[houdini]

I hope I have better luck in this form.
I have a 150cc motorcycle motor that has seized due to running out of oil.
The piston rod seized to the pin running through the piston.

I have ordered a new head so all will be new except the piston rod, which I cannot replace unless I disassemble the entire motor, and the piston rod doesnt disassemble, it is a pressed crank shaft assembly, So I would have to buy the entire thing.

Ok now to the problem at hand, I want to recondition the piston rod for the new pin and piston. The rod has a 15mm bore about .75 width, there are to holes driller into the center of the bore, I assume for allowing oil into the center of the piston rod/pin assembly.
Upon expanding/shrinking when it overheated there is a score mark inside the center of the bore where the expanding pin or shrinking piston rod caused the 2 oil holes to act as cutters and cut a grove in the pin which cut a grove in the piston rod.

I need the best solution to get this back to a polished surface for the pin.

My thoughts were to possibly run a 15mm reamer back through the bore and lap or polish it, or possible since the bore is smooth except for the center to get a round stone or sintered rubber impregnated tool and just remove the score mark to below the rest of the bore and lap/polish.

We do not do any finishing at our machine shop, so I do not no the best materials/tools to get this back to usable polished condition, any help would be appreciated.

[blackbeard52]

Could you upload some pics?... Is the scoring a ridge or groove? if it is a groove then reaming wont help. and leaving it (the groove) could possibly rescore after assembly and running.

Bob

[houdini]

My camera wont take images that close, I tried.
It is actually both at this point the contracting piston rod bore, or the expanding pin.
Has caused the 2 drilled center holes in the rod to push and pull the metal in both the pin and the rods bore for the pin. So it actually looks like someone scratched a grove and then tried to pour metal into it. Hi and low spots.

its only .1 width.
The rest of the pin and rod bore are like glass/smooth.

[blackbeard52]

One option might be to have a .010 deep groove ground into the pin as clearance to the galled area what ever width it is plus clearance...ream and polish the rod back to tolerance. this would allow lubrication in that area and prevent additional galling due to contact with that area. just make sure the recessed area is minor and free of burrs.

[AirChunk]

The auto guys would use a rod hone and hone it oversize and install a brass/bronze bushing in it and hone it back to original size .
But , in the bike business we normaly replace the rod .
Is this a CRF 150 R buy any chance ?

[houdini]

No it is this POS
http://cgi.ebay.com/ebaymotors/150CC...ayphotohosting

[AirChunk]

Houdini,
Hey , that is the same deal . gotta press it apart. What brand is it ??? you might have to do some measuring to see if you can find a match for it .