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  1. #1

    800 DI top end overhaul gone bad

    This is the fist jet ski engine that I worked on but I have worked on other types of engines.

    My son and I worked on it over Christmas. It was a project and we changed the hull because mine had a big crack in it. While the engine was out I noticed some scoring and decided to do the top end.

    Purchased a SBT top end kit for the engine. It was .5mm over sized I think. I had the jugs worked on at a local shop who does all the work for the local jet ski dealers. He had the pistons when he machined the cylinders.

    I struggled when I put the mag jug on. It didn't just slide on. The rings were on correct and correctly aligned with the pins. I thought my struggles were just normal as this was the first time I ever put a jug on. When I installed the pto jug, it almost jumped on on it own.

    We started the ski and then winterized it. Today I finally had time to get it in the water. I checked the compression before we went to the lake. 145 pto 110 mag. I should have tore it down then as I knew the low cylinder was the one I struggled with.

    We ran the ski for about 1.5 hours at the lake. We followed SBT's break in procedure. The ski would not stay running while at idle but seemed to run ok.

    Checked the compression when I got home. I knew something was wrong because the engine didn't start like it should. 75 psi mag 150 pto.

    Tore it down and found the rings were stuck on the piston. There is some very fine scoring where the blow by was going but over all very little damage to the jug.

    What would cause this? After cleaning up the piston and getting the rings free they seem to be ok.

    Should I contact SBT and get another piton/rings set. Not sure if I messed up or there was a problem with the piston.

    Should I re hone the jug?

    Thanks for your help.

  2. #2
    Banned User
    Join Date
    Jun 2010
    Milwaukee WI
    Are you sure the rings werent on upside down? That would make it tight in the bore.

  3. #3
    john zigler's Avatar
    Join Date
    Aug 2006
    Could be many things.

    Did you do a leak down test after assembly?
    Could be a dirty injector, or weak fuel pressure giving a lean condition.

    You may be lean on the one cyl. Or you may have damaged the ring upon install.

  4. #4
    Rasta Mon Condoms We Be Jammin!!!!! TxPro1200's Avatar
    Join Date
    Aug 2006
    i'd suppect either a jug that wasn't machined correctly or the rings on wrong.

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