# 2015 Chevy Cruze LT - Car won't start



## RoninDusette (Aug 21, 2018)

Cylinder one looks like it has low compression when dry and good compression when it's wet which leads me to think that it may be a piston ring or a cracked piston or at least one that starting to go out. That's just a guess though


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## ShadeTreeMechanic (Dec 6, 2019)

Yeah. That's what I was thinking but it's only an 8% difference. I thought it was bad to see something bigger than 10%. I'm afraid it is the piston ring as well. Just seeing if anybody had any other suggestions.


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## RoninDusette (Aug 21, 2018)

These aren't oldschools. The tolerances are much, much tighter, and given your dry test vs your wet tests, unfortunately, it points that way, and these cars have a history of issues with the pistons cracking. To be honest, and I have done it may times, you can likely get away with leaving the motor in the car, pulling the head and pan, then pull the rods and pistons. Get a machine shop to put your pistons on, then hone the cylinders and re-ring. If you can, go aftermarket pistons. I mean, you are already in there that deep, may as well do it better than OEM (especially if the OEM-spec stuff is faulty). You just have to catch it early before you start putting nasty cuts in your cylinder walls (then you need to have the block machined, sleeved, or replaced). 

In the cylinder, if it's dry and wet are around the same, it could go upper or bottom part of the cylinder. Given that oil is what actually makes the seal on the bottom part of the cylinder (top=valves and head gasket, bottom=rings/oil). I smoke a lot of herb, so maybe I have it backwards. It's been a while since I needed to do a compression test, but hey; it never hurts to take it into consideration. 

As far as the difference between the rest; look at all of your other cylinders, dry and wet. Which one sticks out? What is the percentage of difference between those? Then compare the average difference between adjacent cylinders... I mean, there is clearly something funky going on. At least we can narrow it down to one cylinder. I am not a betting man, but I would put my money on the upper ring area of cylinder one not holding pressure with oil coming from the crankcase, which is why putting oil in from the top makes it go up. I am not a professional. Long-time hobbyist, but not an OG.

Don't get discouraged. I mean, we can speculate alllllll day. Won't know until you get in there.WIth the way every other cylinder is looking compared to that one, I would start digging it into it before it potentially gets worse. Plus, while you are in there, f*** it, you can service the head gasket, timing system, and any other component that is a PITA to do while you are in there. Even if you find no issues or just need to re-ring, your car will thank you for it for thousands of miles... probably the piston though.  If I was near, I would totally help too.


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## ShadeTreeMechanic (Dec 6, 2019)

RoninDusette said:


> These aren't oldschools. The tolerances are much, much tighter, and given your dry test vs your wet tests, unfortunately, it points that way, and these cars have a history of issues with the pistons cracking. To be honest, and I have done it may times, you can likely get away with leaving the motor in the car, pulling the head and pan, then pull the rods and pistons. Get a machine shop to put your pistons on, then hone the cylinders and re-ring. If you can, go aftermarket pistons. I mean, you are already in there that deep, may as well do it better than OEM (especially if the OEM-spec stuff is faulty). You just have to catch it early before you start putting nasty cuts in your cylinder walls (then you need to have the block machined, sleeved, or replaced).
> 
> In the cylinder, if it's dry and wet are around the same, it could go upper or bottom part of the cylinder. Given that oil is what actually makes the seal on the bottom part of the cylinder (top=valves and head gasket, bottom=rings/oil). I smoke a lot of herb, so maybe I have it backwards. It's been a while since I needed to do a compression test, but hey; it never hurts to take it into consideration.
> 
> ...


Thanks man. What do you mean get a machine shop to put your pistons on? From what I can tell in basic diagnostics if wet test is better than bottom end is bad. I've learned a lot about these cars during this whole journey but it's really rough given deadlines and what not. Is the standard advice, if you take off the cylinder head might as well do all 4 pistons and gasket? Or can I skip the pistons because their compression numbers are good and skip the gasket because the problem is on the bottom end?


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## snowwy66 (Nov 5, 2017)

The pistons is where your problem would be.

Rings. Maybe walls.


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## RoninDusette (Aug 21, 2018)

ShadeTreeMechanic said:


> Thanks man. What do you mean get a machine shop to put your pistons on? From what I can tell in basic diagnostics if wet test is better than bottom end is bad. I've learned a lot about these cars during this whole journey but it's really rough given deadlines and what not. Is the standard advice, if you take off the cylinder head might as well do all 4 pistons and gasket? Or can I skip the pistons because their compression numbers are good and skip the gasket because the problem is on the bottom end?


Oh yeah. For sure. You are right. I got it backward. I was having a long day. I mis-typed. As for the machine shop[, the pistons are connected to the rods with pins, usually with c-clips at each end of the wristpin. Depending on the engine, the pins have to be pressed in via machine. If you have a press and a good heat source (if needed, depending on application), you can diy, but most don't so it's not bad to spend 100 bucks (usually 25 bucks per rod/piston) to have a shop press them on. Usually takes about a day to get them back. 

As for doing ANYTHING youc an afford while the head is off, yup. While you are in there, if you can afford it, then sure,do the head gasket, rod bolts/studs, OH, and most importantly, DO THE TIMING KIT. Not just the chain. Chain, tensioner, pulley's and guide, oil pump, water pump. I will tell you, the thing I have seen wreck the most engines is lack of timing belt care. Period. 

And yes; home your cylinder walls (or have them machined if they are scratched hella bad), and ALWAYS replace and reseat your rings if you change then. When the egine is broken in, the rings fit to the cylinder. To not do so is sloppy, and you will be right back in there to do it right anyway


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