TUTORIAL – Crushing edge Vespa PX

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

In our second tutorial we describe how to measure and adjust the pinch point of a bgm177 cylinder. Of course, the sequence is applicable for all other cylinders, but the dimensions can vary greatly depending on the manufacturer or the desired application of the cylinder and may 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_bgm1770n

For the heart of Platónika we mounted the bgm177 cylinder dry first.
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 mounted several times to set the correct squeeze size, the threading of the piston rings is bypassed until the final assembly.

The bgm177 cylinder is supplied with several gaskets for the cylinder base with different thicknesses of 0.2, 0.4 and 0.6 mm.

BGM1770G(1) (1)

The cylinder is mounted without a seal for the cylinder base. To map the squeeze size we use soft solder with a diameter of 2mm.

The length of the piece of solder should correspond to the diameter of the hole. A little overlength does not harm to position the soldering tin with adhesive tape on the piston, parallel to the piston pin.

Filme & TV 26.02.2020 14_15_03

The cylinder head is mounted and fixed together with the gasket. By turning the crankshaft the piston is turned once over the TDC = top dead center. There, the solder is squeezed between the piston crown and the pinch-off surface of the cylinder head to the squeeze size, thus forming the current squeeze size.
After the cylinder head is disassembled again, the crushed solder at the ends can be easily measured with the caliper gauge. In our example this results in a dimension of 0.62mm.
The manual of our bgm177 cylinder gives us as recommendation a squeeze size of 1mm.

bgm_177 anleitung

How do I change the squeeze size?

In order to get to 1mm with the existing squeezing dimension of 0.62mm, a cylinder base gasket of 0.4mm must be added; to get to the desired dimension of 1mm purely by calculation.

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