sbc blow by question

I have a new built 383 sbc it has about 600 miles on it now, my question is ever since I got it running it blows oil out everywhere, the valve cover breather , the first 50 miles the front seal started spitting oil out, and even out the dipstick tube one time. I have been doing some searching around here on this and decided the best bet might be a pressure test. A buddy came over with his gauges the motor is on a stand right now, we hooked it up with the piston at tdc started putting air to it and it was blowing right through to the crank case. I did this on every cylinder. Could it be because the engine was cold or am I possibly doing the test wrong, it doesn't seem to hold any psi. any thoughts would be appreciated

 

you didn't happen to line up the ring gaps on the pistons did you ?

 

Do you have proper crankcase ventilation?

 

I'd be looking at proper pcv first.

 

oil out the dipstick tube? not vented right

 

after the front seal I put a pcv on the drivers side and a vented cap on the passengers it seemed to help but I still get oil coming out of the valve cover breather and the front seal is starting to drip a little again

 

Got nothing to do with it..... Rings rotate while an engine runs....they are bound to align at some point.

 

I did rotate all the ring gaps when I installed them, the engine seems to run good

 

When you say fresh built....new pistons and rings along with afresh bore?

You need to ck the "leak down".... This is done with a special gauge that monitors the amount of air escaping past the rings.....this is done with the piston at TDC on the compression stroke....Do not add oil as some will say.

Perfect is 0 to 2-3 percent.....
Gauges cost 100-150 depending on style

 

something isn't right with the rings if it blowing past them that bad....either one or more are stuck in the ring grooves or they aren't the correct size...etc. I would do a compression test and see if its all of them or maybe just one or two cylinders.

 

Who built the engine? Is it possible that the bore dia. Is not correct for the pistons? I know it sounds crazy but it could happen. I'm not talking about standard pistons in a .020 over bore but possibly bad machine work. Is there any air coming out in the valve covers when you put air to it or just down in the block?

 

it is a new bore pistons and rings, my buddy brought over a leak down gauge but im not totaly sure we did it right the piston was at tdc the rocker arms are off, when we started putting the air to it at about 20psi you could hear it in the crank case and I put my finger on the dip stick tube and could feel air coming out

 

I had some serious blow-by on the last SBC I built. When I took it apart I discovered that I had 1/16" rings in pistons made for 5/32" rings. I had bought a kit and being new parts didn't bother to check ring side clearance. I got real lucky. Most of the top and second rings came out in several pieces, but the cylinder walls and pistons were OK. Always check everything.

 

I never thought about that I bought the rotating assembly as a kit I checked the ring gap before putting them on the pistons but didn't realize there were different size, the gaps are all .016-.017

 

Single or double gauge tester? You dont need to take rockers off...just bring it up on compression stroke.

 

A couple of things I first thought of when I read your post were,, wrong rings with a large end gap and a wrist pin that worked it's way into a cylinder wall and is wearing some nasty vertical grooves. The pin thing get worse as time goes on. Try blowing air in the cylinders with the rocker arms loose and the pistons down. You will usually hear some air leaking past the rings when doing a leak down test but not a large amount. If one cylinder is really bad pull her apart.

 

it has two the first one reads the air psi the second one shows the % of leakage

 

IT seemed pretty loud to me that's why I wasn't sure if I am doing it right

 

Sounds like the rings are not sealing for some reason.
You did hone the cylinders to get a nice crosshatched pattern after the cylinders
were bored...right?

 

ya the machine shop honed them when they did the rest of the work

 

You need 100 psi at least of line preasure...set first gauge at 100 with regulator while having adaptor plugged in with air free flowing.

Then install adaptor in spark plug hole and reattach to gauge.... the difference between 2 gauges is the percent of leakage.....example first gauge reads 100psi minus second gauge 78psi= 22 percent leakage.

 

Does all 8 holes leak air ? Wrong rings or broken rings. Have you pulled the heads yet. Check the head gasket for leaks?
If it was, I would have had it pulled apart already, if it was on a stand.

 

Got to breath. She has to breath; just like us. I have a 60's oil fill tube and breather style Edelbrock Alum 4 barrel man. on my 70, 350., and I assumed that that would be enough since it allows an inch and 1/2 opening directly to the lifter valley. Outside of the first 2 minutes of fire up, I blew the left bank valve cover gasket flush out from under my tightened down So Cal sealed finned valve covers. Took me a while to figure it out, but I had an old chrome valve cover sitting around, so I swapped it to the right bank, fired it up and the problem was mostly gone. I later drilled a pipe nipple just in front of the distributer on the manifold and tucked a line from a PVC to that - all of what seemed originally like a wicked case of blow by is gone fixed.

 

maybe thats what I did wrong I plugged in the gauges then hooked up the air the gauges have a regulator on them, then I started turning the regulator valve as it was getting pressure it was blowing by I only went up to about 50 psi then quit

 

Put some oil in the cylinder. this will seal the rings for a short time and leak down test it again. If it leaks a 1 psi it will leak at 100 psi.

 

should you be able to hear it howling from the crank case?

 

I'm with the guys that say you dont have your crankcase exhausted correctly. You need two openings in your engine for it to internally breath correctly. Remember the bottom of the piston is an air pump just as the top of the piston. You should have two openings to the crankcase, one for the inlet air and one for the outlet air. If you just have one (breather) opening the inlet air cant get in if the outlet air is trying to get out thru the same hole. When the engine is running with only one breather the under piston air pressure builds up faster than it can excape so the next exit is thru the seals and this air escape draws the oil with it creating a leak.

Since you already have one valve cover with a breather port go borrow another valve cover with a breather and install it on the opposite bank, Start the engine and check your dip stick for your blow by now. If you still have a large amount of air being expelled thur the stick tube then you have other issues and follow goatropers leak down test procedures.

 

If you have a engine this is right, you mite hear a small hiss. If you had bad rings it will blow by very bad, loud air noise.

 

I do have a breather on the pass side and a pcv on the drivers. To me it sounds allot louder then a hiss and can feel it coming out of the dip stick tube

 

Do what GOATROPER02 said about the leak down test. If it leaks so much air by that the guages won't give you a % of leak down, then put some rearend lube in cylinder and test again. If you have that much air going into the crankcase with a leak down test, it's has nothing to do with the crankcase vent problem. You can vent all you want but if your problem is the rings then its not going to make your engine run better.