Cotter Pin Inquirey for Stainless Steel Sprockets.

I have a pair of older mirage drives that I have been using now for about 5 years. Been rebuilt a few times and been using turbo fins on them for a few years. I find them to be very reliable except for an occasional cotter pin breakage.

In fact, I just put a new set of flippers and new pins on but ended up breaking a pin on the first trip out after 40 miles - yeah a real long trip on the Island.

I actually go so far as to buy & use the Hobie cotter pins #8060111.
Does anyone know of another more durable material or part to replace the cotter pin?
Is there a titainium or such pin?

I know some may suggest using plastic sprockets, but I have a pair of late '06 early '07 mirage drives with plastic sprockets and the thin drums and hollow arms which I don't trust for hard turbo fin use. Besides the problem would only shift from breaking a cotter pin to having the allen screw loosen up.

In 5 years use by my wife and I on these 2 drives, cotter pins have only broken about 7 or 8 times; or about 1 break per 80 outings. I never re-use old cotter pins and do replace them when I'm rebuilding drive or straightening the mast.

Any Ideas?

TIA

Yakaholic

Hi Yak,

As your old stainless sprockets get more worn, I suspect your already loose masts are gaining more and more wobble room as they smack back and forth in their holes up to 3000 times an hour. This, when added to the small oscillating twisting moment the masts transmit from the fins against the cotter pins, gives those pins more stress than they are really designed to take. So your best solution may not lie with pin strength, but wobble management.

Some of the hobby shops should have a selection of thin-wall brass tubing that you could sleeve over your mast bases, sharing the cotter pins as anchors. This would reduce the clearance between mast and hole and relieve some stress on those pins.

As a bonus, you should get improved mast action, increasing your performance efficiency slightly. Every little bit helps!

An alternative might be to increase the size of your mast cotter pin holes (not the sprocket guard holes) slightly to allow the masts to articulate with less stress on the pins. I don't think it's as good a solution though.

Thanks RoadRunner!

On the drive that just broke the cotter pin I had already replaced both Stainless Steel sprockets about 6 months ago.

Turns out that the teeth on the old SS sprocket were a little worn as well as the mast hole.

I did try wrapping the mast end with teflon tape to reduce mast wobble - which did work for a little while. So we are on the very same track of trying to overcome mast wobble. I will have to check a hobby store as Ace Hardware just didn't have the right sized bushings. Been aware of mast wobble on the SS for a very long time - just never pursued a sure fire fix.

What do you think about a small bolt in place of a cotter pin?

Also, what would happen if you greased the mast before you slipped on the turbo fin? Would you not get the same twisting motion of the fin with less twist transmitted to mast and cotter pin?

The greased mast would also help those that use the plastic sprockets because mast twisting is probable the root cause of the occasional allen screw getting loose.

Yakaholic

Yak, I'm not a big grease fan for non-sealed applications like the Mirage Drive. Even the factory assembly grease points I view as a mixed blessing. It seems like grease collects grit and sand out of thin air which starts grinding away at the parts. Even the factory silicon grease on the hatch seals collects debris quickly.

Mast pockets on the fins are a great place for grit to collect and accumulate, hard to flush out if grease is in there. Instead I like to use silicon spray when installing the fins. It probably doesn't stay long though.

If your brass bushings are a little large or small, you can slit them with a fine saw (also from a hobby store) or Dremel, since they don't need to be a 360 degree fit. In that case, you might oversize the cotter pin holes on the bushing for a versatile fit. You could even double layer the tubes depending on how much space there is to fill.

The machine screw idea is certainly worth a try if you have something in mind. I haven't seen anything that thin that is really tough without being brittle but am no expert on the subject for sure! That would make a great long term test!

I would suggest maybe trying a clevis pin and hitch pin clip like this..



They come in many lengths and diameters as small as 1/8 " and some have multiple hole settings for various needs.

There is a locking type that you just squeeze with your hand and open or close as required. I use a set of these for my sidekicks that allow one handed snap and set motion to keep each inflated sidekick onto the end of the bar.



Machine screws should work well also. I would suggest trying a stainless socket head cap screw and nylon insert nut in 316 or 304 grade . They are available in numerous diameters and lengths also



Kepnutz