Simson ignition timing clock

As my next step > SIMSON SR50 inspection I set the ignition. At the same time, I was not able to resist the low-priced opening watch for SIMSON, MZ, Trabant and Wartburg on Ebay. Basically, these ignition timing are nothing but exact dead center for all sorts of engines, but especially for old two-stroke (from the GDR), they are very convenient. The even better versions of the ignition timing clocks work with a digital display. In addition to an ignition timing clock, there are other ignition timing methods:

  • with a "special screw" or a modified spark plug as upper dead center finder and eg with a degree disc.
  • If nothing is available, but only then you can adjust the ignition in an emergency also roughly with the depth gauge of a caliper. This method is really very inaccurate.
  • If the engine including the crankshaft and ignition is original, the adjustment with the original marking of the base plate on the motor housing is sufficient - but who knows exactly after 30-50 years?

Once the ignition of the SIMSON or other two-stroke engine has been properly set and marked on the engine housing, it will not need to be readjusted until a new crankshaft or other ignition is installed. Otherwise, the original demolition mark on the motor housing from DDR plant applies. My > SIMSON SR50 scooter I have a contactless 9 years ago > VAPE ignition donated. The electronic VAPE offers besides a strong 12V alternator performance the advantage of being completely maintenance-free. She has been doing her duty without complaint since 2008. However, the ignition timing was never set exactly after changing the ignition system. I want to catch up now.

Set the ignition on the SIMSON SR50 scooter

First, the right footboard needs to be removed on the SR50. The speedometer cable is unscrewed - and the clutch cable must be unhooked from the alternator cover: Unfortunately, you have to say aloud! Because so no test drives can be made without screwing the ignition cover and the footboard again completely, because the clutch does not funzt so. Driving and briefly adjusting the ignition timing with the screwdriver, so unfortunately falls out. So that the whole screw is still worthwhile, I will later change the chain and the drive pinion.

SIMSON ignition timing

Thanks to the electronic VAPE ignition, I am spared the setting of the ignition contact. Experience has shown that for SIMSON contact ignitions including capacitor must be replaced every 5.000 kilometers, since then both parts are worn. Looking closer, I look at three marks on the engine that should match: The original notch on the motor housing is aligned with the notch of the VAPE Ignition base plate (stator). If the mark on the flywheel (rotor) can also be seen approximately there, then the piston is somewhere near the top dead center.

A rotation of the base plate to the right creates a later ignition point, the rotation to the left is in the direction of pre-ignition. In order to be able to make an exact statement as to whether the ignition is really precisely adjusted despite VAPE installation, Now the top dead center (TDC) of the piston must be determined. Exactly 1,8mm before top dead center should be the ignition timing for the 50 cubic centimeter engines M531 and M541 from SIMSON.

Timing of SIMSON engines


  • SIMSON SR50, S51, S53, KR51 / 2: 1,8 mm before top dead center
  • SIMSON SR80, S83, S70: 1,4 mm before top dead center
  • SIMSON S50: 1,5 - 1,8mm before top dead center
  • SIMSON bird series up to year '80: 1,5 mm before top dead center

Ignition adjustment with the ignition timing clock

Ignition timing clock screwed into the cylinderNow comes the Zündzeitpunktuhr into play. It is just as hand-screwed into the candle thread with the correct spacer instead of the spark plug. If the ignition timing clock is installed with a minimum of wobble, turn the crankshaft of the engine clockwise until the top dead center is reached. This is exactly the case when the clock hand is running back. In this position you turn the dial of the ignition clock on 0 and the pole wheel again exactly 1,8 Milimeter - so 1,8 pointer turns back: This is our ignition!

Release SIMSON holding clips of the vapeThe polar wheel mark must be exactly aligned with the notch of the motor housing. If this is not the case, a new mark is attached to the motor housing, because the old demolition mark is no longer correct. Then the two screws of the base plate are easily released and carefully turn the base plate until all three marks are aligned. The whole thing is a bit fiddly and must be repeated if necessary two to three times before the ignition in the form of aligned three marks 1,8mm before TDC. Done, that's it.

SIMSON ignition markings

The photo is taken slightly obliquely from above, so there is an optical offset of the ignition marks. All three lines must be aligned while the SIMSON magnet wheel is exactly 1,8mm before top dead center. I have the base plate with me about 1 cm further to the left in the direction of pre-ignition must turn.

Changing the chain on encapsulated SIMSON and MZ drives with chain hoses

Anyone who has never changed the chain at SIMSON or at MZ motorcycles, can despair even as an experienced motorcycle wrench, as it runs in fully encased chain hoses. This construction ensures that the chain can last up to 20.000 kilometers and longer. Dirt and moisture remain outside and the chain oil stays in the hoses. The whole thing does not look so nice visually, but is worth gold in everyday life, as the chain care almost completely eliminated. It is enough to see all 5.000 kilometers after the chain lubrication - usually it does not need to be relubricated. Cheap gear oil applied thinly with a brush is sufficient for lubrication completely. Nevertheless, a moped chain does not last forever. Since the alternator cover of the SIMSON scooter is already unscrewed, I use the same and spend the SR50 a new roller chain and a new pinion. Changing an enclosed chain is easy if you know how to do it.

Chain sprocket SIMSON old and new

After unscrewing the gray speedometer drive, the drive pinion bolt must first be loosened if it is to be replaced. To do so, insert the first gear, if possible by a helper still parallel to the foot brake lock and with a jerk, the mother releases from the output shaft. It does not do any good to mount a new chain on a worn pinion or sprocket with sprocket teeth. The new chain then wears out again within a few 100 kilometers and is scrap very quickly. So best to at least change the pinion with the same.

Then the chain lock is searched. Has the chain of a SIMSON never been changed, Incidentally, the opening of the chain lock is invisible on the inside chain side! Finding and clipping with the forceps is really a dirty game of patience. For me, the chain lock was already on the outside. The chain will now open. The old chain lock we still leave: It is needed to introduce the new chain almost as a perfect line in the chain hoses on the rear drive gear.

SIMSON link chainBefore you can turn on the rear wheel with the chain open, no more because the chain then securely hooked in the chain case and quickly damaged this without complete disassembly! In addition, the end of the chain disappears immediately in the chain tube. If the new chain is hung up in the chain lock of the old chain, you may carefully pull on the lower part of the old open chain. So you thread the new chain and pulls out the old at the same time slowly, until the chain lock comes to light.

Chain lock running direction

This will be removed and replaced with the new chain lock. And in the direction of travel so that the chain lock spring caught in the run nowhere - and can fall off. If the chain opens while driving, it will be dangerous. In the best case, she smashes the chain case and falls out. In the worst case, it gets stuck and unexpectedly blocks the rear wheel ... As always, I am not responsible for this guide, they look for a craft doubt or lack of tools rather a workshop.

New chain, new pinion and a clean set SIMSON ignition in one operation

Vape ignition on the SIMSON SR50

Finally, the chain tension is adjusted. The chain must still be able to move up and down by about 2 cm when the moped is loaded. To do this, you sit on the moped, checked by pulling or squeezing on the chain tube the tension and rolls it back and forth a bit. If the chain is set to stem, it rips permanently on the output bearing of the engine and the bearing of the rear drive wheel. Both are very bad for the bearings and the new chain, which is extremely strong. In addition, a chain set too tight course, performance. And that is scarce here.

Adjusting the chain tension with SIMSON and MZ in the chain hoses costs more time than with other two-wheelers. Nevertheless, care is absolutely necessary here. The chain needs almost no maintenance over thousands of kilometers. Incidentally, tensioning the chain is easier if the alternator cover has not yet been mounted, as you will then at least see something else. For new chains, it is advisable to recheck and correct the tension after a filled tank has been filled. The rear wheel must be able to rotate quite easily when idling, and will naturally spin out a few turns when turned by hand on the stand with momentum. If it turns bad, either the brake grinds easily, or the rear wheel is installed wrong. Of course, the chain line should be as straight as possible over both gears as in the case of a bicycle. In the SIMSON repair book is the note to put a straight wooden board on both wheels of the moped and to see if the wheels both just lie against it - so aligned. Of course, this does not make much sense with the chain line if the frame is warped - or the fork is slightly crooked.

The first test drive with the newly set ignition

I strongly advise against starting with the SIMSON SR-Scooter without a running board, because then the rear brake can only be operated with a free-floating foot. So secure the running board with at least one screw before the first test drive.

Completely set VAPE ignition

The ready-set VAPE ignition on the SIMSON SR50, here without a mounted footboard

Is the SIMSON ignition now set exactly?

After the test drive with the newly set ignition, you can often look forward to a little more power. Be it in a slightly stronger suit off the stand or down the mountain at high speeds. Often the engine starts better with an exact spark timing and consumes a little less fuel.

Basically: If the engine ignites too late, performance is lacking and it gets very hot. If the engine fires too early, the piston that just rises gets one on the lid before it is up in the TDC. In principle, this is quite easy since the inflamed flame front takes a few milliseconds to fully expand: in the case of an 50ccm engine, this is approximately 1,5-1,8 millimeters before top dead center. To see if the combustion is basically okay, after the first test drive basically the candle should be turned out once - and the candle image should be visually inspected: The electrode should be "fawn brown" according to the old tradition, the ring of the spark plug thread dark brown to black. There are fuels and two-stroke oils that produce a gray candle image instead of a brown one. That's no reason to worry, here too, only the brightness gradation counts.

Candle face SIMSON

Candle image with correctly adjusted SIMSON engine: The color is deer brown with a dark brown to almost black ring. There I still in the run-in phase of a new cylinder set I put the part needle up one step higher, so the engine runs a little bit fatter than normal. If I hang the needle down again after driving in 1000 kilometers, the candle image will get a little brighter, especially at the current jet black ring.

If the candle image is lighter than deer brown, the engine runs too lean, gets too little cooling gasoline, pulls somewhere wrong air, has leaking crankshaft seals or the carburetor is too lean. > Often it is enough to hang the part-load needle one step higher. This condition is dangerous to the engine as the piston can easily jam due to overheating. Unfortunately, the two-stroke has put the stupid feature a bit too lean to bring the most performance. Especially here: If the candle is too bright, the cause must be found as quickly as possible without much driving. When the engine starts to accelerate - that sounds like an electric coffee grinder - you have to be very cautious. This is an engine failure. By pre-ignition, wrong spark plug, too little fuel because the filter element is clogged in the fuel cock ... usually it is with SIMSON at the spraying, a wrong float height adjustment or the drawing of false air between carburetor and cylinder.

If the candle image is darker, the engine runs too fat. Then either the air filter with dirt added or the spraying in the carburetor is too large (too fat). The exhaust then smokes more, of course, faster with coal and very likely lacks some power at relatively high fuel consumption. But on cold days, the engine probably jumps very well, likes to drink in summer on hot days after a few kicks off. This condition is of course not optimal and should be remedied in the medium term. Often it helps, the part needle in the carburetor > just hang a notch further down.

Of course, if you want to know exactly, you can also connect a stroboscope and check the ignition marks at different speeds while the engine is running. The markers should then not diverge widely at different speeds. In my opinion, this is worthwhile only with tuned engines with changed timing or modified compression, which I would not like to elaborate on here.

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