Got a TT 46 Pro.  Am told the bearings probably need replaced.
Never did anything with bearings.  How difficult is this?  Do I need a bearing puller, etc.?

Dave,
Ball Bearing replacement is not to difficult. Basically, you disassemble the engine, heat the case (I have used a simple touch, some use an oven), the front can be tap out with a wood stick, usually the back can be removed by just tapping the case on a wood surface it drops out. To install again heat the case and push the new bearings in place, use a wood dowl to tap them an make sure they are all the way in. While the case is still hot (could reheat a bit) push the crankshaft in place and spin it. Let it all cool completely then reassemble the rest of the components.

Here is a YouTube video that shows the basics:   

You can get new bearing from Boca Bearing:   https://www.bocabearings.com/

Best,    DennisT

After seeing that video, that was pretty much the method we used.  As I said, the front bearing needed some persuasion to come out.  Other than that, no problems.

Do the bearings in your engine seem rough and gritty when the crank is turned?  Can you feel that roughness?

It might be a good idea to be sure the bearings are needing replacement.  No need to replace something if still good.

If the engine had not been properly stored, then the bearings might have corrosion on them. 

The plobrem is usually CORROSION , going on for RUST , which laps out nice A B C fits in a few frights . Then the whole things useless .

The BEARINGS are the same as the FS & FSR OS , rear G series Tigres etc etc , so No Problem . Dont go cheap & nasty though .

Throw the rear in on the crank , Likely the front too . To gettem SQUARE . Heat Gun means only one ends to hot , Gloves dont hurt in either case .

Pro - 46 Thunder Tiger Parts · Part Description / Location: Bearing 9.53 x 22.23 x 7.14 · Part Description / Location: Rear Bearing 17 x 35 x 8.


maybe , a SEALED front , you whip ONE out , seal to front . seal & sheild are two differant things .

 

   That's because the front bearing is the one that takes all the thrust force. It has to be pretty tight to not work its way out even in the hottest conditions. The rear is usually just snug enough to not move around, it doesn't take any axial loads.

Oops, wrong way round. The rear bearing takes all of the thrust loadings as well as the combustion pressures. The front bearing simply offers support for the crankshaft. In the case of a plain bearing engine the thrust load is on the crank web against the crankcase same as with engines with only a rear ballrace and bushed front end.

I would think the crank and front bearing would ultimately migrate forward until the crank seats against the rear bearing. On Supertigres with the little aluminum spacer ring, the spacer also keeps the front and rear bearings separated enough that they don't squeeze the case.

I would think the crank and front bearing would ultimately migrate forward until the crank seats against the rear bearing. On Supertigres with the little aluminum spacer ring, the spacer also keeps the front and rear bearings separated enough that they don't squeeze the case.

   Right. That means the crank is not pushing up against the back of the rear bearing.  If it does, it would preload the bearing, and shimming it exactly would be extremely critical.

     Brett

You want to check the wist pin is clean & free , while your at it .

Tweezers for piston circlips . maybe in a plastic bag . at least somewhere where if it ' jumps ship ' it wont dematerialise in the scenary . tho if you dont blink you usually find them two days later .

3M scotchbrite to polish / clean steel shafts . Putting the wrist pin on a piece of 1/16 wire , with the ends bent - if polishing on a wheel , saves having to hunt for THAT if its spat out of your fingers .

USED 3M for polishing , and cleaning piston wrist pin lands . or 600 wet & dry on glass - spinning the shafts - Front row guys would use 1200 , then compound , for  a mirror finish . just CLEAN will do .

You heat the case to aprox 300 degrees. You put the rear bearing on the crank and put it in the case. The OD seats in the case and the shaft seats on the ID which pushes the inner race forward.

Holding the parts in that position, you push the front bearing in the case with a flat tool that pushes both inner and outter races the same until the inner race contacts the shaft. The front bearing outter race should not seat in the bearing pocket. The back of the front bearing pocket is only there for clearance.

When the case cools, the two outter races move toward each other and the shaft spins free. When the engine is running the front case doesn't get anywhere near 300 degrees so the bearing clearance stays good, the outter race of the front bearing stays locked in place and the thrust is taken up by the rear bearing.

MM

    Using that theory, how is the preload controlled? Particularly when the crankcase expands faster than the crankshaft - as it heats up, the crankcase will get longer, the crankshaft will stay the same length. Since the front bearing race is hard-locked to both - the inner race between the shoulder of the crank and the tapered washer, and outer in the (as noted earlier) tight press fit bearing - the only thing left to prevent preload is the rear inner race sliding on the shaft.

     Even if you thought the assembly should have preload - which it certainly shouldn't- you would need something a lot better to control it, a sliding element with a wavy washer, etc.

    Brett

Gentlemen,

Lots of wrong information in this thread. in this kind of engines (cheap, low power) the rear bearing should under no circumstances take the axial load. If it does, it will be quickly ruined by the dynamic loads when the bearing turns from radial- to angular contact bearing. When correctly set, you should be able to see a 0,2-0,3mm gap between the rear of inner ring and front face of shaft counterweight.
Front bearing should be pressed all the way to bottom of its housing, otherwise you don't have a reference point. If the reference point is wrong (conrod not well centered in cylinder bore or crankpin rubbing the backplate, you must shim either the back of outer ring or inner ring until it is correct.
Shaft/inner ring fit should be easy-ish sliding fit in the front bearing. It's not super critical as the front inner ring is clamped between drive cone and shaft step.
Rear bearing/shaft fit should be a little tighter. So loose that the ring will find its axial position during the first seconds when the engine runs again, but so tight that the inner ring won't slide on shaft.
It's a typical fault at least in DR's and other eastern stunt engines, that the front bearing press fit is too loose. Apparently they don't use bearings with big enough radial clearance and thus are forced to leave the shrink fit a little on the loose side. In that case, Loctite is an acceptable fix as correctly set bearings will last forever. Badly made setup doesn't last long. L

    Thank you!  It's not super-complicated to figure out how it has to work.

      I note that it is *not at all* uncommon to find cases where people disassembled their engine or replaced the bearings, and end up bound up because one or the other bearings have not been properly seated. With predictable results - it's a race condition between the bearing failing from overload and heat, and the case expanding from heat enough to release the rear outer bearing race and letting it find it's own clearance, or spinning in the case or on the shaft.

   ST46s were well known for having the inner race spin on the crankshaft because the rear inner race fit was a little too loose.

   BTW, you are a guy who would know - has anybody tried preloaded or angular-contact bearings in  model engines?  The notional reason you might want it is to reduce the shock/nonlinear forces when it takes up the slack upon firing. The reason you might not is that it is too hard to control in this sort of environement, and the need for shaft positional accuracy is nonexistent. I ask just because I am much more familiar with preload and angular-contact bearing systems from spacecraft reaction wheel, and more importantly, gyros.

    Brett

No matter how they are preloaded, things will flex, too. For example the crankshaft bends a considerable amount from the combustion forces. For this reason the model engine-specific bearings have not just a bigger C-rating but also a bigger ring groove radius to allow the flexing. Gyros and turbine wheels are another story, they spin with constant speed.
Google the FMV-story, there Robbie explains the bearing setup in their T/R engine. I guess it's kind of a pre-loading, as racing engines require much stronger fittings and the setup must be correct in running temperature. L

    I was going to point out why you don't necessarily want or need precision bearings. full=complement, or ceramic bearings for model applications, just the regular "economy" steel bearings, because you have to accommodate things like the crank bending, etc. and you want it to be loose enough to not bind up.

    I also note, just as an observation, that the best 4-2 break engines I have see run have been *incredibly free" through the bottom end travel. In the Retro and other similar engines, it is by design, in other cases (like some McCoy 40's the late PTG had) just by lapping out the plain bearing to an almost absurd degree. One of the engines had enough play in the bearing that the prop tips would move freely about 1/8-3/16". These engines were originally setup up by Dick McCoy himself, for someone going to the 1960 WC with no time for break-in. Oil flew all over, but it had a remarkably abrupt 4-2 and 2-4, now smearing back and forth over seconds. The Retros I have flown were the same, they feel like TR engines they are so free, but instant transitions back and forth, FAR better than any ST46/60.

    Brett

These things are called SPHERICAL ROLLER BEARING , for Crank shaft WHIP . Which can shatter standard ' parralel roller ' roller bearings .


The NORTON ' superblend ' was a single row barrel roller . Dunstall had done deep track heavy duty Ball races , which waylayed the result of CRANK ' BOW ' where the central flywheel
gets around 4 thou. flex per revolution . Cunning old swine ' pre cambered ' cranks , so as they were STRAIGHT under maximum duress - thereby loosing less output losses , thereby
GOING FASTER .

Theyed tried first , radiused edge parrallel barrel rollers , as symptom was ' the ends dug in ' Failure evidence . The DEEP TRACK Ball Races just carried greater load than standard .
P 24 & 26 Here . http://archives.jampot.dk/general/Dunstall_Catalogue_1969.pdf . ANY ball race would have SOME linear ' side load ' acceptance / capabilty .

Cyclic , oscilating , & more ' skidding 'is a worry . Ducati roller mains & XR H. Dav. benifit from PRE WARMING the OIL , as a countermeasure to oil wedge causing skidding & cosequent failure .

TRIUMPH , at one time  , had ' thrust ' ball race - timing side or worse primary ( drive ) side , open ' ball race . where the groove was removed inward on the inner race - caged outer .
so ' free sliding ' to account for case expansion . Perhaps as much as 10 thou. linear , across the crankshaft housing - in the alloy case .Typical for Ball Races to work loose on the shaft.
Otherwise . fret . Like the shiny marks on a crankcase housing if the bearing outer has ' spun ' .


Id think muddle injuns just run anything thats proved acceptable reliability . As In if theyve continually failed , theyve put a bigger one in for better reserve . Like Most things !   
or a more expensive , better quality , or greater load capeability one . But Mass Production costings get bigger is better , if the accountant want to keep their expense accounts . 

Typically , 7 thou. perhaps ' end float ' is required in a pommy twin , on set up . but not mort than 10 . on a 40 or 45 cu. inch injun . Ours are a bit smaller . 2 thou. might be mentioned .or less .

https://web.archive.org/web/20060923041135/http://home.wxs.nl/~wakke007/fmv/fmv_7.htm



https://www.real-classic.co.uk/2018/02/15/classic-techniques-superblend-bearings-part-one/

Don't confuse high precision with high clearance. You can have high clearance bearings with better precision balls, roundness and grooves. High CLEARANCE is needed, they tolerate stronger interference fits. Typically C3 or C4.
With Retro's it goes so that you take a bunch of CCCP standard bearings and check them one by one. The ones with bigger play are better. L

   I was referring to those available at Boca Bearings, the "economy" type are a relatively loose fit steel bearing. They have, I think, 4 different grades, the least expensive are the ones you want for a model engine.
 
     Brett

I had to look into it as I thought Boca offered C3 (at least for the main) for most engines sets, The TT46 economy set are normal clearance and premium sets are C3. Boca is a great source because they do have just about anything.

  I was getting bearings from a bearing shop. They guys at King Bearing in Mountain Veiw CA were remarkable, they would just glance at your example, walk straight to the right bin (out of thousands), grab it, hand it to you, "That will be $6", bam, 30 seconds total.

     The rear bearing on the OS40/46VF was a special size that was unavailable for a while. Boca somehow got them, and they were far better than the originals, so I started going with them.

     Brett

Seller said it might need some bearing work.

    You can tell the care with which it was stored - buried in a swamp.

    Brett

MM.  Just make it a paperweight.

     I am not sure how this happens, but I have done a lot of various hobbies that involved restoring things - old radios, for instance - and I am continually astonished at how poor a shape people let stuff get. I have had old portable tube radios that I swear, they must have found in a shipwreck or something. I have also seen model engines that have been at the bottom of ponds for a month. It more-or-less looked like that.

   BTW, if that is all there is, the crankshaft is almost certainly still OK, just dunk it in Evapo-rust for a day or two, and clean it up with steel wool. Get new bearings and at least that part of it should be OK.

      Brett

The problem with re-building an old engine is that all the nice new parts are on the inside where no one can see them. Cleaned all the rust off the crank web and went with a little gun blue. The journals cleaned up nice and Boca Bearing came through. Ready for installation.

MM

Swamp Thing lives again!

The TT46 is a very popular RC engine on the resell market.. I went through 7 of them last year.. getting the bearings out is fairly easy .. I have dedicated tools for working on the engines I repair and clean... I don't install high end bearings and have started using a sealed front bearing on all engine I go through... I recently got an Ultra Sonic cleaner .. always take the bearings out before using the cleaner .. I clean bearings with Dawn or Joy dish soap and also use LA Awesome too.. a lot of elbow grease .. I always put the rear bearing on the crank before reinstalling in the case .. I put the front bearing in first ...with plenty of heat it drops right in ... most of the time the case is hot enough to slide the crank in ... I have the prop hub.. spacers or cones ready to go on while the engine is warm... then install a prop so the crank can be spun.. two things happen .. first you can crank the pro down to insure the bearings are seated.. and then spin the crank to "feel" the new bearings.. and if all is right I install the piston rod and piston ... the engine is still warm.. then slide the liner in.. all of this is oiled very liberally.. if the rear bearing does not slide onto the crank .. it needs"Polishing".. I use 600 w/d paper and then fine steel wool and make it shine .. do this until it slide on.. the Merco 49 and 61 engines can be real pains with the rear bearings .... I hate working on Irvine 40s.. the larger Fox and ST GS/S engines are kinda fun to work on.. over the last 15 yrs I have done over 800 engines .. I know a couple of engine guys who never reuse engine bearings .. Its how the feel before taking them out that helps me decide ... Many engines have plenty of life left in them...  there is more details but this is what I basically do ... and try to do it the same way every time.. I use air tool oil for my lubricant .

The front bearing pocket is always cut deeper than it needs to be. No engine manufacture is going to hold that tolerance because it would mean also holding the same tolerance on the shaft or custom matching the shaft and the case. It's just so much easier to let the shafts main journal stick out into the front bearing pocket and position the bearing there. If you put the front bearing in first and seat it down all the way then the crank will be too far back and not in line with the cylinder. Most engines can still run like that but, it's not how it was designed to work. See post #17 above.

MM

  No. Lauri and I both explained why, and if you measure it, it lines up correctly when you seat it completely.

     Brett

 p.s. the only reason that your proposed method works without binding up the entire crank bearing assembly  is that you are doing it at 300 degrees. This makes the case as long as it could ever be, plus some, so when you do your incorrect seating of the front bearing, when it cools, the case shortens and the crankshaft slips backwards providing the required clearance. It's still misaligned but at least it doesn't bind up and fail almost immediately, as it would likely do if you did it at room temperature.

I've been building speed and racing engines for many decades, I'm sorry, you guys are just completely wrong.

MM