Re: crank to rod slack – opinions ?

[Don]

Tim
Sometimes, sideways piston slop in the block can seem like slack in the rods/bearings. But, you seem experienced enough to tell the difference.
In any event, if there is a problem with the needles/retainers/crank/rod journal, it is usually visible to the naked eye. Water damage, pounding damage from detonation, should be visible once the pieces are cleaned up a bit. In any event, the 2000 grit stuff you mention should be fine for cleaning up the journals a bit. Finding it in a roll thin enough to fit inside the width of the crank journals will be the trick. I wouldn’t bother with the lathe, I would simply clamp the crank in a vise (please don’t let it fall out), and work the journals gently. Again, any damage should be pretty evident to the naked eye. You could always compare the measurements of the two journals. Generally speaking, these engines never get enough use to actually put much wear on journals/bearings. Damage usually is from water intrusion, or pounding damage from detonation issues. You could clean up the rod journals as well, and compare the inside dimensions of both rods. I am assuming you have noticed that the rod caps are unique to the original rod and can’t be swapped, plus they will only fit properly together when orienting correctly. Looking at the mating surfaces, you will note they are jagged edges, this is normal. The rod is manufactured in one piece, then actually split apart causing the unique jagged edge fit. Care must be taken when reassembling these rod caps, they must be manually aligned or the mating surfaces will be distorted and ruined when proper torque is applied. But again, you seem very machinery savvy and have probably already noticed this.
This just might be a case of defective needle retainers causing slop, hopefully a new set of needles/retainers will do the trick…
And sorry, I don’t have a manual for this engine so don’t know the actual journal dimensions, I’m sure someone else will chime in.