1981 GS850 engine swap for a 1979

[Guest]

I had some bad things in my oil, so I'm going to swap for my other motor, but I took a closer look at it last night and it is a 1979 motor with kick-start.

It has points, instead of the pickups. Can I just swap the pickup plate from my 81 motor right onto the 79 motor, or do I need to get 1979 coils etc to make this work with points?

[Nessism]

I believe you can switch the ignition between the different engines. The coils should match the type of ignition.

Of bigger concern is that the 79 engine used VM carbs which are smaller than the later CV type carbs, and the cylinder heads are different.

[thewozza]

Of bigger concern is that the 79 engine used VM carbs which are smaller than the later CV type carbs, and the cylinder heads are different.

Do you think I can just swap the carb boots? Or is the port size different?

I'll measure tonight...

[Brendan W]

In addition the valve timing was changed and a higher output generator fitted amongst other less important things.
Download the service manual here............http://members.dslextreme.com/users/bikecliff/

[tkent02]

Do you think I can just swap the carb boots? Or is the port size different?

I'll measure tonight...

Port size is a lot bigger, as is the distance between the bolts.

[Steve]

If you want to use the '79 engine, you should really use some '79 carbs, too.

Not saying that there is no way to put the '81 carbs on there, but it would be far easier to use the '79 carbs.

As far as the ignition goes, there should be no problem swapping that.

Yes, the stator output was higher with the '81 (it started with the '80 model). The '80-and-up bikes lost the kick starter, so they increased the output to charge the batteries better, since you HAD to use the electric starter. You can not simply swap the stator, as the '79 has a 12-pole stator and the '81 has an 18-pole stator. The magnets on the rotors are matched to the number of poles. If you use the wrong combination, you will get NO output.

.

[bwringer]

Assuming it's not also damaged, you could switch the '81 cylinder head onto the '79 bottom end.

Then you could swap the stator and the rotor. And the '81's electronic ignition and advancer will bolt on in place of the points.