The Stovebolt Site Forums The Shop Area Engine Shop 261 Full Flow vs Bypass Oil filter systems

Question: I have a 1954 261 with the bypass oil filter, and a 1959 261 with full flow oil filter assembly. According to a Hysterically Impatient Millennial (HIM) truck owner; he believes the earlier 261 oil filter did a better job of filtering the smaller particulates than the later model 261’s. What are the advantages and disadvantages to each filter system?
Opinions appreciated.

Tom

bypass oil filter vs full-flow oil filter

The terms "passive" and "gravity" could have different meanings for different people.
It could be argued that both are passive and that gravity is at work with both/neither.

The full-flow filter system/canister filters all of the oil.

The bypass filter system/canister filters a small percentage of the flowing oil, eventually filtering all of the oil after a period of time.

I seen no significant advantages/disadvantages under normal driving conditions. I have used both types of systems.

If I bought a new 261, I would probably keep using whatever type of system cam on the engine.
If the 261 did not come with a filter, I would probably put on modern/spin-on filter adapter (and push in a special pin/plug on the block).

Use both systems if you want really good oil filtration. The full flow system has to have a filter with a sufficiently open weave media to flow enough oil to keep the engine lubricated. A bypass filter can slow the flow down and strain out the particles that are small enough to pass through the full flow media without slowing down, let alone getting trapped. The main function of a full flow filter is to strain out the particles big enough to do damage to the engine before they get to the bearings. In an ideal world, an engine would come with both systems, and that can be done on a stovebolt engine by anyone with a little time, money, and ingenuity, even on the engines that didn't have the capability for full flow filtration from the factory. 235's and early 261's need to get some internal modifications to the oil galleries to allow a full flow filter to be used, however.

Edit: Try this experiment- - - - - -brew two pots of coffee- - - - -one by putting the ground coffee into a (clean) athletic sock and repeatedly dunking it into a pot of boiling water, and the other by dripping the water slowly over the grounds through a regular piece of filter paper. Which cup of joe will have the most sediment in the bottom?
Jerry

The downside of the bypass oil filtration system in my mind is that for the significant percent of the time which the oil is not filtered, sediment is falling out and landing on the bottom of the oil pan where it will never be filtered again. Back in the day when these trucks were driven on dirt roads, sucking in dust through the vent slots in the valve cover, you would find as much sludge in the oil pan as you would in the oil filter if you were to remove the pan to look at it
The full-flow filtration system filters 100% of the oil, not giving the chunks much of a chance to settle at the bottom of the oil pan.
Unfortunately the 216 and 235 engines were not deigned to be able to accommodate a full-flow filtration system, while still providing adequate oil flow to lubricate all of the moving parts.
The 261 is designed for the full-flow filtration system, and if I had one, I would set it up to use one.
My 3 cents. (extra typing costs an extra penny. All sales are final. No warranty implied, and no refunds. Even if I am dead wrong.)
Carl

It takes about 2 hours to convert 235 oil galleries to full flow filter routing, but it must be done with a completely bare block to be able to flush out all the shavings the drilling and tapping creates. Then it's still best to run both types of filters.
Jerry

I recently bought an old 261. It has the full flow system on it. Does anyone know where I can buy new oil lines for it? It doesn’t appear to be leaking but at this advanced age I don’t trust it not to have a hose burst going down the road, it would probably drain the engine before I even knew there was a problem.

Any hydraulic shop, and quite a few NAPA stores can make up new flex lines. I like to use "single braid" hydraulic hose that has a working pressure rating of 3000 PSI. 30-50 PSI engine oil doesn't stress it at all, and it's designed to work at temperatures much higher than lube oil ever reaches.
Jerry

So how do we get a filter "with a sufficiently open weave media to flow enough oil to keep the engine lubricated" I picked up a 1955 261 so I'd like to build it one of these days.

Full flow takes the oil from directly from the main galley, filters it and puts the clean oil back into the main galley, feeding the motor clean oil. The bypass filter bleeds a little oil out of the main galley, filters it, and then dumps it directly into the oil pan where it is instantly diluted with dirty oil.

if your engine wasn't designed with one, you have to interrupt the outgoing oil flow from the pump, insert an oil filter appliance into that flow and restore the flow back to the engine. There are different ways to do this. Since I use an electric fuel pump and since I didn't want to drill the block, I ran the lines from the pump to the appliance and back to the engine distribution network out through the old mechanical fuel pump location. I've never seen anyone else do this, but it has worked excellently. I posted images of this previously. Others have drilled and tapped into their block and there are instructions on how they did that here and elsewhere. But essentially the flow of oil must go through the filter before it goes to the engine. How you do it is up to you.

Here are the images once again. You can see how the oil line leaves the pump and goes up over the crankshaft and out the side of the block where the fuel pump originally mounted. You can also see how the returning line goes back into the block in the same place it originally did. When I finished this work I added connection joints and made it so that this could easily be removed and changed at any time by making the mounting piece as shown. I spent something like $20 for various fittings and lines and I had the oil filter gizmo already.

Your 1955 261 will need two holes drilled and tapped for 3/8" pipe fittings, and one internal passageway in the block will need to be plugged. Then any of the remote oil filter adapters for a spin-on filter can be plumbed into the oil circuit between the pump output and the block. That type of filter will strain out the rocks, marbles, and bowling balls that could damage the bearings. Detergents and dispersants in modern oil should prevent the sludge buildup that gives some people on this site a case of the vapors. Sludge buildup was mostly the result of running non-detergent oil way past its normal change interval.
Jerry

Jon G - can you elaborate on the electric fuel pump in another post? And describe it, how you installed, gpm’s, and brand? I need to do this for a 302. Any pics?

Nice work on the filter system!

Yes, but I probably don't need to do another post. I've mentioned it here numerous times. It is an Autobest F4027. This pump is (a) Chinese and (b) has been sold in this country since at least 1997. I first bought one in 1997 and three years ago replaced it...not because it stopped working but because I figured 20 years was long enough and the thing only cost about $18 at the time. So it was a preemptive move. In 2017 I bought 2 and put one under the seat. Mount it externally (in the frame) as close to the gas tank as possible and use the clip and rubber pad they provide with it. Wire it so that it turns on when the ignition switch is on. Electric pumps are made to push and not to pull, so please don't mount one up near the engine. I don't know the gpm rating but these are ideal for the 235 because the psi output is 2.5 (which is plenty). I don't have any pics but you can find these on Amazon. There are probably a dozen just like it sold under different names. I had such good luck with the first one that's why I bought it again. When it senses pressure, it seems to disengage. It runs but the sound changes and you don't see gas coming to the filter. Please avoid any fuel pump which claims to put out 7 or more psi. That's too much in my opinion by a factor at the very least of 2 and might cause problems with your carburetor.

Thanks for the compliment on the oil filter system. As I said, I've never seen anyone else do it like this but it works fine and it uses a very common filter. Besides it was pretty doggone easy and you can do it without having to take the engine out, etc. If a person wanted to do the same thing and use the mechanical pump, they could just drill two holes in the side of the block and run the tubes out those, but I also didn't want the oil filter over by the exhaust pipe.

Oh, before I forget, somebody is probably going to chime in and mention that you need to incorporate a switch to shut the pump off in case you're in a wreck and the engine stops running. And that is a very good idea, but I haven't done it yet. The scheme behind it is if your engine stops running you don't want the pump to continue to feed gas to somewhere (broken fuel line, truck upside down, carburetor knocked off in head on collision, etc). There are switches which are activated by oil pressure and I think that's what most people use.

If you search for electric pumps here Tom you'll find there is one group who thinks they're fine and another group who thinks otherwise. Like everything else, the choice is yours. I really enjoy not having to pour gas into the carburetor or wait for a mechanical pump to fill the bowl in case I don't drive the truck for a couple of weeks.

The simplest method of doing the oil pressure sensing pump switch is to use an idiot light switch for a Chevy Vega 4 cylinder. It has 3 terminals- - - -one to provide a ground for the oil pressure light, and a "normally open" set of contacts that close as soon as the switch sees something like 7 PSI of oil pressure. If you want to, wire up a relay to run the pump, but the switch contacts are plenty capable of operating the pump without the relay. If your truck sits for long enough that the carburetor runs dry you can also add a push button priming switch to fill the carburetor bowl before the first startup, so you don't have to crank the engine long enough to develop oil pressure before the fuel pump kicks in.
Jerry

W/r/t the pump location: if you have some leeway, mount the pump as far below the tank outlet as possible (keeping the pump body and lines well protected by the frame, bumper, etc.).
Gravity pressure is all you have to prime the pump, which is directly proportionate to the height differential between the actual fuel level (not the bottom) and the pump. Pump 12" below tank level has twice the inlet pressure as 6" below, etc.

Holley also makes an oil pressure activated switch designed specifically for fuel pump applications.

Holley Switch

The nice thing about this switch, is that it has both a normally open and normally closed set of contacts, which facilitates the addition of a priming circuit.

On my truck, I replaced the two position ignition switch with a three position switch, and wired the normally closed contact to the crank output on the switch. This provides an easy way to prime the system if the truck has been sitting for extended periods of time.


Best Regards....

.

I appreciate these insights. Thank you.

Apparently up to and including 1962, Chevrolet wasn't sure either, my 62 261 taken out of a 2 ton cabover was still in the bypass mode when it let the factory. It made it 58 years there and it is still going.

That is a pretty trick setup.