Honda-SOHC

Thats not detanation as the cause, what happens is some idiot PO reved the nuts off it when cold and the rings expand to quickly so the top one shatters into pieces, this widens the ring groove then flame passage and heat finish it off.

Used to happen quite a bit on 250K4 and CB175's

I had exactly this on a 550 years ago.  My friend bought a bike that had been standing for a year or so.  Unfortunatley, the seller had taken the bike for a blast to make sure all working OK.  My friend bought the bike but soon complained that it wasn't running properly and was smoking.  When I investigated I discovered that there were broken rings on all four cylinders.  Luckily, they had stayed in place and not scored the bore and a new set was all that was needed.

 thanks for the hints !!

I can't remember racing it when cold,

BUT,from now on will keep it below about 5k for a couple of miles at least,

thanks

John

they could contact me,

my CB500 is running ok now,

also has 4 pipes,

very original,un-restored ,52k miles

ask them to E-mail me for pics

John

John,

I recently had some rings for the 550 from silvers.
The rings are slightly different if you look at them one is square and the other slightly tapered.
It tells you the installation sequence in the manual if you have one, the rings are marked with a "N" this needs to go to the top if I remember correctly.
Hope this helps.

Regards,

thanks,I looked Very Hard,and found the "N"s,as luck would have it,I had fitted them correctly,
as far as the cause,
check out this link,
http://www.motorcycleclassics.com/mc-how-to/project-cafe-rebuilding-a-1973-honda-cb500.aspx#axzz2Vx8B1Md3


a CB500/4 with almost the same issue,
my piston wasn't quite as bad,but the diagnosis is "detonation" ,I guess severe "pinking" ??
my bike never seemed to suffer this,but would over advanced ignition cause it ?
I run Boyer electronic and also a much bigger plug gap,(0.033th) as it supports a bigger spark,
also gives great low/mid range punch,
maybe I should retard the ignition a few degrees ??

thoughts and comments please,

John

It's quite unusual to break rings on a 4 stroke engine if everything is normal, possibly more influenced by the assembly last time it was built.

Also a possibiltiy if it had been stored for a long time for the bore/rings to rust and cause damage when someone tried to start it.

the history,I have owned the bike since 1977,

the barrels have never been disturbed,the head came off about 20k miles ago,after I damages a couple of valve stems while changing
the cam-chain,the bike gets regular use,although only between 2-3,000 a year,

looks like a head-off job !!

 just as summer is finishing!! LOL

 I have recently been forgetting to add "lead substitute" to the fuel,

 and have got what appears to be sticky valve !!!

 as the motor get warm/hot,after cruising around 6K rpm for several miles ,the engine runs rough,noisy tappets,and feels like its on 3 only,

spitting in the carb,and spitting in exhaust.I still have 4 - 4 pipes,

after checking,setting tappets at 3th inlet/4th exhaust,and re-using Morris lead substitute again,the bike runs well again,

is it common?
if so,I hope you take notice,and use an additive as well,


John Webley

PS,I should say I have a '74 CB500/4. and the handbook does say it needs "some" lead in fuel

you can always try a reverse fill/prime,


detach caliper,remove piston,fill caliper with fluid,then insert piston,press in,and watch the bubbles appear on the mastercylinder,.

this may be a drastic last resort.

sometimes,if you use just one pad in the caliper,and pump it full,then push the piston all the way in,this also helps to dislodge air .

John