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  1. #1

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    Another Yamaha GP1200R Engine Failure! Help!

    This is a stock 2001 Yamaha GP1200R with 150 hours on it. The only mod is a D plate and sensor by-pass chip.

    The center piston has a hole in it. Top speed now is about 20mph.

    A little History…..Last summer the engine died. I was told by the repair shop that a piece of a reed valve broke off and scored the center cylinder and piston. After $1900 in repairs last year, and only 3 hours on the water this year, the engine has died again. This time the repair shop said there is a hole in the center piston. They are willing to fix it again for another $2000 or more with still no warranty on their work. I don’t have any confidence that they will actually address and resolve what is causing the problem and have decided to take it home and fix it myself. I have never done anything like this before, but am hoping that with some help from the people on this forum, I can rebuild the engine.

    My first objective while rebuilding this engine is to determine what could be causing this engine to fail twice like this.

    I believe I will have to replace the piston and fix the cylinder at a minimum.

    I will check the oil lines as I take it apart to see if that caused the problem. Regardless, I intend to go the premix route with an oil block off kit as part of the rebuild.

    I also intend to rebuild the 3 carbs. I will be looking closely at the center carb to see if that may have caused the problem. (Although, I am not really sure of what to look for, other then dirt and muck in there).

    I will check and replace the reed valves as necessary.

    I will also install Wave eater clips and couplings.

    Well, this post is getting long. I wanted to introduce myself (Dennis) and begin to provide some information to you all, in hopes that you will be able to help guide me through resolving what is causing the problem, as well as help me do the rebuild.

    First questions ….. Should I plan on pulling the entire engine out of the ski to do this work, or can it be done in place? Should I also plan to open up the lower unit and examine the crank shaft?

    Thanks in advance for any and all advice you are willing to provide.
    Dennis


  2. #2
    My Jet Ski drinks more than yours Glenozzy's Avatar
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    hole in piston in 3 hours is a air leak. motor was not repair correctly.

    motor must be pulled and cleaned. and then leak tested.

    carb also need to be checked / rebuilt

  3. #3

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    I think maybe I posted this thread in the wrong area. If a mod could move it to the 2 Stroke Performance section, I would appreciate it. Thanks!

  4. #4

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    Since the reeds are plastic, probably didn't score the piston the first time it broke because of that, it was probably the same thing that killed it this time. Probably its a good size air leak, or perhaps a plugged jet/plugged carb internal fuel filter, or another fuel system problem that caused the combustion temps to go way up(Like creased fuel pump check valves), although that usually shows burning on the exhaust side top edge of piston also. Lack of oil doesn't burn a hole in piston, it causes it to score on sides and quit moving up and down eventually. With 2 breakdowns, I think I would pull engine, at least to get it totally clean from the piston debris down in the crankcase and possibly on the crank bearings, also to get a real good look at it and easily air test for leaks.

  5. #5
    What they said, it's an air leak or carb problem. My advice on a 1200 with 150 hours is to pull the engine, replace the crank and all pistons and rings. The 1200's had piston problems with the oem's (ring pin comes out and lets ring spin and catches exhaust port) so go with pro-x. This is a real good time to upgrade if you want better performance. Trued and welded crank, bore and port, etc..

    P.S. Get rid of the oil pump and go pre-mix if you want your engine to live long

    PSS It wasn't a reed valve the first time, that's bullcocky

  6. #6

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    I pulled the engine out of the ski today. This is what I found so far.







    I assume I will need to replace the head and the piston. Should I get another cylinder used or should I have this one repaired?

  7. #7

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    Quote Originally Posted by LT1GMC View Post
    Since the reeds are plastic, probably didn't score the piston the first time it broke because of that, it was probably the same thing that killed it this time. Probably its a good size air leak, or perhaps a plugged jet/plugged carb internal fuel filter, or another fuel system problem that caused the combustion temps to go way up(Like creased fuel pump check valves), although that usually shows burning on the exhaust side top edge of piston also. Lack of oil doesn't burn a hole in piston, it causes it to score on sides and quit moving up and down eventually. With 2 breakdowns, I think I would pull engine, at least to get it totally clean from the piston debris down in the crankcase and possibly on the crank bearings, also to get a real good look at it and easily air test for leaks.
    Thanks for the input. I have pulled the engine. I will open the crankcase to clean it good. How do I do an air test for leaks?

  8. #8
    Your crank probably needs to be replaced. All that melted piston in the bearings is not a good thing. You will be better off rebuilding the entire engine or exchange it with SBT.

  9. #9

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    Quote Originally Posted by VOODOO View Post
    What they said, it's an air leak or carb problem. My advice on a 1200 with 150 hours is to pull the engine, replace the crank and all pistons and rings. The 1200's had piston problems with the oem's (ring pin comes out and lets ring spin and catches exhaust port) so go with pro-x. This is a real good time to upgrade if you want better performance. Trued and welded crank, bore and port, etc..

    P.S. Get rid of the oil pump and go pre-mix if you want your engine to live long

    PSS It wasn't a reed valve the first time, that's bullcocky

    Thanks for your reply. You said you would replace the crank and all the pistons. How can I tell if the existing crank is bad? Will it be very obvious? How can I tell if the pistons are bad? I am not really interested in making this ski go faster. I just want to get it running again.

  10. #10
    Moderator OsideBill's Avatar
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    I see lots of heat and deto in that cylinder definitely an air leak or lean condition. here is a link to a motor I just did it shows some pics of pressure testing. http://greenhulk.net/forums/showthre...t=56023&page=2

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