~From: The 12 Port NEWS 1981~

By: Charlie Baker
This month I'd like to get started on the bottom end of the GMC engine. I am going to deal with the oiling system of these engines.

There is no doubt that the GMC engine oiling system is one of the best designed systems bar none. Much has been written about how to get the most out of it with the least amount of effort. Much of the great GMC racing success in the past can be attributed to the fine design of this oiling system, it is very simple and it flat works.

California Bill Fisher was the first to state in his speed manual for the GMC, that a full flow modification to this engine was like a low-cost insurance policy. I want to pass this on to you in this column, the complete detailed procedure for this modification. For an hour's time and less then a dollar, this modification is a must for the street and of equal value for racing on the dirt tracks.

I'm sure you guys all understand the benefits of filtered oil in any type of internal combustion engine. Space here won't allow me to get into these benefits now but it stands to reason that every American engine produced in the last 25 years has an oil filtering system from the factory. So the reasons are obvious. One thing the GMC engine designers finally got wise to is the filtering of this oil. Early GMC engines up to 1955 where issued without any oil filtering device at all. They left this to the detergent oil that was quite popular at the time. This by today's standards, is quite archaic.

In addition, the 1946 Chrysler "full-flow" oil filter adapted to the GMC motor is really a thing of the past. These filter canisters can still be found, but the oil filter element itself can be mighty scarce. Premium prices are usually paid for these elements when and if they can be found. A more simple and less expensive system can be set up with a few choice pieces of readily available equipment on the market today. Trans-Dapt. and Offenhauser offer a remote oil filter mounting kit originally designed for engine swaps where the oil filter can get in the way of steering and other obstructions.


This remote adapter is really a time  saver and when it comes to changing oil filters it can be mounted anywhere you want. The only restricting feature is the length of the oil lines to and from the unit (by the way, it has 3/8 NPT outlets.) A super plus feature of this remote adapter is that it takes readily available spin-on filters. These new filters have very minimal restrictions to the oil flow and a minimum oil pressure drop through them. These adaptors also make changing oil filters a fairly clean routine job. They are a much better plan of attack on the oiling system than the '47 Chrysler units.

The accompanying drawing (figure 1) shows just how easy this modification is. First, remove the pipe plug from the existing 3/8 NPT hole in the side of the block. (A) Secondly, thread the existing vertical hole (B) with a 9/16 X 18 tap. Insert a plug made from 9/16 X 18 cap screw, 1/2 inch long. Saw a screwdriver slot for inserting this plug and Lock Tite threads. The final step in this simple modification is to drill and tap a hole in the side of the block for the outlet hose. Use a 19/32" drill and tap for 3/8 NPT threads. Drill this hole exactly 1 1/8" up from the bottom of the block. (C) There you have it, low cost insurance indeed!