Inliners International Forums General Discussion Engines 261 head

Just looked on the head of my 261 and found 836848 is this a 235 head or real 261. can't see were the head was drilled for steam holes. Is the 261 head end in 850 ???

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Yes, many 261 heads end in 850, a 848 is the so called better 235 head.If your 848 head isn't cracked, drill the steam holes and re use it.

So you are saying that my head off the 261 848 is not factory and should have steam holes. If not then drill them. A factory head for a 261 should be 850 right.

Yes

Not all 261 heads ended in 850. Some ended in 570 mabe some others but those are the two I know about. Regardless of the casting number all 261 heads should have the steam holes in them.

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32 5W Coupe
64 Chevelle convert
53 Bel-Air 2dr sedan

Ok got ya. Now for the next question. I live in Canada and both the 261's I have are out of big old pontiacs 1959's. They both have 848 heads could that be why the heads are not right? They are drilled but it looks like factory, I can not see anybody in the 60's drilling the heads ?

Hi..my 261 is from a 1961 Canadian Pontiac and has the 848 head...it was an unopened low mileage engine.......

So this means that some Canadian 261's had 848 heads that were from the factory, with steam holes.

Well....I looked at a few more Pontiac 261's today and they all had the 848 head...with steam holes...so it would appear GM Canada used the same head for 235's and 261's in cars....what head the Chevy trucks used I don't know.....

My 261 engine, which was not original to my 54 GMC obviously, had a 235 head installed on it when I bought the truck. Many people installed these higher compression heads on the 261's for performance reasons, but I also imagine they were replaced by the 235 heads simply because they were easier to come by than the 261 heads. I had my 235 head drilled for steam holes when I had my engine re-machined. Here is a picture of my head after being rebult and with the steam holes drilled: http://community.webshots.com/scripts/ed...security=OWyhlH

What's the casting date on those Pontiac 848 heads? Is it close to the year of the car? Just curious.

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32 5W Coupe
64 Chevelle convert
53 Bel-Air 2dr sedan

The compression of an 848 head isn't much higher than an 850 head, though. Only 0.8 more.

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1950 Chevy pickup with '62 261, 4 speed.

My late 261 (3769717 casting number) has the head casting number 3836848 on the intake side - but also has these numbers like this on the opposite side:

B40 848
850
When I get this head removed I will CC the combustion chamber and compare it to a 235 "848" head - but I'm pretty sure it will be the same. This head will give lower compression on a 261 due to the larger bore size. Corvette motors used yet another head (3836241) but I think it was basically the same except the casting was different for the unique Corvette water pump.

We have data from original GM blueprints that lists chamber volumes on some of these heads. It will appear in the 12 Port News soon. Any confirmed info on the Canadian heads will be included if someone can provide it.

Jack,
My '62 261 has a 3836850 casting number on the top with the same ones as you have on the side. Very interesting. I would be interested to see your CC numbers.

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1950 Chevy pickup with '62 261, 4 speed.

I installed an 848 head on my 261 years ago, before I ever heard of the steam holes. I never bothered to take the head back off to drill the holes. I don't drive the truck that the engine is in a lot, but have probably put 5000 miles on it since the head was installed. I haven't noticed any problems with it yet. What am I risking by not drilling the steam holes?

Dear Eric;

Nothing really. They are there because trucks carry heavy loads & run in all kinds of conditions etc.

In hot weather slow traffic, or climbing a long steep grade is where they come into play.

Just do it next valve job. You just need the 261" head gasket as tempate.

Good luck, John M., #3370.

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Thanks John, I was hoping that was the case.

The reason for the holes is to prevent hot spots from occurring from air getting trapped due to the siamesed cylinder walls. The same thing can occur with the 400 SBC. You should drill the holes if you can.