HEADS UP!!!

Site upgrade in progress... Core site functions are working, but some non-critical features/functions will be temporarily unavailable while we work to restore them over the next couple of weeks.

Please post any bugs you encounter, but before you do, check to see if it's already listed.

Thanks for your patience while we work to improve the community.

Sign in to follow this  
Followers 0
golybrown

when to replace a piston

9 posts in this topic

i have a08 yz450 and was wondering what the sign of you needing to replace the piston are?

Any help would be appreciated as i am clueless about pistons

Share this post


Link to post
Share on other sites

Tear down, inspection, and measurement are the only sure ways to know, unless there are some outward symptoms of trouble.

Share this post


Link to post
Share on other sites

Compression tests are fairly useless in an engine with automatic decompression. They're fantastically inaccurate in engines without it. Leak down tests are far more reliable. Have one done at a good shop.

Share this post


Link to post
Share on other sites
Tear down, inspection, and measurement are the only sure ways to know, unless there are some outward symptoms of trouble.

So, what would the outward symptoms of trouble be?

Share this post


Link to post
Share on other sites
So, what would the outward symptoms of trouble be?

Burning oil and smoking, poor performance, and possibly some noise.

Share this post


Link to post
Share on other sites

alot of the old bike repair manuels I've read though list, poor starting as a possible sign of a bad piston or rings. Don't over think your way into a repair that didn't need to be made. I've seen alot of yamaha 's with a bunch of hard hours on them, that haven't been touched.

Share this post


Link to post
Share on other sites

You can buy a leak down tester for fairly inexpensive, but the percentage of leakage may not mean a whole lot to you unless you have a new engine to compare it against. Once you see a significant decrease in your leak percentage then you can determine if it's time to rebuild. A leak down tester will also help you diagnose if the compression loss is due to a piston/rings that aren't sealing as well as they used to, or if you have a leak somewhere else, like your valves or a bad head gasket.

I did one on my Husky SMR 510 that I used to have, and was leaking 12%, which I was told was ok to keep running for another season, but without a comparison percentage from when the motor was fresh, who knows.....

that said pistons are cheap, if you have 200 hours or so on your bike, just spend the $150 and do it

here's one on ebay http://cgi.ebay.com/ebaymotors/2006-2009-YAMAHA-YZ450F-TOP-END-PISTON-KIT-W-GASKETS-OE-/110441537034?pt=Motorcycles_Parts_Accessories

not sure why they show a 2 stroke piston in the pic :banana:

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

Create an account

Sign up for a new account in our community. It's easy!


Register a new account

Sign in

Already have an account? Sign in here.


Sign In Now
Sign in to follow this  
Followers 0