Kreidler 6 speed racing engine

Special parts Foekema-Kreidler 50cc-Racing
Latest update Oct 26, 2005
The engine
Here you can see the inside of the Foekema-Kreidler 6 speed racing engine. The engine is based on a standard Kreidler engine. Even there are many important changes, much parts are still standard.
The main changes are:
- Rotary diskvalve inlet system
- Crankshaft
- Cylinder and piston
- 6 speed gearbox
- Clutch

Rotary disk valve inlet
For dimensions if you wanted to made. The valve is connected on the crankshaft and is rotating with the engine RPM. This rotary system is mounted on the left side of the engine. (The Kreidler factory racing engines has 2 rotary disk systems one on each side. It looks good but in practies it has no use and has even some disadvantages) In the valvehome is made an inletlog as big as the inlet diametre of the carburetor. The valve is as you can see not fully round the part that is taken out is the inletperiode. The main advantage of the principal is that you can open and close the inletperiode exactly at the time you want. Before this you have ofcourse to know the 2 stroke principal.

How to made a rotary diskvalve inlet
The left crankcase outside has to be filled up with melted aluminum. The melting point of aluminum is about 660 degrees celcius. So you can do it with a meltcup of steel and heat it up with a weldingflame. At the same time you have to heat up the left crankcase, otherwise the differance in temperature is too big.
You dont have to fill it up completely, you may do it but is not necessary. After cooling down the foundry piece has to be fixed, because it is not automaticle airtight fixed. This you can do with a expoxy resin. After fixing it has to made flat on a phrase engine. Then you have to made the aluminum inside cover and outside cover on a lathe. The inside cover has to be fixed in the left crankcase on the founded aluminum piece. This has to be done not only with epoxy resin, but very imported also with iron 5mm bolts, see picture. If you don't, you take the risk that it will leak after some time.

Outside cover and crankshaft
The 6mm bolts normaly fitted from the leftside, changes to the right side. You have to fix 6mm helicoils in the left crankcase or you can make M8 bolts direct into the aluminum. The outside cover is also made of Durall on a lathe with room for the only seal in the system. One runout has to be made 14mm in diametre till 21mm from the crank.

The 6-edge has an outside diametre of 22mm including a cylinder part of 17mm in diametre, which turns in the seal of the outside cover. Total length of the 6-edge is 21mm. In the runout is made a pin of 2mm to keep the 6-edge with the valve in a fix position. The 6-edge has to be fit easy on the runout, otherwise you can't dismantle it without damaging.

The valve
The valve is made of steel 0.4-0.5mm like a sawblade. It is a little hard to manage but it will do. In the picture you see two ways to made it. One is made with a balanced centre piece, but this is not real necessary. The old VanVeen engines also don't have it. The valve has to loose on the 6-edge to let him freely to shift axially.

Valve timing
Finnaly the valve timing, with this timing you have influance to the power behaviour of the engine. It als depend of many details and is still a point of finetuning. The averidge opening is 3mm after the lowest point of the piston and close 12mm after the highest point. The later it close the smaller will be the power width. The best you may start with a 24mm carburetor, in many cases more than 24mm has no use directly.

There will be a follow up, so come back soon

Dimensions if you wanted to made it by yourself.
Sheldon's site for more rotating valve pictures

E-mail to: 50cc-racing

Open Kreidler 6 speed racing engine

The rotary diskvalve left side of the Kreidler 6 speed racing engine

The rotary disk and the outside disk cover

Standard crankshaft with a little change, 6-edge and valves

Kreidler RS cylinder with 4 transfers which made Luc in 1968 the fastest private driver at the TT of Assen. He was in the headgroup with Anscheidt on Suzuki (worldchampion), Paul Lodewijks (winner), Aalt Toersen and Jan de Vries, both on Kreidler 12V. Ricus Foekema drove 177km/h with a RS cylinder with only 3 transfers, at Tubbergen 1969

Closed pistonported inlet were now 2 extra tranfers

The current SB cylinder, with exhaust boosters with 18 hp it runs to 100km/h in 7 sec.

Piston and conrod of a 12speed Kreidler, used in the 1967 VanVeen 5peed engine.

Als de Nederlandse versie nog niet gereed is wordt u automatisch met de Engelse versie verbonden.
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