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ZF Sachs

Sachs was one of the biggest built-in engines producer of the world with headquarter and production sites in Germany (see also Hercules). The full name of the company that produced Sachs engines is ZF Sachs. ZF Sachs also created motorcycles, motorized bicycles and ATVs.

Much like the Minarelli engine, Sachs engines were put onto a variety of other companies' moped frames including (but not limited to) Grycner, Columbia, Foxi, General, Eagle, Hercules, KTM, Moppet, Sparta, MBK as well as other smaller moped varieties. Unlike Minarelli, ZF Sachs also created their own brand of mopeds with the Sachs name as well as Hercules. The original manufacturers name is Hercules, due to lack of popularity in export markets the label Sachs or DKW were chosen. For example, the Balboa is very similar to the Hercules but with slight trim changes.

50x series Engines

The Sachs 50x series engine is known for its high rate of compression, ease of use, stability, and lack of case gasket. High compression is achieved though the unorthodox use of a combined cylinder and cylinder head. Referred to as a cylinder jug, this can be a mixed blessing as it is difficult to clean carbon deposits at the top of the jug. Also, if a spark plug hole's threads are damaged and rendered unusable, the entire cylinder may need have the hole heilicoiled or worse, the entire cylinder might be scrapped. There are benefits to the engine with a relatively efficient clutch assembly that can be easily changed. The engine case is also split horizontally leading to no use for a case gasket as the transmission fluid sits below the seam of the engine case. Also, interchangeable parts, cases, gears are used between manual and automatic models.

The Sachs 50x series engine were available with 1 gear automatic transmissions (mainly cheap mopeds and export), 2 gears, or as 3 gear manual transmissions. The engine could be ordered with incorporated pedal start, kick-start, handlebar gear-lever, or foot gear-lever. Kick-started 3-gear engines are rare to find as production numbers were significantly lower than the popular 2-gear engines.

The Sachs 50x series automatic engine also features a cable that engages not only the clutch but also a decompression valve. This decompression valve can be bypassed by fabricating a new cable. Doing this can make the moped harder to start but takes the weak decompression valve out of the equation. The valve itself can be replaced by a bolt of the same size.

Electronically, are variations of stator plate/magneto combinations. The most used solution in 505 motors was a Bosch variant of the 3, 4, or 5 wire type that are compatable with Puch. 504 motors have a smaller flywheel that are either bosch or motoplat and do not swap over to other mopeds.

The type of transmission fluid for the automatic engines used should be Type F automatic, filled to the bottom of the plastic screw on the transmission side of the engine. This screw is easily stripped or ruined but replacements are cheap and metal variants are available. For all manual transmissions, use SAE80 gearbox oil.

The cylinder bore was usually a stock 37.98mm.

Nomenclature 50x series

The Sachs engine has its own nomenclature that goes as follows:

50X / Y Z

X is a number representing the model number of the engine.

  1. The 501 was an early, inclined cylinder engine with a kick-start and foot shift. It was available in 3 and 4 speed models.
  2. The 502 was the early single-speed automatic, available in an A and B configuration.
  3. The 503 is a very rare, air fan cooled single speed automatic, 2 speed automatic (in Switzerland there are also catalyzed versions of this), or 2 speed manual, and mainly produced for the French and Swiss market where it is quite common.
  4. The 504 was available in a single speed automatic, or as a 2 speed manual shift. They have 2 motor mounts, and do not have pedals attached to the motor.
  5. The 505 is the most common Sachs engine in the US. It has the pedal crank built into the case, connected directly to the drive gears. Most US 505's are single speed. The 505 is also available in 2-speed and 3-speed manual shift. In later German models even a kick-start was applied instead of the crankshaft.
  6. The 506 was a late model 3 and 4 speed, inclined cylinder engine, Europe only.

Y is a number representing the amount of gears that the transmission contained. In the United States, manual transmission engines were not allowed legally so, occasionally this number was omitted. Automatics are referred to as "1". In Europe 2, 3 and 4 speed manual engines were sold in a variety of applications.

Z is a letter representing the performance-rated configuration of the engine.

Some Sachs engines came with these identifiers, some did not. US distributed 505 and 504 engines use the following nomenclature to describe the engine configuration:

A has 1.8 Horsepower tapered cylinder 12 mm square bing, and a 26mm ID head pipe, 47cc

B has 1.5 horsepower tapered cylinder 10mm square bing, and a 20mm ID head pipe, 47cc

C has 2 horsepower square cylinder 12mm square bing, and a 26mm ID head pipe, 47cc

D has 2.7 horsepower square cylinder 12mm square bing with no needle, and a 26mm head pipe, 49cc

Some mopeds such as Columbia Commuters, have no "Z" designation letter. most of them are equipped as follows:

tapered cylinder, 12mm square bing, 20mm ID head pipe, 47cc. horsepower is probably around 1.5

The A, B and C varieties all use the same 42 mm crankshaft to achieve displacement of 47.6 cc, and a compression ratio of 8:1. The D is much more powerful with 2.7 horsepower because of the 44mm stroke crankshaft, boosting the displacement from 47.6cc to 49.9cc and delivering a compression ratio of 10:1. This, and a shorter intake side piston skirt, gives the horsepower increase.

The piston is a 37.8 mm and most of the replacements are 38mm . This leaves room for honing or wear.
The connecting rod bearing is a 12mm center with a 15mm length and a 15mm outside. It is interchangeable with a stihl chainsaw piston bearing number 9512 003 3061 which fits Stihl 044 chain saws.

Some cylinders also use a slightly different bolt pattern between the base mounting holes, so they cannot be easily interchanged.

HP ratings are taken from data sheets, and seem a little high.

504 vs. 505 engine

The 504 does not have the pedal shaft running through the engine as the 505 does. The flywheel on the 505 is larger than the flywheel on the 504. Crank shafts cannot be swapped between the two because of the larger flywheel on the 505. Some 505s have a coaster brake like rear brake. Inside the engine case there is a sprag set up that allows you to backpedal to use the rear brake. They do use the same cylinder jug, motor mounts, exhaust and clutch assembly. For more information on the differences between engine types, you could refer to: this or this.


One of the most striking features of Sachs mopeds are the "coaster-brakes" or "pedal-back brakes" on some mopeds with 505 motors. This feature means that the rear brake is engaged when the pedals are rotated backwards allowing for sudden stops. This also makes the left-hand lever not engage the rear brake cable as usual but the decompression/clutch cable.

US models have tires with 17 inches around and usually 2.25 to 2.5 inches wide. From Sachs/Hercules, mag wheels as well as spoked wheels were available. The stock rear sprocket for US mopeds is somewhere around 44 teeth. European versions like the Optima 50 with 3HP engine have a stock 32 teeth rear chainwheel. The front sprocket is usually an 11 tooth. Anything larger requires cutting of the transmission side of the case. This can be done carefully because the case is fairly thick.

See Also

External Links