250-500cc big end bearing play

Hi , im rebuilding my 2004 wr250 . It didnt blow up , its just a freshen up so it doesnt let me down.Can someone tell me how much vertical play is allowable in the big end bearing ? I can feel a slight amount of play but am unsure how much is too much .
any help appreciated
thanks Ben

There should be zero up and down movement on the big end rod bearing. There should be a small amount of side to side movement, but zero for up and down play.

It should be almost unpercievable. Of course there is SOME clearance, but it should be dificult to detect any. If you can actually see it move up and down, err on the side of caution and rebuild it, to meet your original goal of it not letting you down. Sometimes I'll pull upward on the rod with steady force, at TDC, then use my other fist to pound the top of the rod. If you feel it clicking, it's time for sure.

If you can feel it its already to much.

their is a slight play aloud but you would only be able to detect that with some precise measurement equipment.

the way you can see it easily is this one put the cylinder and piston assembly together get to the highers point and feel if there is any rotational play in your fly wheel

this way you have the wear out of all components involved (also the piston rod crank shaft connection).

if you big end is gone or on its way of going bad the crankshaft piston rod connection might be worse already and it would consume pistons like crazy (not on the rings but on the piston rod and the rod piston holes connection.

Robert-Jan

Check the factory specs before you get too excited. Sometimes the feel can be misleading. I am also of the belief that if you can feel movement then it is already too much, BUT, when rebuilding my KX500 I could feel slight movement. Damn I though, I need a rod kit. However, the factory spec on that engine is very loose for up and down and what I felt as too much mic'ed out as normal. Needless to say the engine didn't need a rod and ran for many years after that. Cam.