Low Compression in one cylinder

[Dny]

I'm looking at buying an EP3 so we got one checked out and everything came back good except the compression test.

~180ish in cylinders 1,3 & 4

~135 in cylinder #2 cold and it goes up to 155 at operating temp

I know thats still acceptable (barely) but its pretty far off the 10% range that I'd like all 4 cylinders to be in

I didn't do the test myself so I didn't get to run the test again with oil to see if it would seal up the rings.

Car runs great, no (butt dyno obvious) loss of power and doesn't blow any smoke.

Just hoping to get some opinions on how to interpret this and also if anyone else has had any other issues with the JDM K20's

[tinkerbell]

sounds dodgy...

could be valves or rings... either one is expensive to fix...

you need a 'leak-down' test to try and pin point the problem.

[Karl]

Buying a second hand car.. You will always find problems..I had 3 leaks putting water in my boot. Leaking windscreen, over sized tires that were rubbing, Slightly fucked recaro.. List goes on... If you plan to keep the car,, Grab one in the best condition you can find.. Or dirt cheap then fix her up!!!!!!! Mention the problem to the seller, try to get about a G off the price and go from there!!!

[tinkerbell]

um, in terms of 'severity' i think a dropped cylinder is slightly higher on the "oh shit" scale than a leaking boot...

[michaelz]

um, in terms of 'severity' i think a dropped cylinder is slightly higher on the "oh shit" scale than a leaking boot...

lol this.

if it doesn't burn oil / blow smoke it might be more valve train related. all it takes is for one valve to not close fully and you'll lose a heap of compression.

might be a weak spring or something like that. it's cheaper to replace some valve springs than rebuild the bottom end with all new rings but neither are easy/cheap jobs.

[Dny]

how expensive are we talking here in a best or worst case scenario?

Obviously we're pretty keen on the car as its immaculate inside and out with the exception of the compression test results.

I'm not sure the owner will agree to a leak-down test without some sort of commitment from my end so I'd like as much information so I can make the call to walk away or use it as a reason to lower his price.

[tinkerbell]

it is the most expensive thing to fix besides a spun crank bearing...

easiest way is brand new K20A "long block", then sell your bottom end as a 'suit rebuild' one...


but regardless - i would not buy a car without knowing exactly what was wrong with it...

so a leak down test is required, by a independent expert - they will then tell you what they think...

i have my own leak down tester, and it is actually pretty simple test, it is the interpretation of the results that is the most important...

[fatboyz39]

Was compression test done @ operating temps?

Maybe try with another compression gauge and redo the comp test.

WOT + CRANK CRANK.

[tinkerbell]

re-read post one?

[michaelz]

how expensive are we talking here in a best or worst case scenario?

Obviously we're pretty keen on the car as its immaculate inside and out with the exception of the compression test results.

best case = spend no $ and just drive it, put up with the slightly worse compression in cylinder 2 and hopefully it doesn't get any worse.


bad case = take the heads off and replace weak valve springs. this will be cheaper but still looking at up to 2 grand worth of parts and labour.

worst case = engine pull + disassemble. assuming nothing else is wrong with the bottom end, new rings all round. lots of labour = $$$$

and if you do either of the above then you might as well do other stuff such as new head gasket, water pump, thermostat, timing chain which will also add up. essentially anything that involves the engine coming apart is gonna cost. it also wouldn't make sense to skip the maintenance stuff to reduce the repair bill since it's gonna cost you more down the track.

[zeth_an]

Do the leakdown test or find another EP3...

[Dny]

lots of helpful info here, thanks

will see if he agrees to a leakdown test and see how things go

[Dny]

Was compression test done @ operating temps?

Maybe try with another compression gauge and redo the comp test.

WOT + CRANK CRANK.

Would it be worth while getting it tested again elsewhere or with a different gauge or method?

Is there anything else which could affect the reading?
The workshop which did the test suggested that cleaning out some carbon build up from the engine could bring compression back up a little. Is this worth looking into?

Judging from the condition of the rest of the car the owner treats it well. he has a compression test from 2 years ago when he purchased it and it came back good. He also has receipts and logs from regular servicing and even fuel logs for the last 2 years to show me its fuel consumption.
I'm actually a bit concerned as to how this could happen to the engine as I've seen far far worse cars out there which get completely neglected.
And just incase anyone was wondering the engine has done around 90,000km's

[ChargeR]

Do the leakdown test or find another EP3...

I agree with this guy. Will stop you guessing. As for how this might happen to the car, even a careful and meticulous owner can sometimes miss a gear change when driving in a spirited fashion and overrev the motor, and on a K20 this means bent valves.

[michaelz]

So if you miss a gear and bounce off the limiter a K20 will bend valves? Surely not.

Agreed though, don't guess and try to to justify the buy based on appearances. No leakdown allowed then just walk because he obviously has something to hide if he refuses.

The workshop which did the test suggested that cleaning out some carbon build up from the engine could bring compression back up a little. Is this worth looking into?

No. It still won't bring it back up to the other cylinders.

Judging from the condition of the rest of the car the owner treats it well. he has a compression test from 2 years ago when he purchased it and it came back good. He also has receipts and logs from regular servicing and even fuel logs for the last 2 years to show me its fuel consumption.

2 years ago is a long time. Don't let appearances fool you. How good a car "appears" and "well taken care of" should be taken with a grain of salt. For all you know he could have cained it every weekend between the lights and washed it the next day and vacuumed the interior thinking about the resale value. Regular servicing is all well and good but doesn't mean much now that you've confirmed one cylinder is down on compression.

FYI a cylinder lower than the others isn't going to affect the fuel consumption that much. I know because cylinder 1 of my Z is running at 110psi due a dodgy valve spring and the valve not closing. It has a clear misfire at idle but still manages to get pretty much normal mileage. If anything it still goes pretty well too, doesn't burn oil and I haven't bothered fixing it because I can't justify the money right now.

And just incase anyone was wondering the engine has done around 90,000km's

Doesn't matter if it has 20,000 or 200,000kms. Dropping 50psi has a reason and either find the reason then decide if you want to bargain it down and fix it yourself or find another EP.