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General Minitrail Talk
Wanted/Looking For
OEM Honda cylinder # HM-A2
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<blockquote data-quote="69ST" data-source="post: 184359" data-attributes="member: 5"><p>Clearances have a viable tolerance range. Below that, the piston will soft-seize, above that it'll rattle. It really is that simple. Ring endgap specs leave no room for interpretation, too small, they'll close-up and seize, too big they won't seal. </p><p></p><p>Cylinder concentricity (roundness) isn't usually the issue, though it can be with a worn bore. The issue is getting the rings seated. Even with a freshly-machined bore (which should be perfectly concentric) the rings can compress/expand, that changes their radii. That minuscule mismatch is enough to prevent full contact, resulting in high and low spots. Cross-hatching/deglazing the cylinder increases friction & holds oil...allowing the high-spots to wear quickly and the rings to seat, i.e. make full contact. It works very well but...the rings quickly develop a unique wear pattern. Pull the piston out of the bore, once the rings have seated, and you'll never get them reinstalled exactly as they were...with cylinder now polished from break-in, the rings won't re-seat. For that reason alone, after the first few miles, I install new rings anytime the piston comes out of the bore. The piston, OTOH, is pretty forgiving; it also goes back in the same location/rotation every time.</p><p></p><p>I don't really know what grit hones most shops use. Some of the newer-gen finishes are done with #400-600 grit hones but, that's way outside the scope of anything we do...OEM & race. I farm-out boring & honing to a longtime veteran engine builder. It takes him a few seconds, using a drill & dingleberry hone to deglaze, or finish-hone a cylinder. Cylinder boring is one task I shall never do...a new boring mill is like $30K and I've far more years behind me than ahead of me.<img src="/styles/default/xenforo/smilies/cautious.png" class="smilie" loading="lazy" alt=":cautious:" title="Cautious :cautious:" data-shortname=":cautious:" /></p></blockquote><p></p>
[QUOTE="69ST, post: 184359, member: 5"] Clearances have a viable tolerance range. Below that, the piston will soft-seize, above that it'll rattle. It really is that simple. Ring endgap specs leave no room for interpretation, too small, they'll close-up and seize, too big they won't seal. Cylinder concentricity (roundness) isn't usually the issue, though it can be with a worn bore. The issue is getting the rings seated. Even with a freshly-machined bore (which should be perfectly concentric) the rings can compress/expand, that changes their radii. That minuscule mismatch is enough to prevent full contact, resulting in high and low spots. Cross-hatching/deglazing the cylinder increases friction & holds oil...allowing the high-spots to wear quickly and the rings to seat, i.e. make full contact. It works very well but...the rings quickly develop a unique wear pattern. Pull the piston out of the bore, once the rings have seated, and you'll never get them reinstalled exactly as they were...with cylinder now polished from break-in, the rings won't re-seat. For that reason alone, after the first few miles, I install new rings anytime the piston comes out of the bore. The piston, OTOH, is pretty forgiving; it also goes back in the same location/rotation every time. I don't really know what grit hones most shops use. Some of the newer-gen finishes are done with #400-600 grit hones but, that's way outside the scope of anything we do...OEM & race. I farm-out boring & honing to a longtime veteran engine builder. It takes him a few seconds, using a drill & dingleberry hone to deglaze, or finish-hone a cylinder. Cylinder boring is one task I shall never do...a new boring mill is like $30K and I've far more years behind me than ahead of me.:cautious: [/QUOTE]
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General Minitrail Talk
Wanted/Looking For
OEM Honda cylinder # HM-A2
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