The Stovebolt Site Forums The Shop Area Engine Shop 261 oil flow diverter plug in block

The machine shop has my 261 all cleaned up and shiny, ready for the next steps. I took a good look at the block area around the oil lines because I was curious about how the diverter plug worked. I had done several searches and a lot of reading on this site ... very helpful!

My block has the plug in the out position, or flush with the block surface, and it clearly provides for a "bypass" filtration system. I want to change it to a full pressure/no bypass filtering system and measure oil pressure downstream of the spin on filter (to be installed later).

I can see that the diverter plug needs to be driven into the block about 1/2" or so.

What method should the shop use to drive in the plug? Lubricate with PB blaster, etc? Use small, short taps with driving tool? Will it rotate?

I'm searching for advice on how to do this operation and not damage the block. Thanks in advance.

shoeless

One one of my 261's the dowel was set in allready, no problem. On the other engine, the dowel was in the out postion.looking closely at the siuation, the bypass was blocked, the oil would only flow through the filter.By the way,this second engine, from a fire truck, was equipped with a factory AC full flow filter.So I'm thinking the "in or out dowel rule" is not an absolute, but you have closely checked yours ,so hopefully the dowel will drive in without a big hassle.

Thanks Tony. Yes, I verified that the plug is not blocking the oil galley. Also, this engine was using oil lines, but they were already removed when I picked it up. It must have been using one of the bypass filters.

I just recently performed this operation on my 59 261 engine. It was also being used with a by-pass filter and I wanted to go to the full flow design. I found a round punch that was close to the same diameter and then went real slow. I started with a small hammer and increased the size of the hammer until the dowel pin moved, then it seemed to a little easier. It went in about 1/2". Hope this helps.

57 Mike

A few years back one of the Inliner Club 261 experts found a factory spec on pushing this plug in and I'm sure it was in the neighborhood of 0.62 inches. Wish I had a book to verify, but I don't. I attempted to drive mine in on my 1961 261 and it would not budge so I left it alone as I didn't want to break the block. Have also heard of machine shops drilling the original plug out if it wont budge or heat.

I've been trying to tap in the bypass dowel for a couple days now. Engine is installed so I can't soak it in Blaster. I tried heat & lubricant. Anyone had success with a stubborn one like mine? Thanks

Heat- - - -KROIL- - - -tap- - - -repeat as necessary.

www.kanolabs.com

You could also drill and tap the plug and pull it out of the block with a bolt and nut or a slide hammer, polish it a little, and re-insert it. I'd only attempt that if I had a bare block on a stand where there was plenty of access. When I build my Cadillac 261, I'm going to pull the plug out, thread the hole, and go back in with a screw-in blockoff instead of a press fit.
Jerry

Jerry, I believe your idea is the way to go, I got same scenario
from engine guru I know but engine was in the truck so left alone vs. destroying the block.

Why would some of the later 261 engines (58-62) come with a stock AC full flow filter with the dowel in the 'out" or flush with boss postion if this is for bypass only?

Not sure, poss the factory put the filter on all 261s thinking customer or dealer would opt to drive in the pin???

Chaz58, it might be hard to do if the engine is installed because you will have difficulty swinging a hammer hard enough.

I've done three of these using this technique. Spray with Kroil a few times over a period of days. Use a punch that is as close to the size of the dowel, but a little smaller. Hit the punch with a two pound hammer centered on the dowel like you mean it. Light hits won't break it loose. Once it breaks loose, you can back off a bit when you whack the punch.

It goes in 5/8". Take a paper clip, bend it at a right angle, then accurately snip off one end so that it is 5/8" long. Use this as your gauge. You can tell when it bottoms out from the feel of the hammer, but you'll want to back off the force of the blows as the gauge shows that you are getting close to the bottom.

As I said, this would be hard to do with an installed engine without room to swing the hammer.

Good luck,

Matt

That would leave the big filter to do bypass work. Something seems missing with the original setup. I would think with all the smart guys in the room here, someone would have this answer.

Thanks Matt. I'll pick up some Kroil & give it a try.

The most effective way to approach things is to use both a full flow and a bypass filter. One stovebolter I know of is using the original equipment full flow filter, and has a Frantz toilet paper filter plumbed as the bypass. The big filter strains out the rocks, marbles, and bowling balls like all full flow filters do, and the bypass traps the microscopic stuff that the full flow misses. It's the same basic setup Cummins diesel engines used for a lot of years.
Jerry

Chaz58, I was thinking about doing this under the hood with the engine installed. I'd use a 4 lb. short handle hand sledge instead of a 2 lb. ball peen. You'll be able to get the same force on the punch with less of a swing.

Here is an example of the hand sledge that I'm talking about. I have this hammer and find it very useful when I need some umph and don't have room for a good swing.

http://www.harborfreight.com/4-lb-fiberglass-drilling-hammer-61397.html

Here is a link to a post that discusses both how to move the dowel and Jerry's idea to use both a full flow and a bypass filter. You'll get to both subjects if you read through the entire thread. If you decide to use both, you don't need a spin-on filter. You can use the original full flow canister. Just use the same plumbing diagram as shown in the post.

https://www.stovebolt.com/ubbthreads/ubbthreads.php/topics/1199078/1.htm

Matt

While trying to knock in the dowel (making me nervous) I noticed there is no 1/8 bypass port next to the big port under the dowel like I've seen on other blocks. With everything I've read, I'm starting to think some 261s, mine, came full flow only perhaps. I wonder if 1960 manuals mention the dowel. If I turn the engine & oil only comes out of the hole below the "bypass" dowel, its in full flow right? I did receive my block rebuilt & the pin/dowel was slightly recessed, but not much. Serial number was also marked out with another stamped next to it. Strange block. Any opinions? Matt, Deve?

I do not know about your 1960 block, Chaz, but this illustration from the 1960 Truck Shop Manual seems to show the "plug" for the by-pass filter line?

I'll try to remember to check my 261 engine tomorrow (I dimly recall that it is a 1960 261).

I see where the 1960 manual also gives the quart oil amounts for the 235 with and without the filter, but only one amount for full flow in the 261. Hmm

Chaz 58, here is a link to the engine section of the 1960 shop manual--

http://www.canadianmilitarypattern.com/1960%20235-261%20Engine%20Manual.htm

As I recall, the dowel in the 'out' position is recessed between 1/32" and 1/16" in the hole. It is not flush with the outer edge. The two 261's I have in the shop have both the 1/8" and the 1/2" threaded holes in the block under the dowel. The dowel must either be all the way in or all the way out.

When you insert the dowel, you reverse the plumbing for the filters. With the dowel in the out position, you can plug all the holes and not run a filter. Or you can run a bypass filter. It must have a 1/16" restriction somewhere in the filter or in the lines. Using a full flow filter without a restriction will starve the bearings of oil. The same is true with a 235; most bypass filters have the restriction on the oil tube inside the canister.

The bypass circuit runs from the back port where the gauge connects to the 1/8" port (that you don't have) under the dowel. The 1/8" port is not connected to the oil galley and simply dumps the oil into the sump. Others can chime in, but you also might be able to connect the return to the 1/2" hole under the dowel, but I am not sure how that would work since it connects to the pressurized galley. The routing is the same direction as a 235.

In full flow mode with the dowel pushed in, the circuit is reversed. The 1/2" port under the dowel becomes the feed for the full flow filter and the 1/2" port at the back of the engine (oil pressure gauge) is the return. If no filter is used, these two ports need to be piped together because the dowel blocks the galley...they must be plumbed together with or without a filter.

If you spin the engine with your dowel in the out position, you should get oil out of both the front and back 1/2" ports because they are both pressurized and are not blocked. To test your theory about being set up for full flow with the dowel out, yes, you would get oil out of the front port when spinning the engine but not the back IF everything else works like a normal 261.

Hope this helps,

Matt

I think the part of the 1960 manual that Matt refers-to is the illustration that I posted a link-to in my post above.

My 1959 261 does not appear to have the low-pressure oil-system plug to the left of the forward 1/2" hole for the full-flow oil filtration system.

Tim, I'm pretty sure that you use the bypass filter on yours. Is it piped from the 1/2" port at the back of the block (oil pressure gauge) to the 1/2" hole under the dowel? If so, that would answer the grey area question on that particular subject from my above post.

Matt

I use the full-flow filter canister that came on the engine from the factory. I looks like, and is plumbed like, the full-flow canister filter shown in the 1960 Shop Manual.

Well I guess I'm waiting for the kroil to show up in the mail. Oil came out both holes. I was hoping I would get lucky and not have to drive in that dowel.

Tim did yours already have the dowel in when you got it?

MIne already had the full-flow filtration system in it - from the factory.

I got the engine out of 1960 school bus (in 1972). Full-flow oil filter and no PVC system (go figure).

I'm pretty tenacious, but this thing is tough. I built up a reservoir around the boss so the Kroil could soak in. I took the small sledge to it after 48 hrs, didn't move a bit. I took heat to it as well. I guess I'll soak it again and try tomorrow.

Good luck!

Hey Matt, you were right about not having a lot of room to swing the hammer. I've done the heat about 3 times and soaked the dowel in Kroil for a few days. What would you recommend now? Keep going with this schedule or just plug the holes and more frequent oil changes? I was lucky enough to get the later 261, and really wanted to use a filter. Thanks, Chaz

Chaz, you get an A+ for effort!

I think the only way to get enough access will be to pull the engine. Unless you have other reasons to do so now, I'd wait until you need to tackle that job. Yes, it will drive you crazy thinking about that dowel pin, but you'll be able to scratch that itch in the future.

I doubt if your decision will change your oil change frequency. We pamper these trucks and tend to change oil sooner than realistically necessary.

If you install a bypass filter, many will argue that it is better than a full flow because it eventually filters all of the oil through a much finer screen than a full flow. Full flow does all the oil all the time, but catches larger particles than the bypass. Full flow never gets the fines out of the oil.

If you ever pull the engine and have access to the dowel, you'll have the option to plumb both a full flow and a bypass. If you install the bypass now, your equipment will not go to waste.

Matt