Because they came in both Pontiac and Chevrolet form up here!

My understanding is that the Pontiac 261 is a bypass oiler as a rule. They appear to have come with the "848" head. They can on occasion have taller/embossed valve covers. Sound about right?

But is this the ONLY Canadian 261?

The casting number on my 261 (3759365) tells me it is a '59 and came out of a Chevrolet truck. It has an 848 head. As I have yet to see illustrative pictures of both bypass and pressure oiling systems side by side (and where is this pin?), I can't be sure of what's going on with my engine.

I'd like to figure it out.

FACTS:

-Engine was pulled from a 50 chev 1/2 or 3/4 ton.
Obviously someone swapped it in there at some point.

-it has a front timing-plate mount.

-It didn't come with a filter or lines.

-There is a hole in the (drivers) side of the block that gushed oil when I cranked it over to do a compression test. The lack of paint around the boss of this hole tells me it was either plugged with a bolt and washer or had something over top of it recently.

-there is a second hole down low on the block (nearish the triangular side motor mount IIRC) that has a thread-in type plug in it. This plug looks to have been there for a long time.

-I don't see any pin but I'm probably not looking in the right place.

-I can and will post pictures.



So, is the Canadian truck 261 the same as the US model? Is it more like a Pontiac? When we say "Canadian 261" are we referring to the Pontiac alone or is there a Canadian Chevrolet 261?

If the holes are 1/8" npt then it was a bypass setup. If the holes are bigger it would be full flow. Some Canadian trucks had the same setup as the U.S. engines (big oil filter lines, water pump with extra outlet and big thermostat housing) The hole that gushed oil goes directly into the main oil galley so it will gush no matter what oiling setup it had. Anyway there were both types of 261's in Canada.

Curt B.

Dear Tom;

All 59 261s can be "full flow", It's the position of the moveable pin that tells if it had a filter or not. The 1954 model is the only one with a 'by-pass' filter option.**

Someone may have removed this pin if there's a hole W/O threads on the 'drivers side' etc.

Pontiac ran out of engines & the Chevy truck (261) engines were then used etc.

Waiting to see your photos.

**Micky Mouse could add one though.

Was the "oil gusher" hole where the oil pressure line to the guage mounts?

T;

Good points by Curt & Drew.

The oil guage fitting is small (about 3/16) and goes in the 'drivers side' too. On the (moveable pin) models It's on top of some adapters when the filter option is not used.

The hole before the adapters is 1/2 NPT.

Clear as mud, right??

Ok guys, thanks for the help so far.

Here's the pictures:

First, the thermostat and water pump.



Does this show you what you need to see?

Next: the side of the block.


Sorry that ?#1 is obscured by the throttle linkage. There's nothing attached to it and it stands out from the engine on a boss about 1/2 to 3/4 of an inch tall. I'm thinking it has to do with the water jacket, or maybe pedal linkage?

?#2 is a thread-in plug (closeup below)
?#3 is an undrilled boss.

And finally, the closeup of 2 and 3:



Hope this helps clarify things!

Cheers,
Tom

From the pic’s it’s definitely a bypass setup and you have the return marked #2 I. You can keep it bypass and use a spin on or use the original style bypass or plug it altogether as it was previously run. Only the pressure gauge was hooked to ?. Personally I’m an Amsoil fan as it grabs particles down to 2 microns. I mounted mine on the oilpan like this. Good luck.

Curt B.

T;

Your photos show a 261" engine without the (GM) factory oil filter option.

P1= Pivot linkage point for a different application.

P2= Pluged opening to oil gallery.

P3= Moveable pin.

P4= Is labled "gusher" and is opening for oil pressure guage line.

Good luck.

Thanks for the clarifications guys. Now I know how to proceed. Curt -- that filter looks good. Have to see what kind of room I've got once the engine is mounted in the car.

So it doesn't sound like this engine is much different than the Canadian Pontiac.

I wonder if a Pontiac Casting number come up as "pontiac" specifically... My casting numbers DO point to Chevrolet. Interesting.

Attached are some more photographs showing a full-flow filter on a 1954 261, along with a stock 1954 261. Along with the the images that Curt B made available, lots of filter options for a 261 (or 235) show up on this thread.
stock 1954 261
1954 261 with full-flow

There are also images of a couple of 1959-62 261s with the factory full-flow filters. On these, you can see the "pin" in the "in" position. There is a subtle difference between the two late model 261s, as one has the 1/8" NPT plug (same as Tom_Dobson's) for the bypass return, but the other does not have the tapped hole in the block.
Late 261

Late 261 details

Another late 261, no 1/8" return


There are lots of subtle differences between the different 261 models. Also, the casting numbers are not always positive identification. One of my 1954 261 blocks (#3733950) is shown as a 1955-57 in some lists and as 1954-first 1955 (which it is) in others. The other 1954 261 block (#3835911) is shown as a 235 in all casting number lists that I have seen.

Thank you Mr. Hoyt for those fine photographs.

As one can see there is a 'seepage' on both filter lines that run 30-60 PSI of hot oil, when in use.

Around late 59 or 1960 GM issued a WARNING to ALL 'fleet operators' of this danger as some had developed a "pinhole" leak (from vibration) which then caused a major fire/explosion(s).

At the time I had a customer with 70 Chevrolet (C-30) trucks which had these units from the factory. Some had this seepage/leaks & some didn't and I kept a "watchfull eye" etc.

Around mid 1962; another customer had an explosion/fire on a C-30 due to this problem and the driver narrowly escaped DEATH (on the 'freeway') due to the massave damage caused by the intense heat involved in an oil fire.

Needless to say; I removed ALL of these filter units because it was less work/money (safer) than constant vigilance & repair. My customer NEVER had a fire and all the trucks ran over 150,000 miles.

One of these photos shows a "mini hose clamp" on one of these units.

The cause of this EXTREAME DANGER is because of the heat generated by the header pipe (1,000 +/- degrees) next (1-2") to the potential leak (double with headers/duals) and the 180 degree oil inside the lines under high pressure.* :rolleyes:

By the time you know there's a problem (261 full flow) the engine compartment is almost "fully involved" with the cab seconds away. At 'freeway'speeds there's NO time to do ANYTHING about it.

Even with 'aircraft style' or solid lines, the danger is still there, only reduced.

So; As Walt would say, "make your own decision".

Happy trails to all

* The early 216/235 engines ('by-pass' type) rarely had a problem as; they generally ran 15# pressure and only processed about 20% of the engine's oil.

John,

Good comments on your experience.

How does one get the pin from the "in" position to "out", if one does not want to use a filter with the late 261s? I have not had one of them apart, as all of my experience has been with 1954 models.

H;

Easy; drill a 1/4" hole in the center about 1" in and insert the metal screw from a 'slide hammer' & pull it flush again.

My Machine Shop pulled it out & tapped the hole for a pipe plug.

If It's out, leave it and use commercial SAE 30 oil & change @ 3,000 miles.

For the 'later ones' (there's 3 types) a connecting tube is needed and should be solid steel.

I was a "gutsy" guy @ age 20 but this would scare the hell out of anyone with 'good sense'. The local Fire Dept. kept photos of it posted in their #1 Station for years.

Good luck.

Thanks all, this has been VERY informative.

Interesting info. No wonder the pin thing never made sense to me as my 1956 261 doesn't even have that boss. It looks like in Tom's case the boss was added but not machined for the pin. My pic showed the smallest Amsoil bypass filter available and probably won't fit there in a car. Other options are mounting to the intake like this or use a small spin on shown here. IMO hoses are an invitation for trouble.

Curt B.

Oh, oh, thought I had it figured out: if you just run the bypass tube from the outlet to the inlet it seems like there will be very little oil pressure registering on the gauge. If you put the restrictor fitting in the line it might be plugged up with a particle of dirt (no oil filter). Isn't his going to be a problem?
ron

Dear Ron;

You now have questions in 3 different topics here, on the same subject.

Which engine design do you have??