The Stovebolt Site Forums The Shop Area Engine Shop Cylinder leak down test results.

Today I completed another cylinder leak down test after I got the engine up to operating temperature. I ran the engine for about eight minutes at a variety of RPMs and temperature stabilized at 190°.

Shut her down.
Plugs were removed.
Valve covers were removed.
All rockers were loosened so that all valves were simultaneously closed. Valve covers were replaced so that I could listen for air leaking through the oil fill cap, intake manifold, and exhaust systems. The PCV and fresh air intake tubing was also disconnected from the intake.
All cylinders were tested with 100 psi. Leak down test video.

The photo shows a chart of my results. I have blow by in cylinders #2, #5, #8. I also seem to have intake valves that are not sealing properly. I heard some air through the intake on cylinders #5, #7, #8.

Here is a result I DIDN’T EXPECT!
Cylinder #6 tested in the low 60s TWICE on prior leak down tests. It’s now at 93%.

I now have a dilemma.

1. Do I run the engine on the run stand and see if the other cylinders improve, like #6 improved? If I choose this option, I will probably swap the oil for some break in oil. Perhaps a straight 30 weight oil would be best.

2. Do I approach the engine builder with the results I have?

3. Should I remove the oil pan and look for pieces of broken rings?

I would do several more runs and tests if you plan to approach the builder, otherwise he might say 'they will all even out.' Offer to have him come watch.

Ed

I’m gonna squirt PB Blaster in each cylinder. Give it more time.
I thought I’d know something for sure after today’s testing. Now I’m still on the fence. It’s always something.

Further running is probably not going to improve the valve leaks. Until you get some load on the engine, the ring seating might improve slowly, but nothing seats rings better than some controlled lugging. When the pistons are fighting a load, the combustion pressure gets behind the compression rings and forces them tight against the cylinder walls. That's particularly true of the "low tension" rings that have been the industry standard since the late 1980's. Before that, rings had a lot more spring tension, and combustion loading wasn't as important as it is now.

More lubrication of the rings is just going to prolong the agony- - - - -I'd suggest forgetting about PB Blaster or any other kinds or Moose Juice!
Jerry

So Jerry is voting for . . . ???
1. Pushing it over a cliff. Light it on fire first, of course.

2. More run stand time just to prove it won’t help.

3. Dragging it behind my truck with a chain and leaving it in the engine builder’s swimming pool.

4. Putting it in my C10 and pretend nothing is wrong.

5. Something else.

I'm with Jerry on the P (T) B(arnum) Blaster. Out of curiosity, what type rings did you use? Cast, chrome plated top ring, other?

I’m not the builder, so I don’t know.

Either install it and put a few road miles on it - - - -

OR- - - - -

Give me time to scavenge up the bits and pieces of my dyno that's been in storage for 15 years and make a road trip. All it really needs is a good source of water to fill the brake chamber. I used to run a 1 1/2" diameter line on Nashville city water pressure, but I was pushing enough volume through the load cell to handle a 700HP at 6500 RPM engine without boiling the water inside the unit. Lower HP engines can be tested with a lot less volume of water.
Jerry

My experience has been chrome rings are harder to seat than cast and my experience has also been cast rings seat pretty well in the first hour or less of use. Actually I've never seen much to convince me they wouldn't seat fairly well just running the engine enough to set timing, adjust carburetor, check temp, etc. Chrome rings last longer but require the engine to be labored to seat properly (as Jerry already said). I should add I'm not a fan of chrome rings...at least not anymore. I thought they were a neat idea when I was younger, but I've had some that never did seat right no matter what I did. Cast wears quicker, but I'll take that any day. I should add I probably drive like your grandmother, though.

Ring gap is also a concern. The rule of thumb for a non-competition engine is .004" per inch of bore size. I've heard some say as little as .003" per inch of bore size, and while this is on the slim side, it will work. So if your bore size was 3 inches, your gap for the top 2 rings ought to be .012". What you have depends on the machinist/assembler and whether he cared about this or even checked it. Fact...the 235 I'm using now is bored to 40 because the prior owner had it bored to 30 over by some person who thought a ring gap of .038" was ok. The manual calls for .007" to a max of .017". The gap between the cylinder wall and piston was equally as out of whack. In the past, you might see different gaps for the 1st and 2nd ring. Today I believe most agree they can be equal.

Another possible problem is that the assembler didn't "clock" the rings correctly. This is really basic, but I mention it anyway. Things are going to work better if the gaps don't line up.

I wouldn't give the test much merit, the engine needs run much harder then a test stand can provide. If you had a driveline brake on a transmission, you could then add plenty of load to the engine. Either get it in a truck or on a dyne before committing to tear down. Also, rings walk around the pistons so gaps aligning is not a problem.

"Clock" the rings if you feel like it, but it's a waste of time on anything but a 2-stroke engine where the end of a ring can get hung up in a transfer port- - - - -and those pistons have pins in the ring grooves to prevent that from happening. Rings rotate around the piston all the time, and yes, the gaps do align with each other occasionally (for a few seconds). I had a training engine with a quartz window in one of the cylinders, and I used to watch the rings spin around the piston with a delay-flash timing light set to slow down or stop the piston travel.
Jerry

My $.02.
Regardless of the rings sealing, you still have leaking valves on 3 intakes. (What about exhaust valves??) My suggestion is talk to the builder and get his take on his willingness to stand behind his work.

SimS

Good news!
I spoke to the engine builder today and he seemed very eager to help me solve the problem.
I’ll report back when I have a final plan.

Finally had time to run the engine again. The HOT test was after 10 minutes run time and engine reached 190*. Cylinder #5 has issues for sure. These compression numbers don’t look good. I’ll talk to the builder this weekend and make a plan.

Just wondering how this challenge is playing out. My guess is the builder is sticking with a "Ya gotta install it and break it in" response.

RonR

I filed a case in small claims court. Seller has not been cooperative. Waiting for papers to be served to him and then see what happens. I have a very strong case. I’m hoping he’ll turn belly up and refund the money without us needing to go before the magistrate.

Let's hope you get a judge that's a little bit tech savvy if it has to go all the way to a hearing. When I contested a speeding ticket over the way the radar trap was set up, and included diagrams showing how the geometry was intentionally angled to increase the vehicle's apparent speed, the judge got into a very technical discussion with me and the officer who wrote the ticket. It turned out that the judge was a former Air Force navigator who had a very good understanding of the principles of Doppler radar. He lectured the officer on his sneaky techniques, and only fined me "court costs", not the higher amount that was customary. That cop was not impressed- - - -I had to watch my back anytime he was on duty for the next few years. He finally lost his job when he caught his wife in a compromising position with a local banker and "accidentally" shot her. She survived, barely, but his career didn't!
Jerry

This smoke doesn’t require any special technical training to understand.

This is not the site for Police Officer bashing. Let’s leave the occupation out of the equation. Thank you.

Thanks Martin.