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When is it that you need a top end?

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I owned a 05 yz 125 for about a year. I seriously feel bad for that bike i changed the air filter in that one year about 5-7 times. Oil was changed maybe twice, but i never had a problem with that bike! I own a 4 stroke now and change the oil every 2 rides and filter every ride, but i want to get back on the 2 stroke but a ktm 150sx :thumbsup: . Now i owned the 2 stroke for a year or more and rode every single week on either long rides or shorter rides but in between the week as well. I never felt a power difference or anything, no hard starting, no bog, nothing so how do you know when it needs a top end. I started reading some of the 2 vs 4 stroke threads and they say you have to replace the top end a lot more on a 2 stroke

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...would you be able to hook us up with a link where we'd be able to see figures for different models?

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I owned a 05 yz 125 for about a year. I seriously feel bad for that bike i changed the air filter in that one year about 5-7 times. Oil was changed maybe twice, but i never had a problem with that bike! I own a 4 stroke now and change the oil every 2 rides and filter every ride, but i want to get back on the 2 stroke but a ktm 150sx :thumbsup: . Now i owned the 2 stroke for a year or more and rode every single week on either long rides or shorter rides but in between the week as well. I never felt a power difference or anything, no hard starting, no bog, nothing so how do you know when it needs a top end. I started reading some of the 2 vs 4 stroke threads and they say you have to replace the top end a lot more on a 2 stroke

The thing about changing top ends is that you don't notice the lack of power until you go from a worn out top end to a brand new one. The difference is quite astounding. Judging by how much you rode I'd guess that your bike was definitely in need of a new top end, maybe even two. Two sets of rings within a year with that amount of riding for sure. Once you get a new bike, put an hour meter on it the day you get it. Change top ends every 40-50 hours. Bottom ends every 200-300 depending on how hard you ride.

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how do you do a compression test?

Acquire a compression teater. this one costs less than $15 at harbor freight:

image_13660.jpg

Remove the spark plug. Select the correct adapter (the one that matches the spark plug threads in the cylinder head) and screw it onto the tester. Screw the tester into the spark plug hole. Open the throttle all the way (WFO) and then kick the bike over a few times. Record the reading and compare it to the specifications in the service manual for your bike. If your reading is lower than the specs call for, you need a new top end.

Edited by zlathim
Forgot to mention WFO throttle, thanks Top!

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I used a Snap On tester one time, couldn't get any consistent results, so I gave up.

I figure if I am thinking it may be time for one, it probably is. HR's, how hard you ride, and/or physical condition of the piston will tell the tale on when to do it.

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I tested my recently acquired beater 300EXC and it shows 130. I'm told it needs to be 150?

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Shouldn't you hold the throttle wide open to?

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Shouldn't you hold the throttle wide open to?

Excellent point. I forgot that detail. It makes a difference in the test results.

Edited by zlathim

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My '09 200XC-W w/original piston and rings will have about 140 hrs. on it at the end of this riding season. 75% of my riding has been in the low to mid rpm range (lots of single track). The only time it sees mid to upper rpm range is riding road sections from one trail section to another, like on dual sport rides. Oil of choice has been Amsoil Dominator @ 50:1.

I was planning on putting in a new set of oem rings this winter. Should I do both piston and rings? How do I know if I need to go up to the next piston size/rings?

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My '09 200XC-W w/original piston and rings will have about 140 hrs. on it at the end of this riding season. 75% of my riding has been in the low to mid rpm range (lots of single track). The only time it sees mid to upper rpm range is riding road sections from one trail section to another, like on dual sport rides. Oil of choice has been Amsoil Dominator @ 50:1.

I was planning on putting in a new set of oem rings this winter. Should I do both piston and rings? How do I know if I need to go up to the next piston size/rings?

Yes, definitely a complete top end rebuild. Unless your cylinder is damaged, you don't need to go up any in size.

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Yes, definitely a complete top end rebuild. Unless your cylinder is damaged, you don't need to go up any in size.

Gasket kit too or just use the old ones?

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some people dont realize they need a new top end because the loss of power changes cn happen so slow over pretty long periods of time that it isnt noticeable. one thing i usually do is push the kickstarter with my hand and if its easy to push its time to change it. it shouldnt be easy to push by hand. another thing is that ANY 2 stroke with a good top end and proper jetting should start in 1-3 kicks tops, if u kno ur bike is jetted properly and its not starting in 1 to 3 kicks most of the time, then change the top end. And another obvious sign is if u can tell the bike is running weak, change it.

your yz probably didnt need a top end. I owned a 2003 yz 125 for 2 years and didnt change the top end. granted i was 14 and stupid when i first got that bike, and it prolly needed to be changed when i sold the bike.... but fact of the matter is that bike ran as good as when i got it for at leasst a year and a half.

now i race a ktm 250 2 stroke. i do over 20 2-hr harescrambles a year, plus practiceing, plus winter riding and only change my top end once a year. ktms and yamahas top ends will last longer than any other brands because they r the most bullet proof bikes out there

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