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#1349478 Tue Mar 10 2020 05:51 PM
Joined: Feb 2020
Posts: 16
B
Grease Junkie
In a previous post I reported a problem with contact between the oil pump pick up tube and #5 connecting rod in my 57 chevy 235.  Turned out the tube was bent.  I dropped the bottom plate to remove the bent pipe and the gasket was damaged in the process.  Now, it appears, GM #838451 has been discontinued and none of the local dealers or parts stores still stock it. My online search so far is also coming up empty.  From reviewing old threads on this subject, this has been a problem for a number of years now.  Has anyone out there found a source for this elusive part, outside of what comes with a new pump or rebuild kit?

Some of the old posts suggest making a DIY gasket from a piece of paper, being careful to find paper as close as possible to .009" thick.  Is this a safe option?


1949 3600 w/ 57 235
Joined: Feb 2004
Posts: 24,576
H
Kettle Custodian (pot stirrer)
The pump will never miss it if the gasket isn't included in the assembly. I've run plenty of oil pumps without a gasket between the pump housing and the base. Just be sure there's a little vertical clearance between the gears and the base plate to allow for expansion due to heat. If you choose to make a gasket, I'd suggest using a piece of soft aluminum like a Coke can rather than paper. You really don't want a blowout with full oil pressure against the gasket.
Jerry


"Freedom's just another word for nothing left to lose"
Kris Kristofferson

Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!

WAG MORE- - - - - -BARK LESS!
Joined: Dec 2017
Posts: 1,132
D
'Bolter
Send me a PM. I probably have one you can have. I almost never throw anything out from the gasket kits, even if I don't use it.


Mike
Dragsix #1349483 Tue Mar 10 2020 06:57 PM
Joined: Jul 2007
Posts: 530
'
Shop Shark
You can buy a GM NOS oil pump gasket GM # 838451

PIC

https://i.postimg.cc/mkQTns22/Oil-Pump-Gasket-GM-838451.jpg

Availabe @

Friesen's Chevrolet
Sutton , Nebraska
phone : 402 - 773 - 5538

Friesen's has ( 1 ) in stock


Dan's GM Obsolete
Chinook , Montana
phone : 406 - 357 - 2615

Dan's has ( 8 ) in stock


George
'54 3600

Last edited by '54 3600; Wed Mar 11 2020 11:54 AM. Reason: add

1954 3600
Joined: Feb 2020
Posts: 16
B
Grease Junkie
Thanks much for the responses. Just got off the phone with Dan's GM Obsolete and have the gasket on its way.

Steve


1949 3600 w/ 57 235
Joined: Dec 2008
Posts: 1,707
P
'Bolter
The late pumps I've examined show the pump gears below and almost flush with the end of the gear cavity, and a .009" gasket (added to the negative clearance) is wayyy too thick unless your gears extend above the gear cavity.
Correct gear end play against the cover (with the gasket compressed): .002"-.0025".

panic #1349565 Wed Mar 11 2020 03:31 PM
Joined: Feb 2020
Posts: 16
B
Grease Junkie
Originally Posted by panic
The late pumps I've examined show the pump gears below and almost flush with the end of the gear cavity, and a .009" gasket (added to the negative clearance) is wayyy too thick unless your gears extend above the gear cavity.
Correct gear end play against the cover (with the gasket compressed): .002"-.0025".


Thanks for the heads-up! I'll be checking clearances while I wait for the stock gasket to arrive. The existing pump did have a gasket but it must have been installed with sealant, so no way to know how thick it was. If I need a thinner gasket I can at least use the stock gasket as a template. If the gears are indeed recessed in the pump body, what kind of sealant should I use to install without any gasket?

Thanks in advance
Steve


1949 3600 w/ 57 235
Joined: Feb 2004
Posts: 24,576
H
Kettle Custodian (pot stirrer)
NO SEALANT! If necessary, use a piece of plate glass and 1000 grit wet/dry sandpaper and water to polish the mating surfaces of the pump housing and the base plate. I still haven't figured out the necessity for a gasket on a part that seals perfectly well without one, and if there's a seep leak, the oil just drops right back into the oil pan. If the pump has such a low volume output it can't can't compensate for a few drops of leakage, it doesn't need to be installed on the engine.
Jerry


"Freedom's just another word for nothing left to lose"
Kris Kristofferson

Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!

WAG MORE- - - - - -BARK LESS!
Joined: Dec 2017
Posts: 1,132
D
'Bolter
The gasket is important for the hydraulic lifter folks. The idea was to keep air from entering through the mating surface and contributing to aeration of the oil and air in the lifters. Same for using just a bit of thread lock on the pickup tube. Mechanical lifter motors, this is not so much of an issue. That being said, panic is quite right about using a gasket or not. Some pumps came with gaskets and some did not so the end clearances will be different between the two types of pumps. Thus, installing a gasket on a pump that did not have one originally might not be the best move. Conversely, not using one on a pump that did is also probably not the right move. And then there is the quandary of installing a thicker gasket where a thinner gasket had been previously installed.

With the cost of machine work and parts for these motors, it seems to me that maybe the better play would be to source a new pump and pickup rather then risk a potential failure of the motor down the road. I see NOS or RNOS pumps on ebay all the time for less then 100.

Last edited by Dragsix; Wed Mar 11 2020 05:54 PM.

Mike
Joined: Dec 2008
Posts: 1,707
P
'Bolter
Even though the specified clearance range is very small, any more room allows pressure to bleed away under the gears rather than being forced into the high pressure port. This will not affect maximum pressure above cruising speed, but it's a substantial loss at idle when oil volume is minimal.

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