Yamaha KT-100 Engine


Yamaha KT-100 Engine:

  • Junior and Senior classes
  • Cylinder volume 97.6cc
  • Bore/Stroke 52mm x 46mm
  • Carburator Walbro WB-3A
  • Compression 7.9:1
  • Monocylinder, 2-stroke, Pre-mix oil-gas
  • Electronic ignition
  • Single, forward inclined
Yamaha KT-100 Engine Outline Drawings

Yamaha KT-100 Engine Outline Drawings

When you buy a new Yamaha KT100 it’s not quite ready for competitive racing. A minimun of preperation is required. You will find in these documents some hints and tricks to help make your motor a bit more competitive and get a better performance out of it.

Motor Maintenance Frequency

In order to get the most out of your motor it is necessary to maintain your motor on a regular basis. Use the following chart to guide your self on the frequency to change parts on your Yamaha motor. NOTE: These numbers are in hours.

« Performance » Maintenance « Pleasure » Maintenance
Piston 5 15
Ring 5 15
Piston pin and Bearing 18 20
Circlip 5 15
Motor Base
Base Bearings 8 14
Bearing Seals 8 14
Connecting  Rod 20 30
Rod Bearing and Pin 20 30
Washers 20 30

Idealy, the piston, cylinder and ring should be inspected after every race. However, every 2 races is an acceptable compramise. In general, the piston should be changed every 2 to 4 races but if   the measures are still within tolerance and the piston does not show signs of wear, you do not need to change it.

Use the same routine as for the piston on the ring. However, if the ring gap is greater than 0.015”, replace it.

The motor base should be inspected and you should consider revising it every 4 races when using stock bearings. Particular attention should be to the oil seals and bearings. Note that certain brands of bearings are better than the originals. These are recomended as they are longer lasting (6 to 8 races) and will contribute to the perfomance. The down side is that they are more expensive. The connecting rod and bearings should be changed every 8 to 10 races.

Use the chart on this page to guide you in your preventive maintenance. Note that certain conditions such as a wet race day may contribute to premature wear and may require some parts to be changed sooner.

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