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Differences between GMC and Chevrolet L6's
#1216728 Wed May 10 2017 04:10 PM
Joined: Oct 2013
Posts: 331
M
Shop Shark
Fixing to acquire a '53 GMC 400 with a 270 in it. I already a few stovebolt chevrolets and I am wondering what parts - if any will interchange between these two engines. Looking at picture on google images it looks like there may at lease be some parts that do interchange. The cylinder head looks entirely different though - but do they interchange? At first I assumed the GMC engines (248, 270 & 302) were completely different, but now looking at the pictures it doesn't look like they're very much different than the chevrolets. Just curious.


1950 4100 - unrestored and driven weekly for almost no reason at all.
Re: Differences between GMC and Chevrolet L6's
mechanic58 #1216733 Wed May 10 2017 05:05 PM
Joined: Jun 2011
Posts: 3,597
Shop Shark
Nothing much interchanges. GMC's had two(at least) heads, large and small intake ports, not all heads fit all engines because of piston domes being different, for example. Patrick has a good catalogue that explains this. GMC always had full pressure oiling. GMC engines about 3" longer, radiator within core support to accommodate this, rather than behind like Chevy.

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.
Re: Differences between GMC and Chevrolet L6's
mechanic58 #1216741 Wed May 10 2017 05:48 PM
Joined: Oct 2013
Posts: 331
M
Shop Shark
I did wonder about length. It's hard to tell that looking at pictures. For example, the timing covers look to be identical. It's misleading. I did notice the radiator in the Jimmy I am getting is forward of the location of the radiator in my 4100.


1950 4100 - unrestored and driven weekly for almost no reason at all.
Re: Differences between GMC and Chevrolet L6's
mechanic58 #1216742 Wed May 10 2017 05:50 PM
Joined: Oct 2013
Posts: 331
M
Shop Shark
I did notice that the cylinder heads look to have far superior combustion chamber design compared to the Chevrolets. That's why I wondered if the heads would interchange. Guess not.


1950 4100 - unrestored and driven weekly for almost no reason at all.
Re: Differences between GMC and Chevrolet L6's
mechanic58 #1216744 Wed May 10 2017 06:10 PM
Joined: Feb 2004
Posts: 20,811
H
Boltergeist
Some accessories like distributors, fuel pumps, and carburetors will bolt on, but no guarantee that they will work as well as the correct items. I believe starters and generators will also swap.

One trick dirt track racers used to use was to adapt a GMC oil pump to a splash-oiled Chevy engine to get better oil pressure. I'm not sure how much tinkering was involved in that swap, however.
Jerry


The murder victim was drowned in a bathtub full of Rice Krispies and milk.
The coroner blamed the crime on a cereal killer!

Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
Re: Differences between GMC and Chevrolet L6's
mechanic58 #1216748 Wed May 10 2017 06:27 PM
Joined: Dec 2008
Posts: 1,468
P
Shop Shark
Every dimension is wrong (block, deck, bolt pattern, head, length, cam, valves) except crank journal diameters, but the cranks can't be exchanged.
The oil pump looks like it can be swapped, but since the 1955 Gen-2 pump is even bigger no one has tried in 60 years. The distributors may swap?

The basic stovebolt head design was good enough for Mercedes to use until 1971 in the 280 SL ("pagoda" roof), and the post-WW2 Toyota Type “F” L6 OHV engines are based on this head.
I disagree, vertical OHV valves were made obsolete in 1949 by Cadillac and Oldsmobile (and eventually Ford SB, FE, FF, Chrysler LA, B, RB, Pontiac, Buick nailhead, Chevy SB, etc.) flat chamber floors are a terrible idea. The highly rated "H" head's chamber is almost completely open with no squish. The "D" chamber has quench but badly shrouded and placed valves.

Re: Differences between GMC and Chevrolet L6's
mechanic58 #1216771 Wed May 10 2017 10:21 PM
Joined: Feb 2004
Posts: 20,811
H
Boltergeist
Oliver farm tractor inline sixes are almost clones of the stovebolt engine, also. On one tractor engine I rebuilt, I used 235 valves and guides to replace the antique Oliver parts that were no longer available. The only noticeable difference was the diameter of the valve stems, and the Chevy guides fixed that problem.
Jerry


The murder victim was drowned in a bathtub full of Rice Krispies and milk.
The coroner blamed the crime on a cereal killer!

Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
Re: Differences between GMC and Chevrolet L6's
mechanic58 #1217491 Tue May 16 2017 04:45 AM
Joined: Nov 2002
Posts: 365
O
Shop Shark
That sure is crazy talking early chevy 6 cylinders and you bring up an Oliver tractor which I so happen to have there Hotrod Lincoln. This one is a 4 cylinder called a Super 55 which is pretty dam strong. Yeah has a 6 speed with 2 reverse speeds, this was Pops ol tractor when he was farming almonds in the southern california area. Little town called Quartz Hill.

Re: Differences between GMC and Chevrolet L6's
mechanic58 #1217493 Tue May 16 2017 04:58 AM
Joined: Feb 2004
Posts: 20,811
H
Boltergeist
I owned a diesel shop and 24-hour road service in the late 1970's on Highway 99 in Atwatwer, about 70 miles north of Fresno. There were lots of almond orchards up that way, too.
Jerry


The murder victim was drowned in a bathtub full of Rice Krispies and milk.
The coroner blamed the crime on a cereal killer!

Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
Re: Differences between GMC and Chevrolet L6's
mechanic58 #1217533 Tue May 16 2017 06:50 PM
Joined: Oct 2016
Posts: 685
N
Shop Shark
Were 50-53 GMC's 12 volt or 6 volt?


Dave

Clutch head screws have stolen too many hours from my life....

1950 Chevy 3600 (resto-something) - the work resumes...
https://goo.gl/photos/8t5mLuj4JZebvGq49

1963 GMC Widebed Custom

1951(?) GMC flatbed that is now a flower garden:
https://goo.gl/photos/H79pvKhHLxjNiR149

1968 Chevy II Nova- not running, waiting for me to finish the '50 3600
https://goo.gl/photos/Dh7q4pt3WSkKjjFr9
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