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  1. #1

    piston failure gp1200r engine

    Out on boat today (xr1800) twin gp1200r's. Running great. Check spark plugs last weekend and all read great. While out at the end of the day one motor shut down. Started right back up and away I went. Shut down again and fired right back up. Went in to shore to grab something to eat. Went to go back out and motor wouldnt fire and seemed like it was turning over slower.

    Came home did compression check and read 10 on rear cylinder. Took head off and this is what I found. Didnt find any broken pcs. Other two pistons look and feel good. All pistons move up and easily by hand as normal. Can feel two marks on either side of rear cylinder. I will pull rear cylinder tomorrow and see what the piston actually looks like and check crank out. Hopefully I can figure out cause, possibly light hone on the cylinder and new piston.

    Looks like no fuel in that cylinder to me. Would explain the two shut offs. At least its end of season and was planning on redoing both sets of carbs over winter.

    Where would I send to get cylinder honed? can I buy the tool to do myself?

    First pic is of failed rear cylinder and pics of the the other two. Also pic of rear cylinder spark plug.

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  2. #2
    after reading looks like I will just get the cylinder replated. Ideas on cause? How does piston wash look on the other two?
    Last edited by whiteyz; 09-08-2013 at 07:36 AM.

  3. #3
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    Pulled the motor this morning and tore everything down. Piston rings on rear cylinder were froze to piston. Had to press the wrist pin out. Other two pistons had a few marks but nothing near as severe and rings were free. All fuel lines and everything seemed secure when I pulled carbs and converted over to premix. Rear cylinder is def going to need replated but was hoping the center cylinder could just be honed. There are marks on it but can just barely be felt, some of them cant feel at all. Think A hone would be ok?

    Crank got hot as shown in last pic. Very few hours on this crank. Everything turns free and feels good with no excessive play. Think its ok to use? Was hoping to not have to split the cases.

    Any idea on what caused this mess?

  4. #4
    If the fuel line was indeed secure on the the third cylinder I would suspect carb or rear seal. Rebuild carb and pressure test engine to see if rear seal is leaking.

  5. #5
    think the crank is ok with the discoloration as shown in the pic? send of to crankworks to have them check it out?
    Also the center cylinder has some marks in it. The rear def. needs replated as I can see the coating chipping after cleaning with acid. The middle one has marks but 2 spots can just barely be felt by touch. Possibly to hone or anything else beside having this one replated as well. If I can save myself a few hundred that would be great.

    Marks on middle cylinder that can just be felt in two small spots.

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  6. #6
    Happily Self-Employed WFO's Avatar
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    Crank looks okay, but you never know whay type of debris got into the bearings

    Also the piston/cylinder looks like it suffered from lack of lubrication... you say it was premix?

  7. #7
    yeah premix. Amsoil 40:1. I have the group k air fuel separator and electric fuel pump as well. That motor shut down twice when I was doing a bunch of high speed turns but fired right back up. 3rd piston and cylinder were pretty bad number 2 alittle better and front piston not to bad but must of happened all the sudden. Have been checking the plugs every weekend and everything has been looking good. Actually when I came back after it shut down and front and middle plugs still looked great. Rear cylinder was completely grey. This is middle piston.
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    Here is front

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  8. #8
    well took cases apart and pulled crank. Crank looks and feels good. This was the only damage I could find
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    I found some small metal debris very small like powder in the oil in bottom of case. Is there something I can use to flush the crank to make sure the bearings are clean?

    Also something I realized while pulling everything apart is I only got 1 thrust washer off the rear rod. 1 was missing. Has anyone ever had one go and just blow apart?

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