Jump to content
Sign in to follow this  

new top end?

Recommended Posts

When do ik when i need a new top end for a fourstroke? and how often will it need replaced usally (hours)? same for the bottom end? and about how much does it cost to replace for a 250? sorry for all the questions thx tho:ride:

Share this post


Link to post
Share on other sites

? well i hav not bought a bike yet but im loking at a ktm sxf 250 and honda crf 250 and they say how many hours are on the bike and i want to know how close it is to needing a new top end. lik i found a really nice ktm wit 60 hours on it and i also found a honda year older tho with a fully new motor with 30 hours on it and so on.

Share this post


Link to post
Share on other sites

There's a few varibles on when this should be done.Type of riding you do and how hard you are on the bike. Racing maintence/manuals say 15hrs on the piston/rings.This is because a piston starts losing power from the first time it's fired up. Unless your a pro rider you will not notice/need to do this. 50 hrs is a safe time frame and most guy's change out at this time or depending on the Brand of bike, change your piston when you need valves since your allready half way in there. Some Brands have longer valve life so the 50 hour mark is time. I've streatched the last KXF 250 pistons(trail rideing) over 116 hrs on the OEM piston before we just did the valves and piston for safety/piece of mind.No smoking and everything looked good when pulled apart. The second CP 14.0 piston we streatched to 124 hrs before it cracked between the rings on one side.Upon pulling it apart the intake valve coating was worn off.It was time.Never shimmed the bike. At 240 combined hrs between top ends it was too scary not to rebuild from the bottom up even though the rod did not have a lot of play in it and still in spec. Notice I used the word "streatched". Most guys will not recomend these intervals. The key thing here is preventative maintence before it cost you a lot more money for a grenaded motor. We ride trails only and I feel I was not to risky yet risky enough. Any time one of my bikes reach 100 hrs I start thinking about a top end and know it's just a matter of time.I don't think I'll Streatch a 250 over 115 hrs on a piston again.Lucky it wasn't a long tow and I could drive the truck most of the way there. The bike was 30 miles away from camp. Now I have a 450 that just hit 100 hrs but still feel comfortable with it.

Moral of the story. How lucky do you feel? Or do it before it cost to much.

Good luck.

Share this post


Link to post
Share on other sites

well lets say i buy a bike that has 50 hours of rideing on it altogether (trails) . at 100 miles i should replace the piston ring and gaskets? or the piston 2? ha sorry im slow with all this

Share this post


Link to post
Share on other sites

Let's see if I can say this in a fragile enough way as not to hurt Big Reds feelings.Hondas are high maintence. That's all I'm gonna say.

If you bought a bike with 50 hrs on it and it Hasn't had a piston in it in those hrs I would put one in it since you don't know how the bike was treated. At 50 hrs I would do the piston not just the rings. Probably check the valves and put in a new cam chain then you know your good to go for awhile.

Share this post


Link to post
Share on other sites

its really just when you want to. i race my 07 crf250r hard and got to around 175-200 hrs on it with the stock top end and it ran fine the rings just leaked alot so i had to add oil after every ride. and you dont replace thing on a dirt bike by miles, its by hours. so i guess you should replace the top end around 100 hours if your not riding it hard? it all depends. and you should definetly get a piston kit with the piston and rings. and maybe a set of kibblewhite SS valves. but that isnt really needed

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Reply with:

Sign in to follow this  

×