Navigator Pistons/Barrels

hello the piston to cylinder bore tolerances normally are around 3 thou with the piston fitted in the bore with no rings fitted,  as for ring gap these are no more than eight thou to ten thou, in most engines and I am no god of the mechanical world   I am just good at engineering over the last forty-five years,  And I hope this gets it somewhere near were you want to be,  on your navigator  but 40 thou is the next to a new sleeve-fitting  and a visit to  A engineering company,  and big costs,   yours  Anna J      

Hello Dave,

I had to purchase and fit a new pair of pistons as the ones fitted when I purchased the bike were scrap.  I purchased a pair of JP Pistons 20 thou oversize, they came with literature (copy attached) stating clearance of 4 thou.

Dave.

I’m pretty sure JP pistons need a bigger clearance than original Heptolite ones. 

Different pistons may be of different alloys with different expansion rates, so the piston should come with the clearance. But, even so, a piston described as +.040" should fit a cylinder overboard by .040". The clearance (perhaps .004") should be manufactured into the piston.

If your bore is too big by a few thousanths of an inch, only you can decide whether you prefer to put up with a bit more piston slap, or with not having a rideable machine! The manufacturers' data is aimed to give the best solution.

Hello the original pistons used by Norton where the same  piston maker as for Rolls Royce and these where BHB piston only the best, and Hepoilte did copies of them later on and years later they were consolidated into AE pistons based in Bradford plant west Yorkshire there is no finer pistons then these and JP and GPM pistons are both copies off copies and both are that bit heavier then the Originals But the Original pistons are still out there the fun is finding then its like being in a hunt for rare birds    and its much nicer finding a set that make you smile and knowing you have a good set ,   yours Anna j

Hi Navigators, can anybody tell me the bore of the standard barrels please, I am considering a re-bore and the people doing it for me have asked for the measurement but I haven't been able to find it. You seem people of good knowledge. 

Anna

I like a good hunt but I challenge you to find 2 +60 heptolite pistons! Back in the day I only found one, (a heptolite cracked) , I ended up with one bore at +60 and one at + 40, interestingly the engine ran fine with no noticeable increase in vibration! 

63 mm

Peter