Hiya,
Shortening one side will offset the diff housing in the middle of the axle to one side -necessary on most bike engined trikes to bring the propshaft into line with the prop on the engine. If you're using a Reliant engine though, it'll sit centrally down the frame, so the diff needs to stay central. A propshaft will run quite happily at an angle -that's how they're designed to work, but makes more sense to cut both ends of the axle & keep things symetrical doesn't it?
Yeah, we've covered it in several threads. Here's one of them but there are more:
http://www.mankymonkeymotors.co.uk/forum/index.php?topic=3769.0Personally, I prefer to draw the steel axle tubes out of the aluminium diff casing, cut them to the desired length, then refit them, though this can lead to disaster if you're not careful, (as we've found), cos the end of the steel tubes are turned on a lathe to fit the internal diameter of the casing. When you cut them you cut that turned down section off & have to re-do it. If you don't, the casing will split as you push the tube back in. I've always reassembled them cold, but it's easier if you warm the aluminium diff & cool the steel tube first so that one expands & the other contracts.
The drive shafts are cut by the same amount. Cut them in the centre so you don't have to worry about disturbing the splined ends. Then a steel sleeve is machined to cover the joint, (about 4 inches long & a good tight fit over the shaft). Push the shaft ends together inside it. If you've made it long enough & tight enough the shaft will self centre, ensuring it runs true. Then weld around both ends of the sleeve. That's probably enough to take the 40bhp of a Reliant, but to be on the safe side, I also drill through the ends of the sleeve, right through the shaft, & knock in a steel pin, which I then weld in place too.
Other people here do it differently, by choppig the outside ends of the axle tube off, removing the desired amount, then welding them back on -which obviously requires a degree of accuracy to ensure they go back on true. If you cut the tube a few inches back from the end flange, you could use a sleeve inside the axle tube to make sure it sat true.
With axles now getting a bit harder to find, I'd be inclined to go for the second option, cutting the outer ends of the steel tubes, rather than my previous method of cutting the inner end & refitting it in the diff, cos it's not worth the risk of cracking the casing.
