Labor Day Putting down your wrenches or time for
MORE wrenching? 
Plenty of places to share. | | Click on image for the lowdown. 
====
| | | Forums66 Topics128,018 Posts1,055,239 Members48,417 | | Most Online14,466
Apr 26th, 2026 | | AD Chevy Trucks  Over 6,000 pictures Brad Allen has an awesome collection of Chevrolet factory pictures that he has set up from film strips. Check them out!
Lots of work on Brad's part ... pure enjoyment (and references) for you!
| | THANKS!
For helping keep this great
old truck web site
on the Internet for over 30 years! and not clogged down
with Ads!  Again, thanks!
| | | | Joined: Jan 2021 Posts: 6 'Bolter | | 'Bolter Joined: Jan 2021 Posts: 6 | Ok, ok, I know im going to get ALOT of flak for even posting something as sacriligious as this, but...
I am seriously considering puting a chevy 235 in my half ton GMC. This is definately Plan B for me, but using both the "third times a charm" and " three strikes and you're out" rules, I cant get ahold of a GMC engine that can be even rebuilt around here.
However 235s are a dime a dozen and I have seen this setup in several GMCs online. Trouble is, I cant find a goid description of what I need to consider... ive got that 235s are shorter... but what about bellhousing, transmission (wanting to keep my GMC 4 speed), etc.
Does anyone have experience doing this swap?
Thanks!
------------
1947 GMC half-ton
| | | | | Joined: Feb 2004 Posts: 29,740 Kettle Custodian (pot stirrer) | | Kettle Custodian (pot stirrer) Joined: Feb 2004 Posts: 29,740 | Chevy and GMC engine blocks share the same bellhousing bolt pattern, so that's not a problem. 47 was the break point between the crash box and the SM-420 transmission on most of the trucks, so it's possible you've got the later model transmission. Does your shifter have a reverse lockout trigger? If not, you've got the SM 420. You'll need to fabricate a bracket to move the front motor mount back a couple of inches and do whatever adapting the exhaust pipe and throttle linkage requires, but overall it's a pretty simple swap. Good luck!
Jerry
"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!
| | | | | Joined: Jan 2021 Posts: 6 'Bolter | | 'Bolter Joined: Jan 2021 Posts: 6 | Thanks Jerry! I do have the lockout lever, so I must have the "crash box"... im assuming that means non-syncro. Does that change anything?
Thanks, Zech
------------
1947 GMC half-ton
| | | | | Joined: Jun 2011 Posts: 5,096 Crusing in the Passing Lane | | Crusing in the Passing Lane Joined: Jun 2011 Posts: 5,096 | GMC engines are usually easy to find, up to 302 cubic engines, I would look some more, carefully. Once one gets organized, they usually appear. Some appear in milk trucks, vans, etc. SN behind the starter stamped on machined surface start with displ@cement, I e 270xxxx. Valve cover always different than Chevy valve cover. It would save a lot of work if you can find a proper GMC engine.
Ed
'37 GMC T-18 w/ DD 4-53T, RTO-610, 6231 aux., '95 GMC running gear, full disc brakes, power steering, 22.5 wheels and tires.
'47 GMC 1 ton w/ 302, NP-540, 4wd, full width Blazer front axle.
'54 GMC 630 w/ 503 gasser, 5 speed, ex fire truck, shortened WB 4', install 8' bed.
'55 GMC 370 w/270, 420 4 speed, grain, dump bed truck from ND. Works OK.
| | | | | Joined: Feb 2020 Posts: 47 'Bolter | | 'Bolter Joined: Feb 2020 Posts: 47 | Go over to the OLDGMCTRUCKS site and contact Motion Guru. I believe he has GMC engines. Located in Yacolt. I have 2 302"s but I'm In Colville.
Joe
just retired and finally making headway on my project truck. 1940 GMC AC152.
| | | | | Joined: Feb 2004 Posts: 29,740 Kettle Custodian (pot stirrer) | | Kettle Custodian (pot stirrer) Joined: Feb 2004 Posts: 29,740 | Although I've got a couple of crash box 4 speeds stashed away, I'm no expert concerning the differences in them. I'm reasonably sure the Chevy engine will also bolt up to that bellhousing, which has a different transmission bolt pattern than the 48-up synchronized boxes. Definitely follow the leads the other guys have given you. I've got one GMC engine on hand, a 228, but I'm in middle Tennessee- - - -probably more of a road trip than you'd want to make!
Jerry
"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!
| | | | | Joined: Jan 2001 Posts: 5,337 'Bolter | | 'Bolter Joined: Jan 2001 Posts: 5,337 | If I remember correctly, the GMC engine uses a four bolt flywheel, the 235 will have six.
See the USA in your vintage Chevrolet! My Blog | | | | | Joined: Jun 2011 Posts: 5,096 Crusing in the Passing Lane | | Crusing in the Passing Lane Joined: Jun 2011 Posts: 5,096 | Early GMC’s use 4 bolt flywheel, later ones use 6 bolt. I suspect modern 270’s (not wartime) and 302’s all have 6.
Ed
'37 GMC T-18 w/ DD 4-53T, RTO-610, 6231 aux., '95 GMC running gear, full disc brakes, power steering, 22.5 wheels and tires.
'47 GMC 1 ton w/ 302, NP-540, 4wd, full width Blazer front axle.
'54 GMC 630 w/ 503 gasser, 5 speed, ex fire truck, shortened WB 4', install 8' bed.
'55 GMC 370 w/270, 420 4 speed, grain, dump bed truck from ND. Works OK.
| | |
|
|
