The Stovebolt Site Forums The Shop Area Engine Shop 261 Oil Diverter Plug

Well, I read all the posts on the oil diverter plug for changing the engine to full flow filter oiling. It seems that there were a bunch of opinions as to whether or not the plug should be flush with the block or driven in approximately 1/2 inch to divert the oil from the pump, out the normally plugged NPT hole, to the filter and then back in the aft NPT hole where the pressure gauge sometimes sits. My 261 was never set up for the filter and the plug is flush with the block. Is the consensus now that the plug needs to be driven back for full oil flow? Thanks!

I remember talking about this years ago, but refresh my memory as to where this plug is located.

Thanks, Jim

I remember seeing a factory number for this, was 0.62/0.68 inch or there abouts. Most difficult chore is getting the thing to move at all. I've heard all kinds of methods from heating the area to drilling the plug out and threading the hole for a plug. If the motor is out of the vehicle I'd take it to a good machine shop.

I just went through this subject with the machine shop that did some work for me during the rebuild of my 261.I also changed to full flow oil filter.

While he had my block he made the change for me by moving the diverter in 5/8".

The guy seemed very astute on the 261 and did a great job for me.He once raced these engines and was talking way over my head about performance and modifications.

Hobert

How about the canadian Poniac 261.
Do they have full flow or just a by-pass?

How to tell the difference?

Thanks, Frank

Apache, have the same thing with my machinist Paul Hogge. He knows Tom Langdon (Tom recommended him to me) and also built race engines with sixes and eights. Used to do the 1/4 mile events. Extremely knowledgable fellow. My engine is the last one he's going to do as he's retiring at the age of 70+. Will be having him do the plug while the block is open and sitting on his table.

Stovebold,

If you have the Canadian Pontiac engine with hydraulic lifters, it supposedly had the by-pass oil filter for all years.

"Jim Carter: During the 1955-62 Canadian Pontiac application the lifters were the hydraulic type, the cam gear was fiber not aluminum, and it did not have the full flow oil filter. These Canadian made 261's did not add the full flow filter in 1958 as in the U.S."

The 261 engine was used in some Canadian trucks but I do not know (1) if it was used between 1958-1962, and (2) if it was available between '58-'62, if it had full-flow oil filtration (as the USA 261 had). Also, all truck 261s had mechanical/solid lifters and an aluminum cam gear.

Tim

Thanks Tim.

Well the casting # 3837012 makes it a 55-57.

Can´t say if it came from a truck or car, but it has the drilled lifter gallery (came without lifters and cam gear when I bought it), had a tag of a canadien Pontiac Garage/Shop on the side and the main caps say "made in Canada". So that`s why I belive it`s of a canadian Pontiac car.

I got a solid Bulldog cam and solid lifters for it. I think after all the Information I got here it`s safe to bolt on a bypass filter.

Frank

Frank

I'm sure this oil plug only applies to the later 261s which also had the larger 1/2" oil lines. Earlier 261s had only the bypass filter as did the 235s. There may be more info in Tech tips re. modifying your 235/261 for full flow filtering.

I haven't had any experience with 261's but if it is of any help, Inliners.org has a detailed article on modifying the early Chev/GMC engines to full flow filtering. Go to tech-tips,then full-flow conversion.

I've built several later 261'a with the plug.On one engine,the dowel was in the out position,supposedly to bypass the full flow filter.But on close inspection,you can see the dowel plug blocked the internal oil bypass,so the oil flow would have to go through the filter,then to the engine.
I would say to check out the situation first hand before attempting to drive in the plug.These engines have been out of production for nearly 50 years,all kinds of stuff may been in the past.No one over the phone or internet can see what ya got.