Jubilee/Navigator restoration

Hi Dan,

So it's overalls on time.

There are different bore sizes for the 375 carb. The original Jubilee was officially a 25/32" which translates to 19.844mm. The Navigator had a 7/8" carb.(22.15mm). The Jubilee really needs a bigger carb so 22mm sounds a good choice. In the 1959-60 Maintenance Manual & Instruction Book the full Jubilee spec reads; Amal type 375 Choke size 25/32" Main jet 130 without oil filter Throttle valve 3 1/2" Needle position 3 Pilot jet 25

If you go for a secondhand 375 try to get the right jets and slides because buying new Amal bits costs a lot .And the early copper float should cope with ethanol in the petrol. The book doesn't mention the needle but it's a standard B needle to my knowledge.

That's news to me when you say Mikuni do a 22mm with 50mm stud spacings. Every Mikuni I measured was at 48mm spacing and you can actually break through the outer edge of the flange to make them fit the 2" spacing on British bikes. I have seen carbs in use this way on British bikes (but not a Jubilee) and they do seem to survive reasonably well but I feel that it must weaken the flange.

Maybe somebody has already done this and can provide first hand info,? The Mikuni will give the best results but it might take a bit of work getting it just right. The advantage with the Amal is that it fits and the spec is already known.

The best of luck.

Patrick

Hi Dan,

Your picture of a modernafter market Mikuni seems to say that this is adifferent carb to the old original Jap fitment flanged Mikuni from way back. I can see that the new style flangecan easily be made to fit on to the Jubilee manifold. The old Mikuni (I think it's a 24) that I have in my box has two round holes at 48mm centres. The Mikuni will almost certainly give the best results if you do some experimenting with the jetting. The Amal is costly but it would look original.

It used to be easy to get s/h Amals at the autojumbles and the BSA ones are common. The Bantam I think used a 7/8" and the later B25 I am sure also used a 7/8" But you have to downsize the jets when fitting to the Jubilee as it's a twin.

Have you thought of picking up a cheap monkey bike Mikuni froman autojumble? They are cheap as a rule - under £20 new- and you can play around with jetting. One from a 140cc monkey bike would be a startingpoint as they use 22mm or 24mm. Some of them have Mikuni marked on them butI wouldn't like to guarantee they are 'real' Mikuni's. I have used them on different projects in the past and generally they worked well. And the price is right - you have to remember that you can spend the price of a Dominator on rebuilding a Jubilee but Jubilees don't fetch much if it comes to selling it on.

Anyway I'm in Northampton at the moment as i'm going to the MG International Show at Stoneleigh on Sunday.So there will be lots of reliable SU's there. They always worked well on MGB's but I'm biased.

Patrick

Hi Dan,

Interesting. Maybe there's a market for these wooden chain tensioners - have you thought about marketing a hi-tec racing version hard carved in mahogany for maximum performance? Both of my standard Navigators have the nylon version.

What was Norvil's purpose in building their Jubilee? Andy Sochanik said in his recent article about the power being progressive over the rev range which seems to indicate that the Jubilee engine was primarily designed for road use(AKA poor breathing) - good driveability rather than max power. Did Norvil do anything with the cam timing and lift as obviously they must have changed over the position of the cam shafts. In it's day the Jubilee was a high revving engine in comparision to say the Dominator which had more low down torque than a 14 litre Scania.

Obviously as you go for wilder cam timing to gain top end power you lose out on the bottom end (you know this with your two stroke Yams) and then the four speed gearbox becomes a liability. I have a VFR400 as well and it's fun to play tunes with revving to 15000 - a bit pointless as max power is at 13000 but the sound effects are wonderful.

Good luck at the workbench.

Patrick

Hi Dan,

I suspect that you already have a good idea of the answer on the clutch question. There will always be some movement even with everything in good order. If you're lucky the clutch centre nut only needs tightening up but there are all sorts of possibilities - i.e worn splines on the clutch/main shaft, worn rollers in the clutch centre bearing, worn sleeeve gear bearing, worn bushes in the sleeve gear and probably a few others as well - like worn clutch plates/springs etc.

Your suggestion of just getting the engine in the frame and actually running seems the best way of going about things- only replace absolute essentials in the first place. Old British engines were remarkably crude engineering in comparision to the Japanese items but they had one saving grace - they just kept going despite everything being worn and broken. And riders of sixties metal certainly got value from each item and didn't replace anything unless the machine had positively ceased to proceed. So as the clutch is still there there can't be much wrong with it.!!

My VFR 400 H*nd* is the complete opposite to the Jubilee - everything has to be perfection otherwise it simply refuses to even start -it does give 60 horse power and utter reliability even with regular use of 15000 revs so effectively F1 engineering.. The Jubilee will start and get you home even if running on one cylinder - so more agricultural engineering.

Patrick

Hello Dan,

Gearbox change was at engine number 106838 in 1963.

Your engine number surprises me as my earliest Jubilee is 81449 - thats 1959. My Standard Navigator is 97526 which has an official dating letter showing it was despatched on 15th May 1961. So 16000 Norton machines made in just over two years.

Your number is over 100.000 higher so when was it made.

Patrick.

Hi Dan,

I'm just back from a classic vehicle rally with the 1958 Morris Isis - too wet this morning to take the Jubilee. You wouldn't want to do these hours for work but it turned out a nice day.

The P after your engine number will mean Plumstead - that's where the bike was built after Norton moved from Birmingham. In old Norton speak P before the number meant 1959 but they dropped that system in 1960. The later box is supposed to be an improvement but I have no first hand knowledge.

More power is always a good thing- even riders on R1s seem to be feeling underpowered now that BMW are the new power leaders - or so I am told.

Patrick