sure it has been asked a thousand times...

Personally, I never changed top-ends on my KX until I felt the compression lower. When it started getting easy to kick, and I could notice a difference, I changed it.

Not sure if that helps or not. :)

colorador1 said:

I searched the forums for thirty minutes to find answers to these questions.

how many hours before a top end rebuild.

what is a lot of hours overall on an engine.

i am looking at a 2000 yz250 with about 50 hours is this a lot, or a little. I understand it depends on the riding, but I do not think it has ever been raced.

I have had many motorcycles...but never any two-strokes, therefore i am an idiot when it comes to the above questions.

Thanks a lot for the help/answers

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I guess 50 hours really depends on what you consider a lot or a little. I guess thats a good amount of riding time. If you are buying it from him, I would deffinetly do a top end job before you start riding it seriously.

2-stroke top end jobs are a walk in the park. I recently rebuilt my friends YZ 125 top end with him, and when we were done, the only thing we were left thinking was "thats it?!" - As long as you know just a little bit about automotives, the basics and read up on some things (eric gorrs books and website are good!)and you have the general idea of how to put things together, it should be a piece of cake.

I've owned a lot of two strokes in my time, and I do 90% trail riding and 10% moto. Trail riding is much easier on a two stroke engine than moto, in my opinion. Generally speaking, a trail rider rarely revs the engine hard for extended periods of time, while a guy who motos is usually wringing out the engine hard the entire time.

That being said, I never kept track of the number of hours I put on a top end. Our rule of thumb was to change the top end once per year. Using this time-line, I've never blew up an engine and I've never pulled a piston out that was cracked or marred in any way. If I had to make a guesstimate, I would say I put on approximately 120 hours on an engine per year.

Unless the seller can produce receipts to prove they very recently replaced the top end, I always put a new top end in a used bike first thing for several reasons:

1) Can't trust the previous owner kept accurate track of the number of hours on the engine.

2) Can't trust the previous owner cleaned the air filter correctly and on a regular basis.

3) Better safe than sorry. A sleeved/new cylinder and possible bottom end isn't cheap, especially after shelling out a few $grand$ for a "new to you" bike.

4) It helps you to keep track of your maintenance hours from a clean slate, with a bike you know is properly prepped.

Again, I'm not a moto expert; but If I were a moto guy I would not go past 75 hours of engine run time before I replaced the top end.