Running In An Engine

Since the correct way to run in a new engine or brand new parts is a much-discussed subject, I have decided to make a ‘how-to’ explaining what I think is the best way to do so.


First of all, don’t listen to people that simply state that a 100 mile running-in period is necessary for every engine.

When looking at the best way to run in a new cylinder, the main difference can be found between alloy and cast-iron cylinders.

When your cylinder and/or your piston are new, their first few minutes are the most important. Start up your engine, and let it run idle/low revs for some time until it reaches normal operating temperature (~50 C). After that, shut off your engine and let it cool off completely. Repeat this procedure once more, using slightly higher revs.
After this your cylinder is ready to be used. Every time you start up your engine you need to let it reach the normal operating temperature gently before you start giving it full throttle or high revs.


Cast-iron cylinder kits require a running-in period for about 50 miles. This running-in means changing the engine revs frequently, and not using full-throttle for long periods of time. So it actually is possible to drive top speed for a short while during this running-in period. Just keep in mind that you change the load on your engine frequently, as well as your engine revs.


Having your carburettor set up properly is essential for every two-stroke engine. Always make sure you maintain the proper jet and mixture settings in your carb, in order to avoid your engine running lean.

Lubricating your new parts when your engine is under normal running conditions, the oil that’s in your mixture will leave a small lubricating oil film on essential parts like your crankshaft bearings. This oil film will remain there even when you shut off your engine.

Whenever new parts (i.e., a new cylinder kit) are fitted, simply mounting them would result in these parts running without any lubrication the first moment you start your engine.
Therefore, always put some good two-stroke oil on your new parts before mounting them. In addition to this, you could add an extra bit of oil to your fuel the first time you fill your fuel tank. This will decrease the wear on new parts that haven’t been properly finished (i.e., cylinder ports without any proper bevels).


Proper lubrication is not only essential during your running-in period. Using good quality two-stroke oil will increase the performance and reliability of your engine parts! Therefore, always make sure you’re using the proper oil/fuel ratio and oil quality for your specific setup.

Hope you find this helpful.



Shiny Red Tuning

Unit 24, Merretts Mill Industrial Centre






Tel: +44 (0)1453 298212


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