How do I know when to replace my piston or repair my cylinder?

If there is one item of dirt bike maintenance that I feel many people don’t understand is when to replace the piston & rings.

Or when to repair, replate or replace your cylinder.

We would love to avoid a situation like pictured below.

In order to keep your engine making the best power and reliable operation. (Seizing mid-jump can be a pain)

Keeping proper piston to cylinder wall clearance is Critical.

  • This fit is best checking my measuring  the size of the piston with a micrometer.
  • Measure the cylinder bore with a  bore gauge.

The cost of  a quality set of tools to make a precise measurement can cost over $500 or more.

For most rider’s I think your best bet is have a competent machine shop or bike shop make this measurements.

Check your owner’s – service manual for the tolerance and specification for allowable clearance.

Sometimes the cylinder bore will wear.

Many manufacturers use a hard Nickasil hard plating on the cylinder bore.  This plating is very hard and durable.  Sometimes though the plating can be damaged.

  • Look for scratches, marks, wear(the aluminum will show up as a dull grey area if the plating is worn away. (often near the ports on a two-stroke)
  • Vertical lines or gouges can occur when foreign matter gets caught in the piston-ring area

Deep gouges can be repaired by rewelding, then  machining the cylinder and finally replating the cylinder.

Often an overbore is required to make smooth usable bore possible.

Sometimes a cast iron liner can be installed to get a repaired bore.

These cast iron liners are often misunderstood.   Cast iron does not conduct heat as well as aluminum

If you have a bike prone to overheating this will make it worse.

Depending on the bike, replating or relining the cylinder is generally cheaper than replacing the cylinder.

Always keep in mind the cost of the repair vs cost of replacing the bike.

See my article here to help you make this determination.   http://alsdirtbikegear.com/?p=229

Don’t forget as the above picture showed, don’t forget to check the bottom end.

You spend money on the top end and within a few hours the bottom end  lets loose, you’ll feel like you have wasted that money.

Check the bottom end too.
Al Gnuschke

The Dirt Bike Guru

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One thought on “How do I know when to replace my piston or repair my cylinder?

  1. Pingback: How do I know when to replace my piston, repair my cylinder, or rebuild the top end? Part One : alsdirtbikegear.com

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