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Carb issues
M0WBY:
But measuring different ring sets on the same bore won't make any difference as they will all have the same gap because that is decided by the wear on the bore surely? Or am I being stupid? Do you see why I am struggling to get my head around it?
Otherwise the only test is the spingyness of the ring and whether it stays compressed in the ring groove?
Perhaps I am thinking about it too much!
tom400f:
Thinking is good. I am only thinking that if a ring itself is worn then it won't be as wide as a new one and its end gap when inserted into a bore will be larger. I would also imagine a narrower ring would be less "springy". (Note I am choosing my words carefully - I'm not talking about the ring clearance in the piston groove - then I would talk about a ring being "thinner" - just saying).
Since ring wear has been cited (if your bike ran lean for any length of time) then its worth measuring, at least comparatively for now across the sets you have. Likewise the bores - if they are all similar then chances are your barrels are good.
When you get a new ring set you will have absolute measurements and you will know whether you need more.
M0WBY:
--- Quote from: tom400f on October 23, 2012, 10:39:50 AM ---that if a ring itself is worn then it won't be as wide as a new one and its end gap when inserted into a bore will be larger
--- End quote ---
Why? The ring does not wear on the ends surely? Surly how worn the bore is determines the end gap. Larger end gap = more wear on the bore.
It seems the main issue is how willing they are to uncompress in the bore the rings are. This I would guess is determined by the carbon in the ring gap holding the piston ring closed and allowing compressive gasses down the side of the rings?
I am speculating that the hardness of the steel has something to do with this as well because a less springy ring are easier to compress and might allow gasses past?
tom400f:
--- Quote from: M0WBY on October 23, 2012, 11:12:53 AM ---
--- Quote from: tom400f on October 23, 2012, 10:39:50 AM ---that if a ring itself is worn then it won't be as wide as a new one and its end gap when inserted into a bore will be larger
--- End quote ---
Why? The ring does not wear on the ends surely? Surly how worn the bore is determines the end gap. Larger end gap = more wear on the bore.
--- End quote ---
No it wears on the edges, gets narrower and has to expand more to reach the bore. (btw I wasn't trying to suggest it gets "shorter")
As Oddjob says, your measurements at the moment will combine ring and bore wear, until you get a new ring set. Hence I was suggesting eliminating one of those and then the other... just to see a bit more how things are.
Bryanj:
A piston ring wears in two ways:-
(1) They actualy move up and down in the ring groove as the piston changes direction at top and bottom of stoke and strange though it is the steel ring wears more than the alloy piston.
(2) The friction between ring and bore will wear both the bore and the outside of the ring so that the ring has to expand more to touch the bore hence the ring gap gets bigger.
Now in 30+ years(a lot of those in Honda dealers) i have rebored a lot of Hondas but 99.99% of those rebored were dur to siezures not wear! I can only remember a PF 50 years agp that actually had a wear rindge at the top.
What Tom was saying is if you use only one ring on all the bores you are getting atrue indication of bore wear as all the rings will be worn slightly different
Also if you measured all the rings in only one bore yoou would be able to see if one set was a lot more worn than the others
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