RT Rebuild and questions

[graeme]

Hello, I'm new here, but not so new to late model singles and other things older Ducati.

I'm rebuilding an RT 450 that I bought as an unknown bike.
Lots of usual repaires were needed to the engine and everything else, but I enjoy working on Ducatis.
I'm going to leave the head standard, (except for the cam and springs) and the carb the original size for now as it's been a long time since I rode a standard 450.
I have a 1974 450 Desmo that has the usual breathing improvements and the cam cleaned up. This bike has the original Ducati Electronica ignition, and a 12 volt regulator,battery and lights etc.

Now the question re the RT's electrics,

I would like to fit an electronic ignition, mostly to help starting as I'm not as young as I was.
As you know the RT has the 2 winding coil from (I think) the earlier engines and the small brass flywheel, points and no battery.

I have a couple of spare alternators and flywheels from points model widecase 450's, these are not the '74 model alternators which are 5 wire.
Can I use one of these alternators and a 12 volt regulator to convert to 12 volt? I know these were 6 volt, but will they produce more than 12 volts?
Then buy an electronic ignition from one of the modern suppliers like Sachse etc.
A battery would also be installed.
Or do I need to buy a new alternator designed for 12volt from another supplier.

Regards
Graeme

[wcorey]

Welcome to the list!
I've also been playing with an R/T or two and am going through some similar issues. There's a lot of info already here but it's very spread out and involves a lot of digging and reading.

Can I use one of these alternators and a 12 volt regulator to convert to 12 volt? I know these were 6 volt, but will they produce more than 12 volts?

Yes and yes. If you're not going to be adding lights then even the stock two coil alternator would provide adequate charging. A headlight adds a whole new dimension to it though.

Or do I need to buy a new regulator designed for 12volt from another supplier.

A modern mosfet/series regulator such as any of the Shindengen FH types will give you a bit more output and run cooler.


Bill

[DewCatTea-Bob]

By: graeme...
" I'm going to leave the head standard, (except for the cam and springs) "

____ What exactly are you expecting to accomplish concerning the R/T's D.camshaft & v.springs ?


" I have a 1974 450 Desmo "

____ Where did you get that D.model, Canada ?


" Now the question re the RT's electrics, "

____ You ought to be in good-hands with help from 'wcorey', as he has dived-into pretty-much all the related aspects of the charging-system and has a far better than average grasp on that topic !


" As you know the RT has the 2 winding coil from (I think) the earlier engines and the small brass flywheel, points and no battery. "

____ While I believe the stock R/T's original two separate alt.power-coil/windings are somewhat updated (from that of the the oldest engine-models which employed the 'magneto-system'), it's complete wiring-system's scheme is the same...
One power-coil dedicated to just the ign.system, and the other dedicated to the tail & head lights,, only.
That stock scheme is of-course insufficient for legal road-riding.


" Can I use one of these alternators and a 12 volt regulator to convert to 12 volt? I know these were 6 volt, but will they produce more than 12 volts? "

____ ALL the Ducati-alternators are capable of (much) higher voltage than that which alt.output is normally regulated down-to, (all depending on the connected load-system).
So even the stock-R/T's power-coils are capable of powering a 12v.system, but that really depends on how much you intend to load-down your chosen charging-system ! ...
__ The main load is the headlight ! _ So you should really get that ironed-out before-hand.
If you stick with an old (low wattage) headlight, then you can use the stock (low wattage) alt.output, and get-by without any regulator-circuit.
So you really ought to let us know how much you intended to load-down your R/T's charging-system, so that then you can be better directed towards your best options (for choosing a suitable charging-system).


" Or do I need to buy a new regulator designed for 12volt from another supplier. "

____ If it's determined that your chosen charging/load-system ought to include a v.regulator, and you're happy with that which you have on your '74-DESMO, then why not consider whatever that type of 12v.unit ?


Duke-Cheers,
-Bob

[JimF]

I am going to write a generalization here - regulators regulate and rectifiers rectify. Oftentimes the two are in the same 'container' and we just say "regulator" for short.

Any working 12-volt regulator will regulate voltage to 12 volts (perhaps that's 12.7 volts or 13.8 volts but for the sake of simplification we'll just say 12 volts.) So for less than 12 volts into the regulator no regulation takes place. If you put 6-volts in you get 6-volts out. 10-volts in gets 10-volts out, etc. But 12-volts and above in will only see 12-volts on the output. That's regulation.

So any 12-volt regulator will work. Note that with input voltages above 12-volts a power issue arises. The regulation burns off excess power in the form of heat. Some regulators need to be mounted to the frame which will act as an addition heat sink. This is why some people have regulators that fail when they got hot or fail completely - they were meant to utilize massive amounts of motorcycle metal (the frame) for heat sinking and perhaps a customizer affixed the regulator to a fiberglass piece.

Rectifiers convert the sinusoidal alternating voltage (swinging positive and negative) and alternating current to voltage that is one polarity (in our case positive with respect to the frame) and direct current.

Depending on your alternator's output you may find enough AC voltage amplitude to rectify it (convert it to direct) and regulate it so as to have 12-volts rather than six.

But keep in mind that when we talk about AC voltage and current there are three ways to describe it: Average voltage of AC is actually zero volts! That's because the sinusoidal wave keeps going positive and negative and the average is zero. Only engineers ever think of the average value.

Then there is the peak voltage. That's the highest the voltage ever gets when the sine wave reaches its peak. But the AC voltage is only ever at its peak for a split microsecond every sine wave cycle, so that voltage doesn't effectively describe usable voltage.

That's what RMS or "Root Mean Square" voltage is - it's the usable voltage in an AC sine wave of voltage. It's close to 70% of the peak voltage. So to achieve a usable 12-volts from your alternator it's going to have to generate 17 or 18 volts peak voltage.

There are some prior threads on this forum that deal with trying to achieve 12-volts DC from the original Ducati alternators which were intended to supply either 6-volts DC or run the bike strictly on AC voltage.

Lastly welcome to the forum. We have a lot of forum members with strong backgrounds in every aspect of Ducati singles and I hope you'll find the help you need here, and I also hope that you'll help someone here in the future.

Jim

[graeme]

Thank you Bill, "Or do I need to buy a new regulator designed for 12volt from another supplier." this should have read alternator, not regulator. It was a long time ago I changed the '74 450 to 12 volt and I didn't remember replacing the standard alternator. It was rewound but I seem to recall it was re done as standard. The RT will be registered and have lights, so I'll use the 3 wire alternator and a battery. I was looking at a Sachse ignition? Or maybe a Pazon? Bob, I removed the std springs and fit small springs like Pantahs use but lighter. In my mind I can't see the point of heavy springs on a Desmo head to load the bevels and Oldham coupling. The Desmo cams I've seen (4 of mine and a few of friends) all bind the open and closing rockers and required the closing lobe to be lapped to give a constant clearance through 360 degrees.
I live in Australia and have had 3 '74 desmos all 450, and now the RT. the road 450 I have is my favorite bike of all time,
The RT was bought as spares for the road bike but I couldn't bring myself to part a nearly complete Ducati, even if it is a chook chaser. Several mates have RTs and claim they are the best bike ever produced. Regards Graeme, and thanks for your help and advice

[DewCatTea-Bob]

" this should have read alternator, not regulator. "

____ If you wish to spend the money and have a very high load-system to run, then you may want to buy one of the few aftermarket alternators which are available specifically for DUKEs, but, the stock wide-case 6-pole alternator (which you mentioned you have spares of), can be setup to handle most-all regular load-systems.


" The RT will be registered and have lights, so I'll use the 3 wire alternator and a battery. "

____ Still need to know what wattage of headlight you wish to use !?



" I removed the std springs and fit small springs like Pantahs use but lighter. "

____ Interesting! _ Got any pix of that which you have ?


" In my mind I can't see the point of heavy springs on a Desmo head "

____ The std.DESMO-springs aren't really very 'heavy', they're the same v.springs as stock in the (tiny valved) 160-M.Jr.


" The Desmo cams I've seen (4 of mine and a few of friends) all bind the open and closing rockers and required the closing lobe to be lapped to give a constant clearance through 360 degrees. "


____ To what-end did all that pain-staking fine-work actually yield ?
Ever wonder why Ducati didn't bother with it ?
This actual non-problem issue has come-to-be simply because good-intentioned mechanics assumed that the closing-clearance needs to be set right at TDC,, but actually, that's not the sensible/logical location/place to measure/check the 'closing-clearance' !
There has already been a thread which well covers this whole DESMO valve-clearance issue... However fellow-member 'machten' has since changed the original-name of it's thread-title, so perhaps HE can recall it and supply a link to it (here in this thread), so you can then quickly-find & check-it-out.


" The RT was bought as spares for the road bike but I couldn't bring myself to part a nearly complete Ducati, . "

____ Good-reasoning ! _ Always sorta hate to see any Duke pass-away !


DUKE-Cheers,
-Bob

[graeme]

Possibly 40w low and 40w high, not on together. And tail and stop lights. Plus the ignition whatever that ends up. Graeme

[DewCatTea-Bob]

" Possibly 40w low and 40w high, not on together. "

____ I'd recommend the 45/65w light made especially for motorcycles by Sylvania.
As then it would be really worth swapping the R/T's alternator for the more powerful alt.models you have.


" And tail and stop lights. "

____ The brake-light (& horn & turn-signals) use power* stored by the battery (*which otherwise just gets wasted, if not used by those temp.loads).


" Plus the ignition whatever that ends up. "

____ Most consume little different than stock. _ I'd recommend staying-away from aftermarket ign.systems that draw over 3-amps.

____ I should've also asked if your R/T would likely be used for extensive in-town night-riding,, cuz if not, then your contended rather low-wattage load-system may get-by with a minimal charging-system.


Dukaddy-DUKEs,
-Bob

[wcorey]

However fellow-member 'machten' has since changed the original-name of it's thread-title, so perhaps HE can recall it and supply a link to it (here in this thread), so you can then quickly-find & check-it-out.

That's likely in Kev's "1968 250 MK3D rebuild - ex W/C Oil Pump" thread...

viewtopic.php?f=3&t=459&p=4221&hilit=desmo+cam+clearance#p4221


A 40w headlight should indeed be do-able with a stock w/c 6 pole alt, though as Bob has eluded to, it would be borderline if stuck in a situation where revs are low for extended periods. The 'breakeven' point where the alt will produce enough power/voltage to charge the battery with the lights on will probably be somewhere in the 3500-4500 rpm range. There are simple ways to improve on this but the choices to be made on how to proceed with that can be complicated...

Bill

[PhilA]

Wouldn't be a lot easier to fit R/T TS parts (assuming they can be found)? Still 6v I realise but at least you'd know it all fits and works. Not to mention it keeps the bike "original".

As per:

http://www.philaphoto.com/imageLibrary/ ... m=54&pos=1

Phil