The Stovebolt Site Forums The Shop Area Engine Shop 261 question

Located a 261 for my 1/2 ton, but it's a 56.
Bored 30 over, crank 10.
Runs well.
Is it worth it to convert it to full oil or should I keep looking for a 58-62?

Bypass filtering ends up with cleaner oil, especially if you use a very low-micron filter element. Full flow filters are for rocks, marbles, and small boulders. It's a myth that full-flow filtering is somehow a better option.
Jerry

What about on a recently overhauled engine though Jerry? Does a bypass system only filter approximately 20% of the oil? I'm still reading up about these things.

So what you're saying is that it IS probably worth it? 😉

The bypass filter gets around to all the oil, just a little at a time. Since the full volume required to lubricate the engine doesn't need to flow through the filter all the time, the filter media can be made with a much tighter weave. It actually strains out smaller particles than the relatively coarse filter media that is used in full flow applications.

Big commercial engines like the Cummins, Cats and Detroits I made a living on used both bypass and full flow filters. The full flow caught the chunks big enough to damage the bearings, and the bypass element caught the finer particles that made it through the full flow element. A fresh rebuild probably won't have particles big enough to score bearings circulating, so the bypass is really all that's needed as long as the oil is changed regularly. Converting a 235 or an early 261 to full flow filtration is an involved process that tolerates no errors. The block needs to be stripped down to bare bones and thoroughly pressure-washed after the drilling and tapping is done to avoid contaminating the oil system with shavings. Just one or two stray cuttings will destroy bearings and score the crankshaft. Having a full-flow oiled junk engine is no advantage!

Millions of bypass-filtered stovebolts have run untold numbers of miles in the past 75 years or so. Just because some bench-racing "expert" thinks they all need to be converted to a different oiling system doesn't make it so!
Jerry

Thanks for the insight Jerry. I appreciate it. Now, on to the negotiations with the seller.

HL. Your kidding right full flow only filters out the big chunks,does not every automotive engine since the mid 60 s run full flow.ive been a heavy duty Diesel engine mechanic for 26 years working on Diesel engines up to 70 L in dips,less than 5 percent I've dealt with run by-pass filtration and of those must run spinners to spin the carbon out of the oil. Full flow filters will filter out any particles that would be harmful to the engine.

I have posted this illustration before, which is from the Frantz oil filter website. It shows the relative sizes of particles which can pass through a full flow filter, and what can be filtered out using a high-density element in a bypass filter. By flowing oil at a relatively slow rate through a filter with extremely fine media, the oil can be kept cleaner than can be done when the filter media has to pass the full volume to the bearings.

http://www.frantzfilters.com/wp-content/uploads/2015/07/96-percent.jpg

I was the distributor for Frantz filters for central California for several years. Several other brands use similar filtration techniques, and anyone with more than three brain cells to rub together can understand the physics of bypass oil filtration. To get sufficient flow rate to lubricate an engine, a full flow filter MUST make compromises on the size of the particles that get trapped.
Jerry

What he said. I use an Amsoil bypass filter with an effiency rating of 98% at 2 microns. The full flow mod is only as good as the filter being used...it's internal bypass spring/disc decide whether oil is filtered or not.

I have never ever seen a case where an engine seized because the filter was plugged...why? because oil simply goes around when pressure differential dictates. One needs to cut apart a few to really determine what's going on.

Bill Jenkins advised that a really big full-flow filter will prevent the bypass from opening, like the AC 832, but it's huge.