1999 F650 Troubles
 

A friend of mine recently fell into a bit of bad luck with his 1999 F650. He was in Whitehorse NWT. when his engine overheat light came on, So he let it cool down, started it again and ran a little further, light came on again, so he let it cool down again and then started it up and got it to the nearset town. He said it lacked power and all he knows is the compression of the engine he is claiming is 60 psi.
As I work on my Harley he asked if I would look at his bike. I'm unfamiliar with BMW's Rotax engine, but with patience and a manual, I'm confident we can figure it out.
The bike has just over 70,000 kms on it and up until that point had performed flawlessly.
Any ideas?

I'm no BMW expert but if he didn't check the coolant level , I'll hazard a guess .
Sounds like a partial seizure due to lack of coolant/oil/overheating .
A rebore and new coolant pump and/or seals sounds in order .
Check the valves as well .

dam the luck
 

or it may be the carbs that F has 2 of them
or oil over filled
or bad coolent pump (older F650 have pumps with poor impellers in them)
broken fan or just no power to it
bad, burned out powe regulater or Rectifier (the black box under the seat) if it gets really hot thay burn out and do all maner of odd things. moving it from under the seat to any place on the bike with some are flow will felp save the new one.
last thing you want to do is take it to a BMW shop.

look up the chain gang web page
The Chain Gang

Thay will know what is wrong and how to fix it.

Sounds like the classic Rotax issue most owners encounter - faulty head gasket. Head gasket and regulator replacement is an almost standard repair for Rotax engines of that era. If it hasn't been replaced in the past, then that's probably the problem. Look for oil in the radiator (but not just the overflow bottle) or water in the oil as an easy indicator, but even if there's none it is still likely the head gasket. Hope I'm wrong. Good Luck.

Brett

Thanks for the ideas
 

Thanks for the ideas so far, I guess the only real way to tell will be the teardown. I have a manual coming and the bike should be here this weekend, if all goes according to plan.

Thanks DL
 

One thing about the net, seems to be something out there every time when you need info, I will check out The Chain Gang as well.

Is a rebore possible?
 

I imagine you're pretty close by the sound of it, although the BMW Dealer didn't seem to have any part numbers for pistons other than stock bore, this made me wonder if the cylinder is sleeved, or if you have to buy a new cylinder? On the Harley, (which I am more familiar with) the cylinder can be bored to .040 over, and pistons can be had to match. Anyway thanks for the input, it's nice to have ideas when you want to fix stuff.