Inliners International Forums General Discussion Engines Chevy 261 Head Gasket Question

When mocking up my 261 block, I noticed I had two different styles of gaskets on hand. One, typically made by Best Gasket (first image) shows some of the holes towards the front of the block covered or restricted (NOS gaskets like the Victor 3210 seem to have this same feature unless they were marked as for 1954 block); the other gasket, made by Fel Pro has provisions for all hole (as mentioned, the one I saw for a 1954 block matches this). Any reason for this discrepancy? I want to use the correct gasket but I am confused. If I had to guess, it seems after 1954, they restricted or blocked some of the holes on the front of the block to force more coolant flow to the rear of the block, and as such, I should use that one. As a note, it appears I have a 1960-1961 block based on full flow oil provisions as well as casting number. Any help would be appreciated.

I've only had one 261 and that was nearly 60 years ago. We also discovered what we thought was a 235 in my friends '57 pickup was a 261. Try to do some searches here. I think I remember a discussion about 261 heads, gaskets, and extra holes some time back. Maybe Stock 49 can help.

The 261 block and head has additional water passages between the cylinders that the other Stovebolt engines do not have. So, yes the 261 head gasket is specific to the 261 alone, and shouldn't be interchanged with any other application Stovebolt head gasket...

CNC-Dude, I'm well aware of the "steam holes" between the siamesed bores as one among a few defining features of a 261 engine. As my original post states, there is a noticeable difference two different 261 head gaskets, one typically made by Fel-Pro and one made Best. If you review the attached images in the post (one displays, the other seems you have to click on to load) you will see the difference I mention. Basically the Best Gasket covers some of the holes on the front side of the engine while the Fel-Pro one does not. Again, the only thing I can seem to guess is the Fel-Pro one may be based on the gasket used in 1954 (I base this on finding a few NOS 261 gaskets listed as 1954 only), when the 261 was introduced, but they adjusted the gasket from 1955/1956 onward maybe on account of some minor heating issues at the rear of the block. My question was, if my assumption is right as I can't see any literature or discussion on this topic.

Hi Woodrow2002 . . .

The paper trail is pretty good on this one albeit somewhat incomplete. If we look at the
'57 Master Parts Catalog
we see a gasket kit (3709429) and an individual head gasket (3836107) for use on all 54-57 261 jobs.

Strangely, in the '62 Master Parts Catalog we see a change in the kit (3751893) and the individual head gasket (3701296) for use on just 54-55 261 jobs (now the so called first series)

And this is where it breaks down. There is no mention of parts for use on 58-62. Keep in mind that parts counter guy (back then) would have several different vintages of the Parts Master open to find compatible parts from what was on-hand in the bins at that particular shop, some of which could be years old. But I still find it odd that the October of '62 Parts Master is not telling the complete story on an engine that was about to go out of production.

When we switch to the '66 Parts Master they stop referencing the first series designation and call out just gaskets compatible with 55-58 jobs (3751893) kit (3750625) gasket; and 59-62 jobs (376440) kit (3760990) gasket.

Interestingly enough there is an ebay auction for the mid-50's kit (3709429)
which as you have surmised, reveals the earlier design (that Fel-Pro) is following: suffice to say a 235 gasket plus the so-called steam holes.



I agree with your analysis as well. By blocking fully/partially those front most water jacket holes the coolant flow (when the thermostat opens) favors evacuation via the back of the head. Likely this difference was documented in a Service Bulletin at some point. As far as I know Service Bulletins are not online at the GM heritage site.

regards,
stock49

So just wondering what gasket i should use on my 261 it is a 58-62. Does it really matter which one? Seems like both would probably work?

I would venture to guess that since these changes are from decades and decades ago, that the kinks have been worked out by the manufacturers back then as well. Have you been over on the Stovebolt forum to pick some of those guys brains about this...?

No i havent yet done that. I will try and see. Thank you