what causes this?

[Tim Wagner]

2002 125 HP ELPTO
developed a pretty good rap inside the motor.
Checked compression and there was only 60 lbs on cylinder no.2. the others were 120-118-119
After tearing in all apart, here is what I found.
the area were the rod connects to the crank has marks from the bearing too as well as the rod.
no pictures of that though
The score marks on the cylinder honed out quite easily.
I still have to mic all the holes to see if I need block work done or not.

 

[carholme]

Re: what causes this?

With reference ti pictures 1/2 and though the pictures do not show it well, it looks like brinelling or at least false brinelling. Brinelling normally only takes one load application in excess of design and the roller imprints itself in the material.
False brinelling is caused by fretting of the metals and may or may not have anything to do with corrosion but definitely happens with vibrations
Brinelling takes just one overload application whereas false brinelling happens over a long period.

Gerry

 

[wrench 3]

Re: what causes this?

Piston damage like that is either caused by overheating or lack of lubrication.
It's unlikely that #2 cylinder would overheat before #1. The scoring is bad, but not as severe as I would expect from a total loss of lubrication. Probably poor lubrication over a longer period of time.
A lean fuel mixture could cause overheating, and pre-ignition which could have caused the bearing marking.
In other words, check everything.

 

[Faztbullet]

Re: what causes this?

Thats a lean out as both the intake and exhaust sides of pistons are scuffed. That cylinder will need bored....

 

[Tim Wagner]

Re: what causes this?

Thats a lean out as both the intake and exhaust sides of pistons are scuffed. That cylinder will need bored....

Could you explain what "lean out" means????
If that cylinder needs bored, will I need to bore them all or just bore this one, replace it with and oversized piston?
I would think Id need to do them all and put all new pistons in it, right?

 

[Tim Wagner]

Re: what causes this?

here is a picture of one of the crank bearings that seems to have the same condition as the connecting rod.
This particular one is the bearing between the #2 and #3 cylinder.
The worse side is the one adjacent to #2, although both sides have damage the number 2 side is way more excessive.

Was this "lean" condition caused by a malfunctioning or misadjusted carburator?