By-pass oil filter on 261?

[DJMTruck]

My '53 3100 has a 1960 261 installed by the p.o. (who is deceased so I can't ask him about it...) At least the block is a 261 (block casting #3769717, block casting date, D 14 0, so April 14, 1960). But the head is a 235 (head casting code #3836848, don't have the head casting date yet). The block has both sets of captains bars, so given the casting code info I'm sure it's a 261 but the filter system appears to be a by-pass rather than full flow. I posted this info and this photo (https://www.dropbox.com/s/pmql4hm2tl..._2919.JPG?dl=0 ) on Stovebolt a couple of months ago and the consensus was that it's a by-pass (based on the small lines) . So what gives? I thought a 261 built in 1960 would have full pressure oiling for sure.

[Deve]

There is a great document on the 261 that was contributed to by many experts here:

http://devestechnet.com/Home/TheVenerable261

That explains it. Long story short, there is a steel dowel pin just above the small front oil port that allows for switching between bypass and full flow. The dowel being out, flush with the block means its in bypass mode. 5/8" in from flush means its in full flow mode. Remember that once you push that dowel in, it is not really possible to pull it back out, so you will be in full flow mode forever. I did this without any hesitation because I want 100% of my oil filtered, not just 8-12%. There is a full flow oil filtration spin-on system available on the main site in the How-To section.

By the way, ALL 235's and 261's from 1954 on had full PRESSURE oiling. But only the 1958-1962 261 had full FLOW oiling. All of them have 30 psi. I get the two terms mixed up all the time.

[DJMTruck]

Thanks for the info above. I just checked my truck & it appears that it has a square plug sticking out of the hole where the "dowel" should be. Please see these photos. HTTPS://www.dropbox.com/s/3ze9a0bk80..._3066.jpg?dl=0
HTTPS://www.dropbox.com/s/e4y1v1oi13..._3069.jpg?dl=0 I'm not sure what that thing is but it probably confirms that I don't have full FLOW oiling. That seems strange since the block date indicates that it was built in 1960....

[Deve]

So what probably happened at some time in the engines history, it was in full flow mode and this wasn't what the owner wanted, so they drilled out the dowel. With the dowel out oil passes behind the dowel and gives it its bypass properties. Same thing would happen with that plug. If you remove the plug, and there is nothing behind it, all you need to do is remove the plug, put a dowel back in and you can probably get your full flow. The dowel passage is 1-5/8" long and the dowel itself is 1 inch long. You will want to mic the hole to determine the exact diameter, but I think its 1/2". The block is not the problem. Its fully capable of doing what you want. It was choices before you got it.

[DJMTruck]

Aha, well that does explain it. I think I'm over my head now and will probably just continue frequent oil changes. I really appreciate your help, Deve. Thanks!

[Deve]

Anytime. The time to address that problem is when you need a complete engine rebuild. The machine shop can do that sort of thing easily and at pretty low cost.