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On the subject of tight oil control rings... one thing I learned 'the hard way' is Pre-'71 pistons have a shallower oil ring groove.I also discovered this on some original AE Powermax pistons, and I think the High Comp Dunstall (GPM) pistons may be the same, but I can't lay my hands on them right now.I just checked the Service Bulletins and bikes prior to 146584 were affected. After this the Factory went to spring expander type oil rings with a deeper groove in the piston.I think they persevered with the slotted pistons up to '72, so another reason for ditching the early pistons!
On the subject of tight oil control rings... one thing I learned 'the hard way' is Pre-'71 pistons have a shallower oil ring groove.
I also discovered this on some original AE Powermax pistons, and I think the High Comp Dunstall (GPM) pistons may be the same, but I can't lay my hands on them right now.
I just checked the Service Bulletins and bikes prior to 146584 were affected. After this the Factory went to spring expander type oil rings with a deeper groove in the piston.
I think they persevered with the slotted pistons up to '72, so another reason for ditching the early pistons!
