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Discussion Starter · #1 ·
This happened to my 180CC Yamaha 4 stroke air-cooled motorcycle while on a long ride. I was on close to full throttle continuously for about an hour and it started knocking. I think I pushed the bike close to its limits for a long time than I usually do.
The motorcycle in question is a Yamaha FZ16. It was running on a big bore 180CC while this happened.
Upon opening the engine, it was found that the piston and bore were scored and the crankshaft bearing had excessive play in it meaning they failed.
This normally happens due to oil starvation as far as I know.
The engine oil in it at that time was a semi-synthetic Shell AX7 10W40 which was the recommended grade by the manufacturer. I have been using this oil without any issues for few years.
The oil was only about 1000 km old and the level was normal too.
I also noticed there was considerable carbon buildup on top of the piston for the time it has been used (15000 km). Also, the compression rings of the piston were so brittle. It cracked into pieces without much effort.
Please check the attached images.

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Since the bike ran without any issues for a long time including long rides, I can't find any other reasons except the oil for this failure.
I have pushed the bike on its limit before as well but it was running on fully synthetic Motul 7100 20W50 at that time.
I think it was inadequate lubrication on crankshaft bearings that caused them to wear and it is that play from the wear which made piston skirt rub on the cylinder wall.
Please share your thoughts on this as I am not a mechanic and haven't seen this before.
Looking forward to your valuable feedbacks.
 

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The oil she all burned up. Squeeeeeek you're done.
It says that is the standard piston, does that standard piston have an over-size ring available that fits it? With an overbore that might give you the extra clearance you need.
... and add an oil cooler if you possibly can.
 

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The bike has a big bore kit. That makes me wonder who made the new piston, what was the piston to bore clearance, and what the fuel mixture was like. Also the timing. There are many things that can make it seize.
With the ability to edit later. I can agree with Porky. UK
 

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Oil pump failure. Obviously oil starvation.
Sam
 
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