hello guys another write up regarding hydraulic tappets and auto decompression
please note this is not specifically for the UCE engine but a general auto decompression and hydraulic cam lifter theory
as we all know that the bullet is a pushrod type valve train system and in the older CI models the valves were operated via rockers arms that were pushed down by push rods that were further operated by timing wheels fixed with cam lobes, this system required frequent setting of the pushrod and rocker arm clearance and would cause the tik tik sound and, this also had a lot of metal to metal contact and had more wear within the parts itself , mechanics would refer to it as tappet setting what he was actually doing is removing free play between the push rod and rocker arm thats all
the UCE also sports the same arrangement on here because of the hydraulic tappets this free play never has to be set, the difference here is the push rods have a hydraulic lifer, its small cylinder which within itself comprises of a spring, a valve, oil seals and two ports (design may vary from company to company) basic funda is when the valve is closed this hydraulic lifer has its oil ports open and there is no pressure in it, as the cam lobe pushes this lifter oil fills up and closes the outlet port, since a liquid cannot be compressed the hydraulic lifer moves upward pushing the pushrod that pushes the rocker arm that opens the valve, simple enough? there is much more deeper insight to this but this is the basic working, since the hydraulic lifers are always filled with oil when being pushed there is never any clearance or free play between the pushrod and rocker arm,thats why this is a maintenance free system, however these hydraulic lifters do have a life (depends on company schedule) when the spring inside the lifter gets slack or if the lifter itself develops a leak then this needs to be changed
the auto decompression is fitted on the exhaust cam of the bike, it is fitted with a small pin and connected to a small flywheel like mechanism at one end with a small spring, the flywheel moves out due to centrifugal force only at a low RPM, since the flywheel move upward it moves the pin which in turn pushes the exhaust valve slightly so as to have a slight leak within the cylinder to ease starting, this mostly cannot be set as it is preset from the manufacturer, a bad decompression system can cause hard starting (with kick) and a noisy engine as the pin is running loose in there,now i do not know how this arrangement is in the UCE so i cannot pin point everything
the above explanation is a general theory and not specifically for the enfield,i have never seen the inside of a UCE so it's hard to comment as of now, my friend has offered to lend me his UCE to do all my experiments in exchange for a full tank of fuel, a polished bike and mainly a fully working and functional bike
Posted by Yorik
please note this is not specifically for the UCE engine but a general auto decompression and hydraulic cam lifter theory
as we all know that the bullet is a pushrod type valve train system and in the older CI models the valves were operated via rockers arms that were pushed down by push rods that were further operated by timing wheels fixed with cam lobes, this system required frequent setting of the pushrod and rocker arm clearance and would cause the tik tik sound and, this also had a lot of metal to metal contact and had more wear within the parts itself , mechanics would refer to it as tappet setting what he was actually doing is removing free play between the push rod and rocker arm thats all
the UCE also sports the same arrangement on here because of the hydraulic tappets this free play never has to be set, the difference here is the push rods have a hydraulic lifer, its small cylinder which within itself comprises of a spring, a valve, oil seals and two ports (design may vary from company to company) basic funda is when the valve is closed this hydraulic lifer has its oil ports open and there is no pressure in it, as the cam lobe pushes this lifter oil fills up and closes the outlet port, since a liquid cannot be compressed the hydraulic lifer moves upward pushing the pushrod that pushes the rocker arm that opens the valve, simple enough? there is much more deeper insight to this but this is the basic working, since the hydraulic lifers are always filled with oil when being pushed there is never any clearance or free play between the pushrod and rocker arm,thats why this is a maintenance free system, however these hydraulic lifters do have a life (depends on company schedule) when the spring inside the lifter gets slack or if the lifter itself develops a leak then this needs to be changed
the auto decompression is fitted on the exhaust cam of the bike, it is fitted with a small pin and connected to a small flywheel like mechanism at one end with a small spring, the flywheel moves out due to centrifugal force only at a low RPM, since the flywheel move upward it moves the pin which in turn pushes the exhaust valve slightly so as to have a slight leak within the cylinder to ease starting, this mostly cannot be set as it is preset from the manufacturer, a bad decompression system can cause hard starting (with kick) and a noisy engine as the pin is running loose in there,now i do not know how this arrangement is in the UCE so i cannot pin point everything
the above explanation is a general theory and not specifically for the enfield,i have never seen the inside of a UCE so it's hard to comment as of now, my friend has offered to lend me his UCE to do all my experiments in exchange for a full tank of fuel, a polished bike and mainly a fully working and functional bike
Posted by Yorik
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