How do I know when to replace my piston, repair my cylinder, or rebuild the top end? Part One

How do I know when to replace my piston, repair my cylinder, or rebuild the top end?

Knowing when to replace, repair or rebuild the top end on your dirt bike or motocross bike can save you hundreds of dollars.

See my previous post on how to check your piston, cylinder here

I love starting in the middle, so let’s look at what I should have asked you to check first.

Replacing these parts before they break can save you hundreds of dollars if the top end fails and damages the bottom end.

Yes that is a hunk of rod hanging out of the filter and yes this is(was) my bike.

Nice picture of what we want to avoid eh?  Wouldn’t you love to avoid that kind of costly repair?

How are you going to do that, avoid such a costly repair?

Easy simple compression or leak down test.

We will cover the two strokes first, because it’s the simplest to test.

When you bike is new or do this now!!  Give your bike a compression test, and write down the number.

This will be the baseline, when this number goes down more that 10% we rebuild the top end.

But, I’m not sure what the condition of my top end is now?

Perform this simple test:

  1. Take a  compression test reading.
  2. Put a small amount of two-stroke oil in through the spark plug hole(don’t add any dirt too please).
  3. Allow it to set for 10-15 minutes.
  4. Take a compression reading, did it go up more than 5-7%,  if so you need a rebuild.

Pretty easy huh?

For all the four stroke guys read this.

That link will cover everything you need to know about doing the leakdown test and how to make a cost effective leak down tester.

And don’t forget the bottom end.  I did the top end on this bike just 5-10 hours of use before the above picture was taken.

Here is a great how to video on how to repair your top end

Video on how to rebuild your top end

We’ll cover what I should have done to prevent that failure





al gnuschke

the dirt bike guru


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8 thoughts on “How do I know when to replace my piston, repair my cylinder, or rebuild the top end? Part One

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