63 340 HP oil pump

[Richard S.]

I am looking for information on rebuilding my oil pump (or finding a replacement) for my 63 340 HP vett. Any information appreciated

[Duke W.]

Re: 63 340 HP oil pump

It's easy to inspect and rebuild as long as it has never ingested a bunch of debris. Remove the four screws, cover, and gears. Inspect the gears and housing for damage. Any wear on the endplate can be dress down with some wet 220-400 paper on a flat surface. It's also a good idea to inspect end play. Dress down the housing and one gear to acheive about two thou.

Normal 340 HP hot oil pressure is 40-45 psi at 2000, and as long as it produced this pressure prior to disassembly there is no need to replace the spring.

There are no gaskets... either between the endplate and pump body or pump body to block, so if all is well it's no more than a little bit of time

Most used oil pumps are perfectly serviceable, but usually get replace..., most of the time with a "high volume" pump that generates too much pressure.

Don't drink the Koolaid.

Duke

[Richard S.]

Re: 63 340 HP oil pump

Thank you for the detail. Since I would be removing the pump I would like to replace the spring. Any thoughts on where I might find one?
Rich

[Joe L.]

Re: 63 340 HP oil pump

Thank you for the detail. Since I would be removing the pump I would like to replace the spring. Any thoughts on where I might find one?
Rich

Rich------


Real easy.

1963 used two different oil pumps but the only difference between them was the installed oil pressure relief spring. You can determine which one you have by simply looking at your oil pressure gauge.

If the gauge shows a maximum oil pressure of 60 PSI, use spring GM #3814903

If the gauge shows a maximum oil pressure of 80 PSI, use spring GM #3848911

Both springs are still available from GM at a modest cost.

[Richard S.]

Re: 63 340 HP oil pump

Thanks Joe. I had no idea that the spring would still be available or appropriate part number. But also, did not realize that there was an 80 psi unit. I had not seen one of these.
Thanks
Rich

[Duke W.]

Re: 63 340 HP oil pump

There's really no reason to replace the spring as I said in my above post. Only very late 340/360 HP engines would have a 60 psi spring and they would also have an 80 psi dash gage.

Duke

[Gerald C.]

Re: 63 340 HP oil pump

Joe,

Can you tell me what color spring is Part # 3814903 if you can remember?

Thanks

[Gary B.]

Re: 63 340 HP oil pump

Several others have previously reported in the archives, and I agree, that the GM 903 spring is not color coded.

Gary

[Joe L.]

Re: 63 340 HP oil pump

Joe,

Can you tell me what color spring is Part # 3814903 if you can remember?

Thanks

Gerald------


Gary is correct; the 3814903 spring is not color coded. However, it has 21 coils and is 2-7/32" free length.

[Gary B.]

Re: 63 340 HP oil pump

Joe,

Can you tell me what color spring is Part # 3814903 if you can remember?

Thanks

Gerald,

If you want to find out more about GM 3814903, take a look at this thread:

https://www.forums.ncrs.org/showthread.php?131437-Oil-pump-pressure-relief-springs-pegging-the-60-psi-gage-on-SB-C1-C2

There is a link there to a PDF I created that has an engineering comparison of the 3814903 spring and several Melling springs that some people have used to substitute for the 3814903 spring. Which can and does lead to excessively high oil pressures. In my opinion, there simply is no equivalent to GM 3814903 in terms of the stiffness and force/deflection specifications. Which ultimately leads to oil pressure differences if using an aftermarket spring instead of GM 3814903.

Gary