Large Model Association Forum

Hi, anyone seen a bearing failure like this? It is the front crankshaft bearing from a 26cc CRRC Pro V2 and it seems several of the balls have partially melted, the remaining ones are ok.
Was it just a bad bearing?

Only from a bent crank

Hi Alan, I thought that but when clocked in lathe shaft was true. Engine was nearly new and never crashed.
Barrie

Whats the prop driver run like?

Barrie,

I build 2 and 4 stroke motorcycle engines in my spare time, mainly motocross engines..I have only seen bearings fail like this on main cranks, mainly due to continual hard reving of the engine, poor maintenance schedules, lack of lubrication, wrong selection or poor quality bearings.
I don't know the exact details but notice that the bearing has 2 x steel shields fitted....usually a shield is only fitted to the outer side to stop ingress of dust/ dirt ....
I would source a new premium quality bearing, but make sure it is "c3" rated....this type of bearing is used on electric motors where you have large amounts of side loading as you will have with a large model prop....remove the shield on the inside of the motor, it can be easily removed by flicking it out with a jewellers screwdriver....these are the type of bearing that i fit to race engines....make sure you fit both crank bearings even if the other looks okay,,,hope this helps.

Andy

Hi Alan and Andrew,
Both bearings were fitted with 2 seals so no lubrication could get to either one, not sure if this is the norm on Chinese small petrols. I will check if prop driver runs true.

Barrie

Barrie,
fit two new bearings making sure they are c3 rated and remove shields so that bearings are lubricated on the inside.....cant see you will have any more problems.

Andy

Morning Barrie - Looking at the engine drawing for the 26cc CRRC Pro V2, the front crankshaft bearing does not get lubrication from the crankcase. There is a seal 26121 before the bearing. The type of bearing you need for the front is a rubber-sealed pre-packed bearing. The back bearing is open (unsealed) and gets lubrication from the fuel mix.
If you send me an email I can give you details of bearings, seals etc.
Thanks, Ken

Hi Ken, the back bearing was also double sealed and had not failed, I have now got 2 new bearings from Model Fixings to give it a try.
Picture of old rear bearing attached.

Barrie

Barry - The seals you talk about are "metal shields" and not seals and will just stop dust and small debris getting into the bearing. The shield will not stop oil, although it will restrict it a bit, hence the rear bearing is still ok. If you fit a shielded bearing to the front it will not get lubricated and will overheat and fail again. The front bearing needs to be a sealed bearing, pre-packed with grease.
JC Engines use similar bearings on their crankshaft
Thanks, Ken

Barry - I see your latest photo of the rear bearing and this is a sealed, pre-packed bearing, however on your initial photo showing the front bearing this is metal shielded (not sealed) and not lubricated.
If you've been supplied from Model Fixings with sealed bearings as per your last bearing photo then you'll be ok.
Hope that makes sense.
Ken

Yes they are both double sealed. The spacer between the bearings is nothing like shown in the exploded view, it is a tubular spacer with 3 different diameters about an inch long, and is a clearance fit on the shaft between the two inner races.

Barrie