Tech Tips
Honda GX160 Tech Talk: Running in your engine

Honda GX160 Tech Talk:
Running in your engine

by Brian Pollard

Why do I need to 'run in' an engine for racing and how?

If an engine is to be used for racing it must perform outside the boundaries of the designers specifications. To perform at the higher rev range and power band the engine must be 'run in' correctly. Let us first consider what we could do wrong with a new or reconditioned engine. So how do we prepare an engine and 'run it in'?

Ensure sufficient oil is present in the crankcase. The oil level should be checked with engine level, ie both filler plugs at same height. The oil should be half way up the oil filler plug hole. Too much will cause the engine to smoke and too little will starve the bearings of oil and cause excessive wear.

Check inlet and exhaust valve clearances are not too wide or too tight. Clearances of.004" for inlet and .008" for exhaust is a good starting point. (valve setup is a complete subject in itself)

Check kart gearing for any particular circuit, ask at the circuit or via the UK Karting notice board, to ensure correct revs are reached. Gear the kart to give the engine a slightly easier life than it will get at racing speeds. ie gear it slightly higher, with less teeth on the back sprocket.

The optimum gearing for a circuit is the one that allows the kart engine to reach a designated maximum revs quickly enough to accommodate the length of the 'straights' and not over rev, (go over the designated engine revolutions per minute), on the longest straight or fastest corner, for extended periods.

To check revs per minute. (rpm), a rev counter is essential. Many people will manage without a rev counter but will never get the best out of the engine. How else can you confidently say that a one tooth gear ratio change is working effectively? Lap times are notoriously inaccurate because of the many variables of traffic, kart set up, weather conditions etc etc Get the gearing right and the lap times will drop as you get used to the engines power band. Clues to gearing... are you over revving? Then reduce number of teeth on back sprocket. Are you left wanting another gear, try a smaller back sprocket. Are you left on the line at the start? Try a larger back sprocket and or set clutch for faster take up. Are you out accelerated between corners? If it is the kart and not your driving style then try a larger sprocket on the rear axle.

Lets cover the first engine start up...

Put petrol on, you have put petrol in haven't you, move choke lever to fully closed, turn ignition cut out switch to 'on'. Hold throttle in mid position, with hand control. Pull start engine, with kart rear wheels clear of ground, and no onlookers draped over the kart's tyres or leaning on axle Move choke lever back to a quarter open position. Hold engine at 1,000 rpm and blip engine to 2,000 rpm occasionally.

Safety note:
The centrifugal clutch will engage at approximately 2,100 rpm so be aware of sudden axle/ wheel engagement and rotation.


Safety note:
Any loose objects attached to the tyres, including gravel, will now be thrown off, backwards and upwards. Keep clear and safe by guarding your eyes and warn others of start up by stating what you are about to do. Just imagine you are resuscitating a person with charged up paddles and you shout CLEAR, before sending high voltages through the recipient! Dramatising this event will prevent unnecessary injury and keep friends, friends.


Back to that first engine start...

With the engine running, and your hand operating the throttle, gradually decrease the choke until it is fully off. Run the engine steadily at around 2,000 rpm with occasional blips to around 4,000 rpm. If the engine does not sound as if it is complaining then its time for a check of loose nuts and bolts, oil leaks, and if all is OK then take the kart for a run on the track.

Safety note:
It will now be very hot so take care, especially around the exhaust.


Drive the kart with the engine revving to a maximum of 4,000 rpm, at short bursts, for twenty laps. Come in to the pits, check for oil level, oil leaks and loose nuts and bolts.

Safety note:
It will now be very hot so take care, especially around the exhaust


Drive the kart again for twenty laps with maximum revs of 5.000. achieved by short blasts of power. Return to pits, check for oil level, oil leaks and loose parts. A newly built kart sometimes sheds nuts and bolts so take your time and check.

Drive the kart again but this time rev the engine to 5,500 rpm in short bursts. Does it feel Ok? Is the engine complaining? Is there any flat spots during acceleration? Is the engine reaching 5,500 rpm? All these questions need to be answered before you can confidently race the kart and stand a chance of winning. If the engine does not rev easily or sounds as if it is working too hard at 5,000 rpm then it needs more laps to loosen it up. Look after the engine during the running in period and it will perform well during racing.

Note: an engine that has not been subjected to quick, short, maximum rpm blasts will never be a race winner. The process of quick blasts is to adjust the engine to high stress conditions gradually.

The kart will probably not reach the 5,500 rpm due to the fact it should have been fitted with a slightly smaller back sprocket for running in. Now is the time to fit the correct size sprocket and change the engine oil. The oil will contain minute metal particles worn away during the running in period. This is unwanted and must be replaced with fresh oil.

The engine is now 'run in' and ready for race preparation, But that's another article.

This article was produced by Brian Pollard, author of "Preparing the Gx160 for 'open' racing" which is available on CDROM, in multimedia format, as an e-book, and in paper form. All enquires should be sent to the above e-mail address.


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