A55

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The Tomos A55 engine is the latest available model, introduced in 2003 and found on all current Tomos mopeds. It shares many similarity to its A35 brethren but has an all new cylinder, piston, carburetor, intake manifold, and exhaust. The engine has a nikasil plated aluminum piston-ported cylinder. The new cylinder has an exhaust port angle of 25* so exhausts made for the A35 will need to be bent in order to fit. The new Dellorto PHVA carburetor allows for more accurate fuel mixture than previous models and the exhaust has a built in catalyst. Most of the upgrades on the A55 were done in the sake of cleaner emissions, however it is the most powerful Tomos automatic engine to date. The transmission is basically the same as the A35 aside from some small improvements such as larger cutouts for the cylinder transfers.

Technical Specifications

  • A55 Engine
  • 49cc two stroke
  • 38mm X 43mm Bore/Stroke
  • 10:1 compression ratio
  • Automatic 2 speed transmission
  • Dellorto PHVA 14mm Carburetor (#55 main jet, #25 pilot, #40 choke)

Torque Information

  • spark plug: thread M14 x 1.25, 18Nm or 13.27 foot/lb
  • Cylinder head: thread M7, 12Nm or 8.85 foot/lb
  • Cylinder studs: thread M7, 15Nm or 11.06 foot/lb
  • Magneto flywheel: thread M10 x 1, 30Nm or 22.12 foot/lb
  • 1st speed clutch: thread M10 x 1, 25Nm or 18.44 foot/lb
  • 2nd speed gear: thread M14 x 1, 80Nm or 59.0 foot/lb
  • Engine mounting bolts: thread M8 x 1, 25Nm or 18.44 foot/lb
  • Right hand engine cover: thread M6, 7Nm or 5.16 foot/lb
  • Left hand engine cover: thread M6, 6Nm or 4.42 foot/lb
  • Crank case: thread M6, 10Nm or 7.37 foot/lb
  • Mainshaft chaing sprocket: thread M22, 60Nm or 44.23 foot/lb
  • Swing arm bolt: thread M12 x 1.25, 35Nm or 25.81 foot/lb
  • Rear shock absorber: thread M10, 25Nm or 18.44 foot/lb
  • Top fork lug: thread M12, 35Nm or 25.81 foot/lb
  • Front and rear wheel axles: thread M11 x 1, 32Nm or 23.60 foot/lb

Maintenance Information

  • Gearbox oil: Type A (Dexron) or F Automatic transmission fluid. 10 fluid ounces (300cc)
  • Spark plug: NGK BR8ES
  • Spark plug gap: 0.8mm

Maintenance Intervals

see owners manual for full info. Recommended intervals:

  • Gear box oil change: 250, 500, 1,000, and every 1,000 miles after that.
  • Chain: 250, 500, and every 500 miles after that. Chain should have 10mm free play in the up or down position.

Transmission Oil

To check for proper oil level, place bike on center stand and loosen weep hole screw (will add photo). Oil should flow in a weeping manner from this hole. If oil does not flow from the weep hole, add oil until it does. To access the oil fill inlet, loosen the oil fill bolt (will add photo).

For oil change Loosen oil fill bolt and remove oil drain bolt (will add photo) to allow oil to drain completely from crankcase. Replace drain bolt and fill crank case until fresh oil weeps from the weep hole. Replace weep hole screw and fill bolt.

If weep hole screw is stripped or otherwise inaccessible, the crankcase holds 10 fluid ounces.

Recommendations for oil Factory specs calls for Type F automatic transmission fluid for standard performance. Based on individual preferences, if you want a quicker shift out of first gear, then the Dextron / Mercon III automatic transmission fluid is suggested. If you want the engine to stay in first gear for a longer period of time prior to changing to second gear, then SAE30 motor oil is suggested. SAE30 is NOT recommended in colder climates due to hard starts. All of these oils can be purchased at any local auto parts store.

Good video on the process: https://www.youtube.com/watch?v=8lJRPwoqMAw

Shim Placement in Clutch

see following image. http://www.mopedarmy.com/wiki/Image:78Tomos053-1.jpg

Performance Tuning

Tomos A55 Performance