navigator re bore limits and nos shop soiled ?

NOS is the acronym for New Old Stock. So they are as close as you can get to original Norton parts, they've been boxed and sat on shelves since shortly after Noah sailed. Boxes will therefore be grubby and tatty, but contents should be fine.

I have no experience of buying pistons, well not this century, but have read on this forum that aftermarket pistons now leave a lot to be desired. As others have commented, even stuff with the brand names we might recognise from way back bears little comparison to original manufacture.

Given the chance, I would happily buy NOS. As a generalism (and so shoot me down in flames), a lot of stuff "back then" was better made. The Electra I am curently trying to resurect has been rattling around the country with me in numerous crates and boxes since before 1975, and most of it is now cleaning up and serviceable with not a lot of trouble.

Good luck with your Navvy rebuild Richard.

I think 60 tho over is the biggest but they are hard to find, having the barrels relined might be an option. 

Dan 

My navigator barrels are plus 0.060 oversize and recently suffered a seizure which lightly scored the right one . The pistons could be used again after a little work polishing the affected area . However they are after market ( unknown maker) and are considerably heavier than the original norton pistons , and this affected the balance factor.  As I have a pair of almost new standard pistons , I am looking to have the barrels re sleeved . I have learned that Triumph 5T pistons are readily available  at 63 mm ,and around £ 100 a pair, and the gudgeon pin dia is the same at 11/16 ins   .However the piston crown height is approx 2mm lower so the compression would be slightly less .The valve cut outs on the piston top match the Norton ones , so no problem there . The high compression version of these Triumph pistons have a raised dome top , so could possibly be used given a little machining in that area .    I recently contacted a local machine shop who undertake reboring etc , about re sleeving , but he was unable to obtain ready made sleeves , and to have a pair cast and fitted would cost in the order of £500.!  Andy Sochanik has recently put me in touch with a guy who has carried out re sleeving on Navigators before , so I am now waiting to hear if he can help .

Barry,

Not sure if these would be of use to you?

I have 2 of these from my Morini 350. Morini's have a standard bore/stroke of 62 x 57mm, so very close to the Navi. I replaced these with some new liners when I was unable to get new oversize pistons at some time in the past, so their condition is 'worn 62mm" - a vernier measures them at 62.1-62.2mm, but to do the bore size properly needs an internal mike which I don't have, so take these sizes as an estimate only. They are certainly less than 63mm.

The bore overall length is 120mm, O.D is 72mm, flange at top is 80mm and the flange is 4mm thick. The chamfer at the bottom (cam lobe clearance on a Morini) begins at 106.5mm from the top. 

If they would work for you, you can have them for the cost of the postage to you.

Regards,

George.

I needed new pistons for my Norton and also looked at some early Triumph versions as an alternative. I think the crown height was not suitable and possibly the small end was not quite right. I then discovered that some of the old Ford pistons were very close in size. I had to purchase a box of 4 at 63.50mm plus 40 thou for my barrel. The biggest difference between them and the originals is the huge increase in weight.  But after a little work was done to them they are now up and running ok in my engine. Checkout the attachment for two alternative versions.  I don't think I will going drag racing with these pistons inside my engine.

Looking at those images of the Ford pistons it would appear that the pins are thicker than the Early Norton ones. I faced a similar thing trying to get the weight down  on some Commando pistons to match the orriginal Atlas ones .  Was the Atlas and early Commando prone to pin failure  and the pins beefed up?.

Richard,

I was lucky enough to buy one barrel and two sleeves for my Jubilee from NOC shop and had a company called Meridian Services  near Cambridge re-sleeve bore and hone the barrels to standard size.

I seem to recall that Meridian said they could supply sleeves and I know they can press them in so it might be worth giving them a call. They did an excellent job for me a were very reasonably priced.

http://www.meridianengineservices.co.uk/

Dennis

Try, whenever you can, to use Original Hepolite pistons. Their alloy is specially formulated to run in air-cooled engines - which run hotter than water-cooled engines.

Triumph (motorbike) pistons normally have a smaller wrist pin, so bushing the conrod is needed, and the crown is lower (as mentioned above). They are also much heavier, so vibration (already not good) will become much worse.

Ford Car pistons are not recommended - they are designed to run in water cooled engines.- as are a lot of non-original pistons that are becoming available now.

Andy

Putting aside the problem heptolite had with cracking pistons back in the day, I wonder if larger clearances would solve the problem of using water cooled pistons in an air cooled bike? 

Do we know what the differences in the Aluminium are?

Dan