jubilee tuning

Previously david_moore1 wrote:

High everybody I am slowly building my ''self assembly'' jubilee and was wondering has anyone tried to improve the performance of the engine,nothing complicated just gasflowing,raising the comp ratio, making some parts lighter, etc.Also the resent comment about placing the condensers remotely,has anyone details on this as it does look very cramped under the points cover.looking forward to your comments cheers Dave.

Hello David,

I have never done it and probably would not--- but I understand there is a Jubilee on the classic racer circuit--it apparently goes very well.

JPA

I started a thread on the same subject, the best I found out was that Les Emery had worked on one, they reversed the head so they could fit twin carbs reworked flow/compression and used the old inlet as exhaust, they fitted vertex? Pistons Kawasaki valve springs and balanced the crank. It reved to 13,000 rpm! and built power in a linear manner, it was clocked at over 100mph but still wasnât really competitive.

They gave up at that point!

Ive just decided to make mine reliable!

https://www.nortonownersclub.org/noc-chat/technical3-light-twins-forum/141402258

Hello David,

Tuning the Jubilee engine is probably only practical if you have a well equipped workshop and can fabricate parts yourself. I doubt if anything is available off the shelf; even standard pistons etc are hard to get so very little possibility of getting H/C pistons/hot cams etc .

The Club electrical expert has expressed doubts about the fitting of remote condensers but I do use them on the Yamton - that's a 1959 De Luxe Jubilee with a 1975 Yamaha 400 twin engine. Basically you remove the existing condensers, mount new condensers anywhere convenient on the frame (Coils and condensers under the seat in my case) and connect to the CB side of the coil. Loads of old Japanese twins used nice double condensers with a handy plug-in connector so very simple to fit/cost nothing/ and are supremely reliable (I hope).

Patrick

The head and valve angle is a bit of a hindrance there's not much room to enlarge anything, I might try a Mikuni in due course, let us know if you find any pistons that fit raising the comp a bit!

If you are starting from scratch I'd also recommend a 12v conversion and boyer ignition, the existing stator can cope well enough and the wiring is super easy!

Dan

Hi Dave,

What year engine are you intending to work on ?. Also what sort of use had you in mind? What sort of budget had you in mind? Why not fit a Navigator 350 engine if for cost effective road use ?

Most Jubilee barrels and heads are the spigoted type so machining probably means removing the spigot which means you need a different head gasket etc. The last few years production I think did not have the spigoted barrels/heads but I think these would be pretty uncommon. The later head gasket if available probably fits the early engine if the spigot is removed.

Why were you thinking of lightening the flywheels ? Light flywheels are only really of much benefit to a racer where engine response is critical; generally light flywheels make an unpleasant engine for ordinary use. (I had an MGB with a full race motor on the road so can vouch for that). Anything is probably possible but generally tuning is an expensive operation unless you can do the majority of the work yourself - a fellow we shared paddock space at a hillclimb casually mentioned that his engine had cost him 27000 GBP; ours had cost a tenth of that but it is still costly especially if you blow it up in a big way. Jubilee engines were not bulletproof !!.

Patrick

Not bullet proof, and the pistons have a nasty habit of cracking!

Hereâs one I prepared earlier (in 1976 to be precise!)

Polishing inlet ports and a better carb wouldnât be too tricky, but remember it is only two 125 cylinders so if the carb is too big youâll lose not gain .... believe me I know!

Dan

Keep us posted, and let us know what forks you decide on, sadly you cannot use the Jubilee yokes and simply slide new ones in, so youâll need to use different yokes which means watching the offset to avoid creating a chopper or trials bike! Even using roadholders ( the easiest but not cheap fix) requires the navigators down tube or a bit of frame modification. Any TLS braked wheel is generally desirable, but a well adjusted 8â SLS is perfectly adequate for a 250 and norton full width hubs are plentiful and reasonably priced at autojumbles.

Good luck Dave, I'm guessing that gas flowing and raising the CR offers the biggest gain although the valve angle and size is a known limiting factor. I'm guessing the bottom end is strong enough to take any likely performance gains with the same main bearings and big ends across the lightweight range. Take care with the pistons, as Dan points out some sold back in the day had a habit of cracking which I also experienced as a 'Yoof' in the 70s. Just a thought, my older brother ran a Navigator engine in his Jubilee back in the day with a Wal Phillips 'injector'. It certainly went like the clappers but was incredibly fickle to set up which was required frequently! They were really meant for racing but people brave souls did use them on road bikes.....I have attached a picture I found on the internet. I look forward to hearing the updates!

Brave indeed Dave, did you get it running properly and did it improve performance? My brother's set up was a real challenge to get the mixture right - almost a daily process - but it did make the bike fly, sufficient for the back wheel to collapse popping a wheelie on one occasion and the gearbox to self destruct in a spectacular manner! That said I'm not sure that was due to excessive power so much as bushes failing and general mechanical abuse by teenagers!

Nick

I am really curious about this Wal Philips fuel injector as I had never heard of it before. How did it work? Presumably calling it a fuel injector was really a marketing ploy or did it really have a high pressure mechanical injector pump as surely it wasn't electronic in the sixties?

Jubilees suffered lots of abuse in their day as generally they were only used by learners who rode them flat out with zero maintenance. Amazing that any have survived at all. Hepolite pistons were generally known as good pistons but they couldn't always cope with 10,000 revs through the gears from stone cold and neither could the gearbox.

Patrick

Hi Dave, fascinating stuff - I was too young to be hands on at the time (early 70's) but remember my older brother and his mates eulogising about the performance. One lad ran one on his 'tuned' Ariel Arrow which you could hear miles away late at night as he came back from the pub - reputably faster than his mate's Suzuki Super 6 and many much bigger bikes but predictably fragile! Looking at the picture I attached and reading up you are right - 'injector' is a very generous term! It is just a gravity jet and needle valve linked to a butterfly valve and was designed and developed for speed way racing I think. Can you imagine the elf and safety people coping with the idea today??!!!

Nick

You must be a young lad still, Nick. The Triumph TR5 was probably the first British road car to use petrol injection. That was a mechanical system from Lucas and it was good when it was working properly putting down 150 BHP and giving 25 MPG but it was also unreliable. When it went wrong fuel consumption could drop below 10 MPG. The TR5 engine and injection fits straight into the Vitesse or GT6.

The first petrol injected road car I ever remember seeing was a new Mercedes ( a saloon -not the 300SL) owned by a neighbour sometime in the middle/late fifties. It was the talk of the neighbourhood here as it had "fuel injection". I vaguely remember people saying (I was young then) that it had fuel injection from a fighter aircraft. I think Mercedes used the same Bosch injection as used on the Messerschmitt 109.

Patrick.

If only Patrick! I had two Triumph 2.5 PI saloons in the early 80's - the sound of an injected Triumph straight six was a joy to behold! The Lucas system certainly had it's faults but properly set up the car was seriously fast for the day. The best I ever got was just over 20 MPG but I can vouch for 10 MPG when it was misbehaving......or if I was caning it. Happy days! As a Vitesse owner I'm afraid the Lucas system can't be fitted to the 2000 engine but people have fitted the 2.5 PI engine in the Vitesse and GT6 although it requires major surgery to the bulk head and chassis to fit the gearbox and bell housing in.

N