Topic: CB500 help

[mcv80]

Hi all,
Starting to rip the engine apart for the winter and I am looking for anything that I should pay attention to and replace while I am in there. It was burning oil pretty badly when I took it off the road and the clutch was not all the great either. So I am hoping on being able to do a quick hone and put some new std. rings in and be ok. Any opinions? Also I am looking into the clutch kit that dynoman has but I am not sure that if it will work. Any help with that would be appreciated. The bike is a 72' cb500/4. I am planning on doing a cb650 cam and some mild head porting. so any suggestions on valve springs? If there is anything anybody can add to this I would appreciate it alot.

Thank you

[Greggo]

Check out the project threads for some inspiration on tuning enhancements.  A 650 cam and some light porting makes a huge 'seat of the pant' improvement.  Just the 650 cam in my bike (no porting) worked wonders.

Check that the primary chain hasn't been rubbing on the interior of the cases.  Replace it while you're in there (no tensioner on these engines).
Replace your cam chain (with an HD piece)
Cam Chain tensioner pieces.
Check your shift dogs for wear.


If you're going big bore, you can use the 550 cylinders in place of the 500's.

[dave500]

use the standard valve springs.,new plug caps and electronic ignition,if it was burning oil pretty badly id be looking at a rebore,see how it looks when its apart,,pictures please!you can use the XL125 pistons in these 500s and gain compression.

[japscrap]

what year xl125 pistons?

[dave500]

all years i think?i had a 500 bored to first oversize using xl125 pistons,make sure you dummy it together and check your valve clearance to piston,,i actually had this head machined in the combustion chamber to lower the compression slightly.

[grcamna2]

use the standard valve springs.,new plug caps and electronic ignition,if it was burning oil pretty badly id be looking at a rebore,see how it looks when its apart,,pictures please!you can use the XL125 pistons in these 500s and gain compression.

I think what Dave said about a re-bore is the right way to go...cylinders do get out-of-round and just honing it w/ standard rings will be a waste of money; go for at least a .5mm(.020in.) over-bore...that way all your 4 bores will be completely round & you'll be starting fresh; it's better than having to do it over again because your new rings won't seat-in correctly after 500 miles.....ask me how I know.

[dave500]

a point two five overbore will true it all up unless youve have had an explosion and really need to go .5,either way its costs the same there abouts.

[dave500]

sometimes a quick hone and new rings isnt enough,the piston and bore can be too worn to last much further letting the piston rock too much in the bore,this rounds the edges of the new rings away plus they wont seat properly,itll smoke again,if it all measures up ok theres nothing wrong with just rings,,or even new pistons and rings.

[mickey6]

use the standard valve springs.,new plug caps and electronic ignition,if it was burning oil pretty badly id be looking at a rebore,see how it looks when its apart,,pictures please!you can use the XL125 pistons in these 500s and gain compression.

I think what Dave said about a re-bore is the right way to go...cylinders do get out-of-round and just honing it w/ standard rings will be a waste of money; go for at least a .5mm(.020in.) over-bore...that way all your 4 bores will be completely round & you'll be starting fresh; it's better than having to do it over again because your new rings won't seat-in correctly after 500 miles.....ask me how I know.

+1
i had oil burnin like all hell after swappin rings and not having the jugs machined only honed them. Do it right the first time

[mcv80]

Happy new year everyone. Thanks for all the responses. Every little bit helps. I got the top end taken apart and found out why I was burning so much oil. My exhaust valves are covered in oil soot and carbon buildup. No pictures yet will get them to you asap. The cylinders and pistons don't look to bad at all but I think I am gonna go with the xl125 pistons. What do you think the compression ratio is it? How much did you end up taking out of the head?
Thanks for all the feedback.

[dave500]

i had about half a mil taken off that outside edge of the cumbustion chamber,it was running a little close and carbon build up would have no where to go,i had no worries with the valve to piston clearance with the standard gaskets,i got 10.7 or 8 compression ratio,,use good premium gasoline only.here you can see the plasticine has really been squeezed out around the edges,with the head on i could rotate it less the plasticine over and over and the piston wasnt striking the head but i thought its running too close anyway.

[mcv80]

Thanks for all the help Dave500 and everyone else. Just one last question. I  dont know much about the xl125's just curious if there is any specific model i need to get or year. What year year am I looking for. So on. Any and all details welcome.

[dave500]

any year 125,if i was to do it again id just go with the normal oversize piston,with that much static compression a bigger cam would make it all work better,i always felt the compression was too high with the stock cam and with 200psi on the guage i think i was right?and with a flat top piston you wont have to machine the head,although it only cost me 70 bucks for that.