The Stovebolt Site Forums The Shop Area Engine Shop GMC Engines

Hello Bolters! I am new to the list here in registration but have been reading and lurking for years. I have several Advance Design Chevy and GMC trucks. I have been working with these vehicles for around 20 years now. I am no expert but have seen some things. I may chime in now and again with my .02 worth. One thing I have not seen a lot of talk on is the GMC engines. Are there many "Jimmy" buffs out there? I would like to swap stories and source information with some GMC folks. Any takers?

I am always willing and able to discuss GMC's! Just not a lot of info going around about early GMC's I have to go to Oldsmobile websites to get info on my engine.

Hi Big Six 302
I have a 302 side motor mount a 270 motor mount U shape & 248 timeing gear plate type.
The timeing gear plate on 248 has oil driper for cam gear -none on 270 plate should I add one?
I plan to install the 248 in a 55 gmc 1/2 ton what style motor mount did it take? Will any type work thanks Bill

Cool! GMC talk while I slept. I am currently in the processes of building a 228 and a 302 Military engine. It is the side motor mount version from what I have looked at. The civilian 302 that I looked at from a bus hd the same front motor mount that my 228 has. I have to admit that I did not pay attention to the 302 when I took it apart here as I intend on changing that motor mount to one from a 228 engine. My 228 that I am working on has the dripper tube for the cam gear on it. The previous 228 in my Burb had this too. I have not taken down a 248 yet. Have not seen many of these, although I have one setting out in Wyoming waiting for me to come and pick it up. I also have a 270 here that I recently aquired but have not pulled it from the truck yet to work on it. It is going to need some attention I am sure. As to your question....I just went down and looked at the parts from the military 302 and they are made the same as the parts for the 228, with the exception of the two holes at the bottom for a motor mount. They are not drilled out on the military engine but the plate looks the same to me. Oil dripper is in the same location on both engines. I am referring to the plate that bolts to the front of the block here. I would think that all the engines should have this dripper tube for the cam gears. Which version of 55 truck do you have first or second series? I would think that the motor mount would be the same for both, but have not worked on any 55 year trucks. Mongo here has a 54 but that area was a cut up on his frame by a PO. I still think they are similar to the earlier trucks. :rolleyes:

Thanks to the GMC guys out there. I have really become a fan for some reason. I guess it is because there are not as many around. We have a truck club here in Kansas City and there are some Jimmys there, but not nearly as many as there are the Chevy trucks. Chevys are cool too! Don't get me wrong. I have a couple. It just seems that if we share our GMC info some more....perhaps more folks would build one and add to the popularity some. There are quite a few picture of em in the gallery. Keep the chatter coming!

Back in my family's early 1950's dirt track racing days, the military 270's were about the only engines that could keep up with our Blue Oval flathead V-8's. We ran an alcohol/hydrogen peroxide fuel mix and lots of compression, but the GMCs had enough torque to accelerate off the turns with the tighter-winding V-8's. If they ever got the power to the ground, they could really fly!
Jerry

web page: all gmc, all the time...

Yea I just finished drilling holes in the 302 plate it is the same as the 248 plate for mounting I belive. I did notice the back of plate is flat on 270- oil grove in 270 block- oil grove in 248 plate and block. But this stuff may have allready been changed a time or two?
I did use the 270 plate just welded a driper on it. Saved the 248 mount for the 302 then found out I could just drill the 302!
Also I used the 270 plate so I could use the U mount it will bolt to 248 or 270 not the 302.

Oh the 55 is a 2nd series plate on door says it had a 248 and hydramatic . When I got it the motor was a 270 with a rod out the side of block--hyda trans still there.
The 270 still has good parts just put the oil pump(rebuilt it) in 302 and will use the oil pan ,the Millitary 302 pan is a monster. Other stuff wil go on 302 from 270 then I will need another GMC for the 302 to go in. Bill

does a 336 pontiac (V8) count as a GMC engine. . it says GMC on the valve cover. . but u have to order parts for a pontiac :confused:

BrianK

I recently installed a GMC 302 in my 51 GMC 1-ton, and replaced the 5.14 rear with a 4.10 with Detroit Locker. I got a bunch of help from this board, and from the Inliners board, with fan, pulley, and flywheel issues. I'm finally on the road although I'm still working on a few suspension issues. I've always prefered the stock forest green and rust look, so you won't be seeing me at the "Show and Shine", but you might see my rusty farm truck passing you on the interstate.

Thanks to all for the help

Hey 55. you have an extra 270 head you want to part with? I may be interested for the right price. Let me know!

Nice to read about some GMC for a change...

A question for the GMC experts..... I know for a fact the old 248 GMC will bolt on to the original 216 bellhousing..... will the 270 or better still a 302 bolt on to the old 216 bellhousing???? I have to use the old 216 bellhousing since my vehicle is right hand drive and the cluth fork is located on the right side... dreaming of another project.

Thanks for sharing your knowledge.

Bob Carriere
1940 CMP 15 cwt
4x4 right hand drive.

BIGSIX 302
Yes I have a 270 head and I need some hydramatic bellhousing parts , maybe we can do a trade? Email ([email protected]) we can talk.

To RAC1812...you should be able to put any GMC engine of the same era against the bell housing you have. I am even pretty sure you could put any Chevy engine against the same bell housing. Also keeping the era in mind. The bolt pattern on the flywheel end of my my 302 block is the same as my 228 engine block. other components of the GMC engines are also interchangeable. I realized after I typed all this the year you wre asking about is pretty far off from what I have experiences with. The trucks I work with are 48 to 54. The Advance Design series. I would still think the engines would be the same as far as matching to the bell housings. Let us know what you do find out and let me know if I am all washed up or not!

I have a 1956 GMC long bed, 288 V8, Hydramatic, wrap around rear window.

I have a GMC 270 that powers the truck I drove to work this morning.

I also have a '52 GMC that is missing lots of engine parts. I presume its a 228, but I don't know that.

Brian K: I've been told those GMC V-8 valve covers can to used on later motors, including the Pontiac 400 and 455. Not that I'd suggest hot rodding your truck, but I have a 454 I hope to put in mine someday.

For you guys wanting to drill that front mount.
here's some measurements I made last year for a guy drilling out a 235 he was swapping in place of a 216.
[img]http://www.mongosgarage.com/tech/235mount.jpg[/img]
Might be the same for the GMC's maybe someone could measure it and confirm.
MONGO

These demensions are the same as my 228 GMC mount. Seems to be the same pattern I'd say!

To BixSix302.....

My truck had originally a 216... and they bolted a 248 GMC to the original bellhousing.... using what seems to be the original flywheel and 9 inch clutch. Can I assume that a 270 would also bolt on the bellhousing????

I am now committed to rebuilding a 261 1958 ex fuel delifery 3 ton truck.... which bolts on the old 216 bellhousing.... and will be using the 10 inch flywheel clutch of the '58 and the original 1940 4 speed crash box... no synchros...yikes!!!.

I have saved the 248 for a future project.

My 261 will have the central, one only, motor mount bolted to the bottom plate at the front of the engine... actually got mine from another donor 235..... I am also using 235 heads after many recommendations that is was a better mix on the 261...as long as you remember to drill out the steam hole...... it will take me from an original 82bhp to a whooooping 145bhp....

Top speed with the original 216 and 16 inch wheels with 6:39 axles was about 45mph.... I am hoping for at least fifty with the 261...going down hill.... hoping the brakes will hold up...

Would love to do another one using a big 270 or better still a 302 but would expect crank to flywheel incompatibility problems....not to mention the overall lenght of the GMC block.

Sure appreciate all the info and help I have gathered over many hours of reading the Forum.

Bob Carriere

If you already have a248 in the truck the 270 or 302 will fit with no problems to the bell housing and the front mount. You will have to aquire a flywheel that will work with the bigger engines. They are six bolt pattern. I am not sure yet if the 270 and 302 use the same flywheel. I will likely find out a later on this spring, as I have a 270 in a truck that is very tired and a 302 military engine that seems ok. So a transplant seems in order. I also aquired a 248 that seems in good shape too but I am going to use the 302 head that is on it for my 52 GMC Suburban. Once again the flywheel will be the biggest issue. I think Tom Langdon sells a flywheel that will work on the 302 six bolt pattern. Sounds as if you are making some progress. That is always a good feeling. Keep up the GMC chatter fellas. All this info sure helps evryone out.

Just got back to work on my supposedly 1956 GMC 150 since before I had internet! It's got a 288 pontiac V8 that was manufactured in canada for 1 year, 1955. Just thought would let you know,I am also in possesion of an old Motor's Truck Repair Manual,18th Edition that my brother found in a dumpster back in 1979 that covers 1955 through 1965!I look forward to sharing and getting some help myself in the future, Thanks. Rick