1966 Oil Pump ID Help

[Ed R.]

I have an oil pump out of a 66 327/300 with the following numbers:

GM40 8704180 and GM87 3732798.

I've done searches here and that other forum but couldn't find anything to confirm it this is original or not. Any help confirming originality is appreciated.

My other/real question is, is there a way to tell what the oil relief spring would be for this pump. This engine was rebuilt with a new oil pump that pegs my oil gauge at 60#. I'm thinking of pulling the pan and replacing the spring with the spring for the old pump if would get the pressure down.

Thoughts. Suggestions?

Thanks

[Joe L.]

Re: 1966 Oil Pump ID Help

I have an oil pump out of a 66 327/300 with the following numbers:

GM40 8704180 and GM87 3732798.

I've done searches here and that other forum but couldn't find anything to confirm it this is original or not. Any help confirming originality is appreciated.

My other/real question is, is there a way to tell what the oil relief spring would be for this pump. This engine was rebuilt with a new oil pump that pegs my oil gauge at 60#. I'm thinking of pulling the pan and replacing the spring with the spring for the old pump if would get the pressure down.

Thoughts. Suggestions?

Thanks

Ed------


The first number is 3704180 and is the number for the cover. The second number for the body of the pump is either 3732798 or 3732796 (the last digit is notoriously difficult to read but we are talking about the same part, either way). These are the casting numbers for the original oil pump used for small blocks for 1959-82. The part number for the assembly (which appears nowhere on the pump) was GM #3764547. Of course, this could be a replacement since this exact same pump was available in SERVICE for MANY years.

Unfortunately, the same pump body and cover were used for both the standard pressure and the high pressure standard volume pumps. Only standard volume pumps were EVER used in PRODUCTION for any 1955-82 Corvette small block. The only difference between the standard pressure and high pressure pumps was the installed relief spring. Your application used a standard pressure spring. In another recent post I describe the configuration (free length and coil count) for this spring.

[Ed R.]

Re: 1966 Oil Pump ID Help

Thanks Joe. I was following that thread and that's what got me to thinking. I'll review that but, you gave the answer I needed.

[Joe L.]

Re: 1966 Oil Pump ID Help

Thanks Joe. I was following that thread and that's what got me to thinking. I'll review that but, you gave the answer I needed.

Ed-----

You could just remove the spring and inspect it. The high pressure spring has a stripe of white paint. Of course, by now a lot of that might be gone but usually there will be some vestige of it if it was ever there. If not, you have a standard pressure spring which had no paint stripe.

By the way, are you saying that the pump you described is not the one that's actually installed in the engine now? If so, you may have had a pump installed at rebuild which is a high pressure AND high volume pump (all high volume pumps are also high pressure; standard volume pumps may be either standard pressure or high pressure). Some rebuilders just can't resist the inclination to install high volume/high pressure pumps when they do rebuilds. You absolutely do not want or need a high volume pump. So, if you have a high volume pump installed, you should change out the entire pump and not just the spring.

[Ed R.]

Re: 1966 Oil Pump ID Help

Joe,

At rebuild a new oil pump was installed. The builder assured me he only installs standard pumps. Is there a way to determine if a high pressure/high volume pump is installed without pulling pan? Currently at cold startup the gauge reads 60. After warm up it drops to about 50#. As soon as I hit the gas the gauge goes right back to 60# plus.

[Joe L.]

Re: 1966 Oil Pump ID Help

Joe,

At rebuild a new oil pump was installed. The builder assured me he only installs standard pumps. Is there a way to determine if a high pressure/high volume pump is installed without pulling pan? Currently at cold startup the gauge reads 60. After warm up it drops to about 50#. As soon as I hit the gas the gauge goes right back to 60# plus.

Ed------


Based on your oil pressure, I'd say that you don't even have to pull the pan to determine that you have a high pressure spring installed. Of course, you'd need to pull the pan anyway to change the spring. Removing the oil pan on a Corvette is not too difficult, though.

One thing you could do first is to confirm that your oil pressure gauge is giving you an accurate reading. To do this install a known accurate test gauge. Remove the oil pressure gauge fitting from the block and install the test gauge with a short length of appropriate flexible line. Very simple.

[Ed R.]

Re: 1966 Oil Pump ID Help

I agree Joe. I was thinking the same thing. Something to do this winter.

I really appreciate you input.