Smoking CB100N please help!

[Ben_Lamb95]

Hi im new on here but I really need some help with a smoking CB100N. Its burning engine oil like there's no tomorrow, I took the rocker cover off and it appears there's only one valve seal which is on the exhaust valve but from drawings ive seen this appears correct, anyone know if there should be one or two and any general tips would be much appreciated as ive had it apart 4 times now!

[Bryanj]

The only reasons they burn oil is valve guide wear or incorrect piston/bore tolerance

[Trigger]

Will need a top end re-build. How much oil is in: there's no tomorrow? 

[Ben_Lamb95]

There was no play at all in the valves, im waiting a compression tester to turn up to see if that shows anything, i think it may be the rings...

[Bryanj]

If there is definitely no play in the guides you need an oversize piston kit and rebore, suspect its been low on oil and nipped up

[Ben_Lamb95]

The cylinder looks in perfect condition with no scoring I was hoping to just fit new rings maybe slightly oversized rings? The piston has a good tight sliding fit so I didn't think this was the problem but im running out of ideas. Does anyone know if it should have one or two valve seals?

[tom400f]

http://www.dotheton.com/downloads/Honda%20CB100%20CB125%20CL100%20SL100%20CD125%20SL125%20Workshop.pdf

That link works. Page 25 in the PDF (numbered page 21 in the manual, Fig 53) says there is only a seal on the exhaust valve.

[Trigger]

The cylinder looks in perfect condition with no scoring I was hoping to just fit new rings maybe slightly oversized rings? The piston has a good tight sliding fit so I didn't think this was the problem but im running out of ideas. Does anyone know if it should have one or two valve seals?

This is basically a CB100 K1-K2 engine and should only have exhaust valve seal. You can't just put over size rings in on a STD piston. This needs to be measured up and you may get away with new STD rings and a cross hatch on the bore.

[Ben_Lamb95]

That pdf is brilliant, so much better than the useless haynes manual! Putting over sized rings on a standard piston was a stupid idea because the piston still needs to be the right size for the cylinder, hopefull have it apart again tomorrow or the weekend so ill check the piston/cylinder, thanks again for the help!

[tom400f]

It's not clear if you have lifted the barrel? May be you have a broken ring but it's still retained in the piston.

As Bryanj suggests, there aren't many reasons for burning oil. Is your head gasket OK and not breached to an oil way and you didn't notice?

Manual is the genuine Honda one. That site is quite good for resources, though probably all in Ash's dropbox by now 

[Ben_Lamb95]

Just had it apart again, the first thing i noticed was the piston rings are all inline... when i put it together all of them was at 120 degrees to each other, any ideas anyone? I also measured the piston and cyclinder and they are both within the tolerances

[Trigger]

Have you measured with the rings in the bores ?

[tom400f]

Trigger you mean the end gap of the top ring removed from the piston and placed square in the bore?

[Trigger]

Trigger you mean the end gap of the top ring removed from the piston and placed square in the bore?

Yep !

[Bitsa (Ralph Wright - RIP)]

Use the piston to get it true in the bore
Cheers
Bitsa