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TUTORIAL - pinch edge Vespa PX

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How do I measure the pinch edge on the cylinder head?

In our second tutorial we describe how to do one bgm177 cylinder can Pinch edge is measured and adjusted. The process can of course be used for all other cylinders, but the dimensions can vary greatly depending on the manufacturer or the desired application of the cylinder and differ from our dimensions in the video.

zylinder_bgm_pro_177_187_ccm_kolben_made_by_meteor_vespa_px125_px150_cosa125_cosa150_gtr125_ts125_sprint_veloce_vlb1t_0150001_bgm1770nzylinder_bgm_pro_177_187_ccm_kolben_made_by_meteor_vespa_px125_px150_cosa125_cosa150_gtr125_ts125_sprint_veloce_vlb1t_0150001_bgm1770n

For the heart of Platónika we have that bgm177 cylinder first mounted dry.
This means that the piston is initially mounted without piston rings and only with the upper bearing of the crankshaft. So if the cylinder has to be assembled several times in order to set the correct squeeze dimension, the threading of the piston rings is bypassed until the final assembly.

The bgm177 cylinder lie several and with 0,2; 0,4 and 0,6mm different thicknesses Seals for the cylinder base.

BGM1770G (1) (1)BGM1770G (1) (1)

The cylinder is mounted without a seal for the cylinder base. We use to map the squeeze dimension soft solder with a diameter of 2mm.

The length of the piece of solder should correspond to the diameter of the hole. A little excess length doesn't do any harm to position the solder appropriately with adhesive tape on the piston, parallel to the piston pin.

Films & TV 26.02.2020/14/15 03_XNUMX_XNUMXFilms & TV 26.02.2020/14/15 03_XNUMX_XNUMX

The cylinder head is assembled and fastened together with the gasket. By turning the crankshaft, the piston is turned once above TDC = top dead center. There the solder is squeezed together between the piston crown and the squeeze surface of the cylinder head to the squeeze dimension and thus forms the current crush dimension .
After the cylinder head has been dismantled again, the pinched solder can be easily removed at the ends measured with the vernier caliper become. In our example this results in a dimension of 0,62mm.
The Instructions from ours bgm177 cylinder gives us a recommendation Crush dimension of 1mm.

bgm_177 instructionsbgm_177 instructions

How do I change the crush dimension?

In order to get from 0,62mm to 1mm with the existing squeeze dimension, a cylinder base gasket of 0,4mm must be added; in order to arrive at the desired dimension of 1mm purely mathematically.

 

Scooter Center Tutorial Vespa PX - Checking the piston squish (Activate subtitles)

 

https://blog.scooter-center.com/tutorial-stehbolzen-vespa-px/

 

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Transparent cylinder head Many scooter drivers have certainly dreamed of this: a cylinder head that shows the combustion process of the 2-stroke mixture.

Transparent cylinder head made of glass

Transparent cylinder head

Many scooter drivers have certainly dreamed of this: a cylinder head that has the Combustion process of the 2-stroke mixture shows.

Here someone has fulfilled this dream and makes the ignition of the two-stroke vehicle impressively visible. Cool thing, as we think:

Transparent engine goes up

Unfortunately, this head does not have a long lifespan. Spectacular how the spark flips over from second 47:

Cylinder head for scooter

Unfortunately, for the reasons shown in the video, we cannot serve you with a transparent cylinder head. You can find a large selection of inexpensive and durable cylinder heads for scooters here:

Buy cylinder heads here
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Cylinder head Polini Racing for Polini 133ccm Vespa V50, ET3, SS50, SS90

With the appearance of the new Polini Evolution cylinder, the well-known Polini gray cast iron cylinder also received an upgrade and from now on has the addition "Racing" in the designation. A really massive cylinder head with an enlarged cooling surface, CNC machined combustion chamber and a copper gasket.

Due to the greatly increased material thickness and the use of a head gasket as in the Evolution cylinders, leaks on the cylinder head - provided that it is correctly installed - are a thing of the past from now on.

Fortunately, Polini offers the new one Racing cylinder head also available as a spare part that can be adapted to any “old” Polini. The ones required for assembly longer cylinder studs To attach the stronger cylinder head, a cylinder head gasket is included in the scope of delivery. We recommend this for screwing M7 nuts from Naraku.

Due to the increased cooling capacity, Polini has given the new racing cylinder head a little more compression.

We measured the difference for you with a burette.

Compared to its predecessor with 16,8ccm combustion chamber volume, the new cylinder head comes with a combustion chamber volume of 15,9ccm and thus increases the geometric compression from 8,7: 1 to 9,1: 1.

We simulated the volume of the cylinder head gasket by measuring it with grease.

The subtly increased compression, paired with the more modern shape of the combustion chamber, help the Polini gray cast iron to achieve more torque and power without the cylinder head being subjected to thermal overload. Of course, this only applies if the motor is set correctly. Of course, the new cylinder head does not iron out incorrect carburetor and ignition settings.

To be on the safe side, you should re-determine the pinch dimension after assembly and adjust the ignition timing depending on the engine setup. With increased compression it may be necessary to select the ignition point a little later (i.e. fewer degrees before TDC).

The new Polini cylinder head is also interesting for class 5 of the ESC, as it has been approved in class 2012a since 5.

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