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Running In a Rebuilt Motorcycle Engine


Running In a Rebuilt Motorcycle Engine
John H Glimmerveen Licensed to About.com

What Is Running In?

During a restoration, the engine and gearbox will most likely have been rebuilt with new parts. As with a new bike, a rebuilt engine will require a period of "running in" or "bedding in," which is the process of meshing interconnecting engine parts. But how should that running in period be undertaken, and how long should it last?

When a new bike is sold at a dealer's, the new owner will receive advice about the running in phase - either from the sales staff or via the owner's manual. But a classic motorcycle may be too old, or the original owner's manual may not have survived, for there to be any information on the run-in phase.

The original owner's manuals, on machines from the 80s onward, all followed similar run-in recommendations. The new owners were instructed to keep the engine revs below about one third of the max available (2600 rpm where the limit is 8000, for instance) for the first 500 miles.

This limit was then increased to one half of the revs available for the next 500 miles, and finally, the owners were cautioned to take the revs higher only periodically. In addition to riding their machines to these rev limits, the riders had to take their machines to a dealer for frequent oil changes: 500 miles, 1000 miles and 3000 miles, typically.

Check the Oil Pump During Running In

With the classic bike, the mechanic will have assembled it by liberally coating all the touching parts--that is the crankshaft, pistons, gears, even the oil pump gears.

But before the engine is running for the first time, it is very important to check that the oil pump is working and the oil is circulating (See the article on Triumph 'C' series oil pumps). Checking the oil pump in this way should be undertaken with the spark plugs removed. However, the plugs should be grounded and the mechanic must be cautious as pressurized fuel will be ejected from the open plug hole.

If at all possible, this phase should be done without the ignition on. At the very least replace the plugs back in their caps and ground them away from the opening into the cylinder.

Having rotated the engine for a short time (15 second bursts will help protect the starter motor - where fitted), the oil level should be checked. This is particularly important with dry sump systems. When the mechanic is sure the oil system is working correctly (and the plugs have been refitted), the engine should be started but the revs kept as low as possible.

The engine temperature should be increased until it is at the normal operating range. With an air-cooled bike, the normal operating range will be achieved after about three minutes of running time.

Running In the Gearbox and Clutch

Besides the engine, the gears and clutch will need to be run-in. In addition, the clutch may need to be freed the first time the bike is to be ridden, as the clutch plates tend to stick together after being soaked in oil.

To free the clutch, the mechanic should rock the bike backwards and forwards with first gear selected. While doing this, he should pull the clutch lever in. This will free off the clutch and help to avoid the bike lurching forward as fist gear is selected and possibly damaging the gearbox. (This also applies to bikes that have stood for some time).

Running in a gearbox requires the rider to be positive with his selection method (to avoid grating the gears). He should also change gears frequently.

As recommended by manufacturers, the engine and gearbox oils should be changed after the first 500 miles and again at 1000 miles. This is particularly important for unit construction engine/ gearbox designs, where the engine and gearbox share common oil.

Finally, at around 1000 miles, the cylinder head bolts and casing bolts should be re-torqued.

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