1982 XC 250 Top end woes

Hi all, I would be grateful if anyone could give me a bit of help. Racing my bike at the weekend when it started making a rattling noise and put out a bit more smoke than usual. I've got the head and barrel off but I'm not really any wiser. There seems to be a lot of lateral movement in the con rod, I can slide it from side to side on the bearing. There's no thrust washers and looking at the parts manual it doesn't look like there are any. Is this normal? There is also a bit of movement in the small end bearing, I can wobble the piston a few millimeters on the bearing, could this be the cause of my problem? Piston and barrel are good with no scoring, crank turns and feels smooth.
Thanks.

What is the history of the bike? Did it just start rattling? A lean running engine will rattle under load. What does the plug look like? White? tan? Could also be a timing issue.

Thanks for your reply. I got the bike recently, this was my first proper ride. At the start of the day it ran well, but after a bit of a thrashing it started getting noisy. Plug is a light brown. I've had a chance to have a good look today and I suspect the big end has gone. There's way too much movement in the con rod. I've decided to split the cases anyway and do all the bearings and seals. I love riding the bike so I want to make it as reliable as possible.

check the flywheel hasn't lost a magnet or two..although you would notice just moving the crank around. are the rings ok, haven't lost one? is there any up and down play in the rod? also, if your gbox side crank seal has failed, it will suck oil in and this could cause strong pinging (death rattle) and smoke under open throttle.

That's interesting, it was smoking more and I remember thinking the smoke smelled different. The noise was like a metallic tapping, rising and falling with engine revs.

There are thrust washers/spacer washers on the small end of the con rod, like spacers on the wrist pin of the piston. My 83 did not have them when I got it and there was a lot of rod play. I suspect the piston could rock side to side more if the washers are not installed and cause the rings not to seal as well.

if your sucking in extra oil it provides ign spots in the combustion chamber other than the sparking plug (pinging/detonation) and usually you feel a slight loss of power.

sometimes the gearbox oil will smell like petrol as well....

re big end.. its up and down movement that's the biggie. get the rod to the top of the stroke hold it firm (said the bishop to the barmaid ).. then see if you can move it very lightly up and down on the big end pin. check the specs as husky's can have a small amount of play.

as you are going to split the cases, you can check everything proper when its apart...new engine seals are a very good idea....