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#1451147 Mon May 09 2022 06:45 PM
Joined: Nov 2020
Posts: 9
J
'Bolter
Hi,
I'm having some technical issues with my 270 engine in the machine shop.
I'm curious if parts are interchangeable with a 248 and if so where does it state that the parts are interchangeable?
I have a service book for the 100-400 series trucks and cant find if anything is interchangeable. Am new to engine rebuilding
James

JamesPrice #1451183 Mon May 09 2022 11:43 PM
Joined: Jun 2011
Posts: 4,496
E
'Bolter
What are the issues?

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.
EdPruss #1451184 Mon May 09 2022 11:46 PM
Joined: Nov 2020
Posts: 9
J
'Bolter
Shop says conecting rods and cylinder head are for a 248 and not a 270 although they came out of a 270

JamesPrice #1451194 Tue May 10 2022 01:57 AM
Joined: Jul 2014
Posts: 866
D
'Bolter
Here are pages that detail engine specifications - I am not a GMC Knowledgeable person, I found these doing a search and thought they might be useful, covers a lot of information regarding engine specs, casting numbers, etc....courtesy oldgmctrucks.com
right click on image, open in a new tab, then magnify..

The GMC Heads page has some good details regarding head casting numbers and the model year.

Hopefully a GMC expert will be along shortly to provide more information...

Attached Images
EngineSpecs_Pg1G.gif (1.21 MB, 125 downloads)
EngineSpecs_Pg2G.gif (1.08 MB, 124 downloads)
EngineSpecs_Pg3G.gif (1023.55 KB, 123 downloads)
GMC Numbers Game .jpg (175.75 KB, 125 downloads)
gmc_heads.jpg (233.95 KB, 125 downloads)
Last edited by Dusty53; Tue May 10 2022 02:11 AM.

Ron
1954 Chevy 3604 - A work in progress...
Veteran, USMC

" You can't keep dancing with the Devil and wonder why you're still in Hell ! "

"Everything happens for a reason, sometimes the reason is you're stupid and make bad decisions"
JamesPrice #1451766 Mon May 16 2022 12:31 AM
Joined: Feb 2011
Posts: 1,020
T
'Bolter
That info shows what is different between the designations, I can't see them tooling up for different con rods and heads. Even other parts that may need a change are likely done by machining them to different dimensions.
You have to love those odd fractional dimensions of that era, like the Bore and Strokes.


Ret, Machinist , Industrial Engine
Engine specialist

Kicking self for selling off my Taskforce trucks.
JamesPrice #1451768 Mon May 16 2022 12:46 AM
Joined: Jan 2019
Posts: 52
G
'Bolter
Gmc 270 and 248 use the same rods. Some of the early gmc rods used a different big end bearing. The main difference is the small end changed in about 53 they went from a .990 to a .1050 small end.
What is the casting number on the rods you have ?

JamesPrice #1451781 Mon May 16 2022 03:08 AM
Joined: Jun 2011
Posts: 4,496
E
'Bolter
There are only 4 different heads, and certain ones go only with certain pistons. Some have larger ports.

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.

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