Cylinder head -POLINI 207 / 210 cc for long stroke crankshaft 60mm- Vespa PX200 - Ø=68,5mm - stroke compensation by head spacer | Cylinder heads | Cylinder | Engines

Preview: Cylinder head -POLINI 207 / 210 cc for long stroke crankshaft 60mm- Vespa PX200 - Ø=68,5mm - stroke compensation by head spacer

Description

Polini cylinder head for 200ccm engines with cooling fins on the bottom side. Fits both the old Polini grey cast iron cylinders (207ccm, Ø68mm bore, grey cast iron) and the successor (210ccm Ø68,5mm bore, Aluminium)

stroke compensation with head spacer
If you want to use the Polini cylinder head with a 60mm long stroke crankshaft on Polini 207/210cc cylinders, you need a compensation gasket (spacer) as supplied in this kit (thickness 1,5mm for stroke compensation 3mm). Usually the stroke compensation on the cylinder head makes the most sense. The control angles increase only discreetly, the exhaust angle also stays close to the original value, the speed band usually becomes a bit wider, the power and torque increase over the whole band. With a squeezing edge of 2.2mm the head has a healthy compression ratio of 9.6:1 on cylinders with long stroke shaft.

delivery scope

Cylinder head Polini 210/221 with additional cooling fins on the lower side
head gasket: 0.25mm thickness
Additional head spacer for stroke compensation at 60mm: 1.5mm thickness
compression: approx.9,6:1 at 2,2mm squish edge (distance piston crown to squish surface in the combustion chamber)

stroke compensation with foot spacer
If alternatively a correspondingly strong foot seal would be used, the control angles of the cylinder increase strongly, with the tendency to reduce the exhaust angle.
The higher control angles shift the power band into the range of higher speeds. The overcurrent angle, caused by the angular function of the crankshaft, when using a foot seal spacer reduces the exhaust angle. As a result, the power is throttled back at these higher engine speeds. The result is an engine that can continue to rev up but still has less power, the fuel efficiency is lost. To compensate for this shortcoming the exhaust angle has to be increased again. This requires a manual treatment of the exhaust duct, where the upper edge of the exhaust including the duct is increased in height.

forecast outlet
The forecast outlet is the area which the exhaust duct opens before the overflow ducts. The larger this value is, the more the cylinder can be freed from the old gas before new fresh gas flows in.
This and the lower pressure in the cylinder at the beginning of overflow are the prerequisite for good performance in the medium to upper speed range. If the forward exhaust is too large, the specific consumption increases strongly and the engine often loses torque in the lower speed range. Touring engines usually run quite well with values around 25°VA.

tuning
If you want to make the Polini more sporty and give it higher control angles (e.g. by using a 1,5mm foot spacer) and/or exhaust treatment, you can reduce the squish edge (turn off cylinder head or cylinder) to keep the effective compression sufficiently high. Reducing the QK to 1.2mm will increase the compression to 11:1, please keep an eye on the effective compression here. At an exhaust angle of 180° the effective compression is 6.7:1. Touring engines should always aim for values below 7.5:1.

calculation:
E = (Vh(1 - hb/s) + VC)/Vc

E = effective compression ratio

Vh = displacement volume

Vc = combustion chamber volume

Note: The cylinder head is made to fit the crown radius of the Polini piston. If the head is used on a cylinder with Malossi piston, the result is a strongly opening pinch edge angle. This reduces the effectiveness of the pinch edge and therefore the performance. Therefore the head should be reworked in combination with a Malossi piston (piston top angle of the Malossi piston is 14°). The stud bolt holes are cast conically to the combustion chamber opening. Diameter at the sealing surface Ø10mm. The squeezing surface ends without a step in the sealing surface, i.e. the combustion chamber is not twisted/sunk in.

(US)

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€100.95 *

incl. VAT plus shipping costs

Available immediately (delivery time 1-3 working days*)

P For this item you get fidelity point/s

OEM numbers (for comparison purposes only)
Polini	, P

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