PlanetMinis Forums banner

1 - 7 of 7 Posts

·
Registered
Joined
·
550 Posts
Discussion Starter #1
Hey guys,



I have an XR70 bottom end with an 88CC top end on it. I want to throw it in my Z50. So I did a compression check and after like 10 kicks the bike was on like 20 PSI.



I pulled off the head/cylinder/piston. Piston looks OK, has a good bit of carbon build up, but the rings and the cylinder walls looks great, no gouges, I can still see the crossing marks in the walls.



The head has alot of carbom buildup right on the vales, and it's chiping off like small black rocks. I'm wondering if this might be why the bike has little compression? I need to fix this bike for as cheap as possible. What should the valves look like? Any advice appreciated. Thanks,
 

·
Super Moderator
Joined
·
9,534 Posts
You need to rebuild the head, and clean up the valves. Chances are, the backside of the valves have a carbon buildup, preventing them from closing and seating fully, and killing your compression.
 

·
Registered
Joined
·
550 Posts
Discussion Starter #3
Here are pics. I was planning on wire-wheeling the piston but how can I clean up the inside of the head? The same?
 

Attachments

·
Registered
Joined
·
550 Posts
Discussion Starter #7
I checked the piston/cyl bore, the cyl is like 51.9mm and the piston is about 51.5, is this OK?
 
1 - 7 of 7 Posts
Top