Commando cases would crack open from combustion torque pressure not rpm horse power. Rpm horse power bends-cracks the crankshaft shaft ends first, then anything attached to ends, then those end things take out cases and/or pistons then rods. Reviewing a decade plus of Commando failure modes implies rods are rare as first to let go but common to follow weaker items failure, cap bolts to piston parting.
Of course all Al has a fatigue life so of course a bad over used Al rod can be first to go and more likely at hi rpm but I've had em fail in low load nil power-rpm
just holding 50 mph on level road below 4000 rpm -.5 sec tinkle sounds then locked rear squeal. Of course case casting could be faulty too and help top part from bottom.
My Combat prior to me was and still is famous in small city it was sold in as test bike in show room, then passed along to hillbilly thrill seekers, then me who first week on it was on drag strip - after rusting mufflers blew off and opened up top end power - trying to get the jump on wheelie bar'd 1200 Sportster, and did too.
Got out horse powered by 1/16 th mile- ~half way down strip ~80 mph/2nd.
On tear down **Only** to learn to fix oil weeps and refresh wear parts, cases were almost impossible to separate or even put together empty. I had to mark locating dowels to discover the two sides had been engine torqued so hard the cases had twisted on each other putting strong bind on the dowels. I inked dowels to find .003" needed removed from one side of each dowel to allow cases to fit again.
DynoDave's impressive eye sight up close found cob web thick crack in one stress riser of a case clamp bolt flat and welder found two more deep under pristine looking surface. Norton milling machine left sharp corners to be aware of.
Expect case distortion no matter what, especially if Al melted down as much as a full depth fill in requires to reach beginning hidden cracks.
Test for Al ready to weld is soot from Acetylene torch is all burned off.
Ms Peel's Combat cases were tested regularly a bit over 7000 but once beyond tach stop peg stuck throttle that damaged crank, everything attached to both crank ends, alternator, oil pump case, camshaft journals, cam lobe and crank belt pulley side plate screws, but the cases survived fine, still easy to part and mate and seal up dry. Ran fine 2000 miles like this but for no pull power by 5000 rpm.
hobot
