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Improvements to the lightweights


Its been a couple of months since I acquired my Navigator, in that time I’ve worked on and ridden it. First impressions have been good.  Handles well, lively performance for what it is.  As I have related elsewhere on the forum, it's not been without problems.  The main one being oil leaks.  Also, the poor quality of workmanship by whoever assembled the bike. 

I’ve also joined the NOC, read everything I can find about the lightweights.  One thing I was hoping to find are improvements that can be made to the bike.  I should say at this point that I am not a slave to originality, happy to leave that to others.  Having said that I would not change anything that I couldn’t put back to original condition or have an original part to do the same. 

With this in mind I’ve rewired to 12 volts and fitted electronic ignition.  The lack of an oil filter has been remedied.  I’ve trued up the braking surface in the front brake, had the shoes relined and then machined the shoes to fit the drum.  I’ve attended to some of the easy to get at oil leaks.  The clutch wasn’t working well, got that sorted.  Fitted a pair of “Tommaselli” style levers, not essential but I like them!  Otherwise I’ve just sorted out the poor standard of assembly. 

All the time while working on the bike I’m thinking of what else would improve it.  In another thread about oil leaks I’ve followed I eluded to the fact that I think there are some significant improvements that can be made to crankcase breathing.  I’ve lifted the heads to cure a leak only to find a solid copper head gasket, not ideal is it?  I made a head gasket out of what I hope is a far more suitable material.  Something to stop wet sumping, preferably some modification on the pressure side. 

The primary drive, any better way of tensioning the chain?  Some means of accessing the tensioner without removing the cover?  Although steps have been taken to stop the clutch spring adjustment changing it's not very positive, I’ve done already something there out of necessity, the relevant parts were not in great condition.  Anyone tried other arrangements for applying spring pressure? 

The clutch operating mechanism, not the best, I recall it didn’t have much of a reputation back in the day.  So, a better mechanism? Shorter clutch cable, better routing? 

The gearbox, I can see some improvements here.  Better bearing arrangement for a start.  The ratios are not great. First is a little high, I can live with that.  What I think would be better is closing up the gap between third and top, that will require some considerable work to sort out! 

The front forks feel over damped to me, is there something that can be done there? 

Surely I’m not the only owner to think along these lines, anyone else made any worthwhile modification/improvements? 

I expect to see comments along the lines of “it works fine for me, leave it alone”.   Part of my interest in motorcycles is working on them, trying to make them better.  It should be remembered that these bikes, as indeed most things, were built down to a price so they would sell.  What would the designer liked to have done if he, ultimately, didn’t have the accountants telling him to save money? Don’t get me started on the production engineers! 

So, a few more rides then the engine is going to be stripped down.  I’m a little nervous about the engine having seen what the standard of workmanship has gone in to the rest of the bike. 



I totally agree with all that you have done John, 12v conversion using a modern Lucas stator and voltage reg/rect, Pazon electric ignition and a rebuilt carb completely transformed my late Navigator!   It has the later clutch and gearbox which I have always felt are better than the earlier type although the ratios are the same I believe.   I have fitted Norton straight bars and good quality, ball ended levers plus rebuilt wheels and brakes which have all added up to a really enjoyable, surprisingly nippy bike with fantastic handling and brakes for it's era.   I cured the oil leaks by replacing the primary side crankshaft, clutch and gear box oil seals, the timing side points oil seal and replaced the sump plate with the modified and finned sump plate with the magnetic drain plug sold by the NOC shop.   Using two of the rediculously thin rocker box gaskets on each rocker box and silicone sealant on the primary chain case has cured all the oil leaks and it seems happiest running on a straight 40 grade classic oil but each to their own!   Mine has done 32,000 miles on the clock but I have no idea whether it is on standard pistons although the compression is good and there is little or no blow by - a sure sign that the top end is in good condition and the design of the crankcase breathing is adequate if the engine is in good order.   As for other improvements there is very little history of anyone 'tuning' any of the Lightweights.   If you search through the various threads on this forum there is evidence of a racing Jubilee which was tuned successfully with much stronger valve springs to let it rev to frightening levels and supposedly similar power output to a Navigator.  Evidently valve bounce (and probably piston fragility!!!) because of weak original springs limits performance hence use of stronger springs.   Valve angle is another limiting factor along with the inlet ports being so close together and to little space between the head and main frame to fit twin carbs.   The cam followers are prone to wear rapidly which makes the engine noisy and I have read opinion that the valve train is heavy which again limits it's ability to rev but I'm not so sure about that!   Our wonderful technical expert, Andy Sochanik can tell you more.   As and when I need to do an engine rebuild I will explore gas flowing the heads and carefully balancing and blue printing the engine then once it is run in using a slightly bigger carb, say from the Electra - every little helps!   I would welcome hearing how you develop yours, after three years of Navigator ownership I am a huge fan of what is a far better bike than some (who have probably never owned or ridden one) would tell you!   Mine is a 'keeper'!   Good luck and keep us updated.   Cheers Nick             


Just to be clear, I'm not interested in more speed, I'm happy with the performance as it is.  its just improvements to the bike as a whole that would just make the bike technically better, nicer to ride and eliminate any known problems.

If I want more power I would buy an 88 or 650, might happen in the future.

Something else I forgot to ask in my opening post in this thread is what do people do when the valve seats get too pocketed?


My atlas valves looked a bit pocketed, but rather than getting new seats  I got my local old bike engineer to blend in the chamber side  with his cutters . As long as the rocker action is still centered on the valve tips its a reasonable compromise..Might be good to check the spring poundage with it being a higher revving motor.

One improvement to the primary chain cover could be inspection windows for clutch spring adjustment and crankshaft rotor. To be able to finely adjust clutch springs on the side of the road to find the sweet spot between clutch slip and heavy lever action could be very convenient. Similarly a degree disc permanently fitted to the rotor at the end of the crankshaft with TDC and static and full advance  marked on the cover is what I need, further , a clear cover temporarily fitted could use a strobe to check ignition advancement. Images show a mock up of what I am working on.



Hi John,

I like Nicholas Clarke's reply. His are all good suggestions.

Improvements are very personal and depend on the use you make of the bike. These were mine.

Get the bike oil tight. Keep on top of maintenance.

Riding mirror.

Improved centre stand bushes.

Strengthen centre stand shaft between legs.

Get a centre stand with extended leg for foot. (Electra style)

Fit a decent side stand. 

Stainless rims, spokes, handlebars and fasteners wherever I can.

Control levers for brake and clutch with adjusters that you can adjust on the go. (Need special cables)

LED's for power, indicator, Lo/Hi beam.

Handlebar clock.

Strong luggage rack in Craven style.

Pannier frame.

Map holder.

Handlebar mounted device that has three numbered rings (from a number padlock) that can record the list three digits of the odometer when the fuel tank is filled.

And I think you can see what I like about my Norton Lightweight. It's personal isn't it!

All the best with yours. Endless possibilities.




Just reading through the replies to my opener.  Graham S. I agree that access to the primary drive is limited, probably a cost thing?   Got me thinking, a couple of threaded holes same size as the chain inspection hole would do, maybe an elongated cover so the pushrod adjustment could be got at?  Lets us know how your mods progress.

The primary chain adjustment requires the cover taking off, annoying that.  I have an idea for an automatic tensioner. Firstly, I'll need to see what space is available for what I have in mind, then, as they say, watch this space.

I've fitted a Boyer system for sparks and strobed it for accuracy.  To fit the disc I made a nut, the one that fixes the alternator rotor and sprocket to the crank shaft, with a threaded extension the dis center screw on to.  Also made a substantial pointer that would not move when the engine was running.  See attached photo.  I was surprised just how much space there is under the cover outboard of the drive so the nut can protrude a suitable amount.




Hi All,

This thread has made fascinating reading. I love John's ideas of steady improvement (plus Nicholas's thoughts) - not necessarily for speed, but to make the breed better. It was inevitably built down to a price in the day, and with hindsight we can improve on stuff.

In my case, I'm happy on 6v and points. My headlight bulb (from Paul Goff) is a normal filament one, and is focussed just right - so I have no problems at night. If you are staying with 6v, do NOT be tempted to use LED lights!! The original 6v electrical system is balanced (did you notice the resistance wire in the loom?) so as not to overcharge the battery. LED bulbs (esp the headlight) consume less power, thus leaving a greater excess to boil your battery.

But never mind what I do - these days it makes much more sense to upgrade to 12v. Your original Wipac stator (if in good condition) is up to it - just connect the Orange & Green wires together & you have a 2-wire output system. As stated above, a modern Lucas Stator is fine with the strong (Wipac rotor) if replacement is needed. You will need to do some wiring mods - contact me or Al Osborn for details. Once on 12v, the best thing is, that you can add a regulator/rectifier (to replace the original rectifier) & remove the resistance wire from the equation -  plus electronic ignition. Most electronic systems fire both coils in series (wasted spark system) thus you get to keep your existing 6v coils. Alas, Electra owners converting to Electronic Ignition will need to source 2x 6v coils!

An important mod for me was to fit a rear carrier, and then add strength to it by triangulation. Failure to do so wrecks your rear mudguard (as I found to my cost), as the stain imposed by the carrier distorts the mudguard. See picture attached. Its not pretty, but is super strong.

For John, I need to ask your engine number. You may have deduced from the replies above that there are two differing gearboxes used. There is a break point at engine No 106838 (mine is 106840!!). All Electra, plus Jubilees & Navigators after that number, have a re-designed gearbox, and NO parts from it are compatible to the earlier version. Even the frames & crankcase castings are different, leading to different shape centre stand springs & 'C' shape anchors.

Both gearboxes have their good & bad points:

The 'early' gearbox provides a really smooth AMC-type gearchange - and has a kickstart system that never wears out, but has a bad issue with the layshaft bush adjacent to the sleeve gear bearing. It was not pegged in place at the factory, thus has a habit of rotating in its housing (the crankcase) and can create havoc. If the bike is new to you, its worth tearing down your gearbox, to ensure all is OK in that department. (Like a timing belt on a car - if you don't know its history, its worth replacing for peace of mind).

The 'later' gearbox is potentially stronger, as it has a larger diameter mainshaft, and the layshaft bush is pegged to avoid rotation. But, it is clunky in operation & has a piddly kickstart pawl which can fail suddenly, with no warning.

Another thing to look at are the clamping bolts for the rocker shafts. The first Jubilees and Navigators had 1/8" diameter bolts clamping the rockers after adjustment. These can bend and release the rocker shaft - which immediately goes to maximum adjustment & that cylinder cuts out. Its happened once to me when I had an older cylinder head fitted. I was lucky as the pushrod stayed put, but I have seen damaged pushrods (at autojumbles), so others have not been so lucky. Later cylinders heads have 3/16" bolts that are much stronger.

There are two sources of oil leak on the cylinder head, noticeable by oil running down the front of the engine (as its inclined forwards). One is the rocker caps themselves - as only 2 bolts hold them them down. If leaking, the temptation is to tighten the bolts - whereupon the leak gets worse! One person has written above about using two gaskets & silicon (which should work), but my preffered route is a cork impregnated gasket of about 1/16" (1mm?) - similar type to that used on car rocker boxed, but thinner. This works a treat, as it gets compressed by the screws, and is thick enough to absorb any distortion. The other source is the rocker oil feed pipe. The unions are soldered on, and 9 times out of ten, if I have an oil leak upstairs - its because the soldering has let go. To check, remove the pipe from the top of the engine, hold the unions between thumb and forefinger & twist them back & forth against each other.

On pre-106838 engines, the crankcase breather needs re-siting. Sadly, its a job for when the crankcases are apart for a major overhaul. Its present location behind the Primary inner case and above the output gearbox sprocket is not only bad (as the chain can cut into the pipe on the over-run), but one is unable to do anything about it with dismantling the whole primary drive. Engines after 106838 have the breather exiting at the rear of the crankcase - eliminating that potential source of oil leak.

Another idea that has been floating about recently, is employing a reed valve in the engine breather circuit, thus creating a potentially negative pressure under the pistons, thus not 'pushing' oil out of any available orifice. I have not tried it yet - but have heard from 2 people who say its made a vast inprovement.

Also touched on above, is the need to add an oil filter kit and a tap to stop oil draining past past the oil pump and ending up in the sump. Any tap fitted must be full-flow (you can see through it when open) and MUST have an ignition cut-out fitted - otherwise you WILL ride off one day with the tap closed. The oil Filter fits in the return line, so is not ideal - but better than nothing.

Picture of my Navi showing triangulation to the rear carrier and the same bike 30yrs ago without the supports. Next to it is a DeLux JOO 804 which I then sold to a chap for a pittance soon after (£250??). He did not haggle & just chucked it in his van. I felt like I'd been robbed. Sure enough - I had been!! Have a look on the DVLA site for that Number Plate now......(by checking 'Is my Tax due'...)


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