Help needed with oil cooler setup

[M.J.H]

Hi

A bit of histroy to the problem first. A workmate has a Quad bike (Cheap Chinese thing) which runs a 125cc power house of a motor which is oil cooled. first time he rode the thing he killed a motor and got it replaced under warranty. After running in the motor all was good for a while till his mates rode it for to long and blew a headgasket. He asked me what was the best way to keep it going without killing motors all the time and promptly dissmissed my suggestion of a 25occ roadbike motor instead of the 125.
The next idea I had was to have an oil cooler fitted to help keep the temps under control. The only place to pickup the oil from is the drain plug and the only place for a return is the filler plug which is the easy part.
Now here is the hard part, What pump would be suitable to circulate the oil? A mechanical pump could be driven off the sprocket but would need a lot of fab work and which one of the many types to use? Or are there any elec pumps that would do the job?

Thoughts and ideas.

[allencr]

I'd go for better assembly & break in & additional/bigger sump & better airflow around the fins & more fins, before the cooler.
Was it caked with mud? Head retorqued? Properly maintained? Integral trans & sump?