Two Stroke Motocross

Two Stroke Motocross Forum => Technical => Topic started by: joel95 on August 15, 2010, 01:48:32 AM

Title: How often should i do a top end?
Post by: joel95 on August 15, 2010, 01:48:32 AM

Just wondering how often everybody dose there top end. When i bought my bike (2007 yz 125) it had apperently had a top end done and still needed to be run in. I'm now up to 16 hours...was thinking of doing it at 20 and then every 20hours after that, is that a good figure to go by?

Thanks.

Title: Re: How often should i do a top end?
Post by: ford832 on August 15, 2010, 04:53:19 AM

That's a good number.It depends on what you're riding though as opposed to just time alone.I usually rering between piston changes.

Title: Re: How often should i do a top end?
Post by: eprovenzano on August 15, 2010, 05:27:52 AM

It truely depends on how hard you are the the engine, and if you keep the filter clean.  I like to use a compression tester as the basis for knowing when its time.  I test the compression after the top end is complete.  This give me a base line to measure from...  From time to time, throw the tester back into track the drop in compression.  I've always used the rule when i'm down 40 pound of pressure its time to redo the top end.

Just my $.02 worth.

Title: Re: How often should i do a top end?
Post by: maicoman009 on August 15, 2010, 07:26:48 AM

Joel if you do need the top end done by all means do the rings also! The last top end I did on my KTM I installed a Wiseco piston kit which comes with a piston,rings & circlip so in my book if you have to change your piston you should always re-ring the top end.
 As far as having 16 hours on your bike & rebuilding the top end @ the 20 hour mark leads me to believe that you either race MX on a regular basis or your running the ol' YZ like a scolded dog!
 If you feel like your bike needs a new top end it would be worth it to do a compression test on it like enprovenzano said before you buy a piston kit anyway.Damn my mouse is frozen i probably have to log out....

Title: Re: How often should i do a top end?
Post by: Cheb44 on August 18, 2010, 04:06:17 PM

I second the compression test method, I feel many of us do top-ends to often because we read somewhere we needed to do them all the time.

The compression test is the best indicator.  I changed mine about 40 lbs under as well.

Title: Re: How often should i do a top end?
Post by: Hondacrrider on August 18, 2010, 04:57:23 PM

Check your compression first for sure. Also, you may not need to replace the piston, you may only need to replace the rings. I heard from a guy at the local riding area that if you want to keep your 125 competitive, change the rings every 10 hours, and the piston every 30