What's the Difference
by Alan Buehner
From time to time I will get calls from someone inquiring about the availability of a cylinder for their Sachs engine. As far as they are concerned it is just a matter of letting me know that it needs to be for a 100 or 125. There reality is that there are several types of cylinders for the Sachs engine and it helps to know the difference to prevent getting the wrong one.
The first thing to know is there are cast iron cylinders and aluminum cylinders. The cast iron cylinders (photo A) have short cooling fins and were used on the 1968 thru 1971 Sachs engines. The Aluminum cylinders (photo B) have large cooling fins and were used on 1970 thru 1975 Sachs engines. The cast iron and aluminum cylinders are interchangeable in that they both use the same bottom end. The 100 and 125 cylinders are also interchangeable in that they also share the same bottom end. The thing to keep in mind if you want to switch from cast to aluminum (or vise versa) is that the cast requires 4 short mounting studs and the aluminum requires 4 long mounting studs.
There is only 1 style of stock cast iron cylinder and these are available as 100cc or 125cc.
The aluminum cylinders however come in 3 styles and are available as 100cc or 125cc. It is important to know the differences between these for the bike application they will be used on.
Photo “C” shows an alloy cylinder with the bottom 3 fins “cut off” on the right side. These are used on Sachs engines that use a side mount exhaust pipe. These are what are required on the Penton “steel tank” bikes that have the exhaust pipe mounted on the right side of the frame. This cylinder shown is a 100cc. If you look at the bottom of the cylinder sleeve, you will see a slot in it in the front. This is the quick way to identify a 100 from a 125 cylinder.
Photo “D” shows an alloy cylinder with no cut fins and are commonly referred to as “full” fins. These are used on Sachs engines that use a down pipe or an up and over pipe. These are what are required on the Penton 1972 thru 75 CMF bikes where the exhaust pipe goes up and over the cylinder head.
Photo “E” shows a Sachs “D” cylinder that has “full” fins and was available from Sachs in 1975. These cylinders were available on the 1975 Penton 125 bikes.
Looking at this photo you will see a difference on the intake. Instead of having an alloy “snout” to mount the carb, it has a removable rubber manifold to accommodate a Bing 28mm or 30mm carb. There are slight porting changes in these cylinders giving them more horsepower output. These cylinders are highly sought after for vintage racing. The way to tell the difference between the “D” cylinder and the earlier aluminum cylinders is the “extra” v-shaped spacers in between the cooling fins as shown in photo “G”. I have seen many of the early cylinders where the intakes were machined out to bolt on a reed cage or a rubber mount for a Mikuni carb. So be sure to look for the v-shaped spacers as the proof that any Sachs aluminum cylinder that you are looking at is indeed a “D” cylinder. As far as I know, these only came as 125cc cylinders.