The Stovebolt Site Forums The Shop Area Engine Shop 261 steam hole questions

I have a couple of Canadian Pontiac 261’s both of which have 3836848 heads with steam holes that I am certain left the factory that way from GM Canada in Oshawa. I have also read several times that the usual practice for using this head on a 261 in the U.S. is to simply use a head gasket as a template for drilling. The steam holes in both my heads are at a 12 degree angle toward the manifold side which has me wondering if the holes on a U.S. 261 are drilled perpendicular to face or tilted and if anyone who drilled them straight had difficulty intersecting the water cavity on the one very close to a head bolt?
Here’s what I’m talking about and thanks for insight from anyone who knows what’s up with this.

Boy, Curt, that is a great observation and question.

I have an 848 head that is destined for use on my 1960 261 USA truck engine. If the extra water passages are drilled on an angle in my 261 head, I'll probably drill the 848 head to match, unless someone posts a plausible reason not to do so.

Tim

The US 261 heads are also drilled at an angle.

def at an angle. and when i get home, and remember, and find it, i'll post a detailed/photo article on the process that i just happened to find the other night while searching for something else. unless someone else posts one/it

what's their purpose?

The 261's have "siamesed" cylinders, with no passage for coolant between them. The large bore makes that casting process necessary. The steam holes allow coolant to pass close to the cylinder walls on its way from the block to the head, eliminating hot spots where the cylinders meet. The small block Chevy 400 V-8 uses the same type of holes in the head, for the same reason- - -big bore and siamesed cylinder walls.
Jerry

ah. thanks for the expla. and i found the article
http://www.gregsengine.com/350to400.htm

Here is the Chevrolet description/introduction of the 261 engine. The siamesed cylinder-bores and six additional coolant passages are described.

It makes me cringe (but, I'll get over it) when the expression "steam holes" gets used (thanks, I think, to an old Tech Tip by Jim Carter). I doubt if GM designed an engine to have steam running though it.

I realize this is an older thread but since I have been researching this topic and still had questions I thought I would kick in a tidbit of experience.
I had planned to have my 235 head (*913 casting #) drilled for the addition of the steam holes for my 261 block and had difficulty finding anyone who would do this.
I took a good look at the head to see if I did this myself, what I would be drilling into. I used a small piece of phone wire to poke into the water jacket to see how deep the cavity went (This cavity is parallel to the milled head surface). The steam hole closest to this water jacket hole could be drilled straight through, to intersect the cavity. The second steam hole farther away, needed to be drilled at the slight angle to intersect the cavity. I read about drilling at an angle toward the manifold... around 12 degrees. I'm of the opinion that if all holes in the head are angled, it is because the head was tilted to this desired angle in one set-up. I only needed to carefully locate the holes so they would match the block... double... no, triple check!
I bought a titanium 1/4" drillbit from Lowes, located my holes and drilled them with my hand drill, with the head on the ground (so I could put some weight into my drilling). The drill depth was around 3/8" and the titanium bit ate through the cast iron, like a butter knife. It was easy and I fretted all this time for nothing. I'm happy that my block will be able to breathe better!
I hope this helps someone with the same questions in the future.

Jerry

After reading the information provided by Tim in the link noted it is obvious that the several statements I've read over the years of using a 261 cam in the 53-55 Corvette cannot be completely true. If the bearings journals are larger in the 261 as stated then they could not be used in a 235 block. The cam lobes may be the same or similar but not the actual part numbers. We learn something everyday.
So one of you industrious types with all the parts books may want to check this out and let us know what you find.

Dave,

My understanding is that the "261 cam" started being used in Corvettes in mid 1954 and was used on all 235 engines from 1956 onwards. The Master Parts Books show 53-55 for the 261 cam in a Corvette.

Check out the cam bearings in that MPB page.

1954 261 has small journals.

I mic'd the journals on my 261 cam. The journals as the tech bulletin stated, are the same as the 235 cam. The only difference between the two, is the 261 lobes have a higher lift for more kick at higher RPM.
A person could use either cam. The 261 springs are 1/8" longer but you can even buy springs that are "split the difference" to fit either engine. I'll be using my 235 springs and don't expect an issue for my occasional 1/2 T driver.

Jerry