Main Motorcycle: 06 Thruxton
Join Date: Aug 2008
Location: Winter Park, FL USA
Other Motorcycle: '69 Bonneville
Extra Motorcycle: '71 Bonneville
11/30/12, After conversations with Mr. Pete and more research into this matter, I have found that none of my following post has merit. I will leave it up just in the interest of honesty but now I find that there is substantial evidence that rings do indeed rotate in their bores.
((((I've read this article before and didn't really agree with it then. I believe that there is value in honing and will offer my reasoning. If it makes sense to you perhaps you will "buy in" to the idea. If it doesn't, that's OK too.
I have run into valve trains which included rotators that made the valves rotate a little each time they opened. I have noted that sprocket and chain systems are commonly designed so that the chain and sprockets "hunt" and take many revolutions to finally get back to the point of making contact with the same tooth and link as before.
However, I have never seen a system which provides for rotation of piston rings during operation. Not saying that there are none, but if there are, I haven't seen them. What I have seen are pistons that pin the ring in place so that it cannot rotate.
I think what happens as rings seat or bed in is that they develop small grooves in the bore, and once bedded, live there until disassembled by someone. These grooves become sort of like a bar code for that ring and are unique to it. If you remove the piston from it's bore I think it would be impractical to think that you could reinstall them, oriented in such a way, that they would ever go back into their respective grooves. I think what would happen is that the ring would ride on it's peaks and on the peaks of the cylinder until it had worn both down to level. But, you would still be left with all the grooves in both the ring and bore.
When you hone a cylinder which has had rings that have seated in it you "grind" away the tiny grooves from the previous ring set. Does this remove some metal? Of course. Under normal conditions you would still expect to have enough material left to keep piston to bore clearances with in an acceptable range. If not, then the cylinder needs to be bored and fitted with over size pistons to recover proper clearances. I would hone a newly bored cylinder if the shop did not do so prior to presenting it to the customer.
The cross hatch that is always recommended has, as an advantage, that it is less likely to produce bigger than necessary grooves caused by metal and stone becoming clogged in the stone. It also, I think, makes it easier for the new rings to "grind away" the tiny, diamond shaped, peaks that this pattern produces. But, I have nothing to back that up with, it's just conjecture.
I am aware of the line in both my '69 workshop manual and my '71 manual that notes if the old rings are to be reinstalled that the piston grooves should be cleaned. This would suggest that Triumph thinks it's OK to reuse old rings.
If I had an engine which I knew had very little mileage on it, so little that I felt the rings had not begun to seat, sure, I would reuse them if for some reason I had to pull it apart.
If , on the other hand I felt that the rings had begun to seat I think I would hone the cylinder and replace the rings. Further more, I think honing a cylinder that is very polished and looks quite pristine is still the way to go for quicker, better seating of the new rings.)))))
Flame suit securely fastened and all closures taped,
Last edited by BirdoPrey; 11-30-2012 at 12:37 PM.