Looking for an M21 +20 piston - now i have seen some new ones ranging in price from £89 down to £60 from a well known BSA WD dealer , any recommendations from you folks for a quality piston welcome .

Seen a new Aussie made JP+20 piston at approx £100,are these types worthy of the price tag ?.
Or are the cheaper ones just as servicable on these old plodders ? .

The GPN (Italian) pistons are reasonable quality but can be a bit on the heavy side...It is possible to lighten them a little though (if that is necessary for the M21 version...)

I have never used a JP Piston but I have heard they are also on the heavy side in some cases and there may be issues with the rings...

The 'other' pistons on the market come from various sources I think...I have heard of pistons that suffer from 'over expansion'...in other words to stop them nipping up you have to hone so much out of the cylinder it's outside of its tolerances...

However, my experience when I've tried whats on offer is only that the rings weren't very good...In other respects the ones I used were fine...Dimensionally they conform to the originals so I just fitted NOS piston rings when I used them....

The fact is there are no aftermarket pistons to replace standard versions that I would unreservedly recommend without some caveat....Ian

email (option): ian@wright52.plus.com

Thankyou