Navigator cylinders

Hello I too are in the process of dismantling the Navigator Engine and now have the barrels of and there 30 over size and one peace barrels So you have Jubilee's barrels try sores a set from the club along with pistons that may do an exchange if you ask or context our Dan. The light twins Man yours. Anna j

John, as Anna says above if your engine does have separate barrels then they are from the Jubilee - another check can do to be absolutely sure is to count the number of cooling fins on the barrels.  The Jubilee has 6 and the Navigator 7.   As your crankcases are stamped 19 then they will be from a Navigator - the Jubilee cases are stamped 17.   The Jubilee stroke is 44mm (1.7323") and bore is 60mm (2.3622") and the Navigator stroke is 56mm (2.205") and the bore is 63mm (2.480").   That means the crankshafts are different and so are the conrods.   The Navigator rods are slightly longer at 4" 5/16" centres and slightly wider at the small end than the Jubilee but I'm afraid I don't know how long they are - perhaps some one who has a set of Jub' rods can measure them and let you know.   Although the crankcases are the same casting the holes for the cylinders will be wider on a Navigator to allow for the wider barrels.   The camshafts are different between the two engines too.    The cylinder heads are again the same casting and the valves are identical but if the cylinders are the earlier ones with the top spigot then they will be machined to fit the appropriate model.   The carb on a Jub' is an Amal 375/43 and the Navi' uses an Amal 375/48.   The other difference is the gearbox and rear wheel sprocket.   The Jubilee has 17 front and 55 tooth rear sprockets and the Navigator 19 and 52.   In my experience there is a significant difference in performance.   With a light weight rider (sadly no longer!!!) a healthy Jubilee might top 70 or a little more on a good day where as a Navigator feels noticeably more spritely and a good one will make 85 or perhaps a little more if you believe the infamously inaccurate speedo!   How does he bike run and perform?   If you want to know more about the implications of a Navigator engine which has been converted to run with a Jubilee crank, barrels, pistons and heads I would ask the club's Lightweight expert, Andy Sochanik - his email is:   lighttwins@nortonownersclub.org    

I hope the above is helpful.   All the very best of luck and let us know how it goes - and perhaps send us some photos!  

Nick                             

Hi John

Nicholas beat me to it, but I agree, first thing is to double check engine and frame numbers,  the frame number is usually on the rear footrest mounting or the gusset next to it. As has been said, 17 is Jubilee and 19 is Navigator.  The Navigator has a slightly longer stroke so what ever has been done (unless it’s just changing the engine number!) would not have been an easy fix. 

The stamped numbers on the heads are different between Jub and Navigator, but can’t recall them at the moment, same for the Cams.  

What I don’t know is whether you can put jubilee rods, pistons, push rods  and barrels on a Navigator bottom end. The exhaust down pipes and head steady are also different.  It’s not a common conversion if you can! 

Andy the club lightweight guru might know, but some pictures would help!

dan 

Hi All,

I'm in contact with the seller of this bike. He sold it as a Navigator - because thats how it was sold to him. Its been well put together by somebody who clearly knew what they were doing. I have seen pictures of the bike & the only external clue is a piece of packing under the head steady that shows that the engine is not as tall as the original 350cc unit.

This conversion to 250cc is possible, as the Crankcase, Timing case, Primary chaincase & gearbox are all common (except 17T on g/box sprocket vs 19T on Navi).The items that were changed are all to do with the engine:

Crankshaft, con-rods, pistons, barrels, heads, Inlet manifold & carburettor.

Although the cams are different for the two engines - its possible to use either set.

The cam followers are the same (not the pushrods) and all the 'furniture' on the cylinders heads (valves, rockers, etc) is all the same.

In addition, the exhaust downpipes would need to be changed as well.

Its possible to return this to a 350cc again - but all the above would need to be changed.

I think you need to talk to the seller (who was also duped) to find the best way forward.

If its the same bike we are talking about - here is a picture of it

You have wonder why? It’s not like Navigator bits are that hard to find.

dan

I suppose the question is, have any of us got any Navigator top end bits we could sell to John so he can convert it back to a 350. 

Im partially interested if it has 350 con rods and cams, it would be interesting to know how a jubilee goes with those fitted?! If indeed it is possible ........ does it need a spacer under the barrel or is the comp ratio increased?

I have some con rods somewhere and will have a look!

dan

Camshafts - how to tell apart:

Jubilee cams are marked I7 & E7 on the end away from the drive gear, whilst Navi & Electra cams are marked I5N & E5N on the end.

Thanks Andy, I think I have a spare Navigator crank if it helps you John. 

Thanks for all the background information Andy, it's a fascinating hybrid but a major job tracking down all those parts and then doing a full engine strip and rebuild to return it to 350cc spec again - but worth it from the look of the rest of the bike and I'm sure John could recoup some of the cost by selling the Jubilee spares on.   Lets hope whoever did the conversion retained the Navigator cams!   By the way is there any noticeable difference in performance or need to change the ignition timing if you use Jubilee cams in a Navigator engine?   I've often wondered given the availability of NOS Jubilee cams but rarity of Navigator cams.

Nick  

Our dear departed John Hudson once told me that an easy way to pep-up a Navigator, was to use Jubilee camshafts - the valve timings are slightly different. He did not say (or I did not ask?) if this affected ignition timing.

For the technically minded, I have access to both sets of valve timing angles/lift if you are interested. The Electra used Navigator cams, timed differently by positioning the keyway on the crank in a different place.

I am building a Navigator engine and would like to know the gap between the barrel and cylinder heads i.e. spigot height as the heads have been skimmed can anybody help.