Well, we've finally decided my Howard 300 is well and truly ... f i x e d !
Was planning to take up to the Fields today for a decent work-out, but family business prevented in the event.
Bro' and I had to make do with some trepidatious runs up and down his driveway and side bank, BUT with nary a murmur from Howard - RESULT ! Full-load test ("in anger") planned for 2mor, but, really, it will just be a formality - the Howard is running pretty darn good ! (And I'm not even going to touch wood after that statement.)
The technical report for those so minded:
After the 2nd chassis split, chassis-case gears were re-shimmed to prevent any chance of rubbing what so ever if chassis flexed/stressed.
Subsequent rebuild and retest suggested "grumbling" noise reduced, but by no means cured, so gear box taken off once again and dismantled (bro' can now almost do that and rebuild with eyes shut !).
Going with the fact that running in high gear (with fewer gear cogs engaged) is not as noisy as in low gear or reverse (when a multitude of gear cogs on different shafts are engaged), we manually determined that the gears on the drive-shaft stiffen each other up along the shaft in high gear, resisting any gear "wobble" on the drive shaft. BUT, in low gear, the "drive gear" is not bolstered by sideways contact and a bit flabby on the shaft: applying manual sideways thrust to connected gears identified a difference in feel through the "drive-gear" when turned over manually.
The decision was made to re-bush the "drive gear" (noisy culprit or not - nothing to lose cos we had no other ideas). A piece of partially drilled brass rod was chosen, but it still took most of an afternoon to slowly manufacture new bushing on the lathe keeping the gear/shaft tolerance
very tight and finally only loosened up (spinning easily) using Brasso.
The gear box was reassembled and, then, one could hardly tell the difference between high and low when box turned over manually - sweet! When re-installed and run up and down the driveway and with rotors engaged on the the bank everything was still sweet today! Howie is clearly fixed.
Detail above provided for any other owners who might eventually go thro' a grumbling Howard: we suspect that there was so much crud built up inside the gear-box over the years that it was hiding/compensating for the wear. Cleaning out and using fresh oil made slop in the gear-box apparent. (Bro' did "fill out" one other g-box shaft and lathe back to spec' dimension, but it was the "drive gear" slop on the drive shaft, after the clean-out/rebuild, that was the real problem.)
I might manage a photo idc.