Ignition advance, TCI units.

[BrettS]

Great info Errol. I found that very interesting especially the laymans version 

[Eveready1100]

I found this advance unit guide on the Dotcom site. Brett, that one I sent you is off a 78E, so it's the pick of the bunch.

"Interchange Guide: Mechanical Advances
This comes up from time to time, so here's a 'illustrated' identifier...



From left to right, you have 78, 79, and 80 advance units. At a glance, they look the same, but there's important differences. Some parts are the same though, and I'll point those out. Each one has a different 'curve', so there's a very real performance difference and this may be important depending on the motor you install it on and what initial timing number you use. Ok, the differences....

The 78 unit offers 26 degrees of advance, starting at 2150 rpm and it's all in at 4750 rpm, for a 'range' of 2600 rpm. The slots in the reluctor are .515"/.530" long; this is what determines total advance. The springs have 13 coils, and a wire diameter of .033". Remember that the 78 uses 10 degrees of initial timing for a total of 36 degrees @ 4750 rpm.

The 79 unit has 31 degrees, starting at 1800 rpm and it's all in at 5400 rpm, for a range of 3600 rpm. The slots in the reluctor are .565"/.585", and the springs have 15 coils with the same wire diameter as the 78 bits. Initial timing is retarded to 5 degrees, but you have the same total of 36 degrees, although at a higher rpm (5400).

The 80 unit also has 31 degrees (OK, the manual says 30), also starting at 1800 rpm but this is all in by 3900 rpm, for a 2100 rpm range. The slots on the reluctor are the same as the 79 unit, but the springs are lighter; 14 coils with a wire diameter of .028". Again, the same initial 5 degrees and total timing of 36 degrees, but all in at only 3900 rpm.

As far as I can tell, the weights used are all the same (as are the 'bases'), with the differences being in the slots/springs. While the bases appear the same, they do have different numbers stamped into them...



It may be hard to see, but the 78 has 2H7-10/AD126-01 on it, the 79 has 2H7-11/AD131-01, the 80 has 3H5-10/131-02.

If you have or are planning on a motor swap, this is something you might want to check to make sure your timing is set correctly. I'll also note that the vacuum advance units are also different from year to year, but that seems to be a bit less important.

So, what else does all this mean? Well, from my hot rod days, it was desirable to get your mechanical advance in as quickly as possible for the best power; remember the 'recurve kits' for distributors? But you had to be careful not to have too much advance or you risked detonation. The more initial advance you could run also helped off-idle power. So it appears that Yamaha put a fairly aggressive curve in the 78 models, then detuned the 79s a bit. They further detuned the motors in 80 (slightly less compression, milder cams) but tried to restore some of the lost power with a more aggressive curve. So, which one do you use if you're running a non-stock combo or are looking for more power? Well, if you're running the early cams, the 78 unit will give the best results, mainly because you can use 10 degrees initial timing. The 80 unit has possibilities too, particularly if you use a 78 reluctor or shorten the slots to match the early part. It may be too aggressive though, so be sure and watch/listen for pinging. Another thing to remember is these motors were designed to run on 'regular' grade fuel, so if you step up to premium you should be able to run more timing. "

[BrettS]

Popped the one from Errol in today and yep that works great!
Thanks Errol, Ya bloody Champion 

[BrettS]

I am now also confident that the centrifical advance will work but I have found another option?
http://www.elektronik-sachse.de/ZDG3/YAMAHA/XS1100/en_h/index.htm
Still hope some one can have a go at explaining how the fully electronic advance works on the 4RO unit.

[BrettS]

That's Ok Errol it has given me a little laugh. I can't hold you liable for trying to help.
That is a very kind offer though and I would gladly except for the short term at least.
I would be interested in Buying the complete package of centrifical unit and backing plate but don't let me twist your arm if you wanted to keep them ?

[Eveready1100]

What can I say? So sorry, mate. Now I've dug mine out of the box and looked at it to take the photos, i can see that the one you've bought  ( at my recommendation) is only half of the advance unit. It's missing the centifical bit.
I'm certain the early system would work with your TCI, so If you could hang out till maybe tuesday?? (Australia post talk) it'll be in your post box.

[BrettS]

Thanks Pete, Hopefully some one else can suggest how it actually advances the spark. I am very curious now that I understand how the mechanical one works.
Oh and if I am passing by your way I will make sure I drop in so you can have all the fun you want

[BrettS]

I thought for sure that part that is missing would slot into this slot on the backing plate? With mine being a larger key hole I think I could replace the backing plate or just reduce the size of my keyhole ?

[petejw1966]

no worries,
im not exactly sure how it works
but the timing curve is built into the tci unit,

just use the original pick ups and backing plate that came with the engine
 plug the tci in and it should fire straight up.
u wont need to stuff around with anything else.

pity u werent closer
ive missed working on the old bikes.

[BrettS]

Sorry Errol I thought you would have seen the difference with the unit you told me to buy 

Spot the difference 

[Eveready1100]

Brett, I can't see what bit you think might be missing. Here's a couple of pics of a 78E ignition timing plate setup-


 ^ The backing plate, which looks very similar to your pic.


 Timing rotor. Same marks as yours.

 
^Backside of rotor


 ^ Centrifical advance unit.


 ^ Pickups get triggered by this lug on the end of the unit. Outer rotor only shows where the timing is set to

And that's it. No other parts in the early type setup. I'm thinking the large keyway you're referring to is the notch in the backing plate of the pickups. I have no idea why the notch is there. The advance unit advances the rotor, not the backing plate, so all should be good in this department.

[BrettS]

Thanks Pete, It is good to know that the unit will plug straight in.
The other main concern I have is I can not see how that ignition advance works and what parts may be also missing from the Pickup coil assembly for use with the 4RO unit.

So how does the 4RO TCI unit advance the ignition?

I am in Parkes NSW

[petejw1966]

just use the timing plate/pick ups that came with the 5n5 engine,
plug a 4ro tci in and it should fire straight up,
or at worse u mite just need to swap the coil wires over.

where abouts are u located?

[petejw1966]

it will plug straight in,
what arent u understanding i mite have missed something.

all the wiring looms are pretty similar, i fitted the rh loom to
an 80 standard, theres only a cpl of wires that are different,

just refresh me on what u have
u have a 5n5 engine fitted into which model frame?

[BrettS]

I need to clarify that the manual does give reference to the non adjustable timing but it does not seem to give any reference or show what parts are in the "Pickup coil assembly" with a 4RO TCI