Hi Peter,

There are two types of down tubes. Early types were push-on fitting to the motor and later types had nuts that fixed the pipes to the cylinders. Sounds like you have the early ones. If so, can you get back to supplier and change the down pipes for correct ones ? Probably easiest fix ?

Mike.

The ends are flared at the cylinders on the system with nuts, and the nuts are coned internally to fit with that.

The downtubes is the most difficult part of the system as they have multiple direction bends and there is so many tight spots. The cones needs to fit perfectly to the cylinders not to soil the cylinders all over with soot and burnt oil. And both tubes needs to align perfectly to the collector tube below in order to slot in at assembly and keep reasonable tight.

And the collector needs to be aligned perfect with the 3 clamps under (2 at the collector and 1 for the silencer) and also make a slight bend in order to clear the rear wheel better, a detail some repro systems is missing. All details needs to jive up strainless in order to be tight and not brake down in time. It is a system very difficult to make on your own if not experienced and well stocked up with some tranqulisers.

I have to warmly recommend Walkers complete system that is a real mirror of a original and fits like a glove without modification on several bikes I've tested it on. Well, I might have hammer peened the cylinder cones slightly to adjust for different cylinders. OD of the ones I have is 31,6-31,7mm and 1,6mm thick.