need rings - what size?

bgee · Post by **bgee** » Fri Sep 27, 2013 10:01 am

Hello,

I am new to this forum, I have a CA160 that I am working on to rebuild the top end.
Bike started fine, idle fine, throttle response on the stand ok, however have power loss when driving, and never really could get past 35 mph in any gear. Carb was rebuilt and valves adjusted, no difference, then I checked compression, both cylinders gauge out at 120psi equally in each cylinder. I understand should be closer to 160 psi correct?
So I tore down engine, and check pistons and cylinders, no major issues, pistons look fine, cylinder's there was no scratches or gouges or marks, just really shinny! I had both cylinders Hone and Cleaned up. I measured both cylinders per manual locations and again both equally measure 49.97mm. I assume this is still Stock Bore. I took existing rings and put in cylinder's
to measure ring gap per manual for each, and gap ranges from .013" to .018". manual states should be .006" . My question is what size rings do I get, stock?
thanks for your replies,

G-Man · Post by **G-Man** » Fri Sep 27, 2013 11:22 am

Standard bore is 50mm. So just get a new set of std rings.

Unless the bike was smoking a lot you may want to search for other causes of power loss.

G

bgee · Post by **bgee** » Mon Sep 30, 2013 8:53 am

Thank you for your input, I will give the standard rings a try, I mostly was concerned was he compression readings I was getting, Since I don't have a specific ca160 shop manual, the compression should be 160 psi correct? The power loss I feel when trying to drive it, is that the engine feels like it cant get up the rpms. the lower range is fine but not much mid range or no top end, the engine will just bog down and stay in lower to mid range at best. I replaced the plugs and checked after riding for maybe 20 to 30 min, and seem decent not running lean.

I am attaching picture of the piston, don't know if that indicate anything. the cylinder's were not tarnished like piston , just shiny smooth.
thanks!

G-Man · Post by **G-Man** » Mon Sep 30, 2013 1:57 pm

Certainly looks like you are getting some blow-by but the lack of performance you are seeing is quite substantial.

35mph seems very poor. I would have thought the bike would exceed 50mph even with a tired engine. Even with the measured 120psi I would expect better performance than you are getting,

G

LOUD MOUSE · Post by **LOUD MOUSE** » Mon Sep 30, 2013 2:08 pm

Get oversize pistons and rings and bore the cylinders.
It's time! ...................lm

bgee wrote:Thank you for your input, I will give the standard rings a try, I mostly was concerned was he compression readings I was getting, Since I don't have a specific ca160 shop manual, the compression should be 160 psi correct? The power loss I feel when trying to drive it, is that the engine feels like it cant get up the rpms. the lower range is fine but not much mid range or no top end, the engine will just bog down and stay in lower to mid range at best. I replaced the plugs and checked after riding for maybe 20 to 30 min, and seem decent not running lean.

I am attaching picture of the piston, don't know if that indicate anything. the cylinder's were not tarnished like piston , just shiny smooth.
thanks!

mike in idaho · Post by **mike in idaho** » Sat Dec 28, 2013 1:42 pm

Did you measure the cylinder for actual wear?, new standard pistons & rings may be all you need. Is the air cleaner clean? Any obstructions(mouse nests, etc.) in the exhaust? Carb main jet clean? If you close the choke part way when running wfo does it run better or worse?Timing advancing as it should?, use a strobe light to verify that the spark advancer is working. Valves adjusted to spec? It should do better than 35 mph, even with 120 pounds of compression.