I just bought a sf conversion with an '88 motor (was supposed to be '89 per seller but turns out to be '88)
Head gasket was leaking so I took the top end off and it is a bit of a mess. Cylinder is cracked on the outside along a water jacket and repaired with what looks like jb weld, cylinder has been sleeved and the piston has obvious marks from something coming apart and then being reused... On the plus side it has been ported by a reputable shop in the past.
The rod seems ok, has an IMS with no detectable play, but the whole crank moves side to side about .5mm in the cases. I don't have a manual yet but am guessing this isn't normal for a KX and am fearing problems with crank journals or cases. The seller claimed he put new bearings and seals in the bottom end but I am a little dubious at this point.
I can't decide if it is worth it to split cases and fix or throw a new piston in and run til she blows and search for a 89-04 transplant in the mean time. I hate to spend a bunch of money on the earlier motor if parts are going to be a problem or if the performance isn't as good as the later models. I did find a pretty cheap '87 cylinder core which I believe will work but then I would have to get it ported, plated, etc. I'm not sure how the 560 big bore works compared to stock bore but pricing wise ($660) it seems like a good deal if I have to get it ported and plated anyway. I have plans for all of the usual mods (compression release, v force 2, 40 mm smartcarb w/heat, Powerdynamo ignition, etc) to be used in a snowbike application. I have saved a little $ to get some of the goodies I need but hate to end up sinking it all in the motor.
Also, what is the real difference in the powervalve set up in the 88 vs 89 on? I know visually the difference but as far as power, rideability, etc? Looking for as much mid to top power as possible, while running on 93 and not being a time bomb.
Needless to say, I am a little bummed and would appreciate advice on the best way to proceed?
