hello there,
I was wondering if the crm engine originates from the cr250r.
For example, could the crm gearbox fit into a cr engine?

thanks, regards

Brief answer - No way.

no affinity between the 2 engines?

On one hand you have an engine designed to give explosive power that has 5 gears, a mechanically operated power valve, runs on premix, no balance shaft, requires a high degree of maintenance and no electric circuitry apart from the ignition.

On the other hand you have an engine designed to give smooth power that has 6 gears, an electrically operated power valve, has autolube, has a balance shaft, runs with very little maintenance except the basics and runs an electrical lighting circuitry.

They are both made by Honda, have single cylinders, are 2 strokes and have water cooling.... not much more in common than that.………… even different bore and stroke, gear ratios etc etc …..

I know that, simply I thought that crm was a sort of "domesticated" version of cr engine, thats all...

The only Honda parts from the entire bike that I can think of (off the top of my head) that are direct replacements (CR=CRM) are the mudguards, and radiator scoops from the CRM Mk1 & 2 which are the same as the 1989 CR125/250 and the clutch lever for the CR which has a CRM part number for a few years.

I see...
However, any chance to obtain more power from a crm engine?

Yes. Take a look at the FAQ section on tuning.