Weird compression 150-65-120-130 any ideas

[BOBS90TURBO]

The car runs great, nice and smooth and boosts fine, but has started smoking a little blue out of the exhaust, so I did a compression test today and found #1 piston at 150psi #2 at 65 #3 at 120 and #4 at 130.
I then put a tea spoon of motor oil in the spark plug hole on #2 and re-tested and the compression went up to 120psi.

Does this sound like bad rings on #2.

 

[DSMcamaro]

Sounds like bad rings to me.

 

[BOBS90TURBO]

Thats what I am thinking, but why just the one(bad injector), and how the hell the is car still running fine on those numbers????? Anyone ver heard of pulling the head and popping in a new ring on #2, maybee some valve seals,head gasket and arp's, I s it even possible to do without a full piston change/rebuild/boring.???

 

[DSMcamaro]

Thats what I am thinking, but why just the one(bad injector), and how the hell the is car still running fine on those numbers????? Anyone ver heard of pulling the head and popping in a new ring on #2, maybee some valve seals,head gasket and arp's, I s it even possible to do without a full piston change/rebuild/boring.???

Its possible, but that is what people would call half@$$ing it. If your gonna pull it apart, do it right. My .02.

 

[JaxTalonTSi]

Thats what I am thinking, but why just the one(bad injector), and how the hell the is car still running fine on those numbers????? Anyone ver heard of pulling the head and popping in a new ring on #2, maybee some valve seals,head gasket and arp's, I s it even possible to do without a full piston change/rebuild/boring.???

Just depends. Alot of people are against it, but I'm for it depending on the conditions. A complete rebuild can somtimes be a long process, and somtimes it's just practical to re-ring a cylinder and ride out, rather than pull the engine and take the car down for an extended period of time.

I've had two high mileage DSM's that I have both re-ringed at one time. The rering was just the most practical thing to do at the time. I did it over a day or two, and spent less than $400.

What I did was pull the head, and the oil pan, and push all the pistons out of the top of the block. After carefull inspection of the cylinder bores and crank rod journals, I put new stock size bore piston rings in each bore, and checked the ring end gap for spec. I believe (going off the top of my head here) the Hayne's manual says factory ring gap should be between .014 to .017. With new piston rings in the bores, they were all around .020. Definetly a candidate for a rebuild. But I ended up dropping the pistons in with new rings and rod bearings anyway (after carefully honing the cylinder bore slightly). I figured, I may have some blowby issues, but it's the difference between spending a few hundred dollars, and having the car on the road for mabey a year more, or spending $1500 on a complete rebuild, and having the car down for weeks, mabey even months depending. I chose the rering (on two separate cars), and both cars lasted a long time afterwards, and even with the larger ring end gap, still had great compression and low oil consumption.

Regardless what you do, I would definetly have a leakdown test done before you do anything, just to be sure it is the rings.

 

[BOBS90TURBO]

Jax, Thanks a lot for the info, even though I have lots of mods I never drive the car hard, I've only once taken the RPM's to 6k, I have 140k on the car and am still on the stock clutch, I am ok with 14psi of boost at most. I am just needing the fast/cheap way to get the car to normal compression.

 

[justin case]

while your doing a compression test it'd probably be good to do a cylinder leakdown test on the car too just to be sure nothing else is out of order