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Discussion Starter #1
I guess I blew a cylinder on my Waverunner. It is reading zero in the rear cylinder. The other one is reading about 130. I have never attempted a repair like this before but I am mechanically inclined and think I can do it. Any suggestions or thoughts??? Thanks
 

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XLT800 hey? usually a pretty good motor. How did it happen? was it a disconnected oil line,
carb problem, or something else? I would recommend removing the engine completely to rebuild the top end in this motor. The engine is a prick to re-assemble when it is still in the ski. The exhaust manifold bolts are difficult to do up in the ski. It also gives you a chance to check the alignment and shimming of the engine in relation to the drive shafts (a common problem on these). Make sure you get a 800 OEM barrel and not a 1200 Barrel as they have different transfer ports!
 

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Discussion Starter #4
I am not sure what caused it to blow, I believe the oil injector is not working correctly. I was riding full throttle which I do not usually do and it just suddenly quit. Tried to crank it and nothing. I let it sit awhile and it would crank and run slowly then stall. If I fix it I think I will do away with the oil injection and pre mix from now on. This is the second time this same piston has gone out.
 

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In my opinion, I think that most people take the oil pump off for the wrong reasons. I Think oil pumps are great because they feed the correct mixture to the engine at all RPM. If it has been rebuilt before, check the cylinder is not a steel bore or a re-nickalsil. Because, after doing hundreds of the 1200 & 800 yamaha motors, I truly believe only a genuine yamaha barrel with a sized matched pistons are the best option. If it is a steel bore, the carbs will need to be re-jetted along with a bigger needle and seat. If it is a re-nickalsil, well in my opinion they are just a waste of money. If it is a genuine OEM barrel and piston, check the piston and barrel to see why it is failing. Do you know how to read a blown piston?
 

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Discussion Starter #6
Not really. I have a repair manual that I am going by. I am hoping I can get walked through this on this site. Any info you have is greatly appreciated. I am currently just getting started on taking it about. I have the cylinder head off and the one that is reading zero on compression is badly scortched looking.
 

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Ok, so if it was an oil problem the blown piston should look completely dry and grey. It will look grey no matter what but it wont have a wet look. If it was an oil pump failure, both pistons should look pretty dry. If the blown one looks dry and the other one looks wet, it may have dropped an oil line to the carbs. Is there any fresh oil in the bottom of the ski? If it still has a good tan and the exhaust side is partially broken off the piston, it may have simply been too much clearance. Or a ring may have been installed up side down (remember the numbers on the rings always face up) and dropped into the exhaust port. If it has scores on the inlet side and on the transfer ports, it could have simply leaned out. You haven't confirmed whether the bore is steel or nickalsil? Check all these things and let me know what you find. Without this information or even some pictures everyone can only speculate. I do however recommend removing the engine even for only a top end rebuild. Much easier to work on 800 motors on the bench than in the ski!
 

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Discussion Starter #8
i have not gotten that far into it. I will check it better tomorrow and get some pictures for you. I know giving my email address is probably not a great idea but I get so much junk on my hotmail email address so I do not care. Send me your email address and I will send you the pictures if you would like. Thanks for all your help.
 

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Discussion Starter #10
after reading and looking at manual I see it is a rather large job. I guess the exhaust manifold and everything has to come off.
 
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