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Cylinder leak down test results.
#1367733 Sat Jul 04 2020 05:56 PM
Joined: Sep 2011
Posts: 1,987
L
Lugnutz Offline OP
Shop Shark
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. [youtu.be]

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?

Attached Files
2063BC3C-91B5-46E6-B9C0-CEF498D46028.jpeg (313.74 KB, 155 downloads)
Last edited by Lugnutz; Sat Jul 04 2020 06:11 PM.
Re: Cylinder leak down test results.
Lugnutz #1367746 Sat Jul 04 2020 07:41 PM
Joined: Jun 2011
Posts: 3,544
E
Shop Shark
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

Last edited by EdPruss; Sat Jul 04 2020 07:41 PM.

'37 GMC T-18 w/ DD 4-53T, RTO-610, 6231 aux., '95 GMC running gear, full disc brakes, power steering, 22.5 wheels and tires.
'47 GMC 1 ton w/ 302, NP-540, 4wd, full width Blazer front axle.
'54 GMC 630 w/ 503 gasser, 5 speed, ex fire truck, shortened WB 4', install 8' bed.
Re: Cylinder leak down test results.
Lugnutz #1367751 Sat Jul 04 2020 08:38 PM
Joined: Sep 2011
Posts: 1,987
L
Lugnutz Offline OP
Shop Shark
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.

Re: Cylinder leak down test results.
Lugnutz #1367755 Sat Jul 04 2020 08:48 PM
Joined: Feb 2004
Posts: 20,612
H
Boltergeist
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


The murder victim was drowned in a bathtub full of Rice Krispies and milk.
The coroner blamed the crime on a cereal killer!

Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
Re: Cylinder leak down test results.
Lugnutz #1367757 Sat Jul 04 2020 09:00 PM
Joined: Sep 2011
Posts: 1,987
L
Lugnutz Offline OP
Shop Shark
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.

Last edited by Lugnutz; Sat Jul 04 2020 09:19 PM.
Re: Cylinder leak down test results.
Lugnutz #1367764 Sat Jul 04 2020 09:16 PM
Joined: Mar 2014
Posts: 1,563
J
Shop Shark
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?


Jon

1952 1/2 ton with 1959 235
T5 with 3.07 rear end
Re: Cylinder leak down test results.
Jon G #1367766 Sat Jul 04 2020 09:18 PM
Joined: Sep 2011
Posts: 1,987
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Lugnutz Offline OP
Shop Shark
I’m not the builder, so I don’t know.

Re: Cylinder leak down test results.
Lugnutz #1367772 Sat Jul 04 2020 09:31 PM
Joined: Feb 2004
Posts: 20,612
H
Boltergeist
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


The murder victim was drowned in a bathtub full of Rice Krispies and milk.
The coroner blamed the crime on a cereal killer!

Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
Re: Cylinder leak down test results.
Lugnutz #1367776 Sat Jul 04 2020 10:32 PM
Joined: Mar 2014
Posts: 1,563
J
Shop Shark
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.


Jon

1952 1/2 ton with 1959 235
T5 with 3.07 rear end
Re: Cylinder leak down test results.
Lugnutz #1367781 Sat Jul 04 2020 10:42 PM
Joined: Feb 2000
Posts: 4,149
J
Shop Shark
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.

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