I'm in the process of converting one of the older Echo 40s that had points type ign in rear. Out of a back-pack blower. This is my largest cc convert to-date and have no idea of what diameter prop would be best match.

I have some 2" Alum bar stock to make the prop hub. What I would like to know is what diameter face should I plan on? I have MAS and APC 18" props so that diameter is not a problem, but it a Echo 40 cc , 3 ring piston. 7/16" diameter output shaft will swing a larger diameter, I need some guidelines for surface diameter contacting the rear of prop.

Thanks

2 inches is large enough for my 289cc race engine, it should be enough for a 40cc Echo 1 1/2 is plenty....Anything bigger than the width of the prop is just wasted aluminum....
I have a 3/8-24 center bolt and two 1/4-20 bolts on a 1 1/2" bolt circle through the prop...[8D]

Hi RCIGN
nice numbers, I am converting a 70 cc chainsaw engine (italian ALPINA)and think about the right diameter of prop adapter.
What a feeling tuning that beast.
I will pay for a tuning session.
Many thanks for your example.

most of the 3W singles use a 40mm hub. find pics of these engines with various props and see if it suits you.


dave

Just didn't want to error in making the diameter too small! May have just searched in wrong places and the pics scale objects, they all look about the same.

FWIW:1) 2) Also measured a DA50 hub yesterday 1.625"
Eiit added:
3) From Windsor Props: