The Stovebolt Site Forums The Shop Area Engine Shop Correct head gasket for 261 with 848 head

Can anyone tell me the correct head gasket to use?

I bought a Best Gasket engine rebuild kit and it came with the wrong head gasket. It was a Felpro gasket in the Best Gasket kit. The gasket was missing several water jacket holes.

So I did some research and ordered a Felpro 7782B gasket. I was going to install it today, but there is one water jacket hole that is incorrect. The hole on the gasket is about 3/16" surrounded by a 3/8" copper compression washer. The hole in the head for the water jacket is 5/8" and the matching water jacket hole in the block is 1/2". The gasket should have a 5/8" hole surrounded by a copper compression washer, the same as some other holes in the gasket.

If I use this gasket, my fear is that the water jacket will not be sealed off tight.

Here are some pictures showing the holes on the head, the block and the gasket.

http://s844.photobucket.com/user/ma...2282_zpsjvhux6rz.jpg.html?sort=2&o=0

Anyone ever had this issue? What gasket did you use?

Thanks,

Matt

Matt,
That is the same gasket set that I used on my 261 2weeks ago, no leaks it runs fine.

Hope the added coolant holes in the 235 head are drilled in the correct location?

Tim, the steam holes have been drilled in the correct locations and line up with the holes in the 261 gasket.

The Felpro 235 head gasket (7619B) has all the correct holes except the six steam holes. The incorrect small hole on the 261 gasket is correct on the 235 gasket. So...do I use the 235 gasket and punch the steam holes myself or the 261 gasket and expand the one hole that is to small?

Odd that Felpro would have the one hole incorrect on the 261 gasket. At first, I thought the problem was that I switched to an 848 head from the 850 that the 261 was born with. But the 261 block has the larger hole too, so it's not the 848 head.

Tommy, did you open up the small hole when you installed yours?

Thanks,

Matt

That restricted hole might be there to route coolant flow through the steam holes better. I had a student once who was smarter than the people who made the gaskets and opened up some holes on a set of 302 Ford head gaskets. Instant overheating, and a repeat of the job!
Jerry

I used the felpro HS7782B head gasket set for my 261 with the 848 head. It was fine.....and if my memory is correct I ask for the 261 set.

EDIT: I then took the head gasket as a pattern and the 848 head to a local machinist to drill the extra holes in the head. All is good.

Matt,
No I used it like it was. That same gasket set had been on the engine for the last 12 yrs. ran fine.

I would guess that the copper compressed washer on that too-small hole in the gasket is there to keep the gasket from eroding since its perimeter is not supported by the head nor the block. I would not alter anything for reasons mentioned above.
Carl

Guys, thanks for the advice. I'll leave it as is and install it.

The head gasket that came in the 261 Best Gasket kit from Patrick's had a weird looking head gasket. As I mentioned above, it was made by Felpro. The number stamped into it showed a discontinued part number. It was a shiny metal gasket on both sides. I couldn't tell if there was anything sandwiched in between. It fit the design of the 848 head and had the correct steam holes in the correct places, but several water jacket holes were missing and several were under-sized.

When I showed it to Patrick, he said that it was probably a very old gasket and had no idea what head/engine it fit...even though it looked close to correct for a 261. He had no idea where or how Best Gasket sourced it and why they would have put it into the kit. He was going to check with them. I'll report back if I hear anything just because others might find it interesting.

Thanks again for the advice,

Matt

What is the difference between a steam hole and a water jacket hole?

I doubt if Best Gasket uses/used FelPro parts - my guess is that Patrick swapped the FelPto head gasket into to Best Gasket set - after earlier taking out the original Best Gasket head gasket for another customer.

I've often seen the six little holes that are added to the 261 referred to as steam holes for whatever reason. Not sure what the difference is other than one might be more for coolant flow and the other designed more to release steam pressure due to the siamesed cylinder cooling jacket on the 261 block that differs from a 235 block.

The 261 was also designed for a bypass thermostat. Some folks will argue that is only necessary because the larger trucks might have engine strain before proper warm up. As much as I agree, I think this is probably secondary. Others (like me) will argue that the primary reason GM engineers added the bypass thermostat had more to do with the siamesed cooling jacket in the 261 block requiring coolant flow at all times. I think the steam holes and the bypass thermostat were an integrated design by the GM engineers for the 261.

Patrick's had just received the gasket set from Best and I picked it up from him the day it arrived. The package was sealed. The error was on the part of Best, not Patrick.

Matt

The "steam holes" on the 261 serve the same purpose as the ones on a 400 small block V8. They prevent coolant from becoming stagnant and boiling where the siamesed cylinders create a potential hot spot from coolant being unable to circulate between the cylinders. It's entirely possible the undersized hole in the gasket is there to direct more coolant toward the back of the block and less upward flow into the head. The incident I mentioned above on the 302 Ford involved one of my students cutting big holes in the gaskets to match ports in the heads without understanding the gasket was blocking passages at the front of the heads that allowed them to interchange side to side. The result was virtually no coolant flow to 3/4 of the length of the engine on both sides. Smart folks, those gasket designers!
Jerry

They were called additional coolant passages by GM/Chevrolet. I get worried when I hear about steam in an engines cooling system - if you have steam, you have problems.

Jim Carter is the source of the "steam holes" misnomer.

Matt,

It looks like you will just have to take your chances with the 261 head gasket. If you use the 235 gasket, there is no doubt you will block those additional 261 coolant passages.

Let us know how this works out.

I had examples of three different NOS GM 261 head gaskets, all had slightly different hole size.
I think all designs will work fine.

Canadian Pontiac 261's (of which I bet there are more in existence than the truck version) came with the same non-bypass water pump as on 235's leading me to doubt this theory.

I called Best Gasket and asked them about the possibility that they shipped a RS639SA Chevrolet Truck 6 261 1954-62 gasket set with a FelPro head gasket.

I'll let you know their response.

Here is what the Best Gasket head gasket should look like?
Here is the Fel-Pro head gasket.
They sure do look alike.

Tim, take a good look at the manifold side of both gaskets. The Best gasket is missing some large holes compared to the Felpro gasket. Then take a look at the engine front of both gaskets. That little hole that I began this post asking about? Well, it's on both gaskets but the Best gasket also has a matching little one on the other side of the front while the Felpro has a larger hole that matches the head and block.

The one shown on the Best Gasket website appears to be the pattern of the one that I received. Patrick said the Best pattern is not for a 261.

This is why I posted the original question. The Best Gasket doesn't match the head or the block. The Felpro almost matches the head and the block with the exception of the one little hole. I agree with what Jerry says about gasket manufacturers knowing their stuff, but I would be hesitant to use the Best gasket that blocks many holes.

Matt

I give up.

I got a response from Best Gasket, regarding RS639A

"We still use a felpro head gaskets in this set. When we have exhausted our Felpro head gasket inventory, we will reproduce the head gasket with our material."

Sorry, Matt, I tried.

Tim, thanks for checking. Interesting that Best uses a different Felpro gasket with a very different pattern than Felpro lists for the 261!

See why I was confused?

Matt