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Tech. Advice: Series 'B' / 'C' 500cc/1000cc Bikes
Oil loss through breather pipe
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<blockquote data-quote="timetraveller" data-source="post: 16516" data-attributes="member: 456"><p><span style="font-family: 'Times New Roman'"><span style="font-size: 12px">Just to ensure that Tony can visualise what the original breather is like here is a description. The gear which drives the magneto/distributor is the same size as the half time pinion, i.e. it rotates at engine speed, and the gear itself has a hollow tube in the centre of it. The tube has a rectangular hole cut in it so that as it rotates this slot can act as a valve. The combination of gear and hollow shaft rotate on a hollow spindle which itself has a slot and it is the lining up of the two holes/slots which allows air to escape when the pistons are descending and, when the two slots are not lined up, stops air being sucked in when the pistons are rising. Personally I always fit the spindle so that its slot is facing downwards to try to help prevent oil escaping but that might seem a bit over cautious to some people. Phil Irving recommended widening the slot in the tube/gear pinion combination if the bike was to be used for racing. The open back end of the hollow spindle interfaces with the banjo bolt to let the air out. On ‘D’s the whole thing was got rid of and replaced by a different valve spring cap, with its own banjo bolt, but for this to be effective there has to be additional clearance in the various holes on the way to the valve spring to let the air get out to the valve cap and hence the atmosphere. Unfortunately some people do not realise this latter point and fit the ‘D’ caps without ensuring that the various holes are opened up and even worse some people leave the original breather in place which means that the engine now tries to suck air in through the top breather while the pistons are going up and then the engine has to work harder to expel this extra air when the pistons are going down. If you do not already have it then you would probably find it very advantageous to get a copy of the Spare Parts List which shows all parts of the engine and gearbox. Good luck.</span></span></p></blockquote><p></p>
[QUOTE="timetraveller, post: 16516, member: 456"] [FONT=Times New Roman][SIZE=3]Just to ensure that Tony can visualise what the original breather is like here is a description. The gear which drives the magneto/distributor is the same size as the half time pinion, i.e. it rotates at engine speed, and the gear itself has a hollow tube in the centre of it. The tube has a rectangular hole cut in it so that as it rotates this slot can act as a valve. The combination of gear and hollow shaft rotate on a hollow spindle which itself has a slot and it is the lining up of the two holes/slots which allows air to escape when the pistons are descending and, when the two slots are not lined up, stops air being sucked in when the pistons are rising. Personally I always fit the spindle so that its slot is facing downwards to try to help prevent oil escaping but that might seem a bit over cautious to some people. Phil Irving recommended widening the slot in the tube/gear pinion combination if the bike was to be used for racing. The open back end of the hollow spindle interfaces with the banjo bolt to let the air out. On ‘D’s the whole thing was got rid of and replaced by a different valve spring cap, with its own banjo bolt, but for this to be effective there has to be additional clearance in the various holes on the way to the valve spring to let the air get out to the valve cap and hence the atmosphere. Unfortunately some people do not realise this latter point and fit the ‘D’ caps without ensuring that the various holes are opened up and even worse some people leave the original breather in place which means that the engine now tries to suck air in through the top breather while the pistons are going up and then the engine has to work harder to expel this extra air when the pistons are going down. If you do not already have it then you would probably find it very advantageous to get a copy of the Spare Parts List which shows all parts of the engine and gearbox. Good luck.[/SIZE][/FONT] [/QUOTE]
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Tech. Advice: Series 'B' / 'C' 500cc/1000cc Bikes
Oil loss through breather pipe
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