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| | | | Joined: May 2004 Posts: 204 Wrench Fetcher | | Wrench Fetcher Joined: May 2004 Posts: 204 | After doing some research I found that what I thought was a 235 ends up being a 261. I have the following combination:
Block casting # 3759365 1959 GM 261
Head casting #3836848 1956 GM 235
Does anyone have any knowledge of this combination? I am getting ready to rebuild this engine is it worth my time and $ or should I find a different head / block. | | | | | | Anonymous Unregistered | | Anonymous Unregistered | If indeed you do have a 261, you have a real truck motor that is considerably better than a 235. Inline enthusiasts much prefer this motor because it has more cubes, stronger rods and well designed full pressure oil lubrication. I have a '62 261 that I pulled from a low mile dumptruck - not sure which rig it is going into yet. | | | | | Joined: May 2001 Posts: 1,904 'Bolter | | 'Bolter Joined: May 2001 Posts: 1,904 | I now have a '61 261 with an 848 head. The 848 head came from a newer 235 and has a smaller combustion chamber which gives a bit higher compression ratio. I suspect most my additional power comes from the 261's displacement and not the head.
When you put that head on a 261, you must drill some extra coolant holes in the head to match those in the 261. Jim Carter has a good Technical Tip on the 261.
1948 3/4-Ton 5-Window Flatbed Chevrolet 34 Years. Now with a '61 261, 848 head, Rochester Monojet carb, SM420 4-speed, 4.10 rear, dual reservoir MC, Bendix up front, 235/85R16 tires, 12-volt w/alternator, electric wipers and a modern radio in the glove box.
| | | | | Joined: Aug 2000 Posts: 248 'Bolter | | 'Bolter Joined: Aug 2000 Posts: 248 | Sounds like you have a good find there.... There is a good possibility the engine was worked on or rebuilt before by someone knowledgeable of the 235 heads on a 261 block..... I will bet you $5 bucks the steam holes have already been drilled in the "848" head to match the block.
If you rebuild one caution.... when replacing the pistons you may find them tooo short and they will leave to much space at the TDC..... space between piston top and top of engine block.... good specs call for pistons to be recessed .020 to get the advantage of higher compression.
The solution.... which is costly time wise is to install a couple of piston on the rebuilt crank and rotate to take measurements.... then dis-assemble the whole thing.... and have the machine shop mill the top deck of the block to .020 or .030 clearance.... than clean the whole block and re-assemble...... from what I have been told and read there is very little metal that you can shave off the heads and it must be taken off the block deck......
My new found knowledge was acquired in rebuilding my 261..... according to paper calculation from the "Mawsheene" shop expurt I should come out around a conservative 9 to 1 which is a whole point better than stock..... overall a %50 percent improvement on the original 216 BHP...around 150....I hope!!!!
As I am not a real expurt but learning as I go I would appreciate comments from resident "gurus"
Bob C.
Bob C.
CMP Heaven
The Hammond Barn
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