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Doctor Tkart | How to replace a piston on an engine

3
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How to replace a piston on an engine

14 August 2016
Approximately every 40 litres of mixture used, it’s necessary to replace the piston, the true “heart” of the engine. Follow the advice of the doc to find out how
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IN SHORT
Open the cylinder. Remove the old piston and put in the new one. Close the cylinder and head assembly. Check the squish.
time 45 MIN
difficulty DOABLE

Tucked away at the heart of the engine, where temperatures are hellish and forces reach maximum power, the piston is one of the most stressed parts of the engine and, therefore, need to be kept an eye on more than most. Its replacement is an operation that all kart drivers will have to reckon with, sooner or later. There are two main reasons for replacing a piston: they either break or wear. The recommended period for replacing a piston is more or less every 40 litres of mixture used.
Such is the case for amateur kart racers, while in other cases it is advisable to change the piston after each race. The rules apply to any kart engine, be it an old 100, an OK (formerly KF) or a KZ. On this occasion, the Doc is using a direct drive 125 cc engine by Iame, but the operations are more or less always the same.

TOOLS FOR THE JOB
POINTED TIP TOOL
12 MM COMBINATION WRENCH
13 MM T-HANDLE WRENCH
GAUGE
TORQUE WRENCH
OTHER: feeler, tin wire, clip mounter, engine oil
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1
STEP
10 MIN.
easy

Let’s start with an overhaul: firstly, use a 13 mm T-handle wrench to remove the cylinder head. To do so you need to unscrew the five nuts that fasten it in place (some newly homologated engines use six nuts for added safety) and physically remove the cylinder head.

1.

Unscrew the nuts that fasten the engine cylinder head

2.

Remove the head from the cylinder

3.

Unscrew the nuts that fasten the cylinder to the crankcase

Then, use a 12 mm combination wrench to unscrew the four nuts that fasten the cylinder and slide it off the crankcase, making sure not to break the gasket. At this point, the upper part of the connecting rod and the piston still fastened to it will be visible.

4.

Slide the cylinder off the crankcase

5.

The piston, still fastened to the connecting rod, is clearly visible

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