Oil pump Idler gear problem

[Scuba]

Hey there,
NEW Member to the forum, but have been using this place for reference for years. Huge thanks to all of you.

1978 xs1100e
THE PROBLEM: Oil pump Idler gear fell off the shaft. (At least Twice)

I bought the bike from a guy in a non running condition no battery. changed the oil and such and bough new filters etc. basic stuff. Got the bike to run eventually, and got to ride it just a little, but no top end. One day bike dies moments after starting a test ride. I push it back to the house and frustrated and tired, forget to turn off the (aftermarket) petcocks.... next time trying to start i see fuel vapor out of breather vent (PO ran pods, +filter on breather tube) I change the oil and then, I happen to catch a glimpse of something in the bottom of the clutch side of the crankcase. take it apart and its the oil pump idler gear. SO.... I put the gear back on and i put it all back together and take out the spark plugs......squirt a little oil and start the bike ran great. took it out lost power, dies push up hill. well..... I check compression. 115 on far right (4?) and between 170 and 180 on the others, then i check the far right again and its 170. Thought, must be a misread. Started bike, push up hill...... took spark plugs back out and tried to redo compression test, motor seized. Drained oil and found oil pump gear in bottom again. Try splitting cases on a seized motor.

Found a melted conrod bearing, and some severely worn crankshaft bearings, crank looks like it was EXTREMELY hot. it and the connecting rod in the area is black.
OK.... so Here is the ultimate questions....
I want to get a used crankshaft, with connecting rods attached, check the bearings of course, and get new main crankshaft bearings.

I was thinking either a big bore kit, or a new cylinder(cosmetic), and big bore kit,

So, Should I be worried about warpage as far as the crankcase is concerned? Or would new bearings and crankshaft be sufficient?

and about the Oil pump idler gear. IS there anything that could have ultimately caused it to fall off in the first place. And the second time, I believe I may have needed a washer on the outside in between the circlip, and the gear, as well as on the inside? Is this correct? I didnt put one on the outside of the gear the first time. I am nearly certain this was my mistake, that caused this problem the second time. Live and learn.

[skids]

If it got that hot to lock-up the engine, I would look for a low mileage engine to work with. I have had the pump gear off one of the bikes once, but I can't remember how it was installed. In my case I bent the gear wheel when I was installing a clutch basket (dumb).

[motoman]

That idler gear is held on with a high tension snap-ring. If that snap ring is off, it needs replaced as it will NOT hold if put back on. If that gear has come off, guarantee bike has two more added issues associated with the shift fork shaft, which is the same shaft the idler gear rides on.

[3Phase]

That idler gear is held on with a high tension snap-ring. If that snap ring is off, it needs replaced as it will NOT hold if put back on. If that gear has come off, guarantee bike has two more added issues associated with the shift fork shaft, which is the same shaft the idler gear rides on.

The clip also has a 'front' and 'back' side to it. The back has a bevel cut, I suppose to help it slip over the shaft, and the front is cut sharp and square. If you put the clip on backward with the bevel facing out and the square cut facing the case, the clip can pop off the shaft and the gear won't stay in place.