Modern Vespa

Hi All

Got a bit of a strange one, have carried out a rebuild on another VNL2 engine I picked up.
This is the fifth or sixth engine I have rebuilt and had no real problems before.
Have changed all the consumables, bearings, gaskets etc. Before the rebuild I turned the engine over which turned over ok (crank rotates and piston moves freely).
Problem is now I've rebuilt, before I put on the head it turns over and the crank moves the piston through the barrel as should be, but once I fit the head and torque down I go to turn over, the kick start will go fully down and return it seems to feel a bit tight but the crank don't turn it's almost as if the crank could be off its centre preventing full stroke along the piston (is this possible) Before I open her up again any ideas where I may have gone wrong.

Hope this makes sense.........

Headstud has gone in too far & jamming against starter ringgear or flywheel.
Or
You put piston in backwards
Or
Wrong crank (longstroke?)

What happens when you turn by hand?

Huh?

"The kickstart will go fully down and return it seems to feel a bit tight but the crank..."

- The kickstart lever feels stiff? Just the kickstart gear turns but the crank doesn't? The flywheel turns but the crank doesn't? The piston doesn't move but the cylinder does?

"It's almost as if the crank could be off its centre preventing full stroke along the piston..."

- I have no idea what that even means. The crank has disconnected from the piston and can't move inside the piston fully alongside the cylinder on the upshaft?

Could it be clutch related?

I can't picture how this could happen, but could your clutch be semi-engaged? So w/o compression the kickstarter can turn the primary, then clutch and allow the crank to turn. BUT when there's compression the clutch is slipping?

Are you sure you installed the washer behind clutch

Amen to one of the studs being too deep in the cases

Thanks for your replies people, I'll have a look Friday and let you know what I find.

^^That's a good one^^

if the piston goes up the cylinder from the bottom, but gets stuck at the top and won't complete it's stroke and come back down, could it be you've got a head gasket or a head that's not completely centered with the cylinder and the piston is hitting it... stopping the piston from completing the stroke?

I was thinking the crack could be misaligned and it's hitting the rotary pad.