Leakdown/compression results

[JG1966]

I just did my first leakdown/compression test on 340. 11-1 motor. Did test with 90 psi at TDC at operating temperature (although motor obviously cooled down a bit during 2-hour process). Motor runs strong but was getting some blow by. Here are the results
#1 170 compression -- 2.5% leakdown
#2 168 -- 5%
#3 168 -- 3.75%
#4 160 -- 12.5%
#5 167 -- 11.25%
#6 159 -- 4.5%
#7 165 -- 11.25%
#8 151 -- 16%
Nos. 4, 7, 8 are leaking from exhaust valves (exhaust pipe) and rings (breather hole). No. 5 is leaking from rings. I didn't add oil and retest "wet" on any of them.
Also, the leakdown connector was leaking a bit at spark plug hole on Nos. 4 and 6. I think it was connector not sealing perfectly because there was no leak taking compression test (with a much higher psi).

Do these numbers make sense/warrant a teardown this winter?
How can No. 5 have a strong compression number and still have a relatively high leakdown %? Same with No. 7.
Is there a way to try to remedy leaking exhaust valves before/if pulling heads (Seafoam, hitting valves with nylon hammer, etc?)
Motor runs well and I'm a bit of a newbie. Just looking for some feedback. Thank you!

 

[69Bee]

Re-ring it and do a valve job. Deglaze the cylinders with a ball hone (NOT a rigid 3 finger death hone), polish the crank, valve job, and surface heads. Install new rings and bearings when you go together. If pistons look ok, re-use them.

 

[oldbee]

Have to disagree with 69bee, I would 'Seafoam' (or similar) to the engine first,it's cheaper; you could have some carbon buildup and/or sticking rings. Cheaper first is always better IMO.

 

[JG1966]

Have to disagree with 69bee, I would 'Seafoam' (or similar) to the engine first,it's cheaper; you could have some carbon buildup and/or sticking rings. Cheaper first is always better IMO.

Thanks Old Bee. I should add the engine is not old and worn out. It has maybe 1,500-2,000 miles since being rebuilt. I think carbon and sticky rings is much more likely than a lot of actual wear. I'll Seafoam it (actually gonna use the Mopar combustion chamber conditioner) and retest.

 

[oldbee]

Well then- maybe you've got some ring ends that were not fitted very good & they are butting up against each other. I'd still try the cheap way first. OR I could be way off base here.

 

[JG1966]

Well then- maybe you've got some ring ends that were not fitted very good & they are butting up against each other. I'd still try the cheap way first. OR I could be way off base here.

Here's the story for this engine to give more insight.
I bought 340 out of 68 Dart in 1987 and had it bored, honed, crank turned, heads ported, etc. I was an ambitious teenager and (using a "How to rebuild a small block mopar" book), I put it all back together myself. After break in, I drove it maybe 500 miles. Life happened and car -- with bad torque converter -- sat in garage for 15 years. I sold car 7 years ago -- and guy (who lives in your neck of the woods, Oldbee), later told me engine looked very nice when they took it apart. He put motor in a Dart and put about 1000 miles on it while fixing up the 1972 RR (my old car) that it was in. Last summer, I bought car (and my old motor) back from him. Since then I've driven about 200 miles. Engine runs fine but have some oil on plugs, blowby, etc. That's the life of this motor. So when I say motor has 1,500-2,000 miles since rebuild, it's not a typical scenario.

 

[oldbee]

LOL, kinda sounds like mine that sat for 20+. Life gets in the way a lot of times! Sooo did the rings get gapped&checked or what?!!!! Just pullin' your chain. Jeff

 

[JG1966]

LOL, kinda sounds like mine that sat for 20+. Life gets in the way a lot of times! Sooo did the rings get gapped&checked or what?!!!! Just pullin' your chain. Jeff

That's a legitimate question. I'm gonna try seafoam and if need be, yank the motor to give it a once over.

 

[J5 GTX]

Change the oil and filter. DRIVE it ! Run that motor. Do not rebuild or refresh the rings.
Unless you think that motor was terribly abused for it's short life, don't take it apart.

I've dealt with this a lot. The leakdown test is a tool but, not the end all analysis. There are couple of things at work here that make readings show different variations. For differential leakdown, to get a true number, I suggest removing the rocker arms. but, I'd just drive it first. Road speed, 70 mph. Make sure you have the correct thermostat. Do the leakdown test again. You really don't have much data unless you do a few tests to establish a baseline.

 

[mopar 3 B]

Just having the piston off tdc can affect a leak down test. Make sure the test is being done on the compression stroke.

 

[khryslerkid]

When driving it, do some deacceleration. Find some long downhill runs. It helps with seating the rings.

 

[lewtot184]

#5 and #7 with identical numbers would concern me. I think there are some ring issues, but intake gaskets not sealing good and valve seal issues would cause oil problems. oiled chambers can cause detonation issues that will eventually wreck internal parts.

 

[JG1966]

#5 and #7 with identical numbers would concern me. I think there are some ring issues, but intake gaskets not sealing good and valve seal issues would cause oil problems. oiled chambers can cause detonation issues that will eventually wreck internal parts.

Thanks Lewtot. I noticed that as well on #5 and 7. I changed intake manifold recently and maybe didn't get a good seal. I'll check that out. I also suspect valve seals might be causing oil on plugs rather than rings for a couple reasons.

 

[lewtot184]

Thanks Lewtot. I noticed that as well on #5 and 7. I changed intake manifold recently and maybe didn't get a good seal. I'll check that out. I also suspect valve seals might be causing oil on plugs rather than rings for a couple reasons.

with 5 and 7 identical i'd look for possible head gasket leakage between the two cylinders. if you have stock type heads and a high lift cam it's possible for the valve seals to be damaged. I don't think intake gaskets would effect leak down. you probably have several issues going on.

 

[miller]

I think there are some ring issues

With compression #s like you have, if you can get your hands on a bore scope, I'd take a look at the cylinder walls.

 

[JG1966]

with 5 and 7 identical i'd look for possible head gasket leakage between the two cylinders. if you have stock type heads and a high lift cam it's possible for the valve seals to be damaged. I don't think intake gaskets would effect leak down. you probably have several issues going on.

I have stock-type heads and a high lift cam (.509), so valve seals might be problem. If I do have head gasket issue, it's definitely not putting coolant anywhere it shouldn't be.
If it's the seals, I'm not getting a lot of smoke. About 10 seconds of white smoke on start up (seems like exhaust pipe condensation) and no smoke at all during different driving conditions.

 

[lewtot184]

smoke at start up is generally valve seals or guides. I doubt if the stock valve guide boss height will work with a .509 cam. if the valves were ever floated it's pretty certain any umbrella type seal would get beat up. it's possible for the cylinders to leak between each other without loosing coolant. I doubt identical leak down numbers for those two cylinders is a coincidence, but it's possible.

 

[khryslerkid]

it's possible for the cylinders to leak between each other without loosing coolant

Just install your compression tester in the one cylinder and air supply in the other.

 

[wsutard]

JG1966, I'm very interested to hear how the Seafoam works for you. I have been having a very similar issue where I will only blow oil smoke decelerating down hills. So far I have changed the intake gaskets, resealed valve stems that had new seals already and took it to my mechanic for a leak down test. My mechanic decided to take a look in the cylinder with a borescope first and found signs of "ring wash". The edge of the pistons were clean while the rest of the piston was carbon coated. combine this with his knowledge that my car was very hard to start when warm and he didn't even bother doing the leak down test since he was 99% convinced that ring wash was the culprit and wanted to save me some money.

My engine is a relatively newer rebuild so its hard for me to fathom that my rings are already bad, but I guess having that much extra fuel pouring down the sides of the cylinders isn't a good thing. I was all dead set on yanking it and re-ringing/stroking/throwing it away until I read your post. Maybe a $5 can will save me a headache!

 

[lewtot184]

detergent oil getting past the rings will clean the carbon off the top of piston around it's circumference but leave carbon in the center. oil from the intake will wash the carbon off the piston in the area under the intake valve. several ways oil can get into the combustion chambers.