hours for a rebuild top end 2005 KDX200 H series

[DeKay]

Can you please tell me from experience the hours you run your bikes between top end rebuilds.

I have a 2005 H series KDX200 and put an hour meter on it we purchased it was in very good condition when bough but now it has done 50 hours of trail riding only, not racing.

It still runs fine but need some advice on hours i need to do the top end please ?. Also when you are doing the piston ring change can you feel the rod to see if the bottom end needs doing and if so any advice will be gratefully received on how to do this. regards

[kdxsully]

Most people say 20 hours I think, but every bike is a little different. My yz says 15

[bufftester]

There is no hard and fast rule. I know guys that have put over 100 hours on a 2T top end just trail riding and still had better than 100psi compression. I also know guys that race that are changing top ends every 5-7 hours. IMO do a compression check and see what the numbers are.

As for the 2nd question you should not be able to feel any up/down play in the big end. There will be some side to side play, but you need to use feeler gauges to check which isn't too hard with the top end off.

[kdxsully]

^^^ he’s right. 20 hours is just a rule of thumb I guess. I think it’s more about the wrist pin bearing than anything.

[SS109]

I don't change top ends until I notice the compression starting to drop off significantly but this is with forged pistons only. On my old KDX200 I had about 180 hours on the top end (forged piston) and it only dropped about 15psi so it was still good to go. Current KDX220 has over 200 hours (again, forged piston) and still no significant drop in psi. I trail rode both bikes every weekend and raced them on occasion. Best thing to do is a compression check after you get your new piston broken in and then change when you see a big drop in psi (25psi and I do a top end) or you start to notice power falling off, whichever comes first. Stock usable range is 151psi to 95psi so use that as kind of a guide line on how far you can go. Never had small end rod bearing check out of spec either.

That said, I won't run any cast piston over 100 hours max even if the compression is perfect. Cast pistons have a tendency to shatter without warning when they fail and they will fail.

[kdxsully]

I don't change top ends until I notice the compression starting to drop off significantly but this is with forged pistons only. On my old KDX200 I had about 180 hours on the top end (forged piston) and it only dropped about 15psi so it was still good to go. Current KDX220 has over 200 hours (again, forged piston) and still no significant drop in psi. I trail rode both bikes every weekend and raced them on occasion. Best thing to do is a compression check after you get your new piston broken in and then change when you see a big drop in psi (25psi and I do a top end) or you start to notice power falling off, whichever comes first. Stock usable range is 151psi to 95psi so use that as kind of a guide line on how far you can go. Never had small end rod bearing check out of spec either.

That said, I won't run any cast piston over 100 hours max even if the compression is perfect. Cast pistons have a tendency to shatter without warning when they fail and they will fail.

I’ve seen some nasty photos after small end bearings fail. Pretty nasty. Enough to scare me into splurging 20 bucks.

[SS109]

I’ve seen some nasty photos after small end bearings fail. Pretty nasty. Enough to scare me into splurging 20 bucks.

No doubt! Maybe what I typed didn't come across right. I replace the rod little end bearing every time I replace the piston. I just don't go in to the top end only to replace it.

[KDXGarage]

Did you buy it new?

Are there 50 hours on the current piston?

[DeKay]

thanks for the reply i didnt buy in new but it was in very good condition when i got it and the 50 hours have been since i owned as i put a meter on as soon as i got it.

[KDXGarage]

Sooo, you have no clue besides "X + 50"? I would think it's time to check it.

[DeKay]

Yes will check will be a good winter project new top end and clean the KIPS thanks again.

[javjacob]

I do the top end on every used 2 stroke I buy. I would bet the KDX top end would be good for 400+ hours of trail riding. I always use Wiseco forged pistons.

[KDXGarage]

I do the top end on every used 2 stroke I buy. I would bet the KDX top end would be good for 400+ hours of trail riding. I always use Wiseco forged pistons.

400+ hours?? Sorry, I had to.

javjacob.png (1.07 MiB) Viewed 2803 times

[kdxsully]

HA.

[SS109]

Hey, I'm sure there KDX's out there that have way more than 400 hours on a piston and rings. I think I bought two of them!

[javjacob]

400 hours isn't out of reality. there are plenty of KDX's that still have the original top end in them. There is one guy on the KDX facebook group who says he has 1100 hours on his top end... I could see that being a stretch.

[kdxsully]

That’s witchcraft.

[doakley]

400 hours isn't out of reality. there are plenty of KDX's that still have the original top end in them. There is one guy on the KDX facebook group who says he has 1100 hours on his top end... I could see that being a stretch.

I know that guy. Not a stretch. Rides almost every day and races. Although I’m not suggesting his results are normal by any means.

I also redo the top end on any bike I buy. I want to KNOW what is in there. Also use Wiesco pistons. Don’t have an hour meter but keep a running check on compressions.