POLINI SQUISH!!!!!!!!!!!!!!!!!

[shamrockexpress]

Polini 208 SQUISH 1.9/2.0 mm is this exceptable?????
this has a machined head and only a base gasket which i,d like to keep.
The same kit with original 2-ring piston ran a 1.5 squish so i,m guessing the new 2 ring piston must have a little difference
thanx in advance.

[H,POOL GADGE]

could ye fone the people who machined the head and ask, what squish the head was machined at, because it will have been machined for a specific squish to give a certain compression ratio, polini being cast iron, maybe it,s a low compression head to run cooler hence 2mm squish to be on the safe side prone to nip polini,s...

[shamrockexpress]

could ye fone the people who machined the head and ask, what squish the head was machined at, because it will have been machined for a specific squish to give a certain compression ratio, polini being cast iron, maybe it,s a low compression head to run cooler hence 2mm squish to be on the safe side prone to nip polini,s...

thanx for that gadge!!!!!!!!
maybe AL from DIABLO i think he got harry barlow to do it????
so Al could you shed some light on the matter please!!!!!

[shamrockexpress]

BUMP!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

is 2mm ok???????????anybody.
also what about using loctight between head and cylinder ( like MB does with lammies) is this ok on the px???

[santacama]

I think that is too much.

[shamrockexpress]

could ye fone the people who machined the head and ask, what squish the head was machined at, because it will have been machined for a specific squish to give a certain compression ratio, polini being cast iron, maybe it,s a low compression head to run cooler hence 2mm squish to be on the safe side prone to nip polini,s...

thanx for that gadge!!!!!!!!
maybe AL from DIABLO i think he got harry barlow to do it????
so Al could you shed some light on the matter please!!!!!

BUMP FOR diablo...........what is the answer mr polini

[sean brady scooters]

A 2mm squish band clearance just aint a squish that works...2mm is far too much,and if you find that this in any way has alleviated pinking etc its only cos its helped to increase cyl head volume and reduce compression ratio.
a tighter squish of say 1.3mm will increase both power and efficiency not to mention cooling.

[ArmandTanzarian]

This seems to be a Vespa kit thing. This is from the Pinasco write up on WORB5 (as translated by google)

"Cylinder with a piston and head. Squish about 3.5 mm. Geometric compression approximately 1:9,7 57 mm stroke and about 1:10,2 at 60 mm stroke (and 1.5 mm Fudi or Kodi). Why is this such a big silly head squish which can only say Mr Pinasco"

[Diablo]

Sorry only just seen this thread.
Its not so much a Vespa kit thing as a P2 thing. Std P2s run massive squish clearances as std. Not sure why but it isn't the only weird thing about them . For instance the piston at BDC is deliberately above the transfers. This is supposedly to make the incoming charge roll over on itself and not flow straight out the exhaust. Running pretty advanced timing is must also be something to do with it.
Having a side squish head isn't ideal either but I'm sure Piaggios engineers knew what they were doing.
Anyway we start running kits and expansions and crucially unleaded fuel and it cocks things up a bit.
I am quite surprised that 2 polini pistons have different compresion heights but the simplest fix is to have .5mm machined from the top of the barrel.
Unless a deck height was specified before the head was machined its impossible to machine the squish in exactly the right position relative to the piston at TDC. Adjustment of the squish clearance has to be done using gaskets and or machining otherwise.
I would say the squish will work fine between 1.2 and 1.5mm.

[sean brady scooters]

in what other modern two stroke motors would the vespa p200 idiosyncrasy,s be deemed as acceptable .. let alone desirable...? very few indeed and for many good reasons I presume.