Top End Rebuild (Need Help!)

[Rockey5000]

After 3 years of riding, my friends CR80 needs a new top end. We looked into it a bit and have found pistons like SB is a .02 oversize and SC which is a .04 oversize. The cylinder has never been bored, so why would an oversize piston be nesscesary? The smallest I could find was a Pro X SB .02 oversize piston. Is this the correct one? What will come with the piston kit, should we order a Wristpin Bearing too?Will we need to buy a seperate gasket set too? Thanks in advance for any help!

 

[IrishEKU]

Try outTJ Parts Express. You should be able to get all your stock parts and much more! My Brother(Moose95) and I have had great service from them and no problems.
Hope this helps.
Happy Trails,
PK :p

 

[Joepro9]

3 years, I think you will need a oversized due to wear on the cyl wall. You should do piston, ring, wristpin, circlips wp. bearing. It probably needs bored too. I am sure u can find a gasket set. Also definaly check the rod for play. Wiesco is good and also dont over look stock. I hear good stuff about forged pistons, esp on 80s. They seem to be prone to break off skirts.

 

[Rockey5000]

so what over size do you think, SB,SC? How do we know if it needs to be bored?

 

[Joepro9]

Id bet 100 bucks it needs bored, might just do it to be safe, talk to a mechanic about boring, other than that, hone it and get the proper tools to measure the cylinder. This will tell you what size piston you need. I dont know alot about 80s, but i am suprised it lated that long on the piston, but anyway I do no know how long the cyl walls go without wearing alot. If you just bore it, you can get the piston to match the bore.

Also look at the cyl if it really scratched up, or is scortched or dirty, hone or bore. It will at least need hone I can tell you that.
Wow thats alot to take in! If I confiused you tell me ans I will explain it better, I just typed as it came to me lol.

 

[yzeater]

Here's another two cents to add to the pot. Once you get his cylinder apart, take it to a machine shop, and have them measure it. Then you will ACTUALLY know what size piston he needs. You can buy one based on the measurement you get from there

 

[Rockey5000]

Thanks for all the posts, I think we will take it apart and get it measured. If its scratched, he planned to bore it anyway. Can it be bored to a 100, I think this would help performance.

 

[Joepro9]

bore sizes are .010, .020 etc, I dont know if and 80 will bore up to 100, seems kinda big.