What have I gotten myself into?

[DGXSER]

Is the engine from a '79 special different from a '78 standard? I really like the '79's paint and detailing.

Yes, the engines interchange between all of the bikes, but the later 81 and on modles get tricky on the timing setup. For yours its like legos.

I have carbs for both, but I'd like to use my '78 carbs on the '79 engine, as I know the carbs are good, and the boots on the '79 look great. Possible?

Again, yes, completely swap and play.

I assume the frame on the '79 is different, since the seat mounts differently, but how much different? Can I use the front end off my standard? How about the swing-arm and final drive?

Here is where it gets different. The triple trees and frame were different between the special models and the standard models. Swapping that changes the rake of the bike and chnages how it steers. Some side cover stuff and the electrical harness and seat mount as you noted are completely different as well. But the swing arm is the same.

Will my '78 stock exhaust work on a '79 special motor in my '78 frame? How about in the '79 frame?

Yes, should be plug and play in the 78 frame. A standard exhaust system will not bolt right up to a special frame of vise versa though.


HTH!!

[Fix]

Thanks Don!

Now to confirm that the triple tree etc. I picked up are indeed for a special.

The only thing I can figure is that the PO was going to turn the '79 into a touring bike, hence the standard tank, bags and fairing.

Then it's decision time on whether to pick the best stuff to put on my '78 or to get the '79 put together and ride that one, with whatever's missing coming from the '78. Two bikes are more then SWMBO will probably allow.

[Fix]

Based on this image http://motorbike-search-engine.co.uk...ht-special.jpg

I have the shocks and airbox off a midnight special in here. Did any other model have the shocks with those reflectors?

It's possible the wheels and rotors are off a MNS as well.

What a hodge-podge of parts.

[fredintoon]

The rake's progress

- - - Here is where it gets different. The triple trees and frame were different between the special models and the standard models. Swapping that changes the rake of the bike and changes how it steers. Some side cover stuff and the electrical harness and seat mount as you noted are completely different as well. But the swing arm is the same. - - -

Hi DGXSER,
there are some minor differences between Standard and Special frames but they have the identical 29.5º rake angle.
The "look" of the bike was changed by hanging the Special's front axle on the front of the fork lowers rather than below them.
To keep the identical 5.12" trail the Special's triple trees were made shorter to move the fork tubes back by the same distance moving the axle up front moved the axle forwards.
If you put Special fork tubes into Standard 'trees you will reduce the trail (not the rake) and thus quicken the steering.
A complete fork swap, 'trees and all; between Standard and Special models will not change the steering geometry.

[DGXSER]

Thanks for clearing up my foggy medicine head on that Fred!! You are the steering god of the land IMO. I do recall the difference between Rake and Trail now.

So on the Special triple trees they moved the tow circles the forks slide into closer to the center of the frame mount by the same distance they moved the axle forward with its mounting position on the front of the fork.

So putting the special forks in Std triple trees would move the wheel mounting location out further in front increasing trail. While mounting Std forks in the Special triple trees moves the wheel mounting postion back decreasing trail. Hope I got that right this time.

I knew I had something messed up there, just did not expect that much. It's ok, I learn by installment number 34 most times, so only 26 more to go.

[fredintoon]

So on the Special triple trees they moved the two circles the forks slide into closer to the center of the frame mount by the same distance they moved the axle forward with its mounting position on the front of the fork.

So putting the special forks in Std triple trees would move the wheel mounting location out further in front increasing trail. While mounting Std forks in the Special triple trees moves the wheel mounting postion back decreasing trail. Hope I got that right this time.

Well, not quite, you got it backwards.
Imagine the rake angle centerline extended down through the steering post until it hits the road.
The tire contacts the road behind that spot.
The distance by which it trails is called ( you guessed it!) the trail.
Moving the axle forwards decreases the trail and makes the steering lighter.
Moving the axle backwards increases the trail and makes the steering heavier.
Note that these mix'n'match fork components let Yamaha owners who install sidecars lighten the steering for $50 in used parts rather than spending ~$1,000 for a Steerite conversion.

[DGXSER]

Well at least I was consistantly wrong.

Thanks for clearing things up for us kids Fred!