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replacing only one piston on 235?

Discussion in 'The Hokey Ass Message Board' started by hobbyjp, Nov 15, 2010.

  1. hobbyjp
    Joined: Mar 14, 2006
    Posts: 330

    hobbyjp
    Member
    from socal

    Ok my engine probably needs to be rebuilt. The more I dig into it the more I find thats messed up. I pulled the head yesterday after I was done replacing the bearings. I was getting some water in number 3 and had low compression on 1. Well the head gasket came up in pieces so I couldnt tell were water was coming in. the cylinder looks fine but the combustion chamber shows signs of water being in there for some time. I also noticed the number one piston has a small hole on the edge and you can see were something was bouncing on the top of the piston. I have heard that there are balancing problems when replacing only one piston. Can a machine shop repair a piston? This motor has also been rebuilt because everything is 040 over. the odometer only reads 30,000 though! I hate trying to jimmy rig everything but I'm broke. to much more money in this motor and it wont be woth it anymore and I'm afraid that if I buy another 235 it may have just as many problems.
     
  2. HEATHEN
    Joined: Nov 22, 2005
    Posts: 7,591

    HEATHEN
    Member
    from SIDNEY, NY

    I wouldn't worry about replacing one .040 over cast piston with another one, as long as it looks like the same style piston. Not planning on running it at Bonneville, are you?
     
  3. <FANG>
    Joined: Feb 7, 2008
    Posts: 531

    <FANG>
    Member
    from W.L.A.

    40 over sounds like time for a new motor
    However you might call the guys at egge machine shop
    They specialize in manufacturing vintage pistons
    www.egge.com
     
  4. ClayPigeonKiller
    Joined: Mar 3, 2010
    Posts: 203

    ClayPigeonKiller
    Member

    Yes, you can replace one. As long as balance is similar it should be fine. The other 5 cylinders don't care.

    In the 60s and 70s it was a pretty common trick at the race track. Cyl, 1 was rule legal.
    Other cylinders were bored waaay out and had much more compression. When the officials checked displacement and comp. on #1 the engine appeared legal.

    Been there, did that on a Daily driver. It worked fine.

    Adam
     

  5. hobbyjp
    Joined: Mar 14, 2006
    Posts: 330

    hobbyjp
    Member
    from socal

    New motor and too broke dont mix. I guess I'm just to young for this hobby! My pistons are aluminum. I found some on egay but they said they were cast iron but looked aluminum. I guess 1953 stick was the last year of cast iron pistons. I called Egge this morning they are making 040 over now six for 204.00. Still gotta get a head gasket and I dont feel comfortable torquing all those bolts again without getting new ones. I'm trying to keep it dirt cheap. Shit I put a few hundred miles on this motor in this condition. Do you think a nos 040 over piston will be a closer match then a new Egge piston? I do take it up to 70-80 from time to time but I dont plan on running on the salt flats.
     
  6. I flogged an old 289 as my daily for 5 years, when I took it apart to build it up, it had one mismatched piston and 1/2 a old piston skirt in the pan. That motor worked fine.
     
  7. 6inarow
    Joined: Jan 24, 2007
    Posts: 2,353

    6inarow
    Member


    Its an old truck motor. Put a new piston in it and drive it
     
  8. HEATHEN
    Joined: Nov 22, 2005
    Posts: 7,591

    HEATHEN
    Member
    from SIDNEY, NY

    Did you see my response to your piston problem on the other thread you started?
     
  9. medicinal_marinara
    Joined: Nov 24, 2009
    Posts: 139

    medicinal_marinara
    Member
    from Oregon

    40 over isn't that much for a 235, they have thick castings. Standard procedure back in the day was to replace one piston, those motors weren't all that well balanced from the factory anyway. Do check the condition of your harmonic balancer, a poor balance + high RPM running will beat the hell out of the bearings on a 6 cylinder due to crankshaft harmonics. You shouldn't be able to turn the outer ring with respect to the inner ring, if you can the rubber is shot.
     
  10. hobbyjp
    Joined: Mar 14, 2006
    Posts: 330

    hobbyjp
    Member
    from socal

    Heathen, I just went back and looked at it. I'll call them in a few and get one ordered thanks for the part number. It sucks because its been one thing after another. I really wish I had the funds to rebuild it. I half way fix one thing just to find something else is beatup! I just sold my 270 but I'm pretty sure it had way more problems then this motor though. I'm gonna start shopping for another 235 that I can have as a spare and build up.
     
  11. JohnEvans
    Joined: Apr 13, 2008
    Posts: 4,883

    JohnEvans
    Member
    from Phoenix AZ

    We NEVER replaced head bolts on those engines unless there was something wrong with one or more. They can be reused many times. Have the head checked for cracks as the old Chevy 6s were prone to cracking,mostly down in the exhaust valve pocket area.
     
  12. If you are truly concerned with the balance, Harbor Frieght sells a small battery powered digital scale for a couple of dollars. Weigh each of the pistons, if there is a big diffrence, the new piston being heavier, ask one of us, and we can easily walk you through and tell you where to remove material. You will only need a die grinder or even a drill press will work. As mentioned there probably won't be enough diffrence to be concerned with. BDM
     

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