The Stovebolt Site Forums The Shop Area Engine Shop Chevy 261: Do I need an oil filter?

Hi All, new to the site and to the older inline 6. I have a 1946 Chevy 3100 truck project that came with a running engine and shifting transmission. When I researched the casting numbers on the block(3769925) and the head(3836850) I see that I have a 261 cid manufactured between 1958 and 1962 if all the charts are correct. Further research shows that the 261 has a fully pressurized oil system and should have an oil filter on it. Long story short, this engine doesn't have an oil filter on it but has a 1/2 NPY fitting to the right of the exhaust(oil filter return) that is oily and has the ports and dowel hole left of the exhaust(full pressure to the filter) but doesn't look like they have been used. Looks like the engine has been running this way for awhile(by the looks of the plug being eroded) so am I okay to keep running it or will it trash the engine because of lack of oil? I will try to attached some pictures. Any help is appreciated. Thanks

The port with a dowel in it (red arrow on your pic attached) is the vacuum port in the intake manifold. That would be routed to a vacuum wiper motor (assuming you have one), not an oil filter.
The port indicated by the yellow arrow is the pressure port for the gauge in the instrument panel and a filter if installed.
The port indicated by the green arrow appears to be the return port for an oil filter, but plugged with a recessed plug that someone tried to remove (unsuccessfully) with pliers or a pipe wrench.

But a filter connected to those two oil ports would be a bypass filter, just filtering a portion of the oil being sent to the engine. So running without a filter wouldn't kill the engine. There are lots of engines that are running around without filters. You just have to change the oil on a regular basis to drain the crud out.

Welcome to the Stovebolt forums.
You should go over to the Welcome Centre and tell us a bit about yourself and your truck (how you came to own it, etc.) Post pics of the truck as well.

Thanks for the response.
The vacuum wipers were disconnected by the previous owner. Thanks for the heads-up on the dowel port use. Was wondering where they were to be connected.
Being that the engine is much newer than the truck, I wasn't sure its original oil filter configuration. The serial number on the block flat by the distributor is not there. The surface is ground flat with no paint. Thinking that may have been done during a rebuild or the install into the truck. Not sure.
If I wanted to install an oil filter, it would need the green arrow port opened up by drilling it out. Guess that will need to wait for the next rebuild.
Thanks again klhansen.

No Numbers on the block usually indicates that you have a GM manufactured replacement engine. They did not stamp those.

If you scrape the crud out of the hole just above the green arrow in the third pic you will find the end of a dowel pin just below the block casting. If that pin was driven in at the factory it would have had large lines going to a full flow filter in canister mounted to the intake manifold.
This engine was not set up for flow flow filter. If you have the pin driven in you Must have external line to bring oil to the galley.

You can always just not install a oil filter a change your oil more often. Thats the way they did it when these trucks came off the factory floor. The oil filter was an option.

Was there a high-pressure 261 that did not originally come with an oil filter?
(a full-flow filter?)

Yes. I have a 55 1st design 261 (high mount coolant pump) that is not set up for filter, no provision for one.
All later 261 have the ports, the determining factor is if the pin (above the pipe plug the green arrow is pointed to in last pic) is driven in it blocks the galley passage in the block so oil must come out of the hole that plug is in, out to filter & back to block via port with yellow arrow in 2nd pic.
If the pin was driven in no oil would get to galley without external connection between these 2 ports.

Thanks for all the comments.
I am going to put an oil pressure gauge in the port with the yellow arrow of picture 2. If logic is correct, with the dowel not diverting the oil flow to the green arrow hole of the 3rd picture, I should have good pressure there because otherwise that hole would be getting return oil from the oil filter. Going to take a few days to get to that point of cranking the engine over again.
Picked up some original 41 Chevy 2 piece windshield glass today. Will try not to crack it.
Thanks again all.

I'd pull the distributor & turn the oil pump to prime the system.

If you plan to use the truck for any length of time, I'd install at least a bypass filter. With one, and regular maintenance, engines stay relatively clean. Without one they get pretty dirty inside. There are hydraulic-oil filters that are suitable for bypass duty that do a pretty good job. Then there is the Franz toilet-paper filter that works well too. Either is better than the elements available for the factory bypass filter. Those are too coarse to do much but bleed off oi pressure.

Thanks for input. Been gone camping w/o internet so couldn't get any posts. If I was to install a bypass filter on my engine, I would need to remove the plug and move the dowel in picture 3(green Arrow), correct. Or is there another place that I could dump the oil back into the engine? Thanks