High Oil Pressure

[Captain Obvious]

I guess it's possible this one could be a turbo oil pump by mistake.

 

Been a while since I messed with oil pumps, but IIRC, the turbo oil pump is longer to accommodate internally longer rotor gears. In other words, you might be able to tell that from the outside?

[Zed Head]

Wouldn't matter what gear the tranny was in. The fault was upstream from there.

You're right I was trying to reason out why Diseazd thought the throwout bearing was locking the engine.  Still doesn't add up.  He says everything is fine.

 

Now if the throwout bearing was jammed or cocked on to the nose of the transmission,and "welded" to the pressure plate fingers, that would lock the engine.  That's downstream though...

 

Yours works too, if the "ears" jam on the clutch fork.

 

It all sounds scary though.  Better check the transmission case around the fork and the nose that the collar rides on.  The noses have been known to break, especially the aluminum ones.

Edited March 15, 2015 by Zed Head

[Mark Maras]

I've seen the wrong TO bearing (too long) in a 71 Datsun pick-up run with no noise until the TO bearing wore a hole in the diaphram. He got better than 20 K miles out of that TO bearing. Surprisingly, it didn't weld itself.

[Captain Obvious]

Still doesn't add up.  He says everything is fine.

 

Haha! He said the motor is fine. There are clearly some clutch parts that are completely FUBAR, but the rest of the motor is fine.

 

Frankly I'm surprised there wasn't a more spectacular failure with shrapnel.

 

I'm guessing it was squealing like a pig and he shut the motor down. The front of the throw out bearing and a bunch of pressure plate fingers were all liquidy hit in spots from the friction and once it stopped turning, everything welded together before they cooled

[Zed Head]

Hairs are splittin' here.  He said the motor was locked up initally,   He took it all the way apart because he was looking for internal damage.  He didn't find any.  So the remaining question is - what, exactly, stopped the engine from turning, and, my point, is there more damage to be found?  A starter can pump out a lot of torque (I moved my car up a driveway incline that was too steep for me to push it, using the starter in first gear), and it has a lot of leverage on something with the radius of the throwout collar.

 

That's all I'm saying - if it's not the engine internals that caused the lockup, what did?  Is there something being overlooked, that still needs fixing?

[Diseazd]

Bingo Captain......You are dead on.....the collar, immovable throw out bearing and clutch finger became welded together as one piece. One piece not designed to rotate. That explains why the starter wouldn't turn the engine over.....the ears on the collar were lodged against the clutch fork. The squealing noise before shutdown was the ball bearings giving it up. When it finally welded, I was merely backing out of the garage (0 miles per hour) and whamo, it just stalled out. There was no damage to anything since there was no momentum. Oh, the throw out bearing was blue and black and there was a nice groove high up on the clutch fingers, but no other damage what so ever. Good job boys.....I feel better now that the mystery is solved.....or at least I hope it is.

Edited March 15, 2015 by Diseazd

[Diseazd]

BTW.......The tranny, collar, clutch fork along with a new throw out bearing clutch pressure plate are doing fine in the L28 in the car as we speak.

[Captain Obvious]

Well, considering the alternatives, that's awesome news! I am surprised that the failure was enough to actually stall the motor while it was running. I was figuring that it was straining and squealing, but finally locked up good while stationary. Also surprised there wasn't shrapnel. Anyway, awesome news.

 

So I went back to the very beginning of the thread where you were questioning your oil pressure numbers: "My 71 240Z (L24engine) runs 75 lbs. of oil pressure at 3000 rpm."

 

Don't know why I didn't mention it before, but I'm not sure I would have ever even called that a problem. You get 75 lbs at 3000 RPM (when hot, I assume)? So what? Sounds like a healthy bottom end to me. I assume it drops off at idle?

I've seen the "10 psi for each 1000 RPM" tossed about, but my understanding was that was a minimum before you needed to do something about it. Not what you could expect on a new healthy motor. Frankly, if I had a freshly rebuilt bottom end and only got 30 psi at 3000 RPM, I'd be disappointed.

[Diseazd]

You're right Captain......I'm not going to worry about the oil pressure. I ordered a new pump (cheap insurance), but everything in the bottom end and top end look perfect. Sometimes you think something that turns out completely wrong.......I was convinced the squealing was my main bearings going out.....especially when the engine locked up. The probability of two things going wrong at exactly the same time are probably statistically nearly impossible. Thanks for everyone's input......I hope this was the problem.....nothing else that I can think of that I haven't checked.

[240260280z]

The 77 FSM states oil pressure 50-60psi @ 2000 rpm (warm).

[Diseazd]

Sad news. Strange problem. What does the oil filter contents look like? Open it up and have a look. I can only guess that something in the filter went down stream and blocked the main passage to the bearings.

BTW Blue.......I sawed open the oil filter......clean as a whistle.

[Captain Obvious]

The 77 FSM states oil pressure 50-60psi @ 2000 rpm (warm).

 

And later in the lube section it says that the pressure relief valve in the pump limits the pressure at 80psi. With those data points, I consider 70 psi at 3K warm to be just fine for an engine with a well done fresh bottom end.

 

Now, if the pressure was like 90 psi at idle when warm, then I'd be a little more concerned about the bearing clearances, but this one sounds like a non-problem.

 

Diseazd, I know you're not worried anymore, but if you do another turn around and decide you're worried about it again, I'd be happy to trade for my engine!