What is the thread size of the part of the stud that goes into the crank case and if required what size helicoil insert would I need .Thanks in anticipation.
Richard
According to Draganfly they are 1/4, threaded CEI at one end and Whit at the other (presumably the crank case end)
the standard studs crack the sump alloy when tightened imo. i only use 1/4 whitworth studding. aprox 1 1/2" long. cut the head of some old timing case screws.
avoids sump welding repairs
The studs into the casing are definitely whitworth. You will find that for all the threads tapped into ally, casing joint, rocker covers etc, BSA used whitworth.
I have fitted several of these they are 1/4 whit I use stud lock lock tight and only tighten them gently the locktight does the rest to remove double nut and heat casing .