Oil pressure

[Dave Vince]

No oil pressure 95 Z-28. Removed oil pump drive, and re installed.

Dave Vince dvince@tampabay.rr.com

[Joe 1320]

No oil pressure 95 Z-28. Removed oil pump drive, and re installed.

Dave Vince dvince@tampabay.rr.com

Pump gears may have out of spec clearance, bearing clearances may be out of spec, did you check pressure with a mechanical gauge or just relying on the factory in dash gauge? If you suspected the pump, why didn't you replace it?

[Dave Vince]

Oil pressure

Thanks for the reply, this was a complete rebuild. Pump was checked by dissasembly, and priming the motor before the intake was put on. Oil flowed freely to all visible parts. We believe the problem is something we don't know about the pump drive. It is mounted solidly to its base, but there was a space below the mounting arm. There was no space between the block and pump drive. I am very familiar with small and BB chevys and have been building and running them for over 40 years. This is the first LT, and I believe there may be something I don't know about this drive. The pump shaft was moving when we turned the motor.

[fastTa]

The oil pump drive stub shaft is held in place by a very flimsy bracket. Any bit of abnormal cam shaft movement and it can make quick rubbish of the stub shaft in no time.

Was there oil in your filter? Did you verify oil pressure with a mechanical gauge next to the filter mount?

Forgot to add one thing. The stock oil pump driveshaft (not stub shaft) uses weak plastic couplers. Lots of people tend to use a ARP or Melling hardened driveshaft with metal couplers.

[Injuneer]

Then there's that little ball that's pressed into the end of the oil gallery at the rear main. Did you remember to replace it?

[Dave Vince]

Reply

Have checked with all the locals and no one knows anything on this one. Thanks for any replies. The oil pump and all in the block and pan have to be ok, as we drove the oil pump, as we always do with an external drive made to do this to check for oil pressure etc. I can generate 20-30 lbs oil pressure in this way. This worked fine, and assembly was continued. The oil pump drive was then installed, and checked for rotation. This checked ok, but we only turned the crank enough to see if the shaft was turning. The problem occured when the engine was started, and there was no pressure. We are pulling the intake off, and rechecking the drive.

[Dave Vince]

Found problem

Pulled the intake off, and found the problem. The drive tricked me, and I should have known better. As with all Small and Big block chevys the tang in the bottom of the distributor must drop down into the oil pump shaft. To accomplish this you must rotate the motor to make it drop into the shaft. What fooled me is that it looked like it was sitting in the proper spot on top of the block, but it actually drops down into the block. Also watching the shaft turn is not an indicator as it will turn from the pressure of the tang sitting on top of the oil pump shaft. However as soon as the oil puts pressure on it it slips. I hope my goof helps someone out there to not make the same mistake. An easy indicator to find out if it is in properly is the arm that holds the pump drive should be flat on the block, not sitting up a bit.

[Rob B (shoebox)]

... An easy indicator to find out if it is in properly is the arm that holds the pump drive should be flat on the block, not sitting up a bit.

Yeah, same as when you put a conventional rear mount distributor in and spin the engine around until it drops onto the shaft. Glad you found it.