't really need the catch-can for the street...that's a racing rule.
I have only one carb, so this is easier for me.
The rest of the crankcase is sealed up tight, with a non-vented valve-cover cap and even a threaded-in dip-stick.


07-06-2006, 09:41 PM
Sorry I'm late getting back to you Bill. Stupid job gets in the way sometimes.

No I do not have a PCV, just the aluminum finned valve cover vented to the intake. Luckily I have no problems at this time, but I just had a new rear main installed when the transmission was out of the car. I had every gasket replaced when the block was stripped for painting and so far so good as far as any leaks go.

As for the Gunst bearing, if you go with the LUK PP you'll be fine. If you go B&B, you'll have a constant squeal and problems down the road. I have a complete TRF Magic kit with the Sachs PP and the Koyo Land Cruiser T/O bearing waiting to go in.

I was hoping to last the summer with this setup but the squeal is getting worse as I pile up the miles, so in a week or so, out she comes. When it comes out, I'll post pictures of how both the bearing and pressure plate look after being driven for a while.