*Competition part, not road approved! Increase engine displacement!
Here it is finally available, the RRD Competition long stroke 44.9mm crankshaft for MBK 51 / MOTOBECANE AV10, AV7. Designed to achieve maximum performance and maintain the highest revs. It is more resistant than the standard 103 models because it does not have a chamfer and its mass diameter allows a long stroke!
This very high quality crankshaft has been entirely studied, designed and tested in our workshops. It is made from high-end materials in Europe in the best crankshaft factory. This crankshaft offers many advantages:
- Stroke increased to 44.9mm instead of 41.8mm, which offers an increase in displacement , for example:
| Cylinder Ø | Displacement with stroke 41.8mm original | Displacement with long stroke 44.9mm |
| Ø45mm | 66.48cc | 71.41cc |
| 45.5mm | 67.96cc | 73.00cc |
| Ø46mm | 69.46cc | 74.61cc |
| Ø47mm | 72.52cc | 77.89cc |
| Ø50mm | 82.07cc | 88.16cc |
The long stroke also allows you to approach the square stroke again, for example (45X44.9) and to have better engine behavior. In Ø47mm, a high engine outputs 72.5cc with the original stroke, with this long stroke crankshaft 44.9mm, the displacement increases to 78cc!!! With the PARMAKIT 50mm diameter kit, we obtain almost 90cc real in combination with our long stroke, and this, with much more efficient diagrams!
- Specific crankshaft balancing for average piston weights of large kits, calculated on an average MALOSSI / POLINI / AIRSAL ... Around 80 grams.
- Ultra-reinforced connecting rod placed on a 16mm diameter crank pin, ultra-reinforced foot and head cage, improved foot and head lubrication.
- The ignition thread is a standard "right-hand thread", crankshaft thread like the original standard as well. So M11 X 100. Obviously, the thread on the variator side is also like the original, namely M11 X 100 too!
-Connecting rod original size 85mm (interesting to lengthen the connecting rod on the PEUGEOT 103, where it is only 76mm, but not on the MBK 51).
- On certain crankcases, it may be necessary to mill lightly or use an abrasive roller such as DREMEL / metal machining cutter to pass the connecting rod end. A distance of 0.5mm is required between the crankcase and the big end as a precaution.
Ø70.3mm masses / connecting rod head and anti-friction shims which protrude by 1.5mm. Recommended diameter at mass level, 71.1mm. Diameter at the connecting rod end passage recommended 74.2mm (1mm clearance at the radius). Run dry before assembly, the connecting rod head may require a little additional milling on the upper front of the crankcase. Milling that can be done well with the DREMEL. On POLINI casings , you can drill by doing this small milling. Use a two-component epoxy.
*Mounts without machining on original MOTOBECANE AV7 casings (requires machining on original TYPE casings)
*Requires machining for passage on POLINI housings
*Requires machining for passage on casings made in TURKEY, ALIM, OMEGA , EURO CL INDRO
*Requires machining on genuine EUROCILINDRO housings
-The price was taken as low as possible for small, limited quantities, with very high quality materials and workmanship!
The increase in stroke of 3.10mm will require you to use a base shim of around 1.5mm), we sell 1.0mm shims with an original type base shape, to align with your motor transfers . Then, play with your base gaskets to obtain the desired compression ratio (also to be defined according to your diagrams).
The piston at BDC goes down an additional 1.55mm, ideally you will align your lights at BDC. Be careful, do not use this crankshaft with a kit already prepared with very large diagrams on a normal stroke, the diagrams would end up much too high... We recommend at most, diagrams of 196 / 133 if you have enough to exploit them (very high revs). 188° / 129° diagrams will be ideal for most people, very efficient and more easily usable.
Compression ratio : Once you have aligned your cylinder at BDC and with suitable diagrams... Machine your cylinder head so as to have a good compression ratio. On air engines, we recommend a 1.00mm squish with a Japanese compression ratio of 7.3:1. On liquid-cooled engines with a pump, a 0.6mm squish can be used with a Japanese compression ratio of 8 ,1:1. Don’t hesitate to use our compression ratio calculator here!!!
*Parmakit Ø50mm on AV10 with long stroke RRD = 88.16cc or almost 90cc. Diagrams to aim for: 188° / 129°. Shim to place under cylinder: 1mm. Cylinder head machining: Yes, obligatory with installation of a cylinder head gasket if absent. Squish to aim for: 1.00mm. Compression ratio to aim for: 12 to 12.5:1 standard or 7.3:1 Japanese. Chamber volume between 8.01ml and 7.66ml.
*Parmakit Ø47mm on AV7 with long stroke RRD = 77.89cc. Diagrams to aim for: 188° / 129°. Shim to be placed under the cylinder: 1mm (if 1.5mm shim, machine the cylinder or the shim). To be accompanied by an RRD or POLINI RADIAL cylinder head. Cylinder head machining required. Squish to aim for: 1.00mm. Compression ratio to aim for: 12:1 with standard cylinder head and 12 to 12.5:1 with POLINI radial cylinder head (better cooling). Chamber volume between 7.41ml (small cylinder head, ratio of 11.5:1) and 6.77ml (large cylinder head, ratio of 15.5:1).
