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Author Topic: ST51 bearings  (Read 1097 times)

Online Paul Allen

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ST51 bearings
« on: May 08, 2019, 02:13:26 AM »
Just in process of replacing bearings in a G51 C/L motor,ordered Boca Stainless steel replacement set,these are metal shielded
and the ones I just removed are a rubber seal,I am thinking the only difference may be a bit more oil leaking from the front metal shielded bearing.
Any thoughts?
Thanks.
Paul
In OZ

Offline Massimo Rimoldi

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Re: ST51 bearings
« Reply #1 on: May 08, 2019, 03:51:03 AM »
Hi
The conformation of the ball bearing's  rubber gasket avoids (as far as possible) the entry of contaminants in the bearing and only partly helps to prevent the contained lubricant from escaping.
If there is pressure from the outside to the inside the gasket's lip  tends to close, on the contrary if the pressure is towards the outside the lip opens (see attachment)
Under normal conditions, the lack of a gasket can cause small quantities of the fuel to leak out to the advantage of lubrication, but be careful to avoid the accumulation of dirt near the bearing.

Massimo
« Last Edit: May 08, 2019, 06:15:59 AM by Massimo Rimoldi »

Online Paul Allen

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Re: ST51 bearings
« Reply #2 on: May 08, 2019, 02:55:19 PM »
Thanks for the reply's
Paul

Offline Air Ministry .

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Re: ST51 bearings
« Reply #3 on: May 08, 2019, 10:18:48 PM »
Ifin itdoes leak fuel outta the front , the FUEL CONSUMPTION increases .

ACTUALLY , a lot  :-\ of the bearings are machiend for the shield or seal , which some people pop out and put in a unshielded one. :-\
« Last Edit: May 09, 2019, 10:40:53 PM by Matt Spencer »

Online Lauri Malila

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Re: ST51 bearings
« Reply #4 on: May 09, 2019, 02:55:20 PM »
Something has to be really wrong if a front intake engine leaks fuel from front. There is no spesific force that pumps fuel through front bearing. Quite opposite; it's often necessary to broach a channel from carburettor area to near front bearing to get some lubrication to front bearing. It's a sign of a healthy setup if you see a very faint ring of oil inside the engine compartment after a few flights, flown from front bearing.
Personally I see no point in sealed front bearing, unless you crash a lot in soft soil.
In rear intake engines it's a little more tricky to acchieve a controlled slow leak to provide lubrication for front bearing. After some experimenting I have settled to a 5mm long sealing area right after rear bearing, with 0,04mm clearance. Front of that it opens a little to allow shaft deformation without contact with case. That seems to be safe but just in case I squirt some oil to front bearing before a flying session, when I remember.
But mileage may vary, I only use WIB bearings with their (PEEK?) or my own made Tufnol retainer rings. L

Offline Christoph Holtermann

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Re: ST51 bearings
« Reply #5 on: May 10, 2019, 06:17:40 AM »
Leaking front bearing on a ST-51? Yes, I have had this problem as well on one of my ST-51's. Fuel consumption increased dramatically and engine run was instable. After slight heating in manoeuvres, the engine leaned out and the fuel, supposed to enter the combustion chamber escaped through the front bearing or the venturi. Problem was in my case solved by taking the front bearing out and examining the milled groove that connects venturi-opening in the case with the bearing seat. I am no motor man so don't have the good explanation what this groove exactly serves for but I recognized that the groove was not completely milled through but stopped just before the front bearing seat. I filed away the last tenth of millimeter and reinstalled the bearing. From that moment, the leaking was cured, regardless of the shield (rubber or steel) of the front bearing.
So in your case have a look if this machining deficiency also explains your problem.

Christoph


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