cylinder honing

[BLB350]

I recently lost the machinist I have used for years, whom I never had any machining intolernances with. Last winter I used a new shop to bore and hone a set of 95" TC cylinders. I ran them with out checking them this last summer. No problems except that the engine sounded like my 1970's iron head sportster with forged pistons that used to be set up with .006" piston clearance - sounds like obvious piston slap (haven't torn down yet to check). I bought another set of cylinders on EBay (and invested in some torque plates) and had the new shop bore/hone them. I asked for .0025" clearance on the JE forged pistons with a .0001" +/- tolerance. They did the work and called me to tell me that they got them to within .0015" +/-. I had a long talk with them about the process/equipment, told them I would pay for them but I would not use them, as they are .0035 in the middle of the cylinder (w/ torque plates installed). They refused to take my money, have reviewed the procedure they used and want to try it again with another set of EBay cylinders (their cost). The boss is not happy with his employees work and really wants to make it right. They use a Sunnen hone with the automatic feed (cylinder is rigidly mounted and hone strokes at certain rate to give correct cross hatch), not the Sunnen hone that my old machinist used (for connecting rods - hand feed cylinder on fixed hone). It seems to me that the hone will spend twice as much time in the middle of the cylinder as it does at each end if it is moving up and down at a fixed rate. Could this be the reason that they are ending up with a larger bore in the middle of the cylinder? Second question (a stupid one!): What should I shoot for, for an acceptable tolerance?
I will receive a new set of used cylinders in a couple of days and intend to install torque plates on them (they are low mileage 88" cylinders taken off a customers bike that have the original HD bore in them). It will be interesting to see how straight the stock bore is. Brian

[BLB350]

I recently lost the machinist I have used for years, whom I never had any machining intolernances with. Last winter I used a new shop to bore and hone a set of 95" TC cylinders. I ran them with out checking them this last summer. No problems except that the engine sounded like my 1970's iron head sportster with forged pistons that used to be set up with .006" piston clearance - sounds like obvious piston slap (haven't torn down yet to check). I bought another set of cylinders on EBay (and invested in some torque plates) and had the new shop bore/hone them. I asked for .0025" clearance on the JE forged pistons with a .0001" +/- tolerance. They did the work and called me to tell me that they got them to within .0015" +/-. I had a long talk with them about the process/equipment, told them I would pay for them but I would not use them, as they are .0035 in the middle of the cylinder (w/ torque plates installed). They refused to take my money, have reviewed the procedure they used and want to try it again with another set of EBay cylinders (their cost). The boss is not happy with his employees work and really wants to make it right. They use a Sunnen hone with the automatic feed (cylinder is rigidly mounted and hone strokes at certain rate to give correct cross hatch), not the Sunnen hone that my old machinist used (for connecting rods - hand feed cylinder on fixed hone). It seems to me that the hone will spend twice as much time in the middle of the cylinder as it does at each end if it is moving up and down at a fixed rate. Could this be the reason that they are ending up with a larger bore in the middle of the cylinder? Second question (a stupid one!): What should I shoot for, for an acceptable tolerance?
I will receive a new set of used cylinders in a couple of days and intend to install torque plates on them (they are low mileage 88" cylinders taken off a customers bike that have the original HD bore in them). It will be interesting to see how straight the stock bore is. Brian

Edited by BLB350 2007-01-16 5:48 PM

[Mike]

The stock bore will not be too out of round due to the thicker liner, but "seasoning" (basically stress relieving since they start life new with no heat cycling) will show up some change. If full stroke is used the bore should be straight and typ. within .0003 (you'll get .0001+ from temperature changes alone). The Auto stroke Sunnen is very sophisticated and should easily hold these tolerances. The good news is that with used cylinders, they will be seasoned and once bored correctly they'll hold their shape fairly well. Because of increased fin (more rigid cylinder) area and the addition of piston oilers, we can fit pistons closer than in the past. Also, because of larger bore sizes, the cylinders tend to outgrow piston expansion and so, again, allow for closer fits. We routinely fit JE forgings at .0018-.0020 in Twin Cams with a platuea (spl?) finish hone.
Thanks, Mike