2G 1 cylinder low compression and smoky exhaust

[XIT]

I've read a bunch of threads over the last few days and I am still unsure of my issue. I feel like it could be HG or valve stem seals but I'm open to other suggestions. The only reasons I'm not leaning towards rings, is the color of the smoke and the wet compression test results. With that out of the way, here's the story.

I just bought the car. It's a 1998 gsx with low miles (~88k). I bought it from a kid that really doesn't know anything about working on cars. He noticed it smoking while driving and decided to park it until he could afford to take it to a shop or could have a friend help him figure it out. His friend suggested to him that it was the hg. One year later, he sells it to me.

When I went to pick it up, the exhaust manifold and turbo were removed along with the intercooler tubes (stock smic and tubes) and the radiator. The cylinder one exhaust port looked wet but all the plugs looked the same (cyl 1 wasn't wet or black or anything). I put the car back together before buying it so I could see how it runs and test drive it. It started up well and idled fine with no smoke. It did not smoke while revving up, but only while rpms come back down after a rev. Higher rev = more smoke. After revving when the engine catches idle, no more smoke. The smoke is white/very very very light gray but no sweet smell. This was still without refilling coolant (maybe burning the coolant that's still in the engine?). It does not seem to be losing any oil. I went on a short test drive and the car felt like it had good power down low but had a little hesitation when getting up in rpm. I didn't drive it hard, I just wanted to verify the condition of the drivetrain and went around the block. Never had it under full throttle but it did build boost.

I live about an hour from where I store the car so I'd like to go work on it with an optimal game plan. I already ordered an entire gasket and seal set for the engine and ARP head studs. I want to do all maintenance and get it in good running order before I do anything else with the car. The car is pretty much completely stock except for an aftermarket muffler and BOV. The timing belt was replaced recently. I plan on doing a pressurized cooling system test and I have to get some supplies to make a bl tester. I was considering filling coolant and seeing if it smoked more/lost coolant but I would rather not just in case the oil and coolant were to mix and cause more damage.

Any other suggestions or is there anything I'm missing?

The compression test was performed cold. Only cylinder 1 was tested dry and wet.
Compression test results: 1 - 120 d, 130 w 2 - 155 3 - 160 4 - 160

Thank you in advance!

 

[XIT]

You have a piston ring issue in cylinder one if your doing your compression test properly.

Any idea what would cause it? The car has under 90k miles.

 

[motomattx]

Well it can get interesting here, the engine may have developed rust in that cylinder from sitting and then you started it up without removing that rust, doing that can grind the piston rings and cylinder wall down causing your compression issue, that or something might have gotten sucked into that cylinder from being in the intake (mouse nest?) or it could have had detonation damage in that cylinder from its past, several things can cause damage.

 

[DSMPT]

I bought it from a kid that really doesn't know anything about working on cars.

This fact always makes things complicated when you buy a DSM. Anyways check the cylinders with a borescope, that may tell you something if you have some damage.

 

[XIT]

Well it can get interesting here, the engine may have developed rust in that cylinder from sitting and then you started it up without removing that rust, doing that can grind the piston rings and cylinder wall down causing your compression issue, that or something might have gotten sucked into that cylinder from being in the intake (mouse nest?) or it could have had detonation damage in that cylinder from its past, several things can cause damage.

Yeah I guess I won’t know until I investigate further. The previous owner did say he started it up every couple weeks while it was sitting but I did notice a little bit of rust on the intake cam. I did compression test it before starting it at the previous owners house.

 

[XIT]

This fact always makes things complicated when you buy a DSM. Anyways check the cylinders with a borescope, that may tell you something if you have some damage.

Thanks for the advice. I’ll be back in town next week to check with a borescope. I’ll be back with results then.

 

[waltah]

Valve stem seals are fancy plastic. Their job is to control -- not stop -- the oil being sucked down along the stems through the valve guides -- there must be lubrication there. They're designed to squeeze on the valve stems slightly -- some even have garter springs there.

They are good but not marvelous and an engine that has run unusually hot will fry them. Ditto very high mileage. They will nearly always need replacement before much of anything else goes wrong internally. Like 150k miles even if the car isn't overheated.

You have precisely the symptoms for dead valve stem seals. That's not proof but if you are going to put money on something -- and you are! -- that's the best place to put it first.

The smoking on deceleration when cold happens because that's the highest vacuum (most oil sucked) and the engine's not hot enough to completely burn the oil. The 'smoke' is condensed oil particles. The comment to the effect that the somewhat 'off' compression test could be carbon build-up keeping a valve from sealing correctly makes sense.

There are various ways to replace valve seals. I would choose one of the 'head on' methods and do that. Considering the (fairly low) mileage on the car I suspect that'll put you on the road with negligible smoke. Then after a longer drive or three (hoping that the valves have cleaned themselves up) try the compression test again.

Or -- you can go straight to grind the valves. Valve seals will be done as part of that, and there'll be no further question about the valves. The head gasket too will be replaced. Of course any of the parts of that job can be done incorrectly causing still more trouble -- a possible reason to start with the smaller job rather than the bigger ones.

Among other things I'd consider how good a professional you have available to do the work. Getting a rebuilt head from a reliable company should mean less chance of a screw-up on that work -- you're down to installation mistakes, sloppy torquing of the head, and such.

The chance that the problem is worn rings seems very slight and there's nothing to be gained by assuming that.

 

[XIT]

Valve stem seals are fancy plastic. Their job is to control -- not stop -- the oil being sucked down along the stems through the valve guides -- there must be lubrication there. They're designed to squeeze on the valve stems slightly -- some even have garter springs there.

They are good but not marvelous and an engine that has run unusually hot will fry them. Ditto very high mileage. They will nearly always need replacement before much of anything else goes wrong internally. Like 150k miles even if the car isn't overheated.

You have precisely the symptoms for dead valve stem seals. That's not proof but if you are going to put money on something -- and you are! -- that's the best place to put it first.

The smoking on deceleration when cold happens because that's the highest vacuum (most oil sucked) and the engine's not hot enough to completely burn the oil. The 'smoke' is condensed oil particles. The comment to the effect that the somewhat 'off' compression test could be carbon build-up keeping a valve from sealing correctly makes sense.

There are various ways to replace valve seals. I would choose one of the 'head on' methods and do that. Considering the (fairly low) mileage on the car I suspect that'll put you on the road with negligible smoke. Then after a longer drive or three (hoping that the valves have cleaned themselves up) try the compression test again.

Or -- you can go straight to grind the valves. Valve seals will be done as part of that, and there'll be no further question about the valves. The head gasket too will be replaced. Of course any of the parts of that job can be done incorrectly causing still more trouble -- a possible reason to start with the smaller job rather than the bigger ones.

Among other things I'd consider how good a professional you have available to do the work. Getting a rebuilt head from a reliable company should mean less chance of a screw-up on that work -- you're down to installation mistakes, sloppy torquing of the head, and such.

The chance that the problem is worn rings seems very slight and there's nothing to be gained by assuming that.

Thanks a bunch. The explanation makes a lot of sense. I already have a full top and bottom end gasket set and arp head studs waiting to go on the car. I bought them the night I bought the car because I figured it’ll need some things replaced to be in tip top shape before I start trying to throw any parts at it. I’ve rebuilt heads before and have lapped valves so it shouldn’t be an issue. Are there any “while I’m in there” things to do with the head off you’d recommend? I’ve read about smoothing out the oil port on the bottom of the head and I’ll replace whatever gaskets I can in the top end. The timing belt was recently replaced, otherwise I’d do that too.

Thanks again to everyone for the help. Glad to see the community still strong as ever

 

[XIT]

Okay update time. I pulled the head off and have been waiting on the valve spring compressor tool to come in. Started pulling the valves on cylinder 1 (cyl with low comp) and everything looked good at first. The last valve I pulled out of cylinder 1 was an intake valve and I noticed the guide is cracked. Then I looked at how the seat and seat surface on the valve looked and noticed the valve surface was uneven. I chucked up the valve in a drill to clean the back of it off and sure enough, the valve was bent. I stopped disassembly after finding the damage. The car has a fresh timing belt and water pump that was done before I got it. I’m assuming it must’ve jumped timing and smacked the valve. obviously the head is going to have to go to a machine shop. Does anyone know of a reputable shop in southern Wisconsin/northern Illinois? Or would I be better off buying a head off of somebody else and hoping it’s in good shape?

 

[JusMX141]

Bad valve seals / guides for sure. I had a friend's car that had a bad exhaust guide on #4 and it allowed oil to pool on top of the piston. This car had 82k on it. Some ARP studs and a rebuild job on the head and she was back in business.

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[JusMX141]

Does anyone know of a reputable shop in southern Wisconsin/northern Illinois? Or would I be better off buying a head off of somebody else and hoping it’s in good shape?

Rebuild your head for sure. All you're going to get is someone else's high-mileage head that needs rebuilt.