So, I've had my '53 3/4 ton for 24 years or so now, and been using it as a DD most of that time. Since '04 I'm running a stock 216 that was a free gift from a nice gent back in Colorado who was going the SBC route. Well, the 216 was finally showing its age--low compression, almost no power, leaking lots of oil and coolant... so I decide it's time to swap in the sweet-looking 235 I picked up at a local auction for $90. I had the 235 up on blocks, got it all cleaned and painted nice, put in the flywheel from the 216 and a brand new clutch, and finally hoist it into place on the truck.
I'm itching to get everything hooked up to see how she runs. Fiddle with the timing for a few hours (should have realized the timing mark on the flywheel would be useless, as I put my original 216 flywheel on the '53 Powerglide hi-pressure 235), but finally got her to purr! So, let me slide the tranny back in place and get everything else buttoned up. Or so I thought; I've got the SM 420 4 speed up on blocks at the correct height under the truck, ready to just slide back into place. It takes some wiggling of course to get the splines into the clutch disc and then the front of the input shaft into the pilot bushing, but she finally snugs up.
And then the HORROR strikes me: the bellhousing on the new 235 does not align with the bolt pattern on my '53 SM 420!!! And here I was thinking all 1950s GM manual transmission bolt patterns were the same! The darnedest thing about it is it's only off by a little bit, probably less than an inch, so it's not really noticeable on just a casual visual inspection. I actually did measure the width of the bellhousing at the rear engine mount points, to be sure the old mounts would work, but I never even thought about checking that transmission bolt pattern!
Argggh, now I have to yank the whole engine back out, set it down on blocks, pull the clutch and flywheel, pull the bellhousing, install the 216's bellhousing on the 235, put the flywheel and clutch back in, and drop it back into place. I think I just added 3 or 4 hours to an already interminable project! Oh well: lesson learned: CHECK THE BOLT PATTERN!
