cl175 cylinder bore

[sancho]

So, the compression on my bike has been gradually deteriorating form about 140psi down to 125psi. Also the top end started leaking oil and gradually the motor just became nasty. I decided to take the motor apart and rebuild it over the winter. Took the top end apart. Cylinder walls seem ok, no scoring or scratches. I can still see the previous cross hone on the cylinder walls.

Measured the cylinder bore and pistons. Here are the results:

Cylinder bore: 52.01-52.02 Manual calls for: 52.00 - 52.01 (recommends rebuild if 52.10)
Piston width: 51.60 Manual calls for: 51.55 - 51.60

I feel like I am just barely within spec. Is it worth it to go for a piston and ring kit? take it to a machinist to bore it out? maybe + 0.25?

Or should I just go with stock ring set, clean everything, hone the cylinders and put it all back together?

I do plan on servicing the head, cleaning everything, all ports, cleaning and lapping valves, replacing the springs...etc.

Hopefully this should bring my compression back up.

Your thoughts and recommendations are appreciated!

Here are some pics of the really dirty cylinder and head.

 

[Tim]

How confident are you in your measurements? Measuring cylinders and pistons is tricky as you want to measure the cylinder from top to bottom, check for roundness etc.

Based on your numbers it all looks perfect. Not just within spec. Your piston is at the fresh end of the range as is the cylinder. Fresh rings and hone should be fine.

That being said I always end up rebuilding my project bike engines with bigger pistons just because its a onetime thing. Get it done and that's that.

I'd take the cylinder, head and piston to a machine shop. Get them to freshen up the head and measure the piston and cylinders while they're at it. Get their advice.

 

[xb33bsa]

like tim said the bore needs to be measured where it is worn ,and if you are use venier or digital calipers then you cannot get accurate enough, and they will only give you the size of the unworn band at the top ,and from the bottom you cant get where the rings slide,even experienced machinists will not reli on calipers for a precision measure
the only way for a home shop, if you dont have an inside micrometer (and it takes a learned skill to use it)to get an accurate clearance is using .001'' and .0015" feeler gauge strips, used carefully you can determine an accurate running clearance at different locations in the bore
but still far easier to take it to a pro

 

[sancho]

thanks for the advice guys! exactly the kind of info I needed, will take it to a machine shop tomorrow to get it accurately measured, will report back

 

[barnett468]

it needs to be measured in 3 different locations around the circumference like 12 o clock, 4 o clock and 8 o clock.

it also need to be measured around 8 - 10 mm down from the top, then right near the middle, and also 8 - 10 mm up from the bottom.

this will give you a total of 9 measurements.

 

[xb33bsa]

it needs to be measured in 3 different locations around the circumference like 12 o clock, 4 o clock and 8 o clock.

it also need to be measured around 8 - 10 mm down from the top, then right near the middle, and also 8 - 10 mm up from the bottom.

this will give you a total of 9 measurements.

that is some thorough methodology ,it sure seams like good information though especially to check a new fresh bore, how precise the job a guy paid for was,my experience is the area you mention up near the top of ring slide usualy tells the whole story on a used bore,that is whether or not its a go or no go as that is normally the area of highest wear

 

[barnett468]

my experience is the area you mention up near the top of ring slide usualy tells the whole story on a used bore,that is whether or not its a go or no go as that is normally the area of highest wear

yup, and if one simply measures the top in one clocking position and does the same at the bottom and it is out too far then of course they can stop, but if these areas are within spec i always measure the others since the cylinder is already off the engine and it only takes a couple minutes to check . . i'm kinda lazy so i prefer not to have to do things twice.
.