# Crank Case Pressure



## Bensjammin66 (May 12, 2009)

So ive got another one to pick your brains over. 

.060 over fresh 455 with 3000 miles on it. 
New pistons, rings, bore and hone broke in as per a very reputable local engine builders advice. 

I seem to have quite a bit of crank case pressure wanting to escape through the dipstick tube, breathers and anywhere it can around 4000rpm + only. It'll pop the dipstick and mist onto the fender well and fire wall when I really jump on it. 

Leak Tested the engine warm in the car and cold on the stand and i seem to be only leaking 5-12% from the cylinders. That to me is more than acceptable so where is all this commotion down under coming from if not blowing by the rings? Again this is only happening at 4000+ rpm.

I did notice one of my valve cover breathers was clogged almost solid, my own dumb fault as I just reused what I had from before and didnt think much about replacing them. Could that be some of it? My plan of attack is to get some new ones with vent tubes and run hoses to the air cleaner. That way at WOT I have the vacuum from the carb to hopefully evac some pressure once the pcv quits working from the manifold vac drop at WOT. 

As always im all ears to your thoughts!


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## Lemans guy (Oct 14, 2014)

Right Ben, you gotta let that naturally aspirated engine breath. The fresh air enters the crankcase in that oil filler cap vent.....

and gets sucked out through the PCV by manifold vacumn and put back into the intake. So you have to have the vents clear and the PCV hooked up right according to the engine, and clean PCV valves!

Sounds like you are on the right track!


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## Bensjammin66 (May 12, 2009)

Lemans guy said:


> Right Ben, you gotta let that naturally aspirated engine breath. The fresh air enters the crankcase in that oil filler cap vent.....
> 
> and gets sucked out through the PCV by manifold vacumn and put back into the intake. So you have to have the vents clear and the PCV hooked up right according to the engine, and clean PCV valves!
> 
> Sounds like you are on the right track!


The PCV is clean, one breather was clogged solid for sure. Should I just try new breathers first? Foam or K&N filter style ones? Or should go all out and run evac lines from nippled breathers to the air cleaner for WOT vacuum? The PCV quits at WOT cause its manifold vac right? My brothers race car has header evac from his valve covers but the more i read that isnt designed for cars with full exhaust like i have.


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## geeteeohguy (Feb 2, 2008)

12% leakdown is bad for a 3000 mile engine. Normally, 10% is the limit for a broken in engine with wear on the rings. Normal for a fresh build is less than 5% in all holes. I suspect that there is a sealing issue in the cylinders with the excessive blowby, either the rings are not seated or the bores are not true. The 12% is enough to cause your blowby problems.


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## Bensjammin66 (May 12, 2009)

It was between 5%-12% mostly, one cylinder was around 10% and one was definitely 12% the rest were around 5-10%. Motor starts and runs very strong and the plugs looked great. I think im going to try some sort of evac system on it. 6 quarts went in and like 5.99 quarts came out after 300 miles, it burns nothing so im not tearing it down just for this. I think im going to rig up a solid atmosphere vent and roll it.


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## Bensjammin66 (May 12, 2009)

Everyone wants to have a hero engine, but don't believe all the hype you hear about 2 percent leakage engines. No cylinder seals perfectly, especially if the engine is nitroused, supercharged, or turbocharged where the top and second rings are set with wide ring endgaps. Even for normally aspirated engines, respectable leakage numbers would be anywhere from 8 to 12 percent with a variation between cylinders of 4 to 5 percent, but it's possible the variation could be as high as 10 percent.

So if you test an engine and see leakage numbers even in the 15 to 20 percent range, this is not cause for alarm.


Read more: How to do Cylinder Leak Down Testing- Car Craft Magazine
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## Bensjammin66 (May 12, 2009)

That was something I read in Car Craft. I trust those guys articles pretty well so im not going into panic mode and tearing this motor apart for the leakage i seen and heard. Thats lighting money on fire cause odds are ill see the same results. Any one here ever leak down a new motor and care to share their results? Not even a new Ferrari seals perfectly so i bet every one is seeing at least 5%.


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## geeteeohguy (Feb 2, 2008)

There is a reason that one cylinder is 12% leakage and the others are not. That cylinder is not sealing as well as the others due to taper, ring seat, out of round, or piston clearance. This is a fact. If one cylinder is 5%, and the other is 12%, something is different between the two cylinders. From what I can tell, excessive leakdown in only one or two cylinders could cause your problem. But 12%, granted, isn't very excessive. Just a lot for a 'new' engine. I disagree on the 20% limit: engines I've tested that had 20% leakdown were very worn and pumping oil. In your case, seeing that there is virtually no oil consumption, and no oil on the plugs, I wouldn't tear it down either. Check on the AMES forums about the 'Bon Ami' cure. Just more info to consider. Keep us posted, too. Good luck.


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## Lemans guy (Oct 14, 2014)

Ben the PCV a valve works off spring And Vacumn pressure. The spring tries to open the valve, the Vacumn tries to close it. So at light throttle say the valve is open more.....more gases are present the valve opens more.....more throttle valve opens more.....

At idle full Vacumn is trying to close the PCv against the spring though it never a closes completely that is why it rattles real fast.....some crankcase pressure is relieved, but more come with more power and so gases are routed to intake and burned up.

Old cars had a drip tube, rolling down the road it was spitting out all that stuff. Your clogged breather would not allow fresh air in and would hurt that process....

I keep my PCV a as stock setup PCV hoses fork off to one at each intake of the dual plane intake. I have seen lots of guys with one. Really you need both, if you want even idle and running, timing ,mixture etc.

Fix that first and check your head bolts are tight.....especially at the cylinder of interest.....excessive crankcase pressure can blow out seals and gaskets etc, or find a weak place.

Go with the factory style set up closed or open system....you will get it and done right it should relieve the pressure....


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## Bensjammin66 (May 12, 2009)

So ive got an update on my issue. Motor is still out and when I did the first leak down I didnt notice a slight hissing at the plug hole.. I tested again just for kicks last night and thats when I heard it. With a new O-ring on the tester I retested all cylinders and here are my results at 100psi leakdown cold. Cylinder #1-5% #8-5% #4-5% #3-6% #6-5% #5-5% #7-3% #2-5%

Clearly these numbers are acceptable for a 3000 mile motor so it cannot be rings or compression blowby causing my issues. I did have that clogged breather on the one valve cover and was using Moroso baffled breather grommets. What ive decided to do now is have open element K&N breathers on non baffled grommets. I have the BOP valley pan and a pcv in there hooked right to manifold vacuum. Any other suggestions to try? Motor is going back in this weekend! 

The lower dipstick tube is correct now also. The lower tube was not in the block tube the first time around. That may have had something to do with the oil mist coming out of it at 4000+ rpm?


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## Lemans guy (Oct 14, 2014)

those are good readings on the leakdown, the dipstick issue may be the mist as you say and the PCV with right breathers and hooked to minifold vac should help.

sometimes at running temperature a leak can happen at a gasket or flange etc. but right now sounds like you have done the right steps. torque down all bolts correct intake and valve covers even.
If you had a way to force smoke in it while it is out you could get a good look if there are leaks.

I use a smoke machine, but with the motor out you could take it to a shop in back of pickup and ask the to smoke it right in the pickup while you looked.

some guys use a cigar, but not enough smoke....just be careful with creative smoke ideas, be outside....a real auto tech's smoke machine is best any good garage will have it.

but either way you have made some progress ben!:bannana::bannana::bannana:


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## Bensjammin66 (May 12, 2009)

geeteeohguy said:


> 12% leakdown is bad for a 3000 mile engine. Normally, 10% is the limit for a broken in engine with wear on the rings. Normal for a fresh build is less than 5% in all holes. I suspect that there is a sealing issue in the cylinders with the excessive blowby, either the rings are not seated or the bores are not true. The 12% is enough to cause your blowby problems.


Geeteeohguy is spot on here on his take. 12% is indeed pretty bad. I thought there could be no way 12% is bad because i used almost no oil and have great response and no oil on my plugs. A leaky o-ring on my tester caused the higher numbers in leak down. Now that the tester is fixed I tested a buddies Honda 400ex four wheeler known for fouling plugs and burning more oil than Iraq in the Gulf War and sure enough it was 20-22% leakage. 12% would still be a decent running engine but its the beggining of the end if its all getting past the rings.


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