Webra SS sealed bearing update

[Grow Pattern]

Keith,
          I have reported and seen several times that rubber seals can drag. The first sign is that the engine keeps quitting at idle after the first run . You can see the "polish: or scuffing on the crank face. If you don't get the symptom leave well alone. 

I theorize that it might be "chemical" and that the  rubber swells from certain additives or after-run oils that contain petroleum products.

Regards,

Eric.
  ----- Original Message ----- 
  From: Keith Black 
  To: discussion at nsrca.org 
  Sent: Friday, June 10, 2005 12:26 AM
  Subject: Webra SS sealed bearing update


  A while back I put the new SS sealed bearings from Boca into my Webra 1.45. These bearings feel VERY smooth and it ran quite well for about 16 hours of service. This is five to seven hours longer than the standard bearings had been lasting me.

  At the Temple contest on the Friday practice day the Webra started sagging at the top of uplines. I messed with the needles, pump pressure, changed the glow plug and even added a head shim all to no avail. Initially I didn't want to admit it, but my prior experience has shown that reduced performance that can't be fixed with needle adjustments or replacing the glow plug normally means the bearings are going bad. Therefore, I reluctantly did a bearing change even though the bearings still felt REALLY good. I assumed that at high speed they may be rough but I couldn't detect it just from feeling them. In order to proceed with the contest I put my backup Webra, also with the SS bearings, in the Aries and it flew like a champ.

  After the bearing change I put the first Webra into my new Impact and continued to have run problems. I rebuilt the pump and that didn't help. In desperation I opened up more cooling on the Impact (cheek cowls, etc.) in case it was an over-heating problem. I replaced the connecting rod that seemed a bit loose (but I don't think that was the problem), and I started using a foam clunk because I thought it might be getting gulps of air due to the tank setup in the Impact. However, before test flying it I spoke to Art Wagner who had just returned from Jetero. He had problems with his OS 1.60 and had changed the bearings with new rubber sealed bearings but it didn't help. He opened the 1.60 and found that the rubber seals were dragging. His guess was the excess heat caused the rubber seals to swell (or maybe just bad luck). He pulled the seals and, presto, the 1.60 started running awesome again.

  After hearing this I pulled my Webra apart and removed the rubber seals reusing the SS bearing with just a few flights on it. I know the best way to trouble-shoot things are to do one thing at a time so you know what fixes the problem, but considering that the last dead stick ALMOST was curtains for my Impact I just wanted it FIXED!!!

  Today I went out and flew it and it ran like a champ again. What fixed it? I don't know for sure, but I do think it's *possible* that the rubber seals can in some cases drag and cause problems, especially in the hotter weather like we're having now. I didn't see any run problems until the hotter weather hit. This certainly could be a coincidence, I don't know.

  A side note on the Webra I put into the Aries at Temple. It did indeed run very well, however after each flight if I turned the prop back and forth I would hear a squeaky rubbing sound. I had several others listen to this too and we couldn't figure out what it was. At first we thought it must be dragging on my nose ring or something, but I could never find ANYTHING that it was rubbing outside the engine. This only occurred when the engine was hot. So, was this also the sound of the rubber seals dragging due to swelling from the heat? I don't know, but it sounds possible. If so it didn't stop it from running well.

  Obviously I'm concerned that removing the seals will reduce the bearing life, but it also "possibly" fixed my sagging problem, it definitely fixed Art's problem. I'll have to wait and see what type of life I get out of the ones without seals.

  I'm also tempted to remove the seals from the engine in the Aries to see if the squeaking goes away, but I was told long ago, "If it ain't broke, don't fix it".

  Keith Black 




  I don't think in all cases the rubber seals cause a problem, but I think there's the possibility for them to cause a problem.
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