Custom leak down test

I work for a manufacturing company that has a lot of air/plumbing fittings in stock, so it was pretty easy to scrape together a DIY leak down tester. I took the schrader valve out my compression tester line with the spark plug thread end and plugged it inline with a regulator and needle valve. The needle valve basically let's me adjust the orifice size to the point where the engine leakage takes over as the bottleneck.

My #4 cylinder couldn't hold any pressure compared to the others, but I couldn't feel it blowing passed the valves. After pulling the head I wanted to be 100% certain the rings were the problem. So I made a steel plate with a welded an npt coupling to bolt to the block over the individual cylinder. We had some cork gasket sheet lying around so I used that to seal to the block surface.

Still no pressure, even after I opened up the needle valve. Air was rushing out of the oil passage holes by the lifters. I added a decent amount of oil to the cylinder and tried again, but no luck.

Looks like it's a full rebuild unfortunately :(

Setup Picture


GOOD PRESSURE in #3


LOW PRESSURE in #4

It was leaking out of this hole a decent amount. But when I tested the other cylinders with good compression, air would come out of these holes as well, just not as much as this bad one.

Yes, sorry I couldn't think of the correct name for it. My oil pan is still on and sealed, so this would be the easiest way for air to escape

Yep its got no where else to go, normal behavior.   ... sounds like a broken or stuck ring anyhow. If you are looking to be cheap definitely pop that piston out and take a look before getting too crazy.

Autopsy first.

MARK YOUR LIFTERS . They need to go back in the same holes!!

Thanks Joe, that's what I'm worried about is opening up this can of worms right before ski season

The boat has 2100+ hours on the meter. I remember talking with the previous owner about there may have been a rebuild done on the engine a long time ago but I'd be willing to bet the engine hasn't been torn apart this far in its lifetime.

I have the engine sitting on a pallet in it's upright position. Is it possible to remove the connecting rod and push a piston out without flipping the engine upside down?

I should have about 10" of clearance between the engine block bottom and the pallet to get tools in to.

ok great thanks Duane!

shierh wrote: nice test. One question though,   why the test when you have it torn down to this level already? Bare minimum would be hone with new rings if engine is out and down to this level.

I did the plate test just to be 100% sure it was leaking passed the rings. If I found out the rings were sealing at its was a valve I wouldn't go through the trouble of tearing down the engine passed the heads. Now I have to at a minimum pop the bad piston out, then determine if I just want to fix that one or all 8 while I'm in.

Good tip Duane. I always put some clear tube on my rod bolts (especially when sticking the Pistons back in the holes on a fresh motor)