Need to extend my prop shaft to move prop forward 5/8" to clear cowl. This is a Pilatus Porter supposedly set up for ST.61- engine fits ok but prop back plate(drive washer) is 5/8 behind cowl. Can't move engine forward without screwing up the whole front profile of the plane. Any suggestions?

Unfortunately i can't offer any help, but i do have a similar problem. I have an Enya .49X with a prop shaft so short that if i put a spinner backplate behind the prop, the nut won't even completely thread onto the shaft. Recently i switched to a different prop, which happened to be thicker in the center, and there's no way the nut would go on, i had to take my spinner off. Now i can't use my starter and the plane obviously doesn't look as good.

Be sure to make a post here if you find a good solution to your problem wsmalley.

About the only way to do it properly requires a lathe. What I do is turn up an extension that looks similar to the normal prop drive washer but is threaded to match the crank thread. This then screws on until it butts up against the drive washer. Then a special T nut needs to be made that screws onto the crank and I prefer part way through the extension to get enough thread engagement. This nut can be made quite safely from aluminium.

I don't know what threads the 61 has , likely 5/16. I have bought some from Fox for 1/4" threads and they are only $6.00 or so. The one I have set the prop 3/4" forward and are real simple, they have a spacer and a nut that almost looks like a bolt that has been drilled and taped.Hope this helps some. Steve

MiL:

Tru-Turn makes nut adapter sets that compensate for the short crankshaft/thick prop syndrome. Essentially you order the apropriate adapter and then drill the prop out to the OD of the nut adapter. It then screws into prop and onto the cranskhaft. Very simple, very easy and reasonably priced.

wsmalley:

As noted Fox Mfg. Co. offeres prop hub extensions, with the addition of the spacer-hub and special adapter it works much like the Tru-Turn adapter.

Other than that you can have one machined as suggested... This is realatively common on Gassers.

Thanks for the input guys! I figured there had to be some rather simplistic solution. From your comments it would appear this is not an altogetherunusual problem. Does anyone believe this "extension" solution puts any unreasonable strain on the front bearing. Saw an article in MAN some time back where a fellow made a long shaft and mounted a bearing in the front bulkhead- this was a glider with probably a 5 or 6" shaft. By the way, the S.T. .61 has a 5/16th shaft.