Piston Guru's - help please! **pics enclosed**

[bmwsport]

Ok guys,

I've stripped my rs125 down after it stopped running, found bits of metal inbedded in the cylinder head and in the top of the piston, and now after removing the piston i can see where it all came from.. the barrel is scored in the same fashion and if you look at the top of the piston about 2cm round to the right you'll see another dig out of it which has done the same on the barrel.

This is the original piston as far as i can tell, my bikes done 13,000km.My question is, how can this happen? and will this have ruined my bottom end? i've had a look and can't see any signs of metal in the bottom end. Also how much side to side movement should the conrod have on these? as mine moves alot, but looks like it should..


https://i748.photobucket.com/albums/xx123/Apriliars125_2009/Image540Large.jpg


https://i748.photobucket.com/albums/xx123/Apriliars125_2009/Image539Large.jpg

[tutton]

Conrod shouldnt have side to side movement, possibly why your piston is chewed the fook up id suspect...
Any play in the conrod or it not moving smooth means its knackered or the crank bearings are., both of which require bottom end to be ripped open to get crank out..
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Past: '05 Peugeot XPS '99 Aprillia RS125 '94 FZR600R
Current: '02 ZX636 A1P '51 CCM R30

[bmwsport]

Ah great lol, the conrods odd as looks like the bearing is longer width wise than the big end which means it cant not have side to side movement if that makes sense! i'll get some pics..

[alains]

probably a seize due to lean mixture with broken ring (have you the 28 carb or the 34 ?) , check your jetting
side play on the conrod must be 0.2 to 0.5mm , something outside can possibly cause piston malfunction
as i think your engine is a rotax 122 or 123 , it uses coated barrels and i am afraid you cant escape a top-end rebuild
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the worst day fishing is better than the best day working

[bmwsport]

I've got the 28mm carb and it is a rotax 122, the rings look ok besides from where they are welded into the piston by the gouge lol, how can i check my mixture? the bikes been running fairly well, obviously it was coming up for a top end rebuild anyway, my oil pump looks to be set up correctly, the scribes line up and theres no freeplay in the cable, although it doesnt seem to use alot..

My main concern is doing a top end rebuild only for the same to happen again if the bottom end has problems, i'll get some pics of the conrod

[alains]

to see the mixture , just control your plug after 30-40 miles runing and look this table
https://www.dansmc.com/Spark_Plugs/Spark_Plugs_catalog.html
to see which jets you've got in your carb , dismount it and look sizes are marked on top except the powerjet marked around (need good magnifiers)
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the worst day fishing is better than the best day working

[bmwsport]

Thanks bud, just checked my Haynes for conrod movement, a little side to side is ok but no up/down movement, i have alot of side to side and some up and down, full engine rebuild for me then... think i'm going to use PJME for everything, i really wanted my barrel done by stan stephens but would make sense to get it all sorted by PJME, besides i'd have thought there just as good when it comes to replating, any thoughts?

[alains]

have a look here , i dont know UK pricing but they have what you want
https://www.geiwiz.de/index.php?cPath=2_293_295_1061_303_423
you can have also your barrel rebore then replated which you can increase the bore up to 54.5 or 55mm
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the worst day fishing is better than the best day working