FH770D Bent push rods I need a solution.

Discussion in 'Mechanic and Repair' started by captken, Oct 5, 2012.

  1. captken

    captken LawnSite Bronze Member
    Posts: 1,707

    Hello, I am re powering an Exmark Lazer Z. She is now 5 years old and threw a rod. I found an excellent replacement on Craigs List. The price was right and I took the gamble. I ran the engine for 2 weeks at 3200rpm to check everything out. Heard ticking, time to check the valves. Push rod is bent.
    #2 cylinder, intake. I have pulled the head. Took the head to a machine shop had the head checked along with the valves. Valves checked, stems cleaned. Checked seats in cylinder head. No valve guide problems but cleaned anyway. The valve guides have not pulled. All Okay.
    Double checked by mechanic at my local mower shop. Everything AOK. Re assemble engine, start it up let it warm, advance throttle, backfire through the carb, bent push rod again. I have adjusted and re adjusted and gone through 6 push rods to arrive at a solution. I honestly don't know what to do. This is driving me nuts. Any insight into this problem will be gladly excepted.
    Back ground on the engine at Low hours, I believe, on this Kawasaki Test Engine.
    The story goes: "I bought the engine at an auction where the company next door was doing muffler test on the engine." "They were doing db reading on different muffler designs."

    Sticker shows this to be a Sample engine. Engine number appears to be #15 of the production run?

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  2. captken

    captken LawnSite Bronze Member
    Posts: 1,707

    Engine has low hours. What to check now?

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  3. piston slapper

    piston slapper LawnSite Platinum Member
    Posts: 4,240

    Either a sheared flywheel key or the cam is a tooth off...
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  4. BigFish

    BigFish LawnSite Silver Member
    Posts: 2,914

    Check for coil bind or maybe the collar/keepers are hitting the guide/seal. Put a good pushrod in and push down on the valve or rocker with the valve fully open. You should have some movement left before it hits or binds.
    Plenty of clearance in guide/stems?
    I always use moly assy lube on valve stems.
    Are you positive the guides haven't moved? You might can try grinding a little off the top of the guide.
     
  5. piston slapper

    piston slapper LawnSite Platinum Member
    Posts: 4,240

    Fish...taking for granted all the head and valve inspections were done correctly...with no oversghts...its got to be a timing issue...
    If in fact it is a sample engine...or a test engine...who know what some engineer did to it to improve horsepower...fuel economy..or emmision compliance....
    Backfiring thru the carb on acceleration .....got to be timing.....
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  6. captken

    captken LawnSite Bronze Member
    Posts: 1,707

    Me too. I only have their expertise to go on. I cannot find any reason that the cylinder head and valves can be at fault is why I took the head to a machine shop that does head work to get their opinion.
    So far this hunting expedition has cost me down time of the mower, and $10.00 to the machine shop.
    However, I do have a known good cylinder head from my blown engine. I don't know whether or not I'd be wasting time to install that head to see if something was overlooked on the head from the machine shop, or start tearing down the engine. I think I should tear down the engine.
    The adage that "if it seems too good to be true, it probably is" comes to mind. I paid $800. dollars for this engine. Seemed like a bargain at the time.
    Shipped Fedex from seller. Guys, this is almost a new friggin engine.

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    Last edited: Oct 5, 2012
  7. Restrorob

    Restrorob LawnSite Fanatic
    Posts: 11,024

    Ahhh..... Ya know, Ignition timing can cause backfiring as well.....


    Think I'd test the ignition modules (we all know Kawi's eat them) and check the flywheel key just to eliminate them before tearing into the crankcase, But if you end up in there check the mechanical compression release as well....


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  8. BigFish

    BigFish LawnSite Silver Member
    Posts: 2,914

    I would pull the head and compare it to the known/blown head. Check the guides closely. Or just install the known head and see what gives. What do ya have to lose?
    My money's on a valve train issue.
     
  9. piston slapper

    piston slapper LawnSite Platinum Member
    Posts: 4,240

    My money is on an assembly error...
    Crank/cam timing mark off than advanced the timing and sheared the flywheel key...maybe they put the wrong tappet in the engine....
    In any case...this new engine doesn't have a warranty....open er up...
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  10. piston slapper

    piston slapper LawnSite Platinum Member
    Posts: 4,240

    Cracked rocker arm....
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