James c harrell

My Feedback: (18)

Went to the river yesterday to try out a new prop and got my tunnel fired,tuned dropped her in and hit the throttle-instant nothing!! I had noticed that the last time I ran it the prop had dropped back about a quarter inch and figured that it had slipped at the engine collet. I slid it out and greased it from the engine side not really taking notice of the prop end. Re-positioned it and swapped props. Ready for the next run. NOT. It snapped the flexshaft about 3/4 the way from the engine, dropped the prop to the bottom of the river. I dont have any hard bends in the tube and it was fairly new as far as the driveline goes. Teflon lined tube and thrust washers and the cable is a 1/4 stepped to 3/16 that was new too. I bought the "good" cable grease and usually re-grease about every third run. What can I do to keep this from happening again. Twenty bucks a prop and a thirty buck cable hurts when they go to the bottom of the river.

Jerry Dunlap

There's two issues here: 1. Breaking the cable, 2. Loosing stub shaft and prop.

You didn't state what size OB you were running. Looking at the photos, it looks like a 7.5 cable. Cable will break.

I've stripped the threads for the stub shaft in K&B lower units making it impossible to tighten the stub shaft. As you discover, a loose stub shaft can come completely out of the lower unit.

JD

James c harrell

My Feedback: (18)

It is a O.S. 81 VR-M. The cable is a 1/4 inch stepped to a 3/16 but it broke almost 3 inches from the metal step part. Just to clarify, it isn't an O/B it is an inboard.

HendricX

2 Possibilities for this wound up cable :

NO end-play on your drive-dog / or Teflontubing too tight.

Leave cable-diameter as endplay , and ditch the teflon , use bare 7mm or 9/32" brass-tubing.

James c harrell

My Feedback: (18)

End-Play?? Explain this please. It may well be what is wrong if I understand it.

HendricX

Your drive-dog bearing should be 3 to 6mm / 1/8" to 1/4" (if using a 1/4 flex-cable) from your strut .

Flex-cables tend to shorten themselves (wind-up) during acceleration.

The cheaper the cable .. the worse it gets :-)

Try to find the stiffer 'golden-stranded' Sühner cable ... [link=http://www.gizmomotors.com/index.php?option=com_virtuemart&page=shop.browse&category_id=9&Itemid=56]Gizmo's[/link] sells them.

James c harrell

My Feedback: (18)

That would be the problem. I had thought the thrust washers should be a little loose, like as very little loose, and that is how I set it. Live and learn. Gotta learn somewhere. Appreciate the tip and or lesson. Any-one know where I can get a book "R/C Boating For Dummies"? Kidding. You got a link to Gizmos'?

Ron Olson

My Feedback: (1)

Is the boat a Catamaran? You have to be more specific as otherwise we're thinking a tunnel boat with an outboard. I knew the cable looked awfully long for an outboard!
OK, I'm thinking of 2 other things. Most inboard nitro-powered boats use a standard round collet, not one for a square drive. If your using the regular collet setup, ditch the thrust washers, you don't need them.
Failure to have a 1/4" gap between the strut and drive dog will cause breakage, been there. If it's breaking at the same place on the cable then I'd be looking for a kink in the stuffing tube that's rubbing hard in one spot.
This here is the result of a tube without a Teflon liner that I assumed my boating buddy got a kink in somehow during the winter. We took this shot just a week ago.

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