Backfire, capow!

Discussion in 'Technical' started by justin has a 74, Aug 30, 2010.

  1. darren

    darren Member

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    Nice of you to help him out.
    Its tough for someone not experienced to tell what air noise is normal in the crankcase. Didnt want him getting focused on the air in the crankcase without knowing the percentage of leakage. 100 psi will blow by the rings good or bad.
    The right tools make a big difference. Maybe he could rent one if needed.
     
  2. justin has a 74

    justin has a 74 Maverick bandit official

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    Well like ive been saying, thanks for the help guys....

    I ordered a set of rings for that piston.. more info to come
     
  3. yellow75

    yellow75 MCCI Oregon State Rep Supporting Member

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    Why do I have the feeling that we are about to go where no man has gone before with this adventure :cry:
     
  4. darren

    darren Member

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    LOL. The kid has some energy thats for sure.

    Wonder when hes going to fix the valve issue??
    Your rings wont cause the back fire Justin. I assume you realize that.
     
  5. Bryant

    Bryant forgot more than learned

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    its like leading a horse to water but you cant make him drink.
     
  6. justin has a 74

    justin has a 74 Maverick bandit official

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    Something is aparrently wrong with that cylinder, the rings. I know it wont fix the backfire but it needs to get fixed, am i right or am i right? Although i could be wrong.

    i had put oil in the cylinder like you said to try and the compression increased.

    The backfire may still be a lean issue because that cylinder isnt firing?
     
  7. justin has a 74

    justin has a 74 Maverick bandit official

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    Should i try putting oil in the other cylinders too?
     
  8. yellow75

    yellow75 MCCI Oregon State Rep Supporting Member

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    Personally I would like to have you make sure that the valves are working correctly on that cylinder, well all of the cylinders as far as that goes but lets just deal with #2 and get its compression up first.

    Nobody has really confirmed that you have a lean condition causing backfire thats just assumtions since you have a backfire through the carb and you know that the cylinder is low on pressure it indicates the pressure is getting out somewhere only 2 places it can go, out the exhaust or intake valve or out the rings. If the intake valve was open when on compression stroke then the gases would escape out the intake and guess what that would create a nasty flaming firery backfire out the carb.

    I think we were all heading toward an exhaust valve problem but after rethinking I believe it is the intake causeing you problems.

    I just hate to see you have to buy a new head gasket,oil pan gasket,intake gaskets,oil,oil filter and risk the chance of screwing up the cylinder and crank and piston and who only knows what else and still having the same problem when you put it back together.

    I am glad that you are working on it and learning and we have all learned from the school of hard knocks
     
  9. justin has a 74

    justin has a 74 Maverick bandit official

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    Glad to have you old guys around lol joking. (about you being old of course)

    One thing that crossed my mind is would it be too late to concider the spark jumping from one wire to another? on the intake stroke?
     
    Last edited: Sep 5, 2010
  10. cyclonewill

    cyclonewill Member

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    Spark jumping wires is not going to cause the low compression. Start there first, gotta keep the air in the cylinder before anything else matters. Its just like working on anything, you have to have the lamp plugged in before you go condeming the bulb.
     
  11. mashori

    mashori Member

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    comic!! :rofl2:
     
  12. Joe Dirt

    Joe Dirt BBF life

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    wow just wow...

    this thread makes my head hurt.
     
  13. justin has a 74

    justin has a 74 Maverick bandit official

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    Uh.... duh!:D Talking about the backfire

    Took out the piston and it was cracked alond with the cracked piston ring. Cylinder was fine, dodged a bullet on that one:bananaman
     
  14. cyclonewill

    cyclonewill Member

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    I'm not trying to stirr anything up, just gotta try to keep it in a logical series of steps. I sometimes catch myself jumping ahead of things. Compression is #1, then you worry about the backfire. Glad you saved the block. I'm here for wise-ass comic relief anytime
     
  15. Mavman72

    Mavman72 Gone backwards but lookin' forward

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    Now you need to determine what caused the piston to fail...Detonation...Piston to valve clearance (not enough) Hydraulic lock.(not likely) Faulty piston (made poorly) Ring gap too tight causing it to bind in bore(this will wreck ring lands and crack pistons) It can score cyl bores badly as well.
    Gotta figure it out so you can take steps to make certain it doesnt happen again.My money is on improper valve train components... bad valve/guide...Too much cam lift(lack of P/V clearance) or wrong pistons for application. This goes back to P/V clearance,valve sizes and cam lift. Its also possible your valve springs are/were inadequate for your cam selection. Inspect all valves on that head to be certain none are bent damaged...I am guessing your gonna have at least one bad one. Good luck!!!
     
    Last edited: Sep 5, 2010

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