Replacing roller cage bearing ('87 Force 125)

[robby t]

Rebuilding my blown engine and looking for advice...

1. 1987 Force 125
2. exhaust port cover gasket blew in vicinity of bottom piston, spurting water into engine compartment. Don't know how long it ran this way.
3. replaced gasket
4. engine ran great for a couple of hours and then blew... lost power, loud clanking sound.
5a. bottom piston compression 70# versus 150# for other three
5b. top of this piston heavily pitted, other three pistons fine
5c. this cylinder wall scored, other three cylinders fine
5d. roller cage bearings (at connecting rod and crankshaft) for this piston totally melted/burned up, other three fine
5e. crankshaft scored where roller cage bearing goes
5f. rings appear okay

Questions:
1a. Does low compression with rings okay mean that the scoring is deep enough to reduce compression?
1b. Bad roller cage bearing would not have anything to do with compression , would it?
1c. Will honing suffice or do I need reboring? If need reboring, will I also need sleeving because engine previously rebuilt and already have .030 oversized pistons? Would be a pain to hone, reassemble engine, and then discover that really needed reboring.
2a. Can I just replace bearing cage or do I need to have crankshaft ground to get rid of scoring? Can grinding be done instead of replacing crankshaft altogether?
2b. If need regrinding, then will new bearing cage fit? Are there "oversized" bearing cages?

Thanks for any ideas.

 

[pnwboat]

Re: Replacing roller cage bearing ('87 Force 125)

1a - If scoring is deep enough it will reduce compression. The surface area of the ring that is in contact with the cylinder walls is small. Doesn't take much scoring to reduce compression. Again, depends on how deep the scoring is.

1b - Bad bearing on crank has nothing to do with compression.

1c - Again, depends on how deep the scoring is. If it's already been bored .030 over, then it's questionable if you can go to .040. .040 is really pushing it. Sleeving is probably not worth the cost. Hundreds if dollars.

2a - If crank is scored, most likely you'll have to replace it. Also may have to replace the rod.

2b - As far as I know, there are no "oversize' bearings available. They don't re-grind outboard cranks and use oversize bearings like in automotive applications. The surface of the bearing journals on outboard cranks are hardened steel like a bearing race. Difficult to regrind accurately.

I had a similar problem with an 1988 125HP. Talked to a machinist at the place that did my boring etc. He said that when water gets into the crankcase on any 2-stroke outboards, it reduces the ability of the oil/gas mixture to lubricate the bearings. It actually causes the roller bearings to kind of stick, instead of rolling (not sure about his analysis, but what ever the case, it's not good). The result is damaged bearings and crank journals. If you catch it before it scores the journals, there's still a possibility that it has overheated the bearings/journals. This is what I had. Bearings and journals were OK as far as scoring, but they were discolored and had a deep blue color to them. I had to replace the crank, connecting rod and bearings.

 

[robby t]

Re: Replacing roller cage bearing ('87 Force 125)

Could I replace my crankshaft with one from a different year? My engine is 1987 and have found a used crankshaft from a 1986 Force 125. Price seems good - less than $200 including shipping.

 

[pnwboat]

Re: Replacing roller cage bearing ('87 Force 125)

That should work fine.