yamaha 115 v4

[pistonguy]

hi guys im new to this site so any info would be a great help.....i just rebuilt my 1992 yamaha 115 v4 and i started it up with the muffs and it ran good the compression was between 115 and 120 on all the cylinders so i put it on my boat and i ran it for a about 5 mins and the engine siezed up i took the engine back down and found that the bottom piston on the port side has had a major melt down within 5 mins did anyone ever have this trouble before and figured out the cause of it....thanks i got a picture of the piston attached

[99yam40]

looks like it got very hot,
running lean (not enough fuel) on that cylinder and not just idling while on muffs would be my guess if it did that in 5 min.

Rodbolt should come up with info soon

[pistonguy]

do anyone have any more input on what my problem can be

[Tucker]

do anyone have any more input on what my problem can be

Holy Crap!!! Never seen a piston melt like that. Was it stuck in the cyl? Where are all the techs?? Can't wait to read about this... Wondering if you had a vaccum leak on the intake when reassembling?

[Tucker]

Holy Crap!!! Never seen a piston melt like that. Was it stuck in the cyl? Where are all the techs?? Can't wait to read about this... Wondering if you had a vaccum leak on the intake when reassembling?

Oh dude, did you reuse the piston with the broken skirt?

[pistonguy]

no the piston wasnt stuck in the cylinder and im not sure about a vacum leak there are no blockages on any hoses....i wonder if she would be off timing and would that do it

[pistonguy]

anyone know anything on this guys

[BQUICK]

I would say oil injection wasn't working on that cylinder. It's best to run 50-1 mix until you can bleed oil injection and verify that it's working properly.

[pistonguy]

oil injection is not hooked up im mixing the gas 50-1 myself

[Bilge Rat]

Did you reuse the piston with the broken skirt?
Did you find the reason the skirt was broken when you tore down the motor before the rebuild?

The skirt controls the port timing.

[rodbolt17]

***, never saw one that bad.
either NO lubrication or a blocked water passage causing terrible overheat.
what do the other 3 pistons look like?
also what was the piston to wall clearence and who made the piston?

[Backchannelmako]

Should probably be running 25-1 on a non broken in rebuild and running in a barrel/test tank to cool properly. No heat alarm, or was it to late when that went off?

[rodbolt17]

doesnt look like overheat, looks like insufficient clearence.
either a forged pistion in a to tight bore or the bore was to small.

[pistonguy]

the piston was the right piston for the bore the number on the piston is 6r501 the same number thats on all other three pistons....the three other pistons are in exc condition.....i cant seem to figure out what happened to it...do anyone know what the number on the carb is suppose to be for a 1998 c115tlrw

[rodbolt17]

its not a carb issue.
was both the piston and the bore actually measured by you,or whoever installed the piston?