Bone stock '02 LS1 out of a Camaro (currently in a Datsun) with about ~45,000 street miles and about 30 road course track days / races. It runs great and seems to have no problems. However, I just completed an off season compression check just as part of preventative maintenance and 7 cylinders came in at 200 +/- 5 PSI but one is at only 160 PSI. Last time I checked a couple years ago all cylinders were consistent at 200ish PSI (dont remember exactly but I know they were all the same and over 200). So I sprayed some WD40 in the hole and it came up to 180 PSI. So it's rings. I then pressurized the cylinder and you can hear it coming through the rings into the crankcase. I checked a couple other cylinders and you can hear the small leak into the crankcase (rings dont seal 100%) but it's louder with the one cylinder so I know it's something with the rings in this one cylinder causing higher flow. So question is where do I need to go from here? I want to keep the really good reliability and performance I've enjoyed over the last several years with this motor but I also dont want to waste time and $$ for something that's not really broken. So do I need to rebuild it? Do I need to pull the head and check the cylinder for scratches or signs of broken rings? Will it be fine and just run it?

Since it's just one hole obviously something is wrong so I'm thinking I need to take it apart but hoping there are some engine experts here to provide some guidance.

Thanks
Cameron

 

IMO, nothing to worry about at this point. If you know someone with a bore scope, you might get a closer look. Other than that, just keep monitoring the situation...

 

Agreed. Its not worth it yet to rebuild the motor. Its not losing a significant amount of power. When it reaches 115-125 consider doing something then. 160 isnt to bad, obviously something isnt right but youll be fine in my op

 

Usually as long as all your cylinders are within 10% of the average you should be good, since yours is about 20% it isnt the greatest but im going to have to agree with the other guys and say its not enough to rebuild the motor and go through that hassle...you could pull the one piston and re ring it if you are really intent on fixing it, but if it were me i would go thru all that unless i got a consistent misfire from the cylinder and it ruined performance, bc if you are anything like me i cant enjoy my car if ANYTHING is wrong lol...good luck man let us know whats up

 

Presumably, you tested all the cylinders while the engine was as close to operating temp as reasonably possible. If not, that could skew your results slightly. As others said, within 20% isn't that bad.

Bore scope would be a good idea, just to inspect things. If you found a broken ring land, or damage that pointed to broken or butted rings, you may be better off doing something now, otherwise you may leave well enough alone.

FYI - nitrous guys have found that #7 runs slightly leaner, so when pushed hard, they can damage the ring lands. Since your engine is stock, and previously tested well on all holes, that may not mean anything to you.

Which one was it?

 

Checked cold but last night I verified the weak cyl didnt change warm. Dont know the naming convention but its the drivers side second back from the front. The car spends 95% of its time on a road course as its a dedicated track day / race car. I dont think its really down on power but I also dont want it to die on track or worse and knock a hole in the block and have a crash or fire or something. I dont know still on the fence.

Cameron

 

You could have a ring sticking in a ring land from carbon/10 years of grunge. Boroscope is good idea but I'd also try some type of engine flush before putting a wrench to it.

I'm slowly coming to like Seafoam. I'm real old-school and usually don't put much stock in "magic" chemical fixes but your engine might well benefit from it.

A flush IS cheap, your engine has enough years on it to possibly need it, and if it makes a difference you will be glad you did it.

I wouldn't automatically rebuild it for just the low compression for a street car but if I was using that as you are (95% track) it would bug me enough to do something about it.
I'd seafoam, drive 50 miles (on street) softly, change oil, drive 20 min "track-session" hard, immediately run comp test after "session" starting with the weak cylinder first. Do leak-down test with gauge. Document results in a log book. I'd probably redo this after every track weekend thereafter but I am a bit OCD...

That lower compression cylinder IS putting a weaker power input than the other cylinders into the crank. This MAY cause strange harmonics/resonance which MAY over-stress stuff that might be rotating 6K +.
In a street application it should not be a problem but in a track car it will have a far greater effect on engine life.

I believe it is either sticking rings which you should be able to clear or the beginning of the end of that motor in a track application.
Sorry to be the negative poster regarding this. It's your use that is the issue in my book. When the average throttle position is greater than 50% the small stuff really begines to matter.
How often are you using less than 50% of the throttle without being on the brakes on the track?

What sort of Datsun do you have that in? I am an early Z freak and currently own 4 of them. My 78 was supposed to get my 02 LS1/T56 but I think my 98 BMW M3 is a better chassis for the swap (both OBD2).

 

You don't need to worry about a piston coming through the head and hood or anything like that unless You're pushing this engine to 7400 and more . So it's #3 ,,,,,,,,,,most likely some dirt got sucked into that cylinder and caused the pre-mature wear or it could be a land or cracked ring .

 

A) Just add a bottle to the oil pan? I've read about sucking it into the intake as well but is that right? Never used it but seems to have a good reputation ... at least on the internet

B) My thought exactly. Street I wouldn't worry about it but race and there's a lot invested and a much more to go wrong.

C) Not too much, mostly track out leaving turns where I'm rolling into the throttle being traction limited.

D) '72 240Z - highly recommend big engine / little car.

Stock 6200 rev limiter. My thought anyway is if a ring is coming apart it could seize a piston and then throw a rod.


Cameron

 

Slight update. Sea foamed it per the directions both into crankcase and sucked into intake then drove for about 20 miles. Helped maybe 5 psi up to 165. Ordered borescope and am now anxiously waiting for it to arrive.

Runs so well if the cyl walls are not scored Ill leave it alone. We'll see.

Cameron

 

Pull the plug on the low cylinder then get a tablespoon of some oil in there and then run a compression check on it. If it gets better then its your rings, if it doesnt get any better then its your valves.

 

This^ called a wet test

 

Sea foam is over marketed crap. Auto RX is one of the best treatments out there. Many show marked improvements in compression after using it.

Also run some techron through the fuel system to clean that side of it up. Gum out Regane is a good shelf fuel additive with techron although the BEST out there is Redline SL-1... it has the highest concentration of techron hands down.

What kind of oil and filter do you run?

 

Read... he already did that.

 

... yeah I know its ring related just dont know why. Use Penzoil Platinum 10w30 and Purolator filter. Change both after every other track day.

Cameron

 

it really isnt that hard to pull intake and heads and all it will cost you is some time and new head gaskets, and you will gain piece of mind knowing the piston/ring isnt mangled

 

Why pull the heads now - from a few posts up.

Not only can he check it visually without a teardown, he'll be able to monitor things between track outings.

 

If it's a track car then these things happen, things get broken all the time.

It's a part of life and i hey i have had to accept if i want to race my car im going to break stuff.

I'd say pull it out see what the deal is and maybe even just consider another LS engine to put in, do a comp test on one sitting in wrecking yard and get a new one, i dont know what they cost in the USA but you can get complete LS1,LS2,LS3 here for not all that much.

Hopefully you get it sorted out.

 

Unlucky #7 by any chance?

 

So I got the borescope today. Looked into #3 and it looks perfect. Im thinking score all is ok. Then I checked the other cylinders and found similar except #5 (assuming - drivers side third back) where you can clearly see vertical lines. So rechecked compression (cold) and found 1 & 7 at ~200 PSI and #3 at 160 PSI same as before but now #5 is only at 170 PSI. Im assuming that seeing any vertical lines such as what's in #5 is bad?

Crap maybe I do need a rebuild ? .... if so suck

Cameron