See the mechanism on the side of the cam sprocket?
That lowers the compression during starts on this Piaggio "Liberty 150i 3V i-get" engine. Holds the exhaust valve open a bit longer.
Enables Piaggio to use a smaller start motor. (and probably helps the measly 6Ah battery!)
I had to go to Vespa's Robot to find if my guess was correct.
Fish
Re: Strange to see on a little 155cc....
Posted: Tue Aug 20, 2019 10:20 am
by springer1
Holds the exhaust valve open a bit longer.
Enables Piaggio to use a smaller start motor.
I'm thinking it isn't a compression release like my old BSA single had .... rather a variable valve timing gizmo, like any newer cat or truck has. That looks like it's centrifugally driven, the same as the older vintage points plate in the distributor would be shifted by weights & return springs to alter ignition timing..
Re: Strange to see on a little 155cc....
Posted: Tue Aug 20, 2019 3:52 pm
by fish
springer1 wrote:
Holds the exhaust valve open a bit longer.
Enables Piaggio to use a smaller start motor.
I'm thinking it isn't a compression release like my old BSA single had .... rather a variable valve timing gizmo, like any newer cat or truck has. That looks like it's centrifugally driven, the same as the older vintage points plate in the distributor would be shifted by weights & return springs to alter ignition timing..
At 6:47
Fish
Re: Strange to see on a little 155cc....
Posted: Tue Aug 20, 2019 6:45 pm
by Old Grinner
See the mechanism on the side of the cam sprocket?
Oh yeah . . . I see what you mean when he starts describing it at 6:40.
Re: Strange to see on a little 155cc....
Posted: Wed Aug 21, 2019 7:43 am
by springer1
Old Grinner wrote:
See the mechanism on the side of the cam sprocket?
Oh yeah . . . I see what you mean when he starts describing it at 6:40.
Wow, is that cool or what - I love learning about stuff like this.
