Well, in my world, not seeing how bad it is, I would try the hone first, and if it was that bad that it needed to have a machine $hop bore it, I would find another HS40. There should be a groove at the top of the bore, where the top ring stopped to go back down, that should tell you how bad the cylinder is worn.
Here is more than you ever wanted to know about piston rings, but it does show how to gap your rings under checking compression ring gap.
Hastings Piston Rings...Since 1915
You might check here for your rings
Lawn Mower Parts, Small Engine Parts & Much More! | PartsTree.com - Briggs, MTD, Toro, Cub Cadet, Husqvarna, Troy-bilt...
Hastings Piston Rings...Since 1915
You might check here for your rings
Lawn Mower Parts, Small Engine Parts & Much More! | PartsTree.com - Briggs, MTD, Toro, Cub Cadet, Husqvarna, Troy-bilt...
Ray....this is the proverbial "opening a can of worms"....
The "annular" groove is at the top like Tom said it's created by the rings stopping and changing direction...this is usually a pretty good indicator of how worn the cylinder is... The grooves or scratches running from top to bottom are referred to as "score marks"...usually from dirt entering through the air filter or dirty oil, hard carbon deposits breaking loose, etc.....the +.010 rings are available on Ebay..are you planning on running a matching +.010 over piston also in order to maintain the proper piston to wall clearance??....then things start getting a bit pricey those oversize pistons aren't cheap.... boring and honing properlly requires complete disassmbley of the motor..hmmmmm...that connecting rod has some scores in the big end...might as well replace all the bearings, seals and gaskets while we have it apart....:doah:....then wash thoroughly and prep for re-assembly....gonna run up a tab before your done....:deal:
my experience has been that if the motor has significant time on it, the bore will wear tapered to the extent that you can't get it straightened out honing or boring out just .010...usually need to go +.020...your engine guy has probably worked on a lot more small engines than I have so he may some tricks up his sleeve to hone it out "enough" to make it run ok...but running a set of +.010 rings on a std. piston seems a bit sketchy...then again, it's a lawn mower engine not a Formula One engine..... and you can "get away" with a lot.!!!!
The "annular" groove is at the top like Tom said it's created by the rings stopping and changing direction...this is usually a pretty good indicator of how worn the cylinder is... The grooves or scratches running from top to bottom are referred to as "score marks"...usually from dirt entering through the air filter or dirty oil, hard carbon deposits breaking loose, etc.....the +.010 rings are available on Ebay..are you planning on running a matching +.010 over piston also in order to maintain the proper piston to wall clearance??....then things start getting a bit pricey those oversize pistons aren't cheap.... boring and honing properlly requires complete disassmbley of the motor..hmmmmm...that connecting rod has some scores in the big end...might as well replace all the bearings, seals and gaskets while we have it apart....:doah:....then wash thoroughly and prep for re-assembly....gonna run up a tab before your done....:deal:
my experience has been that if the motor has significant time on it, the bore will wear tapered to the extent that you can't get it straightened out honing or boring out just .010...usually need to go +.020...your engine guy has probably worked on a lot more small engines than I have so he may some tricks up his sleeve to hone it out "enough" to make it run ok...but running a set of +.010 rings on a std. piston seems a bit sketchy...then again, it's a lawn mower engine not a Formula One engine..... and you can "get away" with a lot.!!!!
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Ray before you make any moves make sure the crnkshaft length is the same....Tecumseh made a bunch of them I know the hs40's on the RUPP's were longer to accomodate the TAV......seeing as that's the original lighting coil motor I would say it's worth it to have it rebuilt and keep it with the bike.....even though the stampings are only on the shroud I like knowing something is all original:thumbsup: