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Technical 270 GMC pressure plate question.

Discussion in 'The Hokey Ass Message Board' started by iwanaflattie, Jul 3, 2017.

  1. Hey guys.
    I am slowly getting parts for my 270 GMC for my future project.

    I've bought a 169 tooth(12v) flywheel and a 12v starter from a hamber.
    The flywheel has a 6 hole pattern.

    Today,I took my 148 (6v) flywheel ,pressure plate and bellhousing off.
    This flywheel has the 4 bolt pattern.

    Im not looking to brake speed records with this truck,I'm thinking just clean the engine, make sure is a good runner and go for a 3sp.

    My questions are:
    Should I stay with the 6v flywheel and pressure plate,find a 6v starter and juice it with 12v?
    (I was told in another thread that this would hurt the starter)
    Or
    Drill the crankshaft flange or the flywheel then find a pressure plate for the 12v flywheel since the one I have wont fit?

    Is there a lighter bell housing for this engines?
    I think my hernia got a hernia lifting ot from the floor.
    Thanks for the responses in advance.
     
  2. Budget36
    Joined: Nov 29, 2014
    Posts: 13,174

    Budget36
    Member

    Can't answer on your Jimmy, but of the 3 FH V8's I've had (all 6v originally) I switched to 12v neg ground, never had a starter issue.
     
  3. 302GMC
    Joined: Dec 15, 2005
    Posts: 7,856

    302GMC
    Member
    from Idaho

    What's the engine going in ? Gotta know what trans you're using and the vehicle so we can get the right bellhousing. There are no ''light'' cast iron Chev or GMC bells. You'll want to use the 6 bolt wheel, and 10'' or 11'' clutch - whatever fits your wheel. There's even a '60 - '62 hydraulic setup.
    And 6 volt starters last lots longer on 12 volts ....
     
  4. Its going into a 1936 gmc cab with a 1935 chevy frame..
    Most likely a chopped-slight channeled-fenderless,hoodless little truck.
    So if I go with a 6v starter I need to find a 6 bolt,148 tooth flywheel?
     

  5. I could just make my life easier and find a 6v starter so i can try to start this thing.
    Except the prices on 6v starters have gone through the roof.
     
  6. motion guru
    Joined: Oct 18, 2009
    Posts: 169

    motion guru
    Member
    from yacolt, wa

    If your crankshaft is a 4 bolt unit, you cannot use a 6 bolt flywheel, (there are lots of GMC light truck 4 bolt flywheels in the world).

    The 6V flywheels are 139 teeth and the 6V starters work fine on 12V. Starters are also easy to come by, they are interchangeable with similar vintage Chevy starters for 235's. I have run a 6V starter on 12V on my 270 for years with no issues.

    The 12V flywheels are 168 teeth and the starters only work well on 12V.

    New ring gears are available at NAPA.

    There are at least two sizes of flywheel / clutch combinations. One for light trucks (flat flywheel surface) and one for large trucks, (recessed flywheel surface). You will want the flat flywheel / bellhousing configuration.
     
  7. Wow thanks for the info.This 6 cyl came from a big truck with a big Clark 5spd so im assuming it has the big recessed flywheel...i will go check in a minute.
    I have a couple flywheels and a 12v starter for trade now, ha!
     
  8. 20170703_063117.jpg 20170703_063851.jpg 20170703_063109.jpg Here's some pictures.
    Couod i just have this flywheel turned to cut that raise off?
     
  9. motion guru
    Joined: Oct 18, 2009
    Posts: 169

    motion guru
    Member
    from yacolt, wa

    That is recessed on the pressure plate side and uses a large diameter friction disk and pressure plate AND a large bellhousing.

    The light truck units are significantly lighter. If the Clark is an OD 5-spd unit, there are big truck guys who would love to get their hands on it.
     
    302GMC likes this.
  10. RichFox
    Joined: Dec 3, 2006
    Posts: 10,020

    RichFox
    Member Emeritus

    Get a 235 Chevy type bellhousing and a light truck (flat) flywheel. Trying to drill the crank to accept the six bolt flywheel can be done. But it is for a machine shop or someone with the proper equipment and the thought process to do it right. I have seen a crank ruined by inept drilling
     
    302GMC and 6inarow like this.
  11. Thanks for all the good information,
    I will start looking for a 6v flywheel from a truck,a 6v starter and a 235 bellhousing.

    Mr Richfox,I would not try to drill the crank myself so I knew that a reputable shop had to do it.
    Then again,I dont want to disassemble this engine unless i have to.
    Btw i was about to call my boss to tell him i wasnt gonna make it till next monday to give u a hand learn all i could from you about these jimmys but i was a day short!
    Gimpsyhotrods is a great dude tho.
    Thanks again
     
  12. Your crank takes 4 bolts? Find a bell housing, flywheel and starter from a '63 - '68ish Chevy truck, which should be a 168 toother. Then have the flywheel drilled, which may cost you an hour of machine shop time. I just did the 2 patterns in CAD, it is doable. The later starter gets you 12V and you get them anywhere.
     
  13. Quick question, a 270 has shown up locally- if it turns over, is it worth scooping up?
     
  14. 302GMC
    Joined: Dec 15, 2005
    Posts: 7,856

    302GMC
    Member
    from Idaho

    If it's a 6 bolt crank flange, definitely ... if you have room, anything you can get for a decent price is worth saving.
     
  15. Will have to check that out- it's in a WWII era GMC 6x6- thanks for the info!
    Just engine, or tranny too?
     
  16. RichFox
    Joined: Dec 3, 2006
    Posts: 10,020

    RichFox
    Member Emeritus

    If it is a WW2 engine it is 4 bolt
     
    motion guru likes this.
  17. Seth, I have a flywheel, bell, clutch and starter(6v) for a GMC 6, flywheel is 6 bolt though. Let me know if you can use any of it....
     
  18. motion guru
    Joined: Oct 18, 2009
    Posts: 169

    motion guru
    Member
    from yacolt, wa

    This is all from either a 228 or a 248 . . .

    [​IMG]

    Bellhousings prior to I believe, 1954 are set up for the flat mounts which would work better for your 36 frame.

    (The unit pictured is a 1948..53)
     
  19. bump for the late night crowd..........
     

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