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Technical 302 GMC identification

Discussion in 'The Hokey Ass Message Board' started by WJ, Sep 13, 2016.

  1. WJ
    Joined: Feb 28, 2007
    Posts: 26

    WJ
    Member

    I am looking to change the engine in my 1953 GMC 1/2 truck. It currently has a 235 from a 57 Chevy. I have located close to me a GMC 302. But I am unable to find any of the casting numbers to verify the year and size. The casting numbers on the head are 2194818 and the ones on the block are GM01 2324 E44. The only numbers on the machined surface by the distributor are 302 and nothing else. Any help would be greatly appreciated.

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  2. RichFox
    Joined: Dec 3, 2006
    Posts: 10,020

    RichFox
    Member Emeritus

    The serial number next to the distributor starts with the size of the engine.
     
  3. OldBuzzard
    Joined: Mar 8, 2008
    Posts: 878

    OldBuzzard

    The 302 is the size and indicates that it is a factory replacement block. The old number was supposed to have been added to that.
     
  4. WJ
    Joined: Feb 28, 2007
    Posts: 26

    WJ
    Member

    Is it safe to say that the 270 engine had a 4 bolt hole pattern on the crank shaft and the 302 has 6 bolt hole pattern?

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  5. RichFox
    Joined: Dec 3, 2006
    Posts: 10,020

    RichFox
    Member Emeritus

    I have had 270 engines with both 4 (early) and 6 (Late) bolt cranks. Since they stamped the engine size on the pad next to the distributor, I think that is the best way to tell which is which.
     
  6. 302GMC
    Joined: Dec 15, 2005
    Posts: 7,856

    302GMC
    Member
    from Idaho

    Your 302 is definitely a factory replacement, sold as either a partial engine or complete. From what I've been able to tell from tearing complete trucks apart, the 4 to 6 bolt crank flange transition starts in '52 with the "P" series 228-248, a Hydra-matic milk truck type, and all 248, 270, & 302 are 6 bolt by '54. It's probably safe to assume all 302 engines are 6 bolt, as 1952 is it's intro year.
    If you have a 6 bolt 11'' flywheel either early or late, take care of it - they're getting scarce.
     
    Last edited: Oct 1, 2016
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  7. WJ
    Joined: Feb 28, 2007
    Posts: 26

    WJ
    Member

    Thank you all for you input/advise. Going to hear this baby run on Saturday. Most likely I will purchase it to install into my"53" GMC.

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  8. gas pumper
    Joined: Aug 13, 2007
    Posts: 2,957

    gas pumper
    Member

    Let us know the details and pictures too. I know of a stash of GMC stuff in Maine and can maybe help if you need anything else to get it installed in your truck.
     
  9. jimmy six
    Joined: Mar 21, 2006
    Posts: 14,795

    jimmy six
    ALLIANCE MEMBER

    There were a bunch of 270-302's found a few years back and only the 3 numbers were on all of them. I did have one stationary 302 engine I bought that had that too. My military and civilian blocks always had a complete number.
     
  10. WJ
    Joined: Feb 28, 2007
    Posts: 26

    WJ
    Member

    I did purchase the 302. The guy had it all wired and ready to run when I showed up. We were only able to run it for a few seconds as there was no cooling system hooked up. I ended up paying 600 for it but is supposed to have less than 10k on a rebuild. I talked to the previous owner and he says it's a hell of a motor. My next concern is. Will it bolt up to the bell housing that is now bolted to the 235 engine? Probably won't start the swap til later in October as the weather here in Maine is still good enough to run around with the truck with no heater. Haha.

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  11. WJ
    Joined: Feb 28, 2007
    Posts: 26

    WJ
    Member

    Gas pumper: maybe the folks in Maine have a set of fentons to fit your new 302? The old 235 exhaust is just about ready to fall off.

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  12. squirrel
    Joined: Sep 23, 2004
    Posts: 55,934

    squirrel
    Member

    bellhousing, should bolt up. Do you have the flywheel and clutch for the GMC?
     
  13. WJ
    Joined: Feb 28, 2007
    Posts: 26

    WJ
    Member

    Yes. The motor is complete and has a 3 speed standard transmission bolted to it at the present time. I figured I will need to mix and match some of the parts to get it together and operating with the 302.

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  14. WJ
    Joined: Feb 28, 2007
    Posts: 26

    WJ
    Member

    I am planning to use the sm420 that is currently in the truck and then down the road I am changing the rear end gears from 4:10 to 3:55 so I can at least keep up with back road traffic
    Haha

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  15. sunbeam
    Joined: Oct 22, 2010
    Posts: 6,213

    sunbeam
    Member

    True or false I was told that only 302s had rocker bushings from the factory.
     
  16. gas pumper
    Joined: Aug 13, 2007
    Posts: 2,957

    gas pumper
    Member

    Used Fentons are hen's teeth!!! And ones for the GMC are rarer than Chevy. But I think for a street engine you could use a used Chevy 235 Fenton or tube header. The port mismatch isn't that great. and the bolt spacing is very close, a little die grinding and you can make them fit. Not perfect but useable. Maybe for a street engine the cast 302 single would be good. They have a really nice 3 bolt flange and handled those engines at wide open throttle at 3800 rpm.
     
  17. OldBuzzard
    Joined: Mar 8, 2008
    Posts: 878

    OldBuzzard

    Don't be afraid to go for better highway gears than 3.55. With engine torque curve approaching 300 ft/lb @ about 1400 RPM you could cruise at normal highway speed & still pull stumps with that transmission you have.

    302 1952-54: 145@3600 ; 262@1200 7.2:1CR

    302 1955: 155@3600 ; 268@1400 7.5:1CR

    302D 1955: 155@3600 ; 268@1400 7.5:1CR

    302 1956-59: 160@3800 ; 268@1600 7.5:1CR

    Just a little carb & exhaust work will improve these hp & tq numbers a good bit.
     
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  18. RichFox
    Joined: Dec 3, 2006
    Posts: 10,020

    RichFox
    Member Emeritus

    Squirrel is right as always. Bell housing will be a direct bolt on. I always used 25 bell housings on my GMC engines.
     
    Last edited: Oct 1, 2016
  19. 302GMC
    Joined: Dec 15, 2005
    Posts: 7,856

    302GMC
    Member
    from Idaho

    Ask around your area for a '55 1st series Chev or GMC parts truck - all the open driveshaft parts will make your transplant a true bolt-in.
     
  20. jimmy six
    Joined: Mar 21, 2006
    Posts: 14,795

    jimmy six
    ALLIANCE MEMBER

    235 bellhousings are fine, best are from a 55-62 car or early truck so the trans bolt up will be stronger. A early 50's car trans and enclosed drive line from the car or up to 55 first series truck will destroy the u-joint because it the torque the first time u get on it. The 4 bolts are 1/4x28. Good luck
     
  21. WJ
    Joined: Feb 28, 2007
    Posts: 26

    WJ
    Member

    Thanks. I still have the original drive train in it. The 235 is from a "57" Chevrolet but not sure about the transmission other that it's a sm420. Sounds like the u joints are really light duty and I have no idea how many miles are on any of the running gear.

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  22. OldBuzzard
    Joined: Mar 8, 2008
    Posts: 878

    OldBuzzard

    If it is an sm420:

    The Novak Guide to the
    GM Muncie SM420 Transmission
    sm420_transmissionThe SM420 is an impressive, heavy-duty truck transmission designed for and used in ½, 3/4, 1 and 2 ton trucks. The SM420 was made by General Motors from 1947 to 1967. Military specification versions were made through the early 1980s. The SM420 is found in GM trucks, busses, heavy equipment and various military applications.
    The "SM" in the transmission's designation stands for Synchro-Mesh, in the tradition of other GM gearboxes, though we have heard that it may refer to Stewart - Muncie, a merged transmission division of GM.

    Nothing light duty about it.

    More:
    http://www.novak-adapt.com/knowledge/transmissions/manual/sm420
     
    Last edited: Oct 1, 2016
  23. RichFox
    Joined: Dec 3, 2006
    Posts: 10,020

    RichFox
    Member Emeritus

    I used a '62 Chevy 3 speed and then a Saginaw 4 speed. Didn't beat on it. Did go 177 with it. Never any breakage.
     
  24. 302GMC
    Joined: Dec 15, 2005
    Posts: 7,856

    302GMC
    Member
    from Idaho

    The 4 speed torque tube u-joint is heavier than the 3 speed version. The 4 speed type fail only when the u-bolts Rich noted are loose, either from wear or wrong installation. I use allen bolts & Loctite, have never had any come apart yet.
     
  25. Stovebolt
    Joined: May 2, 2001
    Posts: 3,531

    Stovebolt
    Member

    New Nicson Cast-Iron headers are readily available to suit a jimmy.

    If you're interested in a set (not cheap) pm me.
     
  26. WJ
    Joined: Feb 28, 2007
    Posts: 26

    WJ
    Member

    I been doing a little reading up on the 302 and noticed that it has the full flow/pressure oil system that has been added. From my reading it is a great upgrade. My question is should I still use a 30wt. non detergent oil or the newer multi grade petroleum based oils? Or maybe even full synthetic?

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  27. squirrel
    Joined: Sep 23, 2004
    Posts: 55,934

    squirrel
    Member

    good luck getting a straight answer to a question like that! :)

    (fwiw, I use modern multi vis petroleum oil, it's pretty good stuff compared to what they had in the 50s)
     
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  28. jimmy six
    Joined: Mar 21, 2006
    Posts: 14,795

    jimmy six
    ALLIANCE MEMBER

    30wt NON-DETERGENT OIL please you've got to be kidding me.
     
  29. sunbeam
    Joined: Oct 22, 2010
    Posts: 6,213

    sunbeam
    Member

    Save your non-detergent oil for oil bath air cleaners.
     
    gas pumper likes this.
  30. squirrel
    Joined: Sep 23, 2004
    Posts: 55,934

    squirrel
    Member

    I run non detergent oil in my shop air compressor.
     

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