One of the problems commonly found in Sachs engines is the oft-misunderstood clutch system. The clutch is basically maintenance free, but in some cases the pre-load must be adjusted. This may be due to old friction material swelling up, or tampering by a previous owner.
Improper clutch pre-load can cause:
- Stalling at stops.
- Rear wheel spinning while idling on stand.
It is important to make sure that your carburetor is clean and in good working order with the idle speed properly set before continuing. Too fast or too slow of an idle can cause either of the above symptoms.
Start by putting a pan under the engine to catch any fluids in the transmission. Then disassemble the starter clutch as follows:
- Remove the 5 screws holding the clutch cover on the side of the engine
- Remove the long screw from the top of the clutch housing observing the position of the clutch arm, spring and cable.
- Pull off the starter clutch bell.
You now have access to the clutch.
If you need further instruction, Travis has a video detailing the steps for taking apart and assembling a Sachs clutch. https://www.youtube.com/watch?v=e5psYgHFbDw
The clutch plates should have .4mm - .6mm of play (.016 - .024) You can check this by trying to push the outer clutch plated back and using feeler gauges to measure the gap left between the clutch nut and the shim washers, or between the shim washers and the clutch plate.
If there is too much of a gap, you will want to add shims, if the gap is too little or nonexistent you will need to remove shims. You will first need to remove the clutch nut (immobilize the crank by whatever method you see fit). Then remove the little rectangular spacer, under that should be some thin washers, these are the shim washers. Remove or add enough shim thickness to accomplish the desired play. You may need to order some shims to complete this. When reinstalling the clutch nut clean it of all oils and torque it to 25.3 - 28.9 ft/lbs. This is a lot of torque to put on that, so any grease, oil or transmission fluid on the threads could easily allow you to break or strip something. A little red locktite would be a good idea.
Adjusting the clutch is a repetitive procedure. You'll be pulling off the plate, the lever, the bell, the nut, etc. OFTEN to get the clutch to work. Take this into account before locking down the clutch nut with locktite or 30 ft-pounds of torque.
In order to tighten the clutch nut, a tool is available to assist you. This holds the washer under the nut in place allowing you to torque the nut down. It's possible to use a slim C wrench or crescent wrench to hold the washer in place and avoid the purchase of this tool.
This tool is available on a couple of the moped websites.
A cheaper solution is to simply use a 24 mm or 15/16 wrench to hold the flat nut in place while screwing on the nut.
see also: Sachs clutch modifications