Harness interchange

Had a 77 650 Harness burn up and just got a 78 650 donor parts bike. It's all there and was just wondering if anyone knows what I'm about to run into. I believe the 77 has a separate reg and rec and the 87 has a combo. Can anyone confirm this? Also the alternator is different somehow. Can anyone save me some investigative footwork?

yes your right.

Looks like I could change the 77 alternator cover with the 78 cover assembly complete and use the reg/rec combo from the 78. Can anyone confirm this and would there be any benefits other than ease of harness install?

Unfortunately the 77 alternator is a completely different creature from the later models - it´s a 3-phase excited field alternator that employs a field coil where as later models use either a 1-phase or 3-phase permanent magnet setup.

The regulators work differently too. The reg. for permanent magnet setups work by shunting excess power to ground, the reg. for the field coil setups works by cutting off power to the field coil.

There are some physical differences too: the permanent magnet setups have the stator inside the flywheel/rotor - the excited field setups have the field coil sitting inside the rotor/flywheel and the stator on the outside. The 77 cover is also different in that it has the three holes for mounting the field coil, later covers do not have these holes.

Good news is that the crankshafts are the same, so you can transplant a later model alternator to the 77 engine, but you´ll need to swap both the cover, stator, rotor/flywheel and reg/rec to make it work.

I think you will also need to modify the 78 stator cover to fit the 77 cases, if I recall correctly the dowel pins are placed differently.

Here are a couple of pics to show the differences, click to enlarge:

And a 79 stator/cover for comparison:

Edit: Btw, just to avoid any confusion this is not an actual 79 stator, it´s an 18-pole 3-phase Electrex stator that needs a 3-phase reg/rec, the stock 79 stator (which is the same as the 78) is a 12-pole 1-phase.

Eggsulant!!! OnkelB I thank you! I will be modifying the harness since I do not wish to modify the case. Really great write up and with visual aids too! Thanks!

One other difference I can think of besides what has already been mentioned. If your 77 is a B model it does not have a 4 way flasher system. On the 77 C-models and on 78 and later B-models they used a switch on the left controls to operate the 4 ways. I'm sure it won't keep you from being able to use the harness but I thought I'd make you aware of this, it might save you some head scratching down the road.

No problem, you´re welcome. Btw, regarding the different dowel pins you don´t have to modify the cases but rather the stator cover. What you need to do is to enlarge two of the cover holes on the inside to accept the dowel pins, that´s all.

Good info Andy, I didn´t know that - so that´s what the empty hole in my left switchgear is for...

I just checked out a couple of things on my bikes here. I was thinking you might run into some things with the handlebar switches due to the 77's having the wires run inside the bars. I thought they stopped doing this in 78 but as it turns out they still did it in 78 so you will be alright there. Onkelb is correct the covers on the 77 are different they have both locator dowels on the bottom 2 screws of the cover, later models have one on top and one on the bottom. This is why I love this site I learn something new everyday. It also helps to have lots of NOS stuff sitting around to look at and compare.

Yeah... no 4 ways and my 77 lights are switchable too. I can turn them off. Which I like. Great info guys. Thats why I like this place too. Seems like the more I take off this parts bike the more I realize the butchers don't always deal with meat.:woohoo: Man.... is this thing hacked. Glad I only need the harness. Going to keep the top end too. Had a 4 into 1 that I thought was OK until looking at the bottom and the crushed tubes.