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Author Topic: RO-Jett 61 BSE crankshaft bearings  (Read 1285 times)

Offline Brett Buck

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RO-Jett 61 BSE crankshaft bearings
« on: May 28, 2021, 06:58:39 PM »
One of the few weak points of the RO-Jett 61 BSE is the tendency to chip the rear crankshaft bearing due to load. I have had 4 occurrences of this so far (over A LOT of flying). After the most recent, I decided to get the right bearings and just carry them around, and change them myself if necessary.

   For reference, the rear on the 61 BSE is 30x17x7 mm and the front is 22x10x6 mm. This is the same as several other Jett engines. The Boca bearing kit for it is the ENK-17. After talking with several bearing experts at work, I chose to go with the steel bearings rather than ceramic - because the radial loading is more of a problem that the RPM capability and lubrication. That would be the ENK-17HP kit.

     Although I hesitate to encourage anyone to take their engines apart unnecessarily, if something is wrong, you have to fix it. Replacing the bearings in this engine is not difficult.

    You need a CLEAN flat  surface on which to work. Take off the prop, take off the header and pipe (together in one peice, presumably) and clean the engine off of all external debris (varnish is OK), and clean the work surface. If that is not practical, put down a sheet of aluminum foil straight off the roll, which you know is clean. Wash your hands of any debris that can come off.

      First, remove the head button clamp and head button. Then remove the 4 screws on the backplate, and then pull it out. It does not have a gasket, it has an o-ring in the bore of the case, so there will be some resistance as you pull it. Remove the needle, spraybar, and venturi (which seals the same way as the backplate). Push out the liner, noting that the exhaust is the narrow wide port opposite the big squarish intake port. Gently rotate the crankshaft to near TDC, then slip the connecting rod off the back of the crankpin. Note that it has to be within about 45 degrees of top dead center, because it runs in a groove around the bottom (needed to clear the crank and rod with this 61 stuffed into a 40 case). Do not do anything else to the piston and liner, put it in a safe place so you don't ding it or touch unnecessarily. Cold, the liner should just slip out easily (it tightens up when you run it).

    Use a puller (a battery terminal puller will work...) to pop off the thrust washer. It is a pretty steep taper and will pop off easily compared to, say, a SuperTigre. If it is stuck on there good, crank down on the puller to put tension on it, then tap the screw with a hammer or something hard, that almost always pops it right off. I don't recommend cranking down extra-hard on the puller until it comes off, a sharp tap on the screw almost always removes it.

      Then pull off the taper ring. Carefully note if there is a spacer washer behind it - some of them do and some don't. You should now just have a bare case with the crank in it, and the bearings, and nothing else. The crankshaft should just push out the back with light pressure, if it doesn't DO NOT hammer on it, push harder.  Then put the engine in the oven with it set to about 175-200 degrees.

   While you are waiting about 20 minutes for everything to heat up, prepare the new bearings. The bearings will probably come with plastic shields on both sides. For the rear bearing, you need to remove the both. Usually that can be removed by VERY CAREFULLY taking a tip of a knife near the inner edge and slipping it in between the inner race and the sealing surface on the shield, then just pry it out. Don't jam the knife any further in than necessary, and be very careful to not break the tip off it. I don't like using Xacto blades for this, but the stainless ones are touch enough that the tip will withstand the prying. Remove ONE seal off the front  bearing, one should remain to seal the crankcase.

    At this point the crankcase should be heated up enough. Find a clean piece of flat wood, or the edge of the table, that you can tap the crankcase on safely.  Also, find an old maple motor mount  and carve the corners off so it will slip easily up inside the crankcase to the rear of the front bearing.

    Take the engine out with oven mitt or pot holders, go over to the wooden pad, and gently tap the rear surface of the crankcase on the wood. The rear bearing should just fall out of the pocket, although it may turn sideways in the crankcase since it a close fit to the rest of the case. Then while it is still good and hot, push the stick up through the rear until it is resting on the inner race, and then drop/tap  the whole assembly on a hard surface to push the front bearing out. You should not have to hammer on it hard, if it won't go, put it back in the oven and try again. Even at 200, it is a very light press fit. If it is really stuck, you can go as high as 250, but you don't want to really heat it up above that. By the way, this also means that the bearing is probably no good any more, since you hit the inner race and transferred the load across the balls to the outer race.

   Presuming it all came apart, you should now have the bare crankcase. Let it cool, or cool it off under the cold water tap. Clean the bearing pockets out until they are perfectly clean. I use brake parts cleaner which takes out any oil immediately. It must be perfectly clean or the bearings will not seat properly. While you are at it, clean any grease out of the new bearings, and then lubricate them *immediately* after the brake cleaner with oil - I use Marvel Air Tool Oil or any other oil I would use for after-run oil. Don't skrimp on it.

   Find a socket from your socket set that fits on the outer race of the front bearing that you can use as a press tool. DO NOT press it in by the inner race, you have to apply the (light) pressure only to the outer race and nothing else. Take the crankcase out of the oven again, start the bearing in the pocket with the seal side forward, and then press with you press tool and hand pressure to push it in, pushing all the way to the bottom until it clearly bottoms out. Double-check that the edge of the outer race is exactly even with the machined front surface of the crankcase all the way around.

     Put it back in the oven for 15-20 minutes. Get the crankshaft, and make sure it is clean. You can *very lightly* use gray scotch-brite to remove any corrosion or varnishing from the running surface, then clean it again, then oil it lightly. Push the bearing on the shaft all the way to the back. Take the crankcase out, then put the crank in the crankcase, and it should easily drop all the way to the bottom of the pocket - it should free, with no pressure required. Leave it nose-down until it cools, or it might fall out. Once it has cooled off, check that it is full seated by pushing the crank all the way forward until the shaft touches the rear of the front bearing inner race, and see of the crankpin is centered on the crankcase groove, otherwise, the conrod will not fall into the groove when turning it over.

    The hard part is over. Dribble oil on the crankpin, put the piston/conrod in and over the crankpin from the top. Note that there is a front and back to it. If you forget, or can't tell from the varnish on the exhaust side, the front of the conrod (that goes up against the crankshaft) has a chamfer in the front of the big end hold, and is more-or-less a sharp edge at the rear. Wipe the liner with oil inside and out, make sure it is still clean and free of debris, and push it in, and center the piston and push it into the case and over the piston. Try to get it aligned with the exhaust port centered in the corresponding opening in the crankcase, but if you have to rotate it after it is assembled, that is OK. DO NOT try to turn the engine over now, you will get the piston stuck in the liner when it runs up into the taper. Clean the head gasket(s), if any, and the head button insert, and the upper flange of the liner, to perfectly, operating-room clean. Oil the head button, put the gasket on, then push it into the liner. Clean the head button clamp, and oil every screw, then screw them in finger-tight. Pressing down on the head clamp, run them in with a hex driver until they touch down lightly, then go around in your favorite pattern and make them moderately tight. Then, one at a time, back the screw off until loose, then back down again. Then tighten them for real, very snug, but not "ape-grip" tight.

    Oil the o-ring and reinstall the back plate, again, the ape-like mega-tight is not required and doesn't help seal it better, because the seal is on the o-ring, and it will seal unless the entire thing falls out. Reinstall the venturi, taper washer (and any spacers behind it), thrust washer, you can figure it out from here.

    Several cautions:
           Everything needs to be CLEAN, with no grit or crud anywhere, and don't track it back in with your dirty fingers  or by working in a dirty surface.
           Assemble everything with OIL, not really for lube while firing it up, but to avoid flash rust and prevent galling. This is not a Fox, lots of stuff fits with near-interference fits.
           All screws are ****  5-40 *****, not 4-40. If you accidentally grab a 4-40 and try to tighten it, *****  it will strip the case *****. Maybe a 5-40 will tighten in teh stripped hole but you will be missing most of the thread profile. Note this includes the ****   HEADER SCREWS *******.
          No hammers or pounding should be required, if there is, then replace all hammered components with new.

     A PA header is the right size, but the holes will not clear a 5-40 without drilling them out.

    Brett

   
« Last Edit: May 28, 2021, 09:56:12 PM by Brett Buck »

Offline bob whitney

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Re: RO-Jett 61 BSE crankshaft bearings
« Reply #1 on: May 28, 2021, 09:43:52 PM »
Cant go wrong with that
rad racer

Offline Dennis Nunes

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Re: RO-Jett 61 BSE crankshaft bearings
« Reply #2 on: May 29, 2021, 10:35:09 AM »

   For reference, the rear on the 61 BSE is 30x17x7 mm and the front is 22x10x6 mm. This is the same as several other Jett engines. The Boca bearing kit for it is the ENK-17. After talking with several bearing experts at work, I chose to go with the steel bearings rather than ceramic - because the radial loading is more of a problem that the RPM capability and lubrication.
   

Brett,

I had a little difficulty finding the ENK-17 bearing kit. I eventually found it, but the actual Boca bearing kit number is ENK-017. Here is the website for this bearing kit: https://www.bocabearings.com/products/enk-017-1992

I found this kit to be very reasonably priced at $20.34 including tax and shipping. I hope I won't need it any time soon but I'll have one just in case.

Thanks,
Dennis

Online Peter in Fairfax, VA

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Re: RO-Jett 61 BSE crankshaft bearings
« Reply #3 on: May 30, 2021, 12:43:56 PM »
This was a very nice description of bearing changes.  Though it mentioned a specific engine, it was also good general advice.

The idea to use an oven for even heating works well for me.  I'm not a fan of a heat gun or torch, though a combat flier may need to do that between rounds, for expedience.  The small toaster oven is ideal, as it fits in the shop, has a timer/thermostat, doesn't conflict with cooking food and is inexpensive.

The idea of using tap water to cool an engine is kind of OK, as long as the engine isn't too hot.  And tap water is fine for cleaning.  However, I prefer ambient room air cooling, which only takes about fifteen minutes.  In general, shocking a very hot engine with water is considered risky.  For example, in an automotive context during an overheating incident.

As far as drying an engine, I blow off water with compressed air, then heat the engine to 225 degrees to make sure all is evaporated.

But the biggest thing I got from this thread is the front bearing being less than fully seated as ideal.  I'm interested in further comment on that.  My general technique, primarily with O.S., SuperTigre and Fox engines, is to heat the case in an oven, then tap in the front bearing until it seats, then deal with the rear bearing and crank later. 

For those that suggest front bearings should not be fully seated, what engines benefit?

thanks,

Peter

Offline Brett Buck

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Re: RO-Jett 61 BSE crankshaft bearings
« Reply #4 on: May 30, 2021, 04:44:21 PM »
Front bearing must be seated all the way to bottom of its seat. That's necessary for repeatability. With racing engines, it's a quite standard way to secure that front bearing stays where it should with threaded nut (left handed thread).

  Yes. A lot of people do not realize that the front bearing takes all the thrust/axial load, and the rear just takes radial loads, and the crank just slides into the inner race.

   This one is particularly easy, heating to 175 gives plenty of clearance for the rear to just fall into the pocket. If you try to put the rear in first, it wants to fall out while you are putting in the front. Guess how I figured that one out...

  BTW I ran the engine today, it is now the #1 engine for the NATs, and no clattering/coffee grinder noises and constant 4-stroking throughout, even launching at 10100 RPM.

    Brett

Offline Brett Buck

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Re: RO-Jett 61 BSE crankshaft bearings
« Reply #5 on: June 01, 2021, 01:47:40 PM »
OK, after a few emails this weekend, further clarification:

    Obviously, only replace the bearing *if there is something wrong with them now*. If you have to ask yourself whether you have a bad bearing, you don't have one, because the noise it makes is blindingly obvious. And it is far from clear if, say, the Boca "high performance" steel bearings will last longer or work better (or as well as)  than the stock units - I have 11 flights on them, total.

     As far as Boca goes, I claim "mea culpa" on the leaving off the leading 0 for the Boca Bearings ENK-017HP bearing set. I selected them from Boca by size, not kit number, and the fact that these same bearings are used on other Jett engines (like the Jett Sport 50). And yes, if you measure them, then are a half-a-tenth or so under the nominal size. Nobody says that you can't get the same sizes at your local bearing shop, or that Boca is the only place you can get them.

    On seating the bearings - yes, both bearings should be seated all the way to the bottom of their pockets. If you are all unsure, heat it up and push them in - applying them to the outer race only, never to the inner race. The rear bearing does, as Lauri  says, need to "float" as far as end play goes, on the shaft, and you have to have it seated all the way to assure that you have this float. The good thing is that merely heating it up to about 175-200 will cause it to drop into the pocket with no force at all, so take the crank out, heat it up, and let it fall to the bottom.

    I am already regretting this entire thread, because  I can see the potential for people picking up their hammers and vice-grips....

   Brett

Offline RandySmith

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Re: RO-Jett 61 BSE crankshaft bearings
« Reply #6 on: June 01, 2021, 02:05:24 PM »
  " " I am already regretting this entire thread, because  I can see the potential for people picking up their hammers and vice-grips....

   Brett "

One of my customers, a  "Do it yourselfer" used  a  socket  and a ball peen hammer...    :-(

Randy

PS  i would  only use a  phenolic , plastic  type  cage bearing on the  rear


Offline doug coursey

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Re: RO-Jett 61 BSE crankshaft bearings
« Reply #7 on: November 26, 2021, 09:38:27 AM »
dont use ceramic bearings. I used some from Boca, the ceramic ball and  stainless steel race versions and the ceramic balls flaked off and embedded into the piston and other parts inside and ruined it....this was on a RC helicoper 50 size engine using heli fuel with 23% all synthetic oil....the control line engines might not be as hard on the engine as the heli,s we fly and we also use 30% nitro. The bearings were installed like Brett stated and not hammered on,i have installed a lot of bearings using the heated in oven method...
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Offline doug coursey

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Re: RO-Jett 61 BSE crankshaft bearings
« Reply #8 on: November 26, 2021, 12:59:02 PM »
our heli engines also have a clutch assy on the crank instead of a prop..we use 30% nitro and run our engines at a lot higher RPM, even the higher quality bearing end up getting ruff..the front bearing never goes bad just the rear
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Offline doug coursey

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Re: RO-Jett 61 BSE crankshaft bearings
« Reply #9 on: November 27, 2021, 07:01:40 AM »
i have used AAC piston and cylinders on the smaller engines with no problem,the larger ones would be too hard to start with our start systems..
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