Proper Use of Sleeve Bushings

[Fluid]

I have recently heard about a gross misunderstanding of the function of the sleeve bushings used in R/C boats. Some seem to believe that they are bearings that must be attached to the strut or stinger to hold oil and grease. Some even suggest putting solder on the bushings to keep them from rotating. This is simply wrong and gives away some of the advantages of the sleeve bushing.

These were developed years ago by nitro racers to reduce drag and play in their struts. The then-common lead/teflon bearings worked but their size was not very uniform and they quickly developed excess radial play due to their softness. Lead/teflon really works for 'slow' boats - full scale and models - but is pretty poor for high rpm/high load bearing use.

The solution was to use two nesting sizes of brass tubing. These are dimensionally uniform with just the right amount of play to avoid galling. The stuffing tube is commonly 0.25" brass tube, which allows the sleeve bushing for a 3/16" shaft to slide in perfectly. The holes in the bushing allow oil or grease to travel to both sides of the bushing. Why is that important? Because when the prop shaft is rotating the bushing rotates too and both sides need lubrication. This reduces friction by reducing the relative rpm of the surfaces - more power to the prop. Wear is also reduced - I have never replaced a sleeve bushing due to wear, and I've been running them for over seven years in most of my models.

In my UL-1 the original bushing was stuck in the stuffing tube and didn't rotate. I pulled it out and gently sanded it with 600 grit paper until it slid in easily, then polished it with 1500 grit paper (from the auto parts paint store). Now it works great, as designed.

Bottom line - use the sleeve bushings the way they were designed. They work, and very well too - I've set quite a few FE SAW records with them, as have many of the nitro guys. Whatever you do, don't glue or solder them into the stuffing tube!



Ths photo shows one 3/16" bushing I have used in three heats each month for a year. I can't find a dimensional change with a micrometer, it still works just fine. The 1/4" stuffing tube slides into the strut, and the bushing slides into the stuffing tube. I prefer gear oil, but others use grease with good results.



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[DISAR]

I use the speedmaster strut 21 (http://www.offshoreelectrics.com/pro...d=ros-21-strut) with a 1/4' stuffing tube, but the bushing of the strut cannot slide into the stuffing tube. I will take it out and recheck though. I had the bushing fitted (not into the stuffing tube) and it could play a lot in-out-up-down so I glued it. I played with the boat about 5 times till now without any problem yet.
So you recommend first to slide the stuffing tube into the strut and then the bushing into the stuffing tube. Thank you very much for the info. and nobody has mentioned that.

[Jeff Wohlt]

Jay, I think you are thinking the solder is used to solder it in. If you notice most struts have .250 ID but they are actually a bit larger because most are some funky metric holes or just sloppy drilling on the manfuc part. Not sure how many I have made for people but never a complaint except that some are a bit lose fitting.... The differenc in .250 KS and the factory hole of the strut.

I also advise to be able to grease the unit from both sides of the bushing (lube shaft then slide bearing over it and lube outside of the bushing and install it) as this give you a little bit more lube. As you probably know, SS and Brass is one of the best bushing/bearings for least resistance...except for real bearings. Look at speed master and others and it is hard to remove that brass insert. You have to drive them out.

The solder job (very small spots) is to be able to take that slop up slightly (few .ooo is it) so the bushing fits perfectly with out slop yet is removalable...perfectly fine to do.

I can assure you...this is fine and works without issues. Never heard of having a piece of brass inside brass so it can spin. Speed master and most other struts and stingers have the brass pressed in. They do not rotate and are a real bitch ot get out. I also made these for years after seeing how nitro and others used the stuffing tube AS the bushing. No reason to run the stuffing tube inside the strut just for taking up space to run a bushing inside of it.

Your bushing is not spinning or it would be shinny. Prop torque will keep it from spinning.

So I would say I can't agree with your statement of Gross Misunderstanding....as it certainly is not. These are smooth and work very well. Mine also have two layers of brass to come from .25 to 187 which offers even more depth for lube than one simple layer. The will out last the teflon bushing many strut makers use...inlcuding Octura and Fullers.

[Doug Smock]

Not to take anything away from your offerings Jeff I'm sure they work fine, but Jay is spot on here.
Doug

[Fluid]

Your bushing is not spinning or it would be shinny. Prop torque will keep it from spinning..

A close look shows the bushing has a few shiney areas where it has clearly been spinning inside the stuffing tube - photo quality wasn't that great but look again. Adequate lube prevents wear to a surprising degree and only the high spots show wear. I have many other bushings - commercial and home made - showing the same pattern. Just watched dozens of gas guys using their bushings (1/4") at a big race this weekend, and all were free to spin and float. I asked and most replace their bushing once a year - if it needs replacing or not.

No offense Jeff, if you don't believe me contact SpeedMaster, CMD, Areomarine, GrimRacer or just about any gas/nitro racer and get their takes on the subject.




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[Jeff Wohlt]

Only if you run the stuffing tube all the way thru. Then you can use the smaller 3/16" tubing for the bushing. Most run it in the nose 1/4". You can do it both ways The diffence is nothing but running the stuffing tube thru....mine do not do that nor do most others. I make the bushing 1/4" OD with 3/16" ID. Only a couple systems use that method of stufing tube thru the strut...forget what the nitro heads did there are better ways...the rest are the other way with a bushing or teflon bushings such as the rest of the builders such as, Fuller, Hughey, Fine and virtually all the China makers.

I think he thought they were soldered in.

My point is the ones for all other struts are not made that way. His UL 1 bushing is inside the strut and stuffing tube. SV is the same way. Does it mean it is better...not by a long shot.

This has nothing to do with my bushings.. It is just informing others of certain way for only a handful of riggs and most of those are the AC units.

Did anyone ever run teflon? Did you run it all the way thru and run your prop shaft in it....of course not.

There are new ways to do it better and easier. I have only sold 100 of these so they must work well....and I am sure a few have set records since that seems to justify the right and only way.

I just got some big ass stingers in for 6mm shafts and they do it even better...2 brass rings at each end and it is very smooth.

Jay, no biggie but I think you are arguing a point that is not really an issue. Is my speed master strut using the stuffing tube for a bushing....nope. Again, old Nitro ways because the nitro motors were hell on everything since they were IC motors.

I know eactly what you are saying but you seemed to have thought they were soldering them in and I wanted to correct that.

[Jeff Wohlt]

So what it comes down to is if you are running the SV or UL1 and do have the stuffing tube thru the strut just let me know and I will remove a layer of brass so it fits inside the stuffing tube. Either way don't spend the rediculous prices that you see on Tower for the bushing. Jay, every company mentioned were nitro way before FE.

[Doug Smock]

and I am sure a few have set records since that seems to justify the right and only way.

Nice.
Crap like this is why so few very experienced FE racers post anymore.

Later fellas...........................

[Jeff Wohlt]

I doubt this has any bearing on the sport, Doug. I guess we just can't disagree with a record setter? Do you think this made the difference...a bearing that is the same thing or makes about no difference?

From his comment it sure sounds like he thought we were soldering or loctiting them in. I said something on RRR how to fix this so maybe he got my info from there.

I have built a hundreds of struts and combos of everything...many running in Jays club in TX. Funny not a word from my anyone about wow this is too big for my strut, Jeff.

I am pretty sure I have surpassed building more struts with bearings and bushings that run well than most record setters have built boats to set records. You might forget I ship stuff all over the world. Not just a few... and I have no idea what I am talking about?


Yes I grow the sport....I do know that for sure. Silly stuff like this is what takes up space.

[Simon.O.]

Despite the politics and "I'm right, he is wrong" bits, this thread is very informative.
Fwiw I use this method in two of my handmade struts and the bearing sleeve is floating and free to rotate. I did not read about this befor hand I just saw a tube with holes in it once on a thread somewhere and figured that would make a good bearing idea. Stick it in or let it spin ?? um.....ah.... let it spin and see what happens.
2 runs minimum a week over a year with light oil and there is little sign of wear.

Out of interest 3 of my other struts run brass on brass with a smear of light oil and they are showing a little wear. That will get sorted soon.

I have had lengthy discussions with engineers and metal specialists who tell me that brass on brass in this high rpm application is not the best bet and I will see wear and play quickly.
I think we can see who is right here. It does work and the engineers are wrong.
One point for the boaters.

If you have not tried this bearing method then give it a go, it is very cheap and easy to do your self.

That is enough of my rambling for now

[DISAR]

I was thinking how it would be possible for someone (like me) to install the bushing following this way in an already fixed system, but without having to take out the existing stuffing tube. So what I came up with is to cut the 1/4" brass tube about 1" before the strut in a straight part, and glue in position with epoxy or solder a longer 1/4" brass tube which will go inside the strut. The two pieces will be glued and a piece of 9/32" brass tube on top.
I am thinking now, shall I keep it as it is (bushing glued in the strut) which does not have any signs of problems until now or do as above?

[Jeff Wohlt]

I mean no disrespect to Jay and I know he does not either....I hope. I have known Jay for many years and have nothing but good to say about him. I know what he has done and what he has done for our sport. So if I sounded harsh please understand I mean nothing personal.

The system he is speaking of only works for struts with 1/4" noses where you can fit the stuffing tube thru. All others usually have a 3/16" nose for teflon or brass.

I also run almost all wire drives. I like the smaller tubes in the nose of wire drives. Compare a 5/32 tube to 1/4" and you will see what I mean. I would not be surprised if the larger tube becomes another riding plane at high speeds. At least it could induce more drag when running in the water.

Jay runs wire as well on many riggs ( and record setters) so I would only think he does not run a large stuffing tube like that on his boats since I know he does not run teflon but he can jump in on that one.

So you can do both ways but most hardware sold, Fuller, Solinger, etc does not have a 1/4" nose for the larger tube. A few of the nitro systems do... as well as AC because Grim was a nitro racer.

[Jeff Wohlt]

You do not want to glue anything in. Basically you can cut the stuffing tube so it only goes in the nose a good 3/8" or so if you have the 1/4" nose. I usually use shrink around the nose and stuffing tube anyway. Then you can make a bushing...same as I do with 1/4" to 3/16" and then the 9/32 thin slice for the end of the bushing so it does not enter on in the strut. Yo can then take your dremmel and make slices in the bearing and then run a file round file thru it to get any crap out. You can then slide the bearing in and out as needed.

This works for all other struts except the 1/4" like a UL or SV and then I even do it to them because I run smaller stuffing tubes for wire. You can shim the nose with KS if you want to bring the size down and get rid of the teflon...if it has it.

[paulwilliams]

Lead/teflon really works for 'slow' boats - full scale and models - but is pretty poor for high rpm/high load bearing use.

I'm going to have to disagree with you here Jay. I've used lead/teflon bearings for years in all kinds of endurance FE boats, from 700BB+12 cells pulling 18-20k to 4S Hydro 2 at 40k+, and I've never, ever worn out a lead/teflon bearing. Furthermore, many FE racers here in the UK and in Europe also use this type of bearing with no problems.

Let's be clear about what type of bearing we mean here, when we say "lead/teflon". The type I use in my own struts is a split steel shell, lined with a bronze sinter layer, which is then impregnated with PTFE - as best as I can tell, there's no lead in them. They look like this (on the left):



It's important to understand that this type of bearing relies on the shaft floating on a fluid film when running. The PTFE layer is NOT the bearing when the boat is running - the bearing is a film of water that is drawn into the strut, either by capillary action or under pressure due to the boat running at planing speed.

Assuming that your propellers are balanced, this type of bearing will last indefinitely. One way to destroy PTFE bearings in seconds, however, is to rev up the boat with the bearings dry. Without the cooling, lubricating effect of water, the PTFE layer will melt very quickly and transfer to the shaft. When this happens, the bearings are scrap.

Now, I will qualify the above and say that I do not have Jay's experience of running very high power setups (8-10S etc.) so I simply cannot say whether PTFE shell bearings are suitable for that type of application, but I would be pretty confident that they would be OK, assuming a balanced propeller and the presence of water.

The most important thing in any type of bearing is the lubricant. As soon as you have metal-to-metal contact, you have a serious problem. So, the use of all-metal bearings (eg. brass and stainless) is ok, but only if it is kept lubricated, ie., the metal sliding surfaces are kept apart by a lubricant film.

Paul

[txboatpilot]

Not to take anything away from your offerings Jeff I'm sure they work fine, but Jay is spot on here.
Doug

I agree 110%... Jay is on the money!

All the FE, Gas and Nitro racers here at the Dallas RC Thunderboat Race on May 2-3 were useing brass,,, NO lead teflon or bearings of any kind that I saw or heard of..... That is out of 160+ boats entered..

[DISAR]

Jeff -

Ok, I have the speedmaster 21 strut, 3/16 flex and prop shaft, 1/4" stuffing tube without teflon. The 1/4 tube slides into the strut nicely for about 3/8" as you said and heatshrink in the connection.
So for this case your bushing is made of 7/32" tube (entering slightly the 1/4") with a piece of 9/32" tube at the end. Is that right?

[Doug Smock]

Dimitrios,
If you'll dress the 1/4" tube a bit (sand it with 400 grit) it will slide completely through the strut and you'll be able to use it as it was intended.

Doug

[Jeff Wohlt]

Nitro....they need the support (IC motors) and use the larger struts...they were designed that way. I can show you also where they ran the hole out the back and it is open for water to come in so they could adjust there struts.

This comes down to a few nitro struts made to run FE. That is about it. Nothing to do with teflon bearings as most do not run those anymore anyway. They wear and do not give the support a true bushing does the length of the shaft. How many records have been set using Fullers hardware?

The reason our bushing is not meant to spin inside the strut is because it will wear the strut hole larger. Jays method is spinning brass in brass.

So please do not let this confuse you as it is two different methods. One for large dia noses and the the normal smaller 3/16" nose.

[Jeff Wohlt]

Dimitrios,

My speedmaster strut does have a bushing in it and I did not put it there. The 1/4" should go thru unless something else is in there.

[Steven Vaccaro]

Cool topic.

Jay is 100% correct about Speedmaster struts. The bushing slides into the 1/4" stuffing tube the goes into the strut, if you run it that way. Also note that the distance between the drive dog and strut has to be less than the width of the collar on the flanged Speedmaster bushing. Otherwise it can come out of the strut and cause issue(found out the hard way ).

I run a Speedmaster 21 strut with a flanged bushing and with a smaller 7/32" stuffing tube. So I dont have the option of allowing the bushing to spin within a 1/4" stuffing tube. So I do put a dab of CA on the bushing. It does work. Otherwise if I didnt put the glue the bushing will wear out quickly(found out the hard way).

As far as Teflon bushings go. I have been selling the Solinger system for years with lead teflon bushings. Everyone so far loves them. The bushings do need replacing from time to time.

[Jeff Wohlt]

All nitro designed struts do the same. Stuffing tube goes all the way thru.

The teflon coated bushing as Paul and most other struts use do very well when wet. The layer of water is the key. Paul and I have had this discussion and he really is on it as I looked some things up about our conversation and is was right on. Just do not run on the bench much.

My dad was an engine mech for big war ships thru the last WW and Korea...he will tell you water was the best lube. Beats me but I have to believe him since he is my dad and now 83 and was on ships from 17-28 years old. Many lied about their age to go to war...go figure. People that wanted to go fight!!

Solinger, Fuller, Hughey and many more have used these for years. Most of the problem was I had struts with one teflon bushing at the end....so I used to cram two to three down it to support the shaft better. Now I just make a replaceable strut bushing for all my rigs. I need the stuffing tube as small as I can get it. Do not run a 130 or 150 in a 1/4" brass tube without teflon...it is too larger and will whip like hell.

We are talking two different types here. Both are very simple. I prefer the smaller stuffing tube but again, I use mainly wires. If you run 150 cable you can run 7/32 stuffing tubes and shim the nose down with KS. Bigger the stuffing tube the more drag is has for open stuffing tubes such as hydros and single motor cats running one motor.

I love the smaller stuffing tube. With .062 I run a 1/8" stuffing tube. I also turn noses on the lathe to fit the unit.

So, The Vegas, UL, SV, speedmaster and a couple others are made to slide the strut up the stuffing tube. I just prefer a smaller stuffing tube for less drag.

Okay, good stuff but I am burned out on this one.

[paulwilliams]

My dad was an engine mech for big war ships thru the last WW and Korea...he will tell you water was the best lube. Beats me but I have to believe him since he is my dad and now 83 and was on ships from 17-28 years old.

Central heating pump impellers run in a water bearing. If the thermostat fails on the boiler and boils the water too hot, the impeller will expand and jam in the housing.

The pump turbines on NASA's rocket engines are lubricated with the very thing they pump: liquid oxygen @ ~ -250 Celsius!

Modern car engines run for 100,000+ miles with minimal servicing and wear, partly thanks to modern CNC manufacturing, but mainly because modern lubricants are so good.

It's an interesting subject.

Paul

[Jeff Wohlt]

Not sure this is a fact but I heard in the early years the PC harddrives had a water bearing of some sort.

[Flying Scotsman]

A cautionary note this info does not apply to a stinger setup. EDIT OK, I threw this out for an answer, so you young pundits. Right or Wrong .......Dr.House Torrance

Douggie

[Jeff Wohlt]

Well the bushing does fit in the stinger strut just fine. As noted ANY strut with a 1/4" hole will fit either. Depends how you want to set you boat up. I try and use as little of stuffing tube as I can. Not sure what the other stuff means.

[DISAR]

I had a closer look at my strut and bushing yesterday and I can say that for the Speedmaster 21 strut the 1/4" stuffing-brass tube slides in all the way and the bushing slides in the stuffing tube nicely. Therefore what Fluid advised is correct when using the 1/4" stuffing tube. In addition, I noticed that the bushing is just a brass tube 7/32" with holes and a piece of 1/4" soldered in the end. Very easy to make.

[DISAR]

Cool topic.

I run a Speedmaster 21 strut with a flanged bushing and with a smaller 7/32" stuffing tube. So I dont have the option of allowing the bushing to spin within a 1/4" stuffing tube. So I do put a dab of CA on the bushing. It does work. Otherwise if I didnt put the glue the bushing will wear out quickly(found out the hard way).

When running with a 7/32" stuffing tube you can cut it before the strut and solder a piece of 1/4" that will go into the strut, provided that there is enough space before the strut.

[Shooter]

Is it a problem when the strut bushing slides axially? Mine not only rotates, but slides back and forth within the gap that I allow between the drive dog and strut end? It usually ends up at the drive dog end because of the pitch of the flex cable windings. Does anyone else experience this? Is this a problem? Thanks.

[properchopper]

Is it a problem when the strut bushing slides axially? Mine not only rotates, but slides back and forth within the gap that I allow between the drive dog and strut end? It usually ends up at the drive dog end because of the pitch of the flex cable windings. Does anyone else experience this? Is this a problem? Thanks.

Shooter, I'm experiencing the same situation on one of my boats that was set up by the person I bought it from. My thinking is that it shouldn't be a problem; if any forward force exerted on the bushing is created by flex windup it will just push the bushing back forward given that the bushing is free enough to slide in either direction. I do lube after every day's run, BTW.

OTOH, I just set up a hydro with one of Jeff's .078 wire drives which includes his ball-bearing strut and believe this is a great way to reduce parasitic driveline drag.
I grease & lube after each day's run as well and am just thrilled with this setup.

[Shooter]

Thanks. I guess what I am really concerned about now is the fact that the flange on the bushing can come completely out of the strut which eliminates the centering feature. I think I just need to head up to the hobby shop and take a look at a new one. I'm not even sure if the flange should be into the strut or not. Anyways, when the flange slips out, the bushing is cocked slightly in the strut. This can't be any good?? huh??

Where did you get the ball bearing strut? Thanks.