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Bent valves. They don't seat, causing high leak down. This would otherwise show no oil residue on spark plugs. I would expect to see some irregularity on plugs though, showing signs of higher combustion temps, blistering or white crust on plugs to some amount.
Here are pics of the plugs. From left to right cylinder 4-3-2-1. #1 has some oil up by the sealing washer due to that seal leaking a small amount of oil through the valve cover. I have new seals for that.
I'll get videos uploaded of the cylinder walls using a bore scope.
Bent valves. They don't seat, causing high leak down. This would otherwise show no oil residue on spark plugs. I would expect to see some irregularity on plugs though, showing signs of higher combustion temps, blistering or white crust on plugs to some amount.
I thought this too, but the compression numbers don't look that bad. Wouldn't multiple bent valves cause a lack of compression and possibly a misfire? I'm still perplexed with the results vis a vis a good running engine.
I thought this too, but the compression numbers don't look that bad. Wouldn't multiple bent valves cause a lack of compression and possibly a misfire? I'm still perplexed with the results vis a vis a good running engine.
Yes dependent on how bad they are bent/not seating, but after looking at your plugs there is a substantial amount of oil fouling around the base of electrode which is from combustion not tube seals - though you still may have some tube seal issue as well. Id say you more likely have ring and valve guide/seal issues after looking at your plugs and that's where the air is escaping. But to better pinpoint this, you really should have the spark plugs in the cylinders you are not testing, this way it forces air through more concise pathways to tell you where the likely fault is, such as the front breather/crank meaning rings, or out the intake manifold meaning intake valves/guides, or valves on the exhaust side. You should be able to hear where the air is escaping.
Yes dependent on how bad they are bent/not seating, but after looking at your plugs there is a substantial amount of oil fouling around the base of electrode which is from combustion not tube seals - though you still may have some tube seal issue as well. Id say you more likely have ring and valve guide/seal issues after looking at your plugs and that's where the air is escaping. But to better pinpoint this, you really should have the spark plugs in the cylinders you are not testing, this way it forces air through more concise pathways to tell you where the likely fault is, such as the front breather/crank meaning rings, or out the intake manifold meaning intake valves/guides, or valves on the exhaust side. You should be able to hear where the air is escaping.
I was thinking that would be my next step. Reinstall spark plugs and do the leak down test again. Should I leave the valve cover on or pop it off?
Ok, uploaded videos of all 4 cylinders using the bore scope that showed up today. The image quality isn't the best, but I think this will do. I can try again at a higher resolution if needed, but its hard to get the camera all the way around in the cylinders. Looks like the extension I slid down into the cylinders must have knocked a little carbon off of the tops of the pistons.
Amateur opinion here, but those are some awfulllllllly clean looking pistons. You sure you're not losing coolant?
Actually id say 3 out of the 4 contrary to what you are seeing show oil deposits as id expect looking at the plugs. Notice how several of them look shiny/wet while also having deposits. That's cooked on oil deposits and and some fresh oil that hasn't cooked yet. Idealy the piston tops should look dry and clean. Not black and crusty. Over lot of miles the tops of pistons will get discolored and have some deposits due to blow by, the question is at what point in mileage is acceptable and is it a symptom of something more severe. 40% leak down is a concern. Where is it leaking down from. So far most signs are pointing to piston rings. Oil contamination in cylinders can show a high compression number. This is where doing a wet compression test can tell you if your numbers were already skewed from poor oil control rings and or compression rings both.
Last edited by s2000Junky; Feb 22, 2019 at 07:47 AM.
