The Stovebolt Site Forums The Shop Area Engine Shop 261 identification.....

Need the help of 261 experts....

Looking at buying a rebuilt 261.... I know buyer beware....

Casting number is 3769717.... which makes it a 58 -62 block and it has the XXX848 head from a 235.

What does the block serial number means or tells it reads W 312809 ????

I already have another 261 from the same period but it has large 3/4 inch oil lines holes for the filter which was mounted on the intake manifold and now replaced with dual spin on type.

This new block I am looking at has only small 5/16 or 3/8 treaded holes on the side of the block. Why is it different and why such small holes?
This engine came from a pick up truck apparently, so would it also have the solid lifters of the HD truck engine.

Thanks for the advice.

Bob C.

Hy Bob C., my understanding is that not all of the newer 261s had the large oil holes, those engines were also used in our Canadian Pontiacs, so that may be where the one you are looking at came from, hope that helps.

The Canadian Pontiac 261 had by-pass oil filtration in all years and had hydraulic lifters. The smaller diameter oil lines are an indication of by-pass oil filtration. You would have to inspect the lifters to see if they are hydraulic or solid. USA 261s always came with solid lifters.

Maybe someone has information about the 848 head being used on Canadian 261s - that head never came stock on a USA 261 (but was often adapted to serve as a replacement head).

I’ve seen several Canadian Pontiac 261’s and they all had the 848 head. I’m certain GM Canada did it that way. Oddly I asked my local guru for a 261 camshaft and he told me it only came in the hydraulic grind? I haven’t seen a Canadian truck with a factory 261 but I would like to know if any used the same block as in the cars. Bob, do you have an extra large thermostat housing and a water pump with an extra outlet? Is it green? What did your other 261 come out of? A manifold mounted bypass filter would be what you need or plug them and change oil often.

Curt B.

Thanks for the info.... if I do purchase theire is no way I will fire it up without ascertaining if it is full flow or by-pass..... or removing the pan and side cover to check out the lifters.

Right now it is sitting in a 1944 Chev frame at minus 24 Celsius (about -10 Funny degrees for you guys down South..windchill -30C) and for some reason will not turn by hand....?? wonder why???

Any comments on the serial number??? with the "W" prefix I was hopng to truly ID its origin but all I can find is info on casting numbers.

As always thanks for you help.

Bob C.