I've been noodling around, examining design alternatives for relatively easy ways to direct drive props from the flywheel end of various V-Twin engines, and had a need to know what the Bolt Circle Diameter was for Rotax engines.
Rotax prop flanges, at least on the current 912/914s, are as full of holes as a cheese grater. I think the way this worked out is the first engines had the same BCD (75mm, 6 M8 bolts) as earlier 2-strokes. These started to break, so they went with a larger diameter and bigger fasteners (80mm, 6 M11.5). But SOME PEOPLE wanted the US standard SAE#1 prop pattern, so they added 101.6mm (4") BCD, and threaded inserts, metric or UNF, you chose. All on the same flange.
This service bulletin explains it all http://legacy.rotaxowner.com/si_tb_info/serviceinfo/4kul94.pdf
I've cribbed it a bit, and created this diagram for study/reference/system interface purposes. All rights in data are reserved by Rotax.
I'd appreciate any corrections/amendments/additions by anyone with superior knowledge to mine.
In case you're wondering, prop extensions to fit these bolt patterns are available here: Saber Manufacturing - prop extensions, crush plates & bolts
and here Extensions|Airmaster Propellers
and here (scroll down) Warp Drive Carbon fiber Propellers ON SALE, Warp Drive Helice
And here www.airtrikes.net {see their pricing page, called a "spacer"}
Rotax prop flanges, at least on the current 912/914s, are as full of holes as a cheese grater. I think the way this worked out is the first engines had the same BCD (75mm, 6 M8 bolts) as earlier 2-strokes. These started to break, so they went with a larger diameter and bigger fasteners (80mm, 6 M11.5). But SOME PEOPLE wanted the US standard SAE#1 prop pattern, so they added 101.6mm (4") BCD, and threaded inserts, metric or UNF, you chose. All on the same flange.
This service bulletin explains it all http://legacy.rotaxowner.com/si_tb_info/serviceinfo/4kul94.pdf
I've cribbed it a bit, and created this diagram for study/reference/system interface purposes. All rights in data are reserved by Rotax.
I'd appreciate any corrections/amendments/additions by anyone with superior knowledge to mine.
In case you're wondering, prop extensions to fit these bolt patterns are available here: Saber Manufacturing - prop extensions, crush plates & bolts
and here Extensions|Airmaster Propellers
and here (scroll down) Warp Drive Carbon fiber Propellers ON SALE, Warp Drive Helice
And here www.airtrikes.net {see their pricing page, called a "spacer"}