Thrust Faces

Anything related to Lambrettas... ask tech questions, post helpful info, or just read and learn.
156 D
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Wed Jan 14, 2009 5:28 pm

sean brady scooters wrote:just to add as a matter of interest .................
vespas differ to lambos in respect of major thrust face....................
on a lambo ......major thrust face is exhaust side............minor thrust is inlet.
on a vespa ......major thrust face is inlet side...............minor is ex............
I am glad you mentioned that Sean because one of my friends had the old two-stroke three wheeler and it didn`t have reverse gear.....You had to turn off the ignition and then turn the key the otherway to start and it made the engine go the opposite way so that in fact he had four gears in reverse.....leading me to say that your reasons for the opposite thrusts on the Vespa is because the engine turns opposite to the Lambretta as the fan and infact the engine is entirely on one side of the machine.....Does the Vespa run cooler?....
Nostalgia is a thing of the past!....

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sean brady scooters
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Wed Jan 14, 2009 10:32 pm

if you were to take out a vespa engine...............and turn it upside down............and then look at it from the flywheel side............you would notice that it then turns the same way as a lambo...............ie.....clockwise ......
but the difference is, in this case that the exhaust will be uppermost............
the opposite to lambos...............
as regarding cooler running........on vespas ..........generally speaking.........
have you ever looked at and compared say a gp200 barell to say a p200 barell.............
if so the first thing you may notice is the vast difference in cooling fins .........vespas have so much more..........especially around ex port area..............
vespa cyl heads also have far much more fin area..........much bigger fins............
further more......vespas draw in their cooling air from the outside enviroment far much more efficiently than lambos..............
vespas also generally have larger diameter flywheels....................with bigger /more efficient fins..........drawing in cooling air from the exterior of scoot..........
lambrettas unfortunatly,........are still restricted by their basic design in that they can only pull so called "cooling air" from under panels.............which is of course pre heated.
the main culprit on std lambos is maybe the LHS floor board..............just take a good look at one of these as regards cool air intake into fan................ :shock:
but just to make matters worse.........on lambos.......the exit from cyl cowl on lambos ,just helps to pump in more heat under panels............... :roll:
Sean Brady Scooters - 01765 690 698

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RinB
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Wed Jan 14, 2009 11:01 pm

sean brady scooters wrote:if you were to take out a vespa engine...............and turn it upside down............and then look at it from the flywheel side............you would notice that it then turns the same way as a lambo...............ie.....clockwise ......
but the difference is, in this case that the exhaust will be uppermost............
the opposite to lambos...............
You had me thinking about that one Sean but yep it would be the same :)

I noticed on another site this posting has had people saying the opposite about thrust face .


But Hey We know better ;)

:lol:
If its made of Metal Fettle it !!

156 D
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Thu Jan 15, 2009 7:00 pm

Have you two got together?....... :? .......because as you say the Vespa engine revolves clockwise the same as a Lambretta.....if you turn the lambo upside down and look at it from the sprocket side it is the same and as the Vespa.....so therefore there thrusts sides are identical as the inlet is on the top and the exhaust underneath......you are on a conundrum here?.... :)
Nostalgia is a thing of the past!....

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jonny snatchsniffer
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Thu Jan 15, 2009 7:31 pm

but what if they are facing one another ? then they both spin the same way with inlet and exhaust the same

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sean brady scooters
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Thu Jan 15, 2009 11:06 pm

156d..........
if as you say........you turned a lambo engine upside down and veiw it from sprocket side...............then flywheel would appear to be be turning ANTI clockwise.............yes...?

also if you do as jonny says.............put a vespa and a lambo engine facing each other...................then yes they do both turn clockwise ..........but the major thrust is up on the vespa and down on the lambo..................... :D
come on please guys...................its not rocket science..........
just feel that i,m trying to push string here............
dans been here tonight and between us we will try to explain a bit more using some pics etc to help you visualize this more easily...............
but basically what you have to do in order to find major thrust is to look at crank rotation from a clockwise view...........at half power stroke...........then follow angle of conrod FROM crank TO piston.............this points to major thrust.............easy peasy............. :D
Sean Brady Scooters - 01765 690 698

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drunkmunkey6969
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Thu Jan 15, 2009 11:33 pm

Sean asked me to post this:

Image

truls221
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Fri Jan 16, 2009 12:35 am

I think people are letting go to think about the pressure that is on each side of the piston.
How the crankshaft is balanced and how the compression height is according to the inertia of the piston.

If the piston pin height is very low how is the thrust on the piston affected?
(why have modern engines very low pin height and presumably long rods?)

If the crank is balanced towards a certain factor, how is the thrust affected?
Why do we have different balance factors for vertical and horisontal engines?

And lastly, the pressure on the inlet side. How is the pressure here in relation the piston position?
There is a big difference in thrust on the piston for piston-ported and crankcase ported cylinders.

With these questions answered we have mostly covered regarding piston thrust.

So a vespa and lambretta apply to the same laws of physics. so there is no difference unless the cylinder is piston ported and the other not.

hope you understand this

cheers

Truls

156 D
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Fri Jan 16, 2009 11:55 am

.......have a look at this quite interesting?..........

http://www.motorcycleproject.com/motorc ... ffset.html
Last edited by 156 D on Fri Jan 16, 2009 4:38 pm, edited 2 times in total.
Nostalgia is a thing of the past!....

156 D
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Fri Jan 16, 2009 1:35 pm

Well!....i am now the one going round in circles as the lambo is turning the right way when you look at your drawing from the flywheel side because of the left-handed thread on the nut.....truthfully i have forgotten which way on the trans side it should turn and i really thought the straight line of the chain (as in all fourstroke engines) is the pull of the chain....cannot get my head around the fact that the lambo`s pull is on the bottom of the chain as you look at it?...i am going to start at the gearbox end or the wheel and work backwards ,then it has to be correct....... :)
Nostalgia is a thing of the past!....

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