Strut bushings

[NativePaul]

I use ball bearings too. The cheap Chinese 1/8" strut has just enough diameter to drill out for 1/8"x1/4" ball races. I chop the tapered nose off just short of the strut blade, and hand drill each end using a regular bearing on the front and a flanged bearing on the back, it leaves a paper thin wall thickness around the bearing pockets, but has proved to be stronger than a .98 flex cable. It looks like your existing strut has a larger diameter and would be easier and stronger to drill out, maybe even having enough meat that you could use a good pillar drill or mill, and drill a long bearing pocket from the back to preserve the taper at the front of the strut.

CraigP, if when you pull the nail head out you are getting terrible side to side play, then either the floating bushing and/or strut have worn out, or were machined to the wrong size. Your being able to add a 1/4" tube to it without mentioning drilling it out makes me think that it had a 1/4" bore and the only bearing surface in it was the small 1/4" "nail head" at the back. Putting a grub screw in a 1/4" tube soldered to the floating bushing to stop the floating bushing moving defeats the whole point to having a floating bushing. Better would be to extend the "nail head" to the .175"+ that your setup needs with a tiny length of 1/4" tube (soldered or not), and then add the 1/4" tube you added, but a tiny bit shorter to compensate for the extra "nail head" and drill a hole in it and the strut for a grub screw, but not solder it to the floating bushing, and not put the grub screw right through it into the floating bushing. That way you still have a working floating bushing, the nail head can not come out, and the bearing carrier can't disappear up your stuffing tube. Either that or use a matched strut/bearing system.

[CraigP]

That's a good idea Paul. Since the last post, I modified to use (2) 1/4" X 3/16" bushings, the ones available on OSE site. The bushing I did was working very well, but there's something else really bugging me... you guys will probably think this is ridiculous, but I have to do something. I left nitro boats because of the oil contamination in the water while running it. When we had a bunch of boats running together, it really made a mess! Now, I'm losing grease out the back and polluting the water again. I want to minimize this to the absolute degree I can.

I have a good seal where the stuffing box enters the front of the strut. I use a piece of silicone tubing to go over the point where they meet. The action of the flex shaft acts like an Archimede's Screw, pumping grease towards the stern. This is good since the radius in the stuffing tube is towards the back and that's where the highest heat rise is.

Sooo, I ordered some small lipped shaft seals to put in the back of the strut to contain the grease. I have to open the diameter on the back end to 5/16" to press fit in the seal. The pressed-in bushings dropped the grease leak by more that half and has a great bearing feel to it. The whole thing is made more difficult due to the flex shaft shrinkage. The prop shaft has to float back and forth. I've thought of the bearing setup Randy posted, but I would have to have the inner races tight on a piece of tubing and then let that tubing float on the prop shaft. In the end, not much different over all the other setups discussed. Only a lip seal will hold that grease back.

Anybody else feel the same about this water contamination issue? I'm not a "green guy" in the traditional sense, just hate seeing oil marks coming off the back of my boat!

[CraigP]

Here's a pick of the silicone seal on the front. You can make out the clearance needed on the back...

[RandyatBBY]

Here's a pick of the silicone seal on the front. You can make out the clearance needed on the back...

I have seen this done with shrink wrap a little thinner application.

[CraigP]

Shrink wrap is what I should use with a bit of silicone underneath.

[CraigP]

Well, it's time to eat some crow... I decided to use a SS tube for the stuffing box because the clearance was tighter. Looks like I have created a very efficient screw pump with the grease! Looks like my grease pumping problem is probably much worse than what others are experiencing, due to the tight clearance that I put in there... Thinking of changing to a 0.150" flex and use a teflon liner. OSE is flat out of stock on all those parts, except reverse cables..

[CraigP]

Strut sealed, grease leak mitigated...

I got the seal into the back of my strut as I was talking about. I ended up using a EPDM Rod U-cup seal. It has a 3/16" ID and a 5/16" OD. It's about 1/16" thick in the cross section. I milled a counter bore into the back of the strut 0.060" deep for the U-cup to sit in. Since this isn't a metal cup seal, it is not press fit. I fashioned a small metal place and affixed it with two, 2mm SS socket head screws to hold the seal in and compress it slightly. I am losing very little grease now. I ran it, and didn't have to lube at all over the course of 4 runs. I dissambled when I got home, no water and the grease was fine! Propbably could get many runs before servicing the shaft. I'm using ProBoat Blue Marine lube with Marvel's Mystery Oil mixed in. The two lubricants seem to "get along" just fine. Pictures below...

[CraigP]

Randy, water got into the strut with heat shrink, even with silicone applied. I'm not getting any water with the silicone tubing. A bit strange, since it hangs in the water more than thin heat shrink... I think the heat shrink is peeling up, letting water in.

[NativePaul]

You can get heat shrink tube that is lined with a hot melt glue, I use it for attaching boom tubes on riggers, it is thicker than normal heat shrink, but much thinner and much more secure than silicone tube.

[CraigP]

Hmmm, haven't heard of that, I'll look around for it. Is it still pliable after shrink? I use different angles on the prop for different props. My M445 likes some positive angle and all my lifter props like negative. All in, I need about 3-4 degrees of freedom at the joint.

[CraigP]

Update: I replaced the SS tubing on the stuffing tube, put back in a K&S brass 1/4" tube, traditional approach. I went back to the 3/16" flex shaft, no liner. The 0.150" flex was too springy, it won't take 8s torque for long. The whole SS tubing thing was a bust! DO NOT try that! The heat buildup in the stuffing box was way too much! I'm sure I was the only one foolish enough to try... BTW, you can get brass tubing at your local Hobby Lobby store. Not sure why OSE seems to have trouble keeping that in stock...

[Chrisk7]

https://www.modelgasboats.com/magazine/how-to-articles-mainmenu-606/328-make-your-own-strut-bushings