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After the engine rehabilitation, why would the driver recommend not to exceed the driving speed of 40 km per hour for at least two days ??

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  • 1 year later...

Interesting that you are advised 40kph for 2 days...I used to do "hobby" engine rebuilds (some 30 years ago) for friends (FoC) and recommended 500-800 miles (800 -  1300km) below 50 mph and low revs.

It is basically to do with new components requiring time to bed-in. When new they are tighter than in "normal use". By restricting the speed, you restrict the load and minimise the friction-based thermal effects as a result of the initial tightness, allowing the "primary wear" to take place without the components overheating - which would otherwise increase the risk of the engine seizing or worse...broken rings and a need for a rebuild! There are additional considerations too. There are capillary oilways that take time to fill properly and expel all of the air trapped therein.

The key thing is really "mechanical sympathy". There is little makes me cringe more than someone revving a cold engine!

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