Hi guys

I was changing out my fan and orings, and water pump on my backcountry 300 pro, which I've shown pictures of here in the past.

With the head off. I was cleaning the top of the piston and cylinder top face, when i noticed: my piston (not that old) has a tiny bit of play on a circular axis. Not up and down, not side to side.

I never really have handled the piston in the cylinder like this==with this particular motion, so I am not sure if it may be normal or an indication of a rod bearing issue.

TY in advance

If you can turn the piston clockwise / anticlockwise you have a bearing issue that needs further investigation (Probably the little end bearing)

Edited May 22, 201313 yr by suzuki250

Not. Necessarily, if it moves a couple mm in each direction that's normal

Remember that's a motion that never happens when the engine is running so it has no meaning

It also has no spec to measure

So....not to say you don't have motor problems but that is not how you check it

As above slight rotation is normal

Thanks so much,

the top is pretty fresh, I suspected it was normal, thought i'd chk

If you did NOT have this circular play then you WOULD have a problem.

The piston has to some what float in the cylinder head as the centre of the barrel, as it bolts down to the cases will never be deadly accurate. That is also one of the jobs of the piston rings to help seal this slight non concentric play.

A little bit of play left and right at the piston pin

A little bit of front to back from the con rod

A little bit from the piston as it fits in the rings

All this equals some play.

Edited May 23, 201313 yr by billyt