M21 JP pistons - need opinions based on experience!!
I am pulling together a M21 engine and have a barrel at +60 thou and worn out so I have two options, reline for a standard or use a JP +80 thou piston. Has any one had experience of JP pistons…..
Re: M21 JP pistons - need opinions based on experience!!
Gday Scott. My M21 has a JP piston in it, My bore was STD but worn. I honed it parallel and JP made a piston to suit with the correct clearance. I checked the ring gaps,perfect. That was about 15 years ago and thousands of miles. I also have JP pistons in my Tiger 110 with no problems.
Mick Australia,
Re: M21 JP pistons - need opinions based on experience!!
I have a JP piston in my rigid 350 AJS trials bike. I fitted it when I rebuilt the engine in about 2011, but it was very heavy as bought. We removed quite a lot of material from inside the crown to get the weight down. The whole skirt of the piston was coated with a baked on teflon type coating. The barrel was bored to give about 3 thou of clearance. It has been faultless ever since and has done lots of hard work since.
