I'm fitting my bike engine dose the sprocket adaptor have to perfect inline with the diff or can it be of set a little bit ? I now it helps if it is but inline but its easier for me if I can have it a little bit over ?
Dan

It should not be perfectly in line anyway so step over a little.

I'm getting mk to make a prop for me and they said they have 3 uj joint . So have to off set a little ? .
Cheers mark

Ideally you want the engine drive flange and diff flange to be parallel to each other but off-set.

If not parallel then it will cause vibration in the joints/shaft. They should be off-set so that the joints have a small angle in them which causes the bearings in the joints to move; If they don't move they wear quickly.

The centre lines at both ends of the shaft can offset from each other but should be parallel to reduce UJ vibration to a minimum.

In simple terms you want the gearbox output shaft as close to parallel to the differential input shaft as possible. but the gearbox centre line can be above, below or to either side of the differential.

As Mark posted a small amount of offset is good for Hardy Spicer style universal joint as it allows the needle rollers in the UJ to move a little and avoid flat spots and premature wear.