Zero Compression on #5

[SarahLovesHer300zx]

I just bought a freshly rebuilt TT with zero compression on cylinder #5. The engine has ~5 miles since rebuild, but it was finished a couple years ago and has been sitting since. We don't think its the piston rings, no smoke. We're guessing a stuck lifter. I picked up some Mobil1 full synthetic oil and Marvel Mystery Oil to run through it.

Are we on the right track or are there more tests we should do to further narrow it down/verify?

[nissanfreak12]

Do a leak down test. That should tell you where the air is escaping and giving you an idea where the problem lies.

You can also get a camera in the cylinder to look at the valves to see if they are seating properly, little more expensive, but really gives a good insight what it looks like without tearing apart the engine.

[SarahLovesHer300zx]

I just did the oil change. The drain plug bolt has a magnet on the end of it, and it looked like a freakin DQ ice cream cone.. I'm hoping thats normal for a fresh rebuild and break-in?

But does this look ok? I've been maintaining our other vehicles for years and have yet to see it quite this light and swirly



I also noticed a pretty steady coolant leak up front, and an oil leak coming around the bottom of the oil pan, not sure if its the gasket or if the oil is dripping from above. PO did say it was leaking at the rear main seal, not sure where or what that is though, but I've heard it before.

I'm also picking up the leak down tester today and I'll post up what I find in the next couple days.

[evildky]

Nope not normal. it would appear you have 2 different fluids that are not compatible, did you add the marvel oil? anything else? Did you run any of it through a coffee filter? good way to look for flecks or metal.

[SarahLovesHer300zx]

Nope not normal. it would appear you have 2 different fluids that are not compatible, did you add the marvel oil? anything else? Did you run any of it through a coffee filter? good way to look for flecks or metal.

I didn't think so... Crap.

This is whatever came out of the engine from the PO. I added about 3qts Mobil1 10w30 and a little under a qt MMO.

I didn't think to run it through a coffee filter. I'll do that when I empty it from the drain pan, that's a great idea. But the drain plug magnet did have a good amount of shavings and bits on it. Nothing really big though

[nissanfreak12]

Check your coolant. It looks like coolant/water from the picture, but since it has ran it should look like a milkshake, not swirl.

If the oil has metal in it, it will make that swirl look. If that is the case, that is quite a bit of metal. Have you checked to make sure the piston does move up and down?

Is the coolant green? Does it have any bubbles when it runs? Just some thoughts.

[SarahLovesHer300zx]

Check your coolant. It looks like coolant/water from the picture, but since it has ran it should look like a milkshake, not swirl.

If the oil has metal in it, it will make that swirl look. If that is the case, that is quite a bit of metal. Have you checked to make sure the piston does move up and down?

Is the coolant green? Does it have any bubbles when it runs? Just some thoughts.

I thought it was coolant too, but expected it to be lighter/milkier. Whatever it is, it has settled to the bottom since sitting in the drain pan. All I see now is the blackness of the oil.

I'm doing the leak down test tomorrow, and I'll have to get the piston to TDC, so we'll see if it moves then.

I noticed a coolant leak while I was under there, and it was bright green. I haven't ran the car long at all, so I don't know if it bubbles. Is it going to hurt it to run it with the cylinder not working? I just don't want to risk breaking or messing up anything else lol The coil pack is unplugged and I'm pretty sure the injector is too, I'll have to double check in the morning.

[nissanfreak12]

If it settled to the bottom, its metal, not coolant. Coolant will stay the milkshake color, almost like a mud color.

Try turning the engine by hand first, several times. If there is no binding, go ahead and start it but make sure you unplug the injector, gas in oil is not good for it either. The downfall that if the metal shavings are small enough it may go into the bearings, and could damage those. But who is to say that it already didn't.

It sounds like either way you are going to have to pull the engine, If you can take oil pan off, do that. It should tell you what is in the oil, hopefully.

[evildky]

Any metal, no matter how small is too big to be in your oil, it means something is self destructing.

[SarahLovesHer300zx]

Ok, I'm doing the leak down test today or tomorrow, to find TDC on #5 I'm using a piston stop tool and just want to verify how to use it.

Every YouTube video I see and how-to I read says turn the crank CW until it stops and mark it, then CCW and mark it, and the middle of those two marks is TDC. However my husband is saying never turn a motor backwards (CCW in this case right?).

Is this a correct method to finding TDC, or do any of you have a better method?

[evildky]

You can spin a motor backward, they say not to because you could loosen your crank pulley in the process, just be sure to re torque the crank pulley when done. A dial gauge is better than a stop as you can actually find the dwell at the top.

You already know you have no compression in that cylinder so the leakdown test won't tell you much, You can pressurize the cooling system to see if you have a leak from a coolant passage. The head is gonna have to come off anyhow, so I'd just pull the plenum and cam covers and rotate the engine until the cam lobes for that cylinder are both on their base circle.

[SarahLovesHer300zx]

I'm actually doubting a lot of the information I was given about the car, given some half-assery I've seen under the hood. So I am performing a compression test on all 6 cylinders just so I can verify what was meant when the previous owner said "no compression" and get a good baseline to start to figure out why.

I depressurized the fuel system per the FSM, and when I went to unplug the crank angle sensor it moved. I read this thread cas-crank-angle-sensor-trouble-need-help-t533823.html already, so it looks like I'll have to reset the timing when I get the bad cylinder figured out.

[nissanfreak12]

Since the engine is cold your compression numbers will be low, but should still have a number. I honestly just used a long screw driver to find TDC. It doesn't have to be exact, just at its farthest point up.

[SarahLovesHer300zx]

I had some time this weekend to tinker with the car.

We did a compression test and leak down test for verification. Every cylinder was within 10PSI of each other except 5, which indeed had 0 PSI. Leak down test confirmed that air was escaping from the exhaust side.

I've got the exhaust valve cover off on that side. Now what?

Should I check the lifters as described in this thread http://www.twinturbo.net/net/viewmsg.as ... _id=917346 (Short version: squeeze it, if it bottoms out it's bad)

or get a camera in the cylinder to check how the valves are closing (or not)?

I've been reading the service manual but haven't found a "if this, then this" to tell me what to do next.

[nissanfreak12]

Basically if the air was escaping out the exhaust side, the valve is not closing. Chances are its a bent valve. Have you actually checked if the piston moves up and down? Just stick something in there and rotate the engine by hand, see how it moves.

If you can geta a scope in there, that would be best, but if the valves are not closing, that head needs to come off. HOpefully the piston is ok, but you still need to find out what is causing the metal in the oil. That case I would also take off the oil pan.

[SarahLovesHer300zx]

The piston does move up and down, we had to get it to TDC for the leak down test.

I'll scope it today, check condition of the top of the piston, see if it had struck the valves at all and look around.

The oil pan gasket is shot, so I plan on dropping that soon too.

[evildky]

Pull the head. You confirmed a leak through the exhaust, so you have a bent valve or a broken valve seat. either way the head has to come off and go to a machine shop.