fyrstormer

iTrader: (1)

I have an old engine with a fully-threaded crankshaft, and the crankshaft is too short for a clutch bell to fit on. The threaded portion has an outer diameter of 6.2mm (1/4"), and I need a pilot shaft that will screw onto this and adapt it to fit 5mm clutch bearings. I can find lots of pilot shafts when I search for them, but not a single damn one of them specifies what size threading it's designed to screw onto or what size clutch bearings it's designed to fit. Please help.

RCTecher12

iTrader: (1)

What engine are you working on? A 6.2mm OD shaft is just a hair under 1/4" (6.35mm) which is the typical size of many crankshafts. (The threaded section often is 1/4-28 UNC)

Some engines have metric threaded cranks, but I doubt a 6.2mm measurement is such a situation.

fyrstormer

iTrader: (1)

It's an old O.S. airplane engine. I just measured it in Metric and English, in case one measurement made more sense than the other to someone who's dealt with this before. 1/4" seems like the more likely measurement, since it's a nice round number and it's apparently a standard size for crankshaft threading.

So...how do I find a pilot shaft that fits a 1/4" threaded crankshaft? Like I said in my original post, none of them list their actual sizes as far as I can tell, they just specify which vehicles they're intended to be used with.

RCTecher12

iTrader: (1)

Most .15 and larger engines have a 1/4-28 thread. Some engines I've had that had the same crankshaft thread was an SH .28 and 3 Mach 427s. Even my Picco P3 and Nova .28-8 have 1/4-28 cranks I believe. I think it's going to be a "take your pick" type of thing. Shoot for something larger than 2.5cc/.15ci.

What engine is it exactly? .21 FSR?

1/8 IC Fan

iTrader: (102)

Hpi used to have some, years ago we had to do this. I had to cut cranks to fit the Delta Flywheel on my Delta Fireball. Not sure if the M5 will work.

fyrstormer

iTrader: (1)

No, unfortunately that one won't work. I have several HPI engines which use that pilot shaft, and the M5 threading on that HPI pilot shaft is WAY too small to fit.

You know the small bit of threading on a SG-style crankshaft? That's how big the threads are on the entire length of this crankshaft.

Interesting, I didn't realize most engines with short crankshafts have 1/4" threading. The only short-crankshaft engines I have personal experience with are HPI .12, .15, and .18 engines, which all have M5 threading.

RCTecher12

iTrader: (1)

I've had several Traxxas engines myself and they too have M5 threads. I forget the thread pitch though. Some tiny OS engines have metric thread pitch as do some Enyas (odd like M5X.60 or M5.5x.60).

fyrstormer

iTrader: (1)

You're right, I forgot about the TRX 2.5Rs I've used before.

This engine is not like those; it's an old airplane engine, and the crankshaft is 1/4" threaded the whole length, so the propeller retaining nut can screw-on all the way at the end.

HaulinBass

iTrader: (16)

Is this the what you need? www.rcplanet.com/Ofna_Clutch_Nut_Pilot_Shaft_p/ofn10090.htm

fyrstormer

iTrader: (1)

Funny you should mention it, I bought that one thanks to Sharkey_t's recommendation. Hopefully it gets the job done; I have my eye on a Kyosho one if the OFNA one doesn't work.

fyrstormer

iTrader: (1)

The OFNA pilot shaft arrived this afternoon. It fits. Problem solved.