I have made several 2 stroke diesel model aero engines, which are amongst the most critical for cylinder bore finish.
I fine bore to get as good a finish as I can, feeding by hand.
Boring a deep hole usually means that there is a very slight taper along it, the bottom end is slightly larger, which is ideal.
I then turn an aluminium lap which is a very tight fit in the bottom end of the bore, ie will just about enter it.
This has several groves turned in it to hold lapping paste. I use fine valve grinding paste.
The lap is held in the chuck and rotated at low speed, the bottom of the liner is fed onto it and gradually worked along, using oil and paste.
This needs great care as the cylinder can seize onto the lap, and start spinning with it.
You end up with a smooth grey finish, the cylinder must be thoroughly
cleaned, an ultrasonic cleaner is ideal.
The lap can be made expandable by sawing down lengthwise, after first
drilling and tapping for a
grub screw, which when inserted will expand the lap.
I fine bore to get as good a finish as I can, feeding by hand.
Boring a deep hole usually means that there is a very slight taper along it, the bottom end is slightly larger, which is ideal.
I then turn an aluminium lap which is a very tight fit in the bottom end of the bore, ie will just about enter it.
This has several groves turned in it to hold lapping paste. I use fine valve grinding paste.
The lap is held in the chuck and rotated at low speed, the bottom of the liner is fed onto it and gradually worked along, using oil and paste.
This needs great care as the cylinder can seize onto the lap, and start spinning with it.
You end up with a smooth grey finish, the cylinder must be thoroughly
cleaned, an ultrasonic cleaner is ideal.
The lap can be made expandable by sawing down lengthwise, after first
drilling and tapping for a
grub screw, which when inserted will expand the lap.
