The shaft fell out!!

[bccanucker]

Last week I backed out of the slip, turned 90 degrees to go down the channel and found I was going nowhere. Hit the bow thruster to point back into the slip and threw a line to a fellow boater who pulled me back in. The shaft had pulled out of the collar to the transmission. Nothing broke. The two 1/2" bolts that go through the collar and dimple into the shaft fell out and the keyway fell out. The 2 bolts had wire connecting their heads so they wouldn't undo but this wire broke. We bought this boat last April and the shaft was replaced about a year before that and as the boat was up for sale for the year had no hours on this re & re.
I am mostly writting this to suggest if you have this transmission collar arrangement to make sure things stay tight.
When you look at the design of this arrangement you probably don't want this engineer to design your helicopter.
My mechanic wants to change this over to a borg warner collar which is split halves and more secure.
For now I have put all back together and added jam nuts to the 1/2" bolts. They were probably left out when the shaft was replaced about a year ago because they are a British thread. Our standard is 1/2" X 13 tpi and these bolts are 1/2" X 12 tpi. Took a considerable hunt to buy a pair of these. Cost me $25. for the pair.
Things sure shift smooth when the shaft falls out

[jcollins]

Things sure shift smooth when the shaft falls out

At least you didn't loose your humor.

[jleonard]

My mechanic wants to change this over to a borg warner collar which is split halves and more secure.

Yes this is the way to go without a doubt.
Replace the oddball hardware with standard US hardware. And the best grade steel (not stainless) bolts/nuts/washers you can find.

[RobS]

Yes, hardened bolts, not stainless at the shaft coupler. No time like the present to check your alignment.

Not sure of your rudder arm setup. Another one to check periodically.

[yhc]

jleonard & RobS,

Would you explain re: stainless vs. hardened steel?

yhc

[RobS]

Bolts are hardened by heat treating them. Carbon in the steel is needed for this process. Since Stainless has low carbon content it cannot be hardened via heat treatment.

Bolt depot is a good source for hardware. Here is a link http://www.boltdepot.com/fastener-infor ... rials.aspx explaining the different hardware types and you can browse the site form there.

For the coupler use grade 8 nuts and bolts. Grease the bolts and grease between the coupler flanges.

[DougSea]

jleonard & RobS,

Would you explain re: stainless vs. hardened steel?

yhc

Rob wrote a nice explanation but the simple version is: stainless is corrosion resistant but fairly weak. Proper "hardened" steel is significantly stronger and less likely to fail due to mechanical stress.

Ever twist the head off of a stainless screw? They really aren't very strong.

[yhc]

Thanks for the info gentlemen.

[RobS]

Stainless bolts are known as "butter bolts" when it comes to a connection requiring strong hardware.

[jleonard]

Another reason to stay away from stainless is that stainless bolts and nuts are very likely to "gall" when being assembled. Even at ratchet wrench speed the threads will gall. This happens due to the heat of friction. It pulls surface material off the threads and basically acts like cross theading. The tighter you torque them the more likely they are to gall. (Where I work we assemble stainless to stainless every day by the thousands and we must be very careful)
There are thread lubes you can use but since regular steel bolts are stronger there is no need to go thru the trouble of using stainless in this application.