Author Topic: C50 XL Maintenance  (Read 394 times)

Offline Adrian Mansell

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C50 XL Maintenance
« on: 17, June 2017, 10:37:29 PM »
I know a few people are still using this classic motor, as am I, and I've had a few conversations with people about how to fix them.  So here is a brain dump of what I've learned.  I'm sure Hacker would wince at some of this...and please feel free to correct or add extra nuggets.


The Motor Rotor


  • Be very careful handling the rotor, the magnets are bloody strong.  It is very easy to put it down next to something metal and - BANG - they whack together and damage the tape on the rotor.  Please don't ask how I know this.
  • This should have two 0.1mm shims on the front of it.
  • At the rear it should have an aluminium or brass spacer which is stud-locked to the shaft, followed by a crinkle washer
  • If you get dust at the back of the motor, it is often because the rotor has been overheated, has gone out of round and has rubbed against the lining on the inside of the windings.  If this has happened, the rotor tape may well be discoloured brown due to the heat and rubbing.  It is knackered and the rotor should be replaced.
  • With the motor assembled, you should be able to press firmly on the end of the output gear and see a small amount of movement as the crinkle washer compresses.  If not, the rotor has expanded lengthwise and should be replaced; I think this mostly affected the older design of rotor.  Conversely, there should be no free end-float beyond that provided by the crinkle washer; if there is, the rotor has shortened and should be replaced.
The Motor Bearings
  • An abnormal high pitched whine is a sign the bearings are knackered.
  • There are two sizes of bearing ("1260" for the older motors, "1360" for the newer ones - please see the hacker website for details of how to tell which motor type you have.
  • These bearings, particuarly in the harder revving C50-13XL, operate above the accepted maximum speeds for bearings running in grease.  This is why they don't last long.  Only buy good quality bearings. I use these for 1360 motors http://simplybearings.co.uk/shop/p2633/6862Z+Metal+Shielded+Deep+Groove+Ball+Bearing+6x13x5mm+/product_info.html
  • The bearings are a drop in fit, so MUST be secured in place with bearing lock.  If you don't, they will spin in the housing and bugger it up.
  • To remove the bearings, press them out using a suitable socket or tube to support the end-cap around the bearing and a bolt or shaft to press the bearing.  If the bearing lock has been done properly you will need a fair bit of pressure and it will go with a bang!
  • Clean up the bearing housing with a suitable solvent; I use superglue debonder.
  • Refit the bearings with bearing lock/retaining compound.  I use loctite 638; four very small drops on the bearing and four on the housing, then rotate the bearing into place to spread it.  Reassemble the motor and leave to dry.
The Gearbox
  • An abnormal low pitched rumble or humming is usually a sign that the propshaft bearings having gone
  • An abnormal wowing noise or mid-range whine is usually a sign that a planetary gear bearing has gone
  • (2) is often accompanied by discolouration of the offending P-gear bearing, caused by it running hot.
  • (2) & (3) are usually accompanied by a flat being worn on the load bearing side of the pin P-gear pin.  This is caused by the needles skidding in the P-gear bearing.  Clean up the shaft and have a good look with a magnifying glass for any such wear marks.  See the attached photo for the example of a very knackered pin.
  • (2), (3) or (4) mean the propshaft should be replaced as well as the offending P-gear bearing (I always do all three)
  • When cleaning/greasing the gearbox, mark the shaft with a marker pen so that you can put the P-gears back on their original pin when re-assembling.
  • Replacing the propshaft bearings.  The rear bearing can be tapped out from the front using a suitable drift, taking care not to damage the aluminium spacer between the bearings.  With the rear bearing removed, the front can be knocked out with a larger drift. Press the new bearings in using a suitable tool that presses on the outer race.  The bearings should be pushed until they are up against the internal circlips.  The aluminium spacer should be able to slide from side to side when pushed - if it is tight, the bearings have been pushed too far.  (I don't actually know why this spacer is there - it doesn't seem to serve the usual purpose of preventing preload.)  The bearings can be sourced from http://simplybearings.co.uk/shop/p6750/SKF+6082Z+Metal+Shielded+Deep+Groove+Ball+Bearing+8x22x7mm/product_info.html
  • End-float and shimming (should be checked if you have replaced the bearings).  This is a fiddle, here is how I do it.  The rear of the propshaft should have a 0.2mm shim on it.  Insert the shaft in the gearbox and put a 0.3mm shim on the front, followed by the circlip.  Then put a prop on it and finger tighten the prop-nut.  Check you can feel some end-float by pushing/pulling on the shaft, you should be able to feel the shaft slide in and out of the gearbox (make sure the shim has not slipped into the circlip slot).  Progressively tighten the prop nut, checking that there is still end-float as you go.  Once the nut is tight, if there is still end-float, dissassemble and increase the front shim by 0.1mm and repeat the process.  Once you have fitted a shim that results in no end-float with the prop nut tightened, you are done.  In all of my gearboxes this is a 0.5mm shim.  The shims are 8mmx14mm and spares can be got from https://www.thebearingcompany.co.uk/
  • Replacing the planetary gear bearings.  The bearings can be pushed out with a 6mm drift and a suitable tube or socket to support the gear.  Push the new bearing in from the bottom of the gear with an 8mm or bigger drift - the bottom of the bearing should be flush with the bottom of the gear and this is the easiest way to guarantee that.  The top of the gear is the end with the slight bevel machine on it.  The engraved end of the bearing should be at the top of the gear.  Suitable bearings are http://simplybearings.co.uk/shop/p8191/HK0306TN+Drawn+Cup+Type+Needle+Roller+Bearing+With+Two+Open+Ends+3x6.5x6mm/product_info.html
  • Greases.  The hacker grease is Lithium based and obviously works pretty well.  I have tried Clay based Shell Aeroshell 22, which seemed OK but there were signs of the P-gears running hot.  I am currently using SKF LGHP2, which is a Polyurea grease and generally accepted as better than Lithium-based.  My gearboxes are noticeably quieter with it and showing no signs of high temperatures or wear.
  • If you have grease appearing around the cooling slots in the motor, you are putting too much in the gearbox when you regrease it.
  • If when you reassemble the motor and gearbox you find it has gone tight, this can be because the gearbox case is worn where the retaining bolt heads are, and the end of the bolt is now poking through and fouling the cooling fan.  Pop a couple of small washers under the heads of the four bolts or shorten the bolts by no more than 1mm.
Running In
« Last Edit: Yesterday at 11:20:05 AM by Adrian Mansell »

Offline Mark Allen

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Re: C50 XL Maintenance
« Reply #1 on: 18, June 2017, 10:17:25 AM »
Thanks Adrian, a very comprehensive guide full of useful tips.
I hadn't considered running in bearings off load so that's a trick learned.


Do you use a bearing arbor press?  Careful alignment in a vice probably does the job.


Mark

Offline Adrian Mansell

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Re: C50 XL Maintenance
« Reply #2 on: 18, June 2017, 12:06:01 PM »
Hi Mark,


I have turned up a set of arbors for each of the jobs and I use my Axminster vertical mill/drill as a press - although to pop the motor bearings I use a vice as they can take quite a bit of force to unstick.


Looking forward to hearing a nice quiet motor in your model... :-)


Offline Alan Williams

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Re: C50 XL Maintenance
« Reply #3 on: 18, June 2017, 01:58:44 PM »
Thanks Adrian, this will be really useful when I need to do an overhaul.


Al. Williams

Offline Mark Allen

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Re: C50 XL Maintenance
« Reply #4 on: 18, June 2017, 04:17:19 PM »
Hi Mark,


I have turned up a set of arbors for each of the jobs and I use my Axminster vertical mill/drill as a press - although to pop the motor bearings I use a vice as they can take quite a bit of force to unstick.


Looking forward to hearing a nice quiet motor in your model... :-)


Yes me too, I need to tune into C50 running sounds to detect issues.
I bought the bearings straight after the Stansted comp but have yet to receive the gear shaft, should be here in the next few days

Offline Nigel Armstrong

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Re: C50 XL Maintenance
« Reply #5 on: 29, June 2017, 06:14:10 PM »
Just out of interest. Do you wait until the motor sounds different in the air before stripping it to diagnose the problem? Or, is there a set number of flights before the "preventative maintenance" program is instigated and the motor and gearbox is stripped and checked for signs of distress?

Offline Ashley Hoyland

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Re: C50 XL Maintenance
« Reply #6 on: 16, July 2017, 12:00:40 PM »

C50 - Experienced a 3 hour re-grease this morning.


After cleaning and re-assembly which took me about 30 minutes the motor was fine until I put the last eighth of a turn on the gearbox retaining screws, then it all locked up.  Releasing them the eighth turn and the motor turned over smoothly.


My instant thought was distortion - wrong sequences of washers and all things which I could have got wrong.


After checking many times I had the same results.


After a cup of tea I noticed the end of the retaining screws were not as smooth as I expected and although they worked OK before I disassembled the unit I started to wonder if the retaining bolt seats had worn or the bolts had stretched.  Neither would I have thought possible and a poor finish on the end of the bolt shouldn't really make any difference.


However I took a few thou off the end of each bolt and success.  The bolts were touching the hidden part of the cooling fan when fully tightened.


We live and learn.

Offline Alan Williams

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Re: C50 XL Maintenance
« Reply #7 on: 16, July 2017, 06:38:47 PM »
Nigel,
following an overheating issue with my C50, I sent it back to Hacker for an overhaul. Among other things it needed a new rotor. I took the opportunity to ask about maintenance and the reply from Christin Hoffman is that they recommend re-greasing the gearbox every 70 flights or so and only to send it back if it starts to make unusual noises, or the overall sound level goes up. He did not indicate that preventative maintenance of the bearings/motor was needed. Mine was returned very quickly and having flown with it today for the first time, it is transformed from how it was before. It was very old as I bought it second hand and flew it for a year or so.
I need to find another one now as a spare!

Offline Nigel Armstrong

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Re: C50 XL Maintenance
« Reply #8 on: 16, July 2017, 07:44:50 PM »
Thanks Alan. That's exactly the information I was looking for.