Have the crank wheels on that cylinder actually moved apart ?? Can you measure the distance ?? Sometime what happens is that the thrust washers get chewed up a bit, the filings get sucked up the transfers and spit out the exhaust port. This is SOMETIMES evident on the piston crown and cylinder head and sometimes not. The thrust washers are a phosphor-bronze compound and are not very hard...plus the small size of the filings sometimes will not mark the piston crown or cylinder head. If you look down into the crank chamber, sometimes you can see them glittering in various places. Use a MagLite for this as you need a good high-intensity light source. The munched thrust washers make it APPEAR as if the crank wheels have moved apart. Regardless...if the thrust washers are toast OR the crankwheels are spreading apart, you better get it looked at. IF the outboard crank wheel has moved on the big end pin, it is now putting a tremendous axial load on the outboard main bearing (and I believe there's also a thrust washer in there somewhere) and, if left unattended will cause the BEARING to MOVE, with major expensive consequences (as I'm sure you can imagine). At least in your case it's an outboard rod/pin problem and can be fixed relatively easily (if you don't count having to remove/dismantle the engine to do it) compared to the centre cylinder. The trick is to find a rod/pin/bearing kit with thrust washers. I can't remember if the washers come in the kit or are sold separately. Check with Paul Miller for the rod kit and the outboard crank seal (might as well replace it at the same time). Keep us posted on this. As to power, I wouldn't think you're getting anything like 70 HP with chambers and mild porting .....more like 55-58-60-62...somewhere in that range.