Pressurized crankcase - ring gap?
 

I have a new build that has a lot of crankcase pressure. The motor is a 555 BBC with 10:I compression and a brand new Dart block with a really good hone. I have been reading on the causes of this issue and a lot point to worn rings. I have new rings but I am questioning my ring gap. My ring brand instructions called for .0045 x bore. That comes out to be .020. The instructions said this is the minimum gap. Since a marine engine is under constant load I increased that to to .025. This gap is the minimum gap for a nitrous engine according to the instructions. Could that ring gap cause the high crankcase pressure? It blew a press in oil cap out and doesn't seem to have the power it should. I also have a pcv valve.

Any ideas?

ring gap is correct if not on the tight side ring break in we use cheap 10-30 oil and run it on the stand for a while to get ring seal (1500-2500)........we use a bit more ring gap because the block is often on the to cool side so the bore has not expanded like it does at 150 160 degrees do not run synthetic to break in

It is said alot (engine builder write ups) ring gap has less to do with crankcase pressure than does piston to cyl wall clearance.

who did the engine assembly?

I ran Brad Penn straight 30 wt on break in. I am not sure on the piston to wall clearance as the machinist set that up.

I also have the coated piston skirts and thought those were supposed to wear in to the cylinder wall?

Are you running breathers in both v covers ?

I assembled it. I have done quite a few drag and boat motors. All big cubic in. I just assembled this motor with no issues except hauling ass.

I ran a pcv valve and a press in oil cap. I will be changing the oil cap with a K&N breather.
https://cimg2.ibsrv.net/gimg/www.off...9ef0669a03.jpg

the reason i asked who assembled it is i once had a friend do his own assembly and he had the same issue you are having.when i took the engine apart i found that he had installed the 2nd compression rings up side down.i am not saying you did that but i can see that type of mistake happening.btw,i have a very similar engine in my hondo flatty,572,16.71 blower with a superchiller like yours.my block is black and with all the polished alumunum it looks bad azz.

I may have to check that as I was filing rings and my buddy was installing and clocking them on the piston. My rings didn't have the dot that shows you how to install them face up but mine you had to look at the bevel. Very easy to screw up I guess.

Time to pull it again. Getting pretty good at it now.

Thanks for that info.

I once had high blow-by on a fresh SBC build. Also had hand filed rings and everything was checked and double checked. Compression test narrowed it down to a single cyl. Pulled head and found a small chunk of piston missing from just above top ring. Cyl looked fine and rings re-measured OK. Replaced the single piston (& it's rings) and blow-by was completely gone. 15 years later, it's still running great. Never did figure out exactly what happened. Best guess was that I caught a ring edge when installing pistons.

Second ring upside down will cause oil smoke but I dont think it should affect blowby that much.

I appreciate the comments. Pulling engine today and checking my work.
One other problem I had when I first started it on the hose was the oil was milked.. I thought one of the head gaskets had leaked.
I found one of the exhaust manifolds had a crack and was the issue. I was given these by a friend and he had no idea. Could this of caused the new rings not to seat? It wa started a few times before I found it.
I flushed it with 3 oil changes and it is clear now.

How much time have you put on the engine? I’m just curious with no value to add to the problem.

I used the Brad Penn 30w break in oil and it worked great for me. Fwiw, I think I heard Brad Penn had been sold and the oil isn’t as good as it use to be. I haven’t verified that though.

https://www.speedsterowners.com/topi...-new-ownership

I don't even have an hour. Probably 10-15 minutes on the hose a few times. Only twice on the lake 5 minutes and 7 minutes.

I have it apart and did a ball hone on it and installing new rings. Hopefully that will fix the issue. All the rings are oriented correct with the bevel up on the top ring and bevel down on the second ring.

I think the immediate milking of the oil caused the rings not to seat? Don't see any other problems.

An update. I pulled the engine and took it apart. I installed new bearings and rings. I also honed the bores with a ball hone to make sure the rings had a chance to seat. The engine now has no crankcase pressure. I think since the motor was milked from startup the rings never seated correctly. All of the original rings were installed correct with no upside down rings. Always nice to find your problem.
https://cimg0.ibsrv.net/gimg/www.off...95405a27f0.jpg
Fresh hone

Interesting. Wonder if the instant milkshake caused the rings to overheat due to excessive friction making them loose their tension??
Anyone ever try to measure ring tension? Don't remember ever seeing it spec'ed.

How did the bearings look?

The bearings looked OK but not perfect so I replaced them. I live 3 miles from Summit so getting parts is easy.

It could have been caused by glazed cylinder walls. Running a motor on a stand for longer than it takes to set timing and look for leaks is just not good for them. It takes load to build cylinder pressure. It takes cylinder pressure to seat rings. I've found that by putting an engine on a Dyno and getting it underload ASAP not only gives less crank case pressure they make more power. As soon as timing is set we run a computerised break-in that runs the engine to about 3000rpm and back to about 1200rpm at 60% load. You can do same thing in a boat. Run it on hose just long enough to set timing and look for leaks. Then launch and get underway and accelerate/decelerate repeatedly for about 15 minutes. You'll be surprised at how much better it'll run. Once break-in is done go over the valve train and double check the timing. Change oil and filter if you want. Then go run it full throttle and back to idle several times on about a 10second pull and get out of it as if you were making Dyno pulls. Then use it however you want.
If your near the Summit in Akron look up Chris Wright at Pro Car & Associates at 1100 Triplett Blvd. Tell him Smitty sent you.

Thanks Smitty but I live in Reno so I go to the Sparks store. It is really easy to spend some money there when it is only 10 minutes from your house

It's real easy to spend some money at Summit and Sparks with mail-order! haha!