'84 Cr125

The biggest issue with the 84 - 86 is the clutch cover was made of magnesium and if anything other than radiator fluid, ie water, was in the coolant system the pump housing would corrode. These covers are becoming harder and harder to find. I had one and it was a fun bike to ride. A lot of parts from the 85 and 86 will fit. I do believe the only real difference between an 86 and an 84 is there is one more fiber and metal disc in the clutch.

Use distilled water and phosphate-free coolant.

I've used standard Prestone for years in mine and have not had any problems. I speak from experience with the magnesium as I rebuilt my 84 and had to replace the whole cover, it was pricey. The main issue is Magnesium and Water do not like one another. Other than that they are good solid bikes with the right amount of work and aftermarket parts can be as fast as any modern 125, just not as well suspended. As far as an 89 and 84 parts swap; they are completely different machines. There are not many parts that are interchangeable. All things being equal, I'd go with the 89, more parts are available and the cylinder can be overbored; first year of the electro-plated cylinder for Honda CR 125s. Some of the lower end parts are interchangeable with the 90 - 98 lower ends; however, the crank will not as the flywheel end is different.

Evans coolant works well too, but pricey. My Cannondale has a mag valve cover, so thats what I use. No problems so far.