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Crank Shaft Bearings Split


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Hey Guys,

I hope you guys have been having some more fun this summer than I am.

Last week I had the motor cease on me.I have a 50 hp yamaha 1995 Model.

I had bought this motor as a rebuilt motor and to my surprize I have been shafted by the mechanic.I had opened up the motor last week to reveal an unbelievable amount of silt buildup and crappy ripped gaskets which proved that the motor has never been rebuilt of opened.

We had opened up the powerhead and found that 2 of the bearing had failed with the ball bearing melting inside one of the pistons causing the motor to ceaze.

According to the mechanic when he first had a look at the motor the problem was because of the use of unleaded petrol which is a load of crap.I believe the problem was due to a male function in the oil pump and having run the motor for aproximately a year the heat buildup may have caused this problem.I am having the block honed and rebuilding the crank with new rings and pistons ie: a hefty bill coming my way.Could anybody know what the cause could be?

Now I have had a lot of suggestions that I should disconnect the oil pump and premix with the petrol hence ensuring that a sufficient amount fo oil is runung through the head.

Could somebody explain how I can disconnect the pump and how if I do disconect the pump how the oil will get to the crank shaft and bearings.I am no mechanic and your help guys will be much appreciated!

I wish I have reciepts for the motor in order to get this nechanic back.

Any suggestions will be appreciated guys!.

Please note that motor since rebuild has not run more than 10 hours all up.


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is it a 2 or 4 stroke? if its a 2stroke the fuel mix lubricates the engine hence why 99% of people who know anything about 2strokes pre mix it them selfs to exact mixture using a measuring cup and discconect the premix. mechanic items do fail anytime in result to engine damage

another tip dont buy premix from bouzer on the water its nasty stuff.

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Guest Aussie007

wow the little end bearings melted i have never seen that happen before since it happen on more than one cylinder i would say it didnt fail because of worn parts however if u bought the engine as second hand well anything can happen if it was a reconditioned engine than the bearings should have been replaced and since your little end bearings are toast i bet the big end bearings,conrods and crankshaft are rooted as well thats going to be a costly bill the crankshaft alone will need to be machined down and new bearings made to suit how is the cylinders?

Edited by gazza
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Hi, sorry to hear of your dramas and straight off the bat I doubt it would be cost effective to properly rebuild an engine of that age and considering the nature of the crankshaft design on Yamahas. If the cylinder bores have not been damaged then I highly doubt the failure was due to an oil injection issue, so what do the bores look like?

Unfortunately you seem to be another victim of the classic "rebuild" scenerio that we see all the time-people buy an engine and the previous owner claims the engine has been rebuilt which usually only means a tidy up and paint. If a guy comes in here that I do not know and wants to trade an engine that they claim has been rebuilt I devalue that outboard because who know who did it and what their skill levels are and there are many things that need to be done if you are to properly "rebuild" an outboard.



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Thanks for your help guys.

The moor is a two stroke outboard.At the moment me and a couple of mates who are mechanics will try and rebuild the motor.We have a manual which we are working off.

ATM the crank shaft is being rebuilt and pressed as it has proven dificult to source any cranks.

Ill keep you guys posted.


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Hi mate sorry to here your problem.

One thing to see is if the con rods have a small weep hole from the web between the big end and small end beaing jurnals. Some motors have a small hole that allows residual oil sitting in this recess to flow into the small end. If the piston are assembled the wrong way up this hole faces down and no oil goes into the small end and this is big problem.

I once had a 55 evindurde do something similar and i rebuilt it myself. I modified the small end so it did not have a cage they were needle rollers and instead of having say 10 needles and a cage i ended with about 18 needles. It was difficult to assembe but never gave me any grief in the 10 years i ran this engine after rebuild.

Good Luck

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