Nissan Z18ET compression/oiling issue

[BlownCorona]

Hi all. 

 

Trying to figure out why my fathers nissan S110 racecar engine wont run properly. 

we took it to a track day recently and it ran superbly but towards the end of the day we noticed a fair bit of oil in the catch tank and the PCV was fuming quite a bit so called it a day. (car still ran fine, but suspected damaged head gasket between oil/water)

 

my brother did a pressure test on the coolant system and found it was not holding pressure, so it seemed like it had done a head gasket. replaced the gasket. but no joy. still the same issue. 

 

i suggested to take the head off again and go get it crack tested. came back fine and no warping. so we refitted the head with a new gasket and another known good torque wrench. still no joy. 

 

dug my compression tester out and results are 

 

1 - 117

2 - 70

3 - 60

4 - 115 

 

i cant actually find what the z18et is meant to be, obviously 2 and 3 are down, but for a 1.8 turbo, is 115ish about right? still seems low to me. 

 

have check the valves and cant see anything wrong. 

 

any thoughts? 

 

and because pictureless threads suck, here it is running well! cant wait for it to be back on track!

 

 

[Gomaxgo]

do you have access to a leak down tester? will probably tell you where all the compressions are disappearing to

[BlownCorona]

i dont unfortunatly. 

all i have access to is a coolant system pressure tester and a compression tester. 

[Hemi]

Snapped /koozered rings? That could cause excessive blow by which would fill the catch can real quick.

[BlownCorona]

Any way to test for that without stripping the engine?

[Hemi]

A compression test, which you have done. and given the head has been checked for trueness and youve done the gasket twice. There's not too many others things left that could cause that. maybe do an oil change and something might come out? or whip the sump of. But by then you're pretty much commited to removing the pistons anyway.
 

[johnny.race]

Gomaxgo had the right suggestion - leakdown. Its going somewhere and its cost you a fair little bit both in time and dosh chasing it down so far. While not a leak down test, a cheap stethoscope and a fabricated adapter made from a sparkplug that will allow you to put a 100psi into the pot will go a long way towards giving you some insight as to whats going on. Its there is a hole, gap or a crack, you'll know about it. Get busy with the listening device in the confines of a quiet shed and you'll track it down. Cost - a little bit of time and next to no dosh. 

[Seedy Al]

when you had the head checked, did they vac test the valves or anything like that?

although, nothing anyone has suggested helps with why your coolant pressure test isn't holding.

Have you checked the block with a straight edge at all?

[BlownCorona]

Yeah and another symptom I forgot about was that it filled the radiator reservoir with Coolant and no sign of oil.

Dad didn't think to check the block was flat, but if/when the head comes off again we will do. I'd have expected the alloy head to go before the iron block though.

Also dad said they pressure tested the head, so I assume the valves are good

[Seedy Al]

Pressure test usually means that's how they test for cracks, and or use a spray compound that finds and shows cracks

But people may indeed call this differently.

however a vac test is where you apply vacuum to each intake and exhaust port to find out how they are sealing.

If your getting your resiviour filled and it is failing a coolant system test then you very much have a problem somewhere, but it is hard to know where.

but one guess could be the block is warped between 2 and 3, if it had ever had a blown head gasket before etc, that or by chance the valves are not sealing on 2 and 3.

[BlownCorona]

Does anyone have an issue with 1 and 4 compression of around 115? This seems low to me.

But I'm biased from the engine at work being a high comp 2 stroke giving about 160

[Frosty]

If you want to confirm bad rings without pulling down the engine.

Do a wet test.

Same procedure as a normal compression test but you put a couple of caps of engine oil into the cylinder before you test.

If the rings are buggered this should tell you, all your results will appear normal, ie all around 115psi.

 

May want to consider a cylinder wall crack as well.

[BlownCorona]

ive certainly considered a cylinder wall crack, but i really hope its not. also it would have had to crack two cylinder walls, into a oil and a water galley for it to present all the symptoms is has. 

unless its more than one problem which is just as likely

 

that said theres probably some datsun fiends here who have hoarded away a z18 block

[Frosty]

Cylinder head blow causes a hot spot in and around it, so if it just happens to be between 2 and 3 that section if cylinder wall gets to hot causing a crack aggravated by high pressure steam in the combustion chamber, all contributing to piston, lands and rings being damaged which causes fuming and oil consumption.

I think that pretty much covers your list of woes.

 

There's more than one reason for water / oil contamination when a head gasket blows.

1. Head gasket blow between water gallery and an oil passage letting water find it's way into the sump directly down an oil return slot. Doesn't always blow into a combustion chamber.

2. This time between a combustion chamber and a water gallery, this can also result in water in the oil but it takes longer as it has to bypass the rings to get into the sump but with a few hours running it will result in chocolate milk for a lubricant.

3, what I think is our problem here, blow between 2 and 3 also picking up a water gallery and an oil return, an unholy trifecta that can result in all your worst fears coming to fruition. Oil in the water, bad fuming and oil consumption, damaged pistons, eroded top of block and the surface of the head due to high pressure steam and combustion pressure swapping between the two cylinders.

 

I do hope the block is fine but at the very lest check it for true, I think you will find the section between 2 and 3 is eroded, this alone might account for the low readings in 2 and 3, much more likely the rings or ring lands have been damaged though...................

[BlownCorona]

only pic of the block that i have. but the bores dont look too bad. can even see hone marks still. (which does mean its possible it wasnt run in properly)

 

i had a look at the old gasket closely and there wasn't anything obviously wrong with it

 

[NickJ]

Is it just the camera angle or is that gasket all wonky and out of round?

[BlownCorona]

its definitely out of round, and i dont know why that would be, the new gaskets where concentric.

[Hemi]

I wish #2 +3 were as good as #1 in the pic.
Still , i cant see any blows. 
shape of the fire rings is a bit weird though.

My money is still on rings. but i am removing/keeping to the side the coolant not keeping pressure. as you havent mentioned it making its not* way into the oil?

 

For the effort you have already gone through i would:
A:Do what frosty mentioned with the oil.
B:Just bite the bullet and do a tear down and confirm visually. ( This is my personal choice as you have already gone through doing the gasket once, doing it again without checking the long block is silly IMO).

Keep in mind that while Im a mech I dont work on small petrol engines much, esp old ones so im only running on my personal experience in my field.

[fuel]

I think it has cracked ring lands. Did the same to the G63B in my Galant coupe - went to a track day presumably running on all four with presumably good compression across the board, came home running on three cylinders, shooting the dip stick out, burning oil etc. I too thought it was a coozed head gasket but turned out to be cracked ring lands on two pistons. Compression figures were similar and bores looked fantastic when the head came off.

 

[BlownCorona]

you reminded me that one time the dipstick did get pushed out, at the time we assumed we just didn't put it in properly. 

 

certainly wont be doing another head gasket without more investigation. 

 

its possible the water is getting into the oil as the oil sitting in the head is super thin for some reason, yet still looks like oil should and not milky.