Crankcase backpressure

[Crawler]

I have an early 80's SB350 that seems to have an excessive amount of crank case back pressure. I have the PCV valve installed and it is NOT plugged. When running on the highway at rpms around 3000 it will blow the oil dipstick out of its seated position. I installed a valve cover breather filter to alleviate that but this thing seems to pump oil out of every nook and cranny at high rpms.

Any thoughts on what would cause this much pressure in the crank case? My initial thoughts are that the valves are too tight. Is there any easy way to check that?

 

[BCGPER]

I'm assuming you're plumbed directly to manifold vacuum?? Likely source is bad rings..... :-\

Got a vacuum guage to see if you're actually pulling any?

I have an early 80's SB350 that seems to have an excessive amount of crank case back pressure. I have the PCV valve installed and it is NOT plugged. When running on the highway at rpms around 3000 it will blow the oil dipstick out of its seated position. I installed a valve cover breather filter to alleviate that but this thing seems to pump oil out of every nook and cranny at high rpms.

Any thoughts on what would cause this much pressure in the crank case? My initial thoughts are that the valves are too tight. Is there any easy way to check that?

 

[mbryson]

........... My initial thoughts are that the valves are too tight. Is there any easy way to check that?

Learn me: How would you adjust that? You've just got seats and valve springs there. You thinking rockers?

 

[Shawn]

Likely source is bad rings..... :-\

This is my bet, been there done that several times...

 

[timpanogos]

yep, no compression - warn rings

 

[Crawler]

yep, no compression - warn rings

I did a compression test on it and the compression is good. all cylinders were close to 150psi.

I question the valves/rockers because when they were originally adjusted the guy that didn't seem too concerned with making sure they were all the same. Just wrenched on them while the engine was running. I've never adjusted them before so that may be the correct way to do it.

 

[BCGPER]

If the valves were too tight, you'd have low compression. Even if they were too tight, there's nothing in the valve train that can cause blow-by.

Having decent compression doesn't always mean your rings are good. Try a cylinder leak down test to determine the condition of your rings.

Start back at the basics. Have you pulled the PCV valve while the engine is running? Maybe the vacuum hose has colapased internally? Hooked up to manifold vacuum and not venturi vacuum? Oil overfilled? Water entering the oil? Could be a hundred "easy" fixes as well.

I did a compression test on it and the compression is good. all cylinders were close to 150psi.

I question the valves/rockers because when they were originally adjusted the guy that didn't seem too concerned with making sure they were all the same. Just wrenched on them while the engine was running. I've never adjusted them before so that may be the correct way to do it.

 

[Crawler]

Thanks for the ideas. I will do some simple troubleshooting this weekend and hopefully find something. The Oil level is an interesting question. I have an aftermarket dipstick and wonder if it is the right one.

If the valves were too tight, you'd have low compression. Even if they were too tight, there's nothing in the valve train that can cause blow-by.

Having decent compression doesn't always mean your rings are good. Try a cylinder leak down test to determine the condition of your rings.

Start back at the basics. Have you pulled the PCV valve while the engine is running? Maybe the vacuum hose has colapased internally? Hooked up to manifold vacuum and not venturi vacuum? Oil overfilled? Water entering the oil? Could be a hundred "easy" fixes as well.

 

[BCGPER]

If all else fails, drain it out and see. Should be around 4 1/2 qts. in it if the pan is stock.

Thanks for the ideas. I will do some simple troubleshooting this weekend and hopefully find something. The Oil level is an interesting question. I have an aftermarket dipstick and wonder if it is the right one.