rev degree before TDC
To assemble the VForce membrane, the membrane box has to be widened by 8 mm (from 45.5 to 53.5 mm. This will end up in remaining wall thicknesses below 1 mm. To be on the safe side it is recommended to increase the wall thickness of the membrane box by filling the spaces between the ribs with cold metal. I also use a 5mm spacer between the membrane and membrane Box. The complete action is a lot of work, but takes 10% more power.
Fig.: Membranes: RD 250, YPVS, VFORCE Fig.: Membrane Spacer
Fig.: Wall thickness of the membrane box increased by filling with cold metal Wall thickness of the membrane box increased by filling with cold metal
Fig.:Cylinders with studs Fig.: Pack of spacer and V-Force-membrane
To get the new membrane package sealed, the screws must be tightened properly. To minimize the stress in the aluminium block studs should be used that can be easily produced from a 6 mm threaded rod. For the above shown modification studs with a length of 50 mm are ideal.
At Walldürn 3 + 4 June 2011 the engine ran over 60 km on the race track. Main Jet # 200 was installed. Temperatures was between 24 and 27 degrees.
On the piston you can see very clearly the effect of different squish gaps left and right. The carbon deposits are a sign of the piston temperature. The left piston, i.e. the one with the 0.85 mm squish gap clearance has no coking all around the edge. That means the piston remains cool at the edge. Unlike the right piston with 1.2 mm squish gap. Coking is seen from 9 o’clock to 3 o’clock. It is much warmer on the edge as the other piston.
Figure 10: Piston after 160 km, of which 60 km race mode