Honda GX160 Tech Talk:
Honda GX160 Tech Talk: Running in your engine
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
So how do we prepare an engine and 'run it in'?
- We could over rev the engine immediately it was started
- We could overheat the engine
- We could seize the engine
- We could accelerate wear of the bearings
- We could encourage valves to drop and cause mechanical damage
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.
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.
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.
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
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
The engine is now 'run in' and ready for race preparation, But that's
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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