Commando engine running upright

Your first step should be to have the crank re-balanced for rigid mounting, or the vibration will likely break your special frame. Lots of people have run Commando engines in featherbed frames, so upright shouldn't be a problem.

Colin.

The '72 crankcase has a poor scavenge arrangement. While you have the cases apart for a re-balance do the Mick Hemmings fix for this. Details at http://www.oldbritts.com/n_c_case.htmlhttp://

I'm not convinced that the breather on the timing chest is a good idea although of course others may have differing opinions. One of the chaps on the American Commando forum did some computer modeling of the pressure dynamics of that set up and showed it to be rather ineffective in reducing crankcase pressure. You just end up wasting energy by pumping a large volume of gas back and forth through the small holes to the primary chest. This is also borne out by trials which respected engineer Jim Comstock conducted with a pressure transducer to measure crankcase pressure. His solution is a reed valve breather which can be bolted to the back of the '72 crankcase and gives negative crankcase pressure throughout most of the rev range. They are supplied by CNW and are rather expensive, but I managed to make one for under a tenner. I would also recommend looking at his primary case oil drain modification. Details on the American forum........

I run an Atlas engine in a slimline 99 frame - the vibration levels are perfectly acceptable, even reducing once you reach 4,200 rpm. The Atlas balance factor should be right - of course other things could be to blame - a loose head steady for instance. Gordon.

I am recommissioning a Commando engined slimline 99 - don't remember the vibration being too bad - how can I tell if it has been rebalance when I get the barrels off? Steve