another 'whats my problem' question...

[sclay115]

if you recall i was having trouble with my Z burning crazy oil and smoking something fierce, and after putting new valve seals, and a new head gasket on it, it's back at it. i ran the compression test again, with the new HG, same results as before. the only thing i didn't do is check the head for level, i had no means to, and well, i needed the car back(silly i know). but when the motor was apart, i looked at the pistons/cylinder walls, the pistons showed no signs of problems, and by problems i mean that they were uniform in color and buildup. i heard once that bad rings can leave a clean ring around the outside of the piston, true? maybe, who knows, but either way, they were uniform in buildup. the cylinder walls still showed signs of the previous hone job, and were quite shiny i might add, which i've read up on is a sign of a poor break in job. so while doing the latest compression test, i added oil to the cylinders(car was at operating temp) and noticed no change in the readings from when i did it dry. so what gives? am i just the victim of a poor ring seat job from the previous owner? or should i look into something more? i was thinking i would just go ahead and put rings in the motor, but i dont want to waste my time trying to save something that isn't worth saving. the head/valves looked pretty good when i had the head off, some carbon buildup, but nothing out of the ordinary. my plan was to just run this motor until she gave up, while building another motor with my own devious plans, so i'm trying to avoid spending huge money on the motor that is in there. so should i just bite the bullet, throw rings in there, rehone the cylinder walls and give it a shot? or should i be concerned about more drastic problems that would end up costing me an arm in a leg?

steve

btw, yah i like to write novel sized posts.

[Arne]

Have you looked into the PCV system?

[Ed]

I would think the PCV system too. Maybe the rings are bad or maybe they were installed wrong. Which is increasing the pressure in the crankcase. Causing oil to travel through the PCV system and burning up in the combustion chamber.

Why don't you try disconnecting the PCV system. Take the hose that goes from the tube on the block (under #1 exhaust) and disconnect it. Buy one of those small breather filters from your auto parts store that will fit on the tube. This will allow the crankcase to still breath but no oil will be force fed into the intake system. Check the filter often to see if it's dripping oil.

[kenz240z]

Hmm, you said you added a little oil to the cylinders, re-tested compression, and got the same readings... To me that would indicate valve trouble, either worn valve guides or bad valve stem seals. If the rings are going bad, adding oil will usually raise the compression.

[sclay115]

Hmm, you said you added a little oil to the cylinders, re-tested compression, and got the same readings... To me that would indicate valve trouble, either worn valve guides or bad valve stem seals. If the rings are going bad, adding oil will usually raise the compression.

that was one of my concerns, as i really dont have any experience changing valve guides, but i was reading up that the shiny cylinder walls are a sign of poor break in, could be wrong. but as per the PCV system, anybody have any pictures of that? because i have that pipe right there, but it's not connected to anything! :eek: where is it supposed to go?

steve

[sblake01]

If you mean the pipe that's in the block just ahead of the exhaust maniford, a hose goes from there to the pcv valve on the bottom of the intake manifold. Now I'm talking about a 280Z since that's what I have but the 240 is similar as shown in this scan.

[sclay115]

If you mean the pipe that's in the block just ahead of the exhaust maniford, a hose goes from there to the pcv valve on the bottom of the intake manifold. Now I'm talking about a 280Z since that's what I have but the 240 is similar as shown in this scan.

ok so i have a TWM manifold with webers...where am i 'supposed' to go with the pcv hose? as i mentioned, mine is attached to nothing, nor is the deal on the valve cover. the one on the valve cover has a breather on it, but that's it...

steve

edit: and there is no way that could be causing the heavy smoking could it? even if it was the problem?

[sblake01]

Sounds like you have no pcv valve then. If there's no provision on your intake for one I don't know where it would go. My car is stock (basically) so it has the stock pcv setup. Since yours is not hooked up, there's no way it could be forcing oil into the combustion chamber as surmised above. Maybe someone else with experience with aftermarket manifolds will chime in.

[Ed]

edit: and there is no way that could be causing the heavy smoking could it? even if it was the problem?

Disregard my last post. I thought you were someone else. You might have bad valve stem seals.

[sclay115]

Disregard my last post. I thought you were someone else. You might have bad valve stem seals.

the valve stem seals are brand new, i just did those when i got the car(original idea of what would fix it..) but what about the guides themselves? maybe?

steve

[skyline_stu]

Geez, you'd want to have bad guides for such low compression. It's a rather large leakage path by the sounds of it.

May I suggest you try a leakage test. this will pin point the leak nice and fast. easy to do.. you'll need a few things though.

1. an old spark plug

2. a section of 10mm or 3/8 tube about 15cm long (6")

3. a fitting to suit your air compressor line.

4. Silver solder AND brazing rod. flux for both too

5. Access to an oxy torch

6. An air compressor

7. a 2 foot length of 1/2" hose.

get an old spark plug and break out all the ceramic. don't damage the threads or gasket on the end though. Find someone with an oxy torch. have them braze in the tube into the threaded spark plus remains. grind off the ground electrode. silver braze in the air line fitting onto the top of the tube. silver solder stops brass fittings from melting when joining. if it's steel, use brazing rod. will look like this when done

_________________________:---:______

==== / ///////]

==== \ _________________________ _//////_] <- Old s/plug

:---:

/\

Air line fitting

sorry about rough drawing.

Procedure :- remove all spark plugs to make engine easy to turn over. remove tappet cover and turn your motor over until both cam lobes on cyl 1 point UP. put your handbrake on and chock the wheels. put the car into 4th or 5th gear and release the clutch.(an auto would need the inspection cover off and a screwdriver to lock the motor. This will stop the motor turning over. fit your air delivery adaptor into plug #1. apply 30psi pressure. Use the 1/2" hose like a stethescope and listen to

1. Exhaust pipe

2. Open the throttle and listen down the carby or throttle butterfly

3. Poke the hose down the front timing cover.

If you hear air rushing air

@1 - burnt/damaged/incorrect valve clearance on EXHAUST

@2 - as above, but INTAKE valve

@3 - leakage past piston/rings

This is a hard and fast method. If you don't have an air compressor, you can use a tyre as a storage vessel and fill it up at the local servo. adapt the hose as necessary..

Hope this helps Stu

[sclay115]

Geez, you'd want to have bad guides for such low compression. It's a rather large leakage path by the sounds of it.

May I suggest you try a leakage test. this will pin point the leak nice and fast. easy to do.. you'll need a few things though.

1. an old spark plug

2. a section of 10mm or 3/8 tube about 15cm long (6")

3. a fitting to suit your air compressor line.

4. Silver solder AND brazing rod. flux for both too

5. Access to an oxy torch

6. An air compressor

7. a 2 foot length of 1/2" hose.

get an old spark plug and break out all the ceramic. don't damage the threads or gasket on the end though. Find someone with an oxy torch. have them braze in the tube into the threaded spark plus remains. grind off the ground electrode. silver braze in the air line fitting onto the top of the tube. silver solder stops brass fittings from melting when joining. if it's steel, use brazing rod. will look like this when done

_________________________:---:______

==== / ///////]

==== \ _________________________ _//////_] <- Old s/plug

:---:

/\

Air line fitting

sorry about rough drawing.

Procedure :- remove all spark plugs to make engine easy to turn over. remove tappet cover and turn your motor over until both cam lobes on cyl 1 point UP. put your handbrake on and chock the wheels. put the car into 4th or 5th gear and release the clutch.(an auto would need the inspection cover off and a screwdriver to lock the motor. This will stop the motor turning over. fit your air delivery adaptor into plug #1. apply 30psi pressure. Use the 1/2" hose like a stethescope and listen to

1. Exhaust pipe

2. Open the throttle and listen down the carby or throttle butterfly

3. Poke the hose down the front timing cover.

If you hear air rushing air

@1 - burnt/damaged/incorrect valve clearance on EXHAUST

@2 - as above, but INTAKE valve

@3 - leakage past piston/rings

This is a hard and fast method. If you don't have an air compressor, you can use a tyre as a storage vessel and fill it up at the local servo. adapt the hose as necessary..

Hope this helps Stu

will this also check for worn guides? is there really any way to check for that? other than removing the head and checking the wear by checking the diameter? i was thinking i should just get a new cylinder head as well, but i dont want to spend the money on it if i just need rings...btw, thanks for the awesome help, and the great diagram i really appreciate it.