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Tech. Advice: Series 'B' / 'C' 500cc/1000cc Bikes
Gearbox oil level rising/Primary falling
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<blockquote data-quote="Hugo Myatt" data-source="post: 54828" data-attributes="member: 99"><p>I had better put in my penny's worth although I am not sure how relevant it will be. This was some years ago after I had had the engine professionally rebuilt. I suddenly discovered the oil in the gearbox had risen considerably and the chaincase was completely empty of oil. Now I had gone to great lengths to seal the dynamo drive housing and had been completely successful. I suspected that somehow the gearbox was pressurising. I removed the filler cap and dip stick and fitted a condom over the filler neck then took the bike for a run aound the block. The expansion of the condom had to be seen to be believed! The gearbox was definitely pressurising and some.</p><p></p><p>After many travails and investigations this was the explanation. The engine rebuilder had fitted a sealed bearing to the drive side main shaft. He had removed the inner side membrane to allow for lubrication but had left the outer membrane, i. e. the primary chain side, intact. Unfortunately this acted as a very efficient flap valve. As the pistons descended pressure was forced into the primary chaincase but as they ascended the flap valve neatly closed trapping the pressure. Thus with every downward stroke of the pistons the pressure in the primary case was increased exponentially. This combined with my total sealing of the primary case caused this pressure to force the chaincase oil out of the primary by any means it could and into the gearbox. The solution was to remove the offending seal, a.k.a flap valve, and equilibrium was restored.</p></blockquote><p></p>
[QUOTE="Hugo Myatt, post: 54828, member: 99"] I had better put in my penny's worth although I am not sure how relevant it will be. This was some years ago after I had had the engine professionally rebuilt. I suddenly discovered the oil in the gearbox had risen considerably and the chaincase was completely empty of oil. Now I had gone to great lengths to seal the dynamo drive housing and had been completely successful. I suspected that somehow the gearbox was pressurising. I removed the filler cap and dip stick and fitted a condom over the filler neck then took the bike for a run aound the block. The expansion of the condom had to be seen to be believed! The gearbox was definitely pressurising and some. After many travails and investigations this was the explanation. The engine rebuilder had fitted a sealed bearing to the drive side main shaft. He had removed the inner side membrane to allow for lubrication but had left the outer membrane, i. e. the primary chain side, intact. Unfortunately this acted as a very efficient flap valve. As the pistons descended pressure was forced into the primary chaincase but as they ascended the flap valve neatly closed trapping the pressure. Thus with every downward stroke of the pistons the pressure in the primary case was increased exponentially. This combined with my total sealing of the primary case caused this pressure to force the chaincase oil out of the primary by any means it could and into the gearbox. The solution was to remove the offending seal, a.k.a flap valve, and equilibrium was restored. [/QUOTE]
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Tech. Advice: Series 'B' / 'C' 500cc/1000cc Bikes
Gearbox oil level rising/Primary falling
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