PSA: Low Compression Fix Adventure

HawkeyeGeoff

HawkeyeGeoff

MSO Chicks
I've been on this platform for ~5 years now and I've never heard of anyone trying this...here's my story.

I am purchasing an 06' MS6 w/ 61k on the clock. We tested the compression and it came out the following:
Cyl1: 190
Cyl2: 180
Cyl3: 155 (went up to 170 with a cap of oil)
Cyl4: 190

@ALPINEST4RS suggested I try the following product since the car hadn't been driven really all that hard and might possibly have seized rings from carbon build up:
GM Top Engine Cleaner
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We pulled the plugs, threw ~4oz in each cyl overnight, sucked out the super dark fluid with a pump, changed the oil (immediately after since a bunch obviously seeped past the #3 ring), fired it up...and here are the results.

Cyl1: 175
Cyl2: 175
Cyl3: 165
Cyl4: 180

Ah. Holy shit. These tests were all done when the engine was at operating temp. So from this we can gather that carbon build up CAN effect compression (positively or negatively). Cyl 1, 2 +4 were getting artifically higher compression and Cyl 3 was losing compression because of it. The numbers are much more uniform, which is what you want, and my butt dyno suggests a smoother car overall.

I will monitor the motor as I drive it more, I'm going to perform a driving cycle similar to that of a break in procedure and see if #3 comes up more. Limit it to ~10 psi and do lots of decel.

If your motor has highly varying compression and it sits a lot...it's time to give this a try before building or replacing the motor.
 
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Interesting, I'm curious how your leak down results would differ, I'm in a state of low compression currently

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brainbot1 said:
Interesting, I'm curious how your leak down results would differ, I'm in a state of low compression currently

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I should have done a leak down....but I didn't. *shrugs* It runs great so I'm not going to really put any more effort in than I have to.
 
Pretty neat! I know i've had slightly lower compression in cylinder 3 for a while now (about 10 psi lower). I might have to give this a try.

As a side note, i kind of figured carbon buildup on the piston top would yield higher compression due to less space in the combustion chamber but I guess if its also interfering with the rings seating it could make some sense.
 
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nekret said:
Pretty neat! I know i've had slightly lower compression in cylinder 3 for a while now (about 10 psi lower). I might have to give this a try.

As a side note, i kind of figured carbon buildup on the piston top would yield higher compression due to less space in the combustion chamber but I guess if its also interfering with the rings seating it could make some sense.
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Yeah the thing here is I guess it can actually seize the rings....since #2 and 3 are always running the hottest (not sure if this is right @phate i'm sure could fill us in), I think it has a higher likely hood of carbon build up on the rings. #1+4 seem to build it up on top due to being the coolest.

Again i could be totally wrong that's my scientific wild ass guess on the topic.
 
HawkeyeGeoff said:
Yeah the thing here is I guess it can actually seize the rings....since #2 and 3 are always running the hottest (not sure if this is right @phate i'm sure could fill us in), I think it has a higher likely hood of carbon build up on the rings. #1+4 seem to build it up on top due to being the coolest.

Again i could be totally wrong that's my scientific wild ass guess on the topic.
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My compression numbers would agree with you
1: 180
2: 155
3:160
4:185

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@VTMongoose what do you think? My intake valves have never been cleaned to my knowledge but I thought direct injection takes care of carbon build up in the cylinder or on the piston. I'd still like to do a leak down before and after

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brainbot1 said:
@VTMongoose what do you think? My intake valves have never been cleaned to my knowledge but I thought direct injection takes care of carbon build up in the cylinder or on the piston. I'd still like to do a leak down before and after

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This all depends how the vehicle is driven; city cycle will create more than highway cycle driving. This DI....not necessarily the best case for "clean burning" because of the poor piston design. It is not quite as efficient as it should be.
 
HawkeyeGeoff said:
This all depends how the vehicle is driven; city cycle will create more than highway cycle driving. This DI....not necessarily the best case for "clean burning" because of the poor piston design. It is not quite as efficient as it should be.
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I suppose there was a thread on the old forum talking about how the gen2 pistons are better for this reason. All the more reason for port injection and lots of boost

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brainbot1 said:
I suppose there was a thread on the old forum talking about how the gen2 pistons are better for this reason. All the more reason for port injection and lots of boost

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Exactly right. The gen2 pistons are significantly better in all of those regards.
 
brainbot1 said:
@VTMongoose what do you think? My intake valves have never been cleaned to my knowledge but I thought direct injection takes care of carbon build up in the cylinder or on the piston. I'd still like to do a leak down before and after

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I was arguing with Geoff earlier in shout about this...everything I have read tells me that once you have stuck rings or clogged oil control rings, you are fucked. Piston soaking has been around for a while. Some claim it works, others claim it does nothing. It clearly does something, but everything I have read indicates its effects are limited to the short term.

The only real fix is to remove the pistons, clean the ring grooves and drill out any clogged oil return holes, and reassemble.
 
VTMongoose said:
I was arguing with Geoff earlier in shout about this...everything I have read tells me that once you have stuck rings or clogged oil control rings, you are fucked. Piston soaking has been around for a while. Some claim it works, others claim it does nothing. It clearly does something, but everything I have read indicates its effects are limited to the short term.

The only real fix is to remove the pistons, clean the ring grooves and drill out any clogged oil return holes, and reassemble.
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If the oil return holes were truly clogged....wouldn't it burn oil? This vehicle burns negligible oil.

Also, you own a Gen2, so you do not understand the heartache that is low compression in all of the Gen1's :'( we need everything we can get!
 
I know one local with low compression in cylinder #2, we tested his car and he made I think 175-155-180-180. It's not just a Gen1 thing. The pistons and rings are not really designed for how we use them.
 
VTMongoose said:
I was arguing with Geoff earlier in shout about this...everything I have read tells me that once you have stuck rings or clogged oil control rings, you are fucked. Piston soaking has been around for a while. Some claim it works, others claim it does nothing. It clearly does something, but everything I have read indicates its effects are limited to the short term.

The only real fix is to remove the pistons, clean the ring grooves and drill out any clogged oil return holes, and reassemble.
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Have you researched the old shade-tree mechanic fix of carefully metering in water to steam-clean the engine, clean out the carbon, and freeing the rings? There's lots of info out there about it that it's legit and many swear by it, even with old engines that've sat a while. It's also one of the benefits of running 50/50 or so WMI instead of pure 100%, but I don't know if that method of water injection is as effective.
 
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We used to free up rings on GM northstar vehicles weekly with this method from oil consumption/low comp. I figured what the hell, mind as well try it. Just soaking the pistons overnight made a difference. The car ran much smoother too. I suggested to geoff that a compression test is needed after a few good runs. Just to see what happens.

The trick is to run the vehicle hard to seat the ring again. Also, the top engine cleaner works wonders on stem cleaning aswell. This method works and its been proven, just not on our cars. If the ring is bad, its bad. So far it did something. Time will tell.
 
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Did this over the weekend with the help of @VTMongoose .
-removed the spark plugs
-poured 2 ounces of cleaner into cylinder
-cranked engine a few times to get it moving
-let it sit for a little less than 24 hours
-sucked it out with cheap fluid pump
-assembled everything back together and started car
-took it on a few 3rd and 4th gear WOT pulls
-checked compression with the following results
Original reading on 8/11
1:180
2:155
3:160
4:185

Before soaking 11/12
1:195
2:170
3:165
4:185

After soaking 11/13
1:185
2:165
3:165
4:185

cylinders two and three are still showing diminished results which leads me to conclude my rings are bad.

unfortunately ran out of time and didn't get to do leak down.
 
brainbot1 said:
Did this over the weekend with the help of @VTMongoose .
-removed the spark plugs
-poured 2 ounces of cleaner into cylinder
-cranked engine a few times to get it moving
-let it sit for a little less than 24 hours
-sucked it out with cheap fluid pump
-assembled everything back together and started car
-took it on a few 3rd and 4th gear WOT pulls
-checked compression with the following results
Original reading on 8/11
1:180
2:155
3:160
4:185

Before soaking 11/12
1:195
2:170
3:165
4:185

After soaking 11/13
1:185
2:165
3:165
4:185

cylinders two and three are still showing diminished results which leads me to conclude my rings are bad.

unfortunately ran out of time and didn't get to do leak down.
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Well at least your numbers are a little more uniform now! :-D
 
My question is, have you experienced noticeable or measured power loss?
 
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