MattTenFour

Despite the length of my post, this really is a fairly simple question. I wanted to provide a detailed background so I can hopefully figure out a solution to my issue. My question is in regards to my S13 with a blacktop SR20DET. The engine is internally stock; GTIR T28 turbo, 750cc injectors, Enthalpy tune, Z32 MAF, FMIC, full exhaust from the O2 housing back. Not long after I purchased the car, one of the coolant hoses under the intake started leaking and it overheated on me. I replaced the hose but I continued to have cooling issues from that point (car would overheat when driving, but not at idle). Instead of diagnosing the problem like I should have, I replaced or upgraded literally every single component in the cooling system one by one. OEM Water pump, Koyo Copper radiator, silicone hoses, OEM thermostat, GKTech fan blade, fresh coolant etc. I guess it was the same mentality of not checking your bank account when you know you don't have any money. Eventually I pulled the head and sent it to my machine shop. They determined the head was not cracked or warped excessively, they machined it down and replaced the valve seals. I meticulously cleaned and prepped the block mating surfaces in accordance with the FSM and installed an Apex'i metal gasket along with ARP head studs.

The install went well and the overheating issues did not return during several brief test drives that would normally cause it to overheat. Prior to all of these issues, I did a CD009 swap and was excited to finally be able to drive the car. About thirty minutes into my maiden voyage, the car began to feel like it was losing power and I noticed some light smoke from the exhaust. The smoke became progressively heavier and I stopped to check it out. I noticed that oil was coming from my uncirculated blow off valve and the inside of my exhaust tip was coated in oil. Presuming the turbo was the culprit, I decided to limp the car back home another fifteen minutes. During the drive home, it seemed like the car developed a misfire. When I got home, I pulled the intake pipe off and confirmed my suspicions. My GTIR T28 had enough side to side shaft play that the blades on the exhaust side were contacting the inside of the turbo housing. All of the blades on both sides of the turbo were still intact, but it was obviously in need of replacement.

At that point, I ordered a GT2871r and had Odyssey Fab modify a stock cast manifold for a Tial 38mm external wastegate. New lines, gaskets, studs, the works. I started the car up and it was still smoking, which I expected with the amount of oil in the exhaust and intercooler. I noticed that it still appeared to have a misfire and I performed a power balance test to narrow it down to cylinder 1. I figured the plugs were oil fouled and I replaced them with a fresh set of NGKs. Cylinder 1 has spark and fuel, coils and injector check out, swapping the coils around makes no difference. I conducted a compression test, cylinders 4, 3 and 2 were fine, but I found that I had zero compression on cylinder number one. By zero, I mean the gauge does not move whatsoever when cranking the car and it stays at zero the whole time. At this point, I’m thinking that I have a cracked ring land or a hole in piston number one. Since I’ve had an ongoing dialog with Martin at RS Enthalpy, I decided to asked him for his opinion about the situation. Martin also thought it was odd that the compression gauge didn’t move at all and seemed to think that it may be something simple like a rocker arm holding a valve open. Martin informed me that when a car has a broken ring land, it would normally show some compression before dropping back to zero. I visually inspected the rocker arms and all of them were in place. I turned the engine over by hand and the valve springs and rocker arms appeared to move up and down as they should. Looking through the spark plug well, I cannot see any obvious damage or holes in the piston.

I’d rather not pull the head, order another $200 head gasket and remove all of the parts I just installed on the car to find out something else was causing this. If the valve seals were not installed properly, could it cause the cylinder to not have compression? When the machine shop had my head apart, I noticed that they did not keep the rocker guides in order. I told them that the guides are different thicknesses and they are supposed to go back exactly where they came from. The owner of the shop told me that it did not matter and because it has hydraulic lifters, they will adjust themselves. Could the rocker guides be causing a valve to hang open and allow compression to escape? What could have caused this? Surely the engine didn’t come apart just because the turbo crapped out on me. I’m sure most of you will say “just pull the head off dip shit” but I want to make sure I cover all my bases before I overlook anything.

Thanks in advance for the assistance and sorry for the length of this post.

derass

Ha! That's a funny line! Reminds me of avoiding my grades in college. Anyways...

The next step in diagnosing low (or non-existent) compression is to do a leak-down test. This will tell you where the compression is being lost before tearing the engine down, whether it be the valves, rings/piston, head gasket or other.

Did you notice oil build-up on the turbine wheel and inside the turbine housing? If the seal goes on that side, those parts are usually covered and wet with oil. I'm just curious since you mentioned the tailpipe being coated.

As for the rockers/guides/shims, you're almost right and the machinist is wrong. The rocker guides are all the same thickness (to a degree due to manufacturing tolerances) and it's the shims that are different. That's their purpose: to make up for those manufacturing differences and have the rocker sit "level" over its two valves. It doesn't matter that the lifters are hydraulic as they act on the opposite side of the rocker.

In any case, I don't think mixed up shims would cause the cylinder to have zero compression. Worse case, wear will be accelerate on the valvetrain.

So my advice is to do a leak-down test and go from there.

brndck

+1 for leakdown. For the engine to have ZERO compression, either the piston has detached itself from the rod, at the top of the stroke, or the rod has detached itself from the Frank.

Otherwise, even if the ring lands are toast, or there's a hole in the piston, you should see SOME movement on the gauge, even if it's just 10-15psi and then drops right back to 0.

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mewantkouki

Only time I've had zero compression was with a piston that had a window in it... lol Even cracked ringlands / washed cylinder walls will show something on a gauge.

MattTenFour

That definitely makes me feel better about the shims/guides. At least knowing that improperly placed shims wouldn't cause this particular problem means I have one less thing to worry about.

And yes, there was oil on both the turbine and compressor side of the turbo. This is the fifth 240SX I've owned and fourth car that's had the SR20DET swap. Somehow I've never had a turbo fail on me. I always figured the turbo would die gradually, not in one fell swoop. I didn't notice any oil smoke from the exhaust until a short time before its catastrophic demise.

A leak-down test is definitely the next thing I'll be doing. Thanks for taking the time to read my autobiography of failure!

MattTenFour

This was my train of thought. I figured it should have given me some sort of reading on the compression gauge. The other thing that I found odd was the fact that, despite the misfire, the engine seems to run fairly well. Its not making any kind of knocking or grinding sound that I would expect from an engine that has come apart.

When I turn the engine over by hand with the plugs out, it rotates smoothly and all I hear is the sound of compression escaping from the spark plug wells. If I look down the spark plug well when I'm turning it over, I can see the piston moving up and down.

Looks like the OTC leak-down test kit is only $67 on Amazon prime. Unless I can find a friend who has one, I'll be ordering that this weekend.

derass

See if you can rent the tester from an auto parts store before buying it.