Frankenframe: Ironhead rear frame section grafted onto an Evo Sportster

[alfajuj]

By the way, here's a nice picture I found of a 1975-76 XLH showing how the bracket that supports the battery box and oil tank goes. It fits between the solenoid and the starter (removed in the picture). It's right where the middle of the starter motor is on an Evo.

[alfajuj]

Now the next challenge is how to actuate the rear drum brake. Here's a rundown of the different ways the motor company did it:

1952-1974: The brake linkage has a cross over shaft which runs in bushings in the frame with the brake pedal on the left side. Obviously the shifter comes out of the right side of the transmission and passes through a bushing in the cam cover.


This is not such a good plan for an Evo Sportster for a lot of reasons. Since Evos shift on the left, You'd need to somehow actuate the brake on the right. I'm sure some creative thinking could lead to a linkage system for this, but the chain and the exhaust are really in the way. So I passed on this method.

1975-1976: This system had the right footrest incorporate a cable operated rear brake pedal, with an awkward crossover shift linkage where brake linkage used to be. So the shift lever still came out of the right side of the transmission but the linkage was hidden under the sprocket cover. So using the 75-76 cable operated system is tempting for the Evo project. It would just require fabricating a mount for the footrest bracket on the frame. (75-76 still mounted the footrests on splined stubs on the frame). This would probably be the easiest way to do it.

[alfajuj]

But the method I finally decided upon is not the easiest, but I do think that it's the best.
That would be the 1977-78 method.

Here the shift lever shaft comes out on the left side through the primary, like it does on an Evo. They used the remnants of the old right side shift to put in a brake pedal operating shaft 42549-75 which was suspended by a bushing in the right case on one side and the bushing in the cam cover on the other. The splined end is for the brake lever. And the shaft pulls the brake cable.


There's now an additional inner sprocket cover 34893-75 which holds the cable and the brake light switch.

Now the only problem is that there is no such bushing in the cam cover of an Evo and the remnant of the old shift lever shaft bushing in the right case is now just a locating dowel. But at least it's still centered on the shift lever shaft which is the same exact location as the 1977 brake operating shaft.

Evo Sportster locating dowel:

Evo Sportster cam cover:

[alfajuj]

Here's what the 1977-78 cases should look like with the bushing for the brake pedal operating shaft

And the cam cover with the bushing for the other side of the brake pedal operating shaft


So that's what we need to emulate with the Evo parts

[alfajuj]

So here's the part of the right case that needs to be machined to fit the bushing. I turned the inner side of the operating shaft to a slightly smaller diameter so that I could use a smaller bushing which would leave more meat in the case in that area.



Bushing installed


It has to be aligned with the bushing in the cam cover





Needs some filing

One piece of advice for this machining is to do the final fitting for the operating shaft with the crankshaft in place. Since there are 2 dowels on the Evo cam cover and we've taken one of them away, you need to have the crankshaft pinion there to make doubly sure that your cam cover is perfectly aligned. I had thought that 1 dowel plus all the screws would be enough for alignment, but they weren't. When I assembled it with the crank in place, the operating shaft got all tight. I had to final fit it with valve grinding paste to get it to move smoothly.

[flatman]

I really like what your doing and thanks for all the pics

[cdwillis]

Very cool. I came across the Inuchopper blog before and was trying to figure out how he crammed that evo engine into the ironhead frame. Mystery solved.

[alfajuj]

For the 1977-78 brake setup you need the inner sprocket cover 34893-75 along with the cable and brake light switch.

You also need the cable type brake side plate 41662-75

I was going to use my Evo sprocket cover and just grind down the inner ribbing to make clearance for the inner sprocket cover. But with all the disc brake master cylinder mounting stuff on it, it would look half-assed. So I've decided to buy the 1977-78 XLCH sprocket cover 34850-77. That will look a lot cleaner.

I've already got the 77-78 right footrest on the way.


That should make for a nice clean installation

[alfajuj]

Well, here's the frame all welded up and painted.

And here she is with the case installed

And the solo seat installed

[alfajuj]

I bought this internal throttle off the bay and was going to install it on some Biltwell bars I had.

But then I scored some original 1960's Laconia (aka Sport) bars.
These particular bars are the type that have the spark advance side welded solid and only the right throttle side working. The right side did not have a hole for a starter button or a kill switch, so they most likely would be from 1970-72 XLCH, since those had coil ignition with automatic advance. Or I guess they could be from a 1965-67 XLH, since those didn't have a starter button yet and had automatic spark advance. Either way, they're perfect for my purposes.

Here's a shot the handlebar section of the 1978 XL parts manual showing details of the up to 1973 bars:

The bars came without the guts of the internal throttle. The only things still in there were the original crusty throttle control coil (cable sheath) with the end bobbin (numbers 57 and 58 from the diagram above) held in with a set screw (50) but without the wire inside. There was no plunger (56), roller pin (11), rollers (51), spring (46), end screw (52), or grip sleeve spiral (47). Well I started pricing these parts out and they're pretty spendy. But then, even if the grip sleeve spiral were present, I couldn't have used it anyway, because it would have been a "push" spiral (56220-53) for a Linkert or a Tillotson carb, and of course I would need a pull spiral for my Evo's CV40 Keihin carb. Here's a pic from the internet showing the difference between push and pull spirals. The 56220-58 is pull and the 56220-53 is push.


Then I got to looking again at the internal throttle kit I had bought earlier. Lo and behold, the design of this kit is just like the old Harley internal throttle. The smaller diameter tube with the slot from this kit is about the same as the end of my handlebar. I got lucky here, because most of the internal throttle kits out there are a different design from the old Harley type. I tried its plunger and it fit right into my handlebar! Even the end screw was the same thread as my bars! Could it be that for once something in this project is fortuitous and easy?
Nah! Not so fast:
When I tried to slip on the grip sleeve spiral, its internal diameter was about 0.4mm smaller than the outer diameter of that part of my bars. So I started honing it and I eventually got it to fit. But then I found that there was about 17mm of end play once it's installed. (if you pull outward on the sleeve it pulls out 17mm until the internal shoulder is stopped by the end screw) If I had the original Harley spring 56216-53, it probably would have fit perfectly. But I decided that a tubular spacer would be good enough, so I turned one up on a lathe. And now it fits fine and saved myself some money in the process.

[alfajuj]

Here's my Laconia bars




They're only drilled for a horn switch and the high-low beam switch on the left bar. This particular configuration most likely makes them original to a 1970-72 XLCH.

This is the look I'm going for:

[alfajuj]

I painted the rear shocks and test fitted the rear fender. These are real Harley shocks, but the chrome springs were rusty, so I painted them black. (I like black way better anyway).


It turns out the 1974+ fender strut reinforcing straps were interfering with both the fender and the fender buffer. The fender is a 900 XLCH part. I had to grind the reinforcing straps quite a bit for clearance. I'm really considering just grinding the straps right off. Apparently the 1973 frames didn't have the straps, but the frame tabs that the fender struts bolt to were cracking, so they added these clumsy reinforcing straps. I think they're pretty ugly. The earlier frames with forged lugs didn't need reinforcing.


I test fitted the rear wheel. You've got to love the sexy flanged Borrani rims!


I got the front forks squared away and mounted. The top tree and fork legs had some dings, so I sanded and polished them. I painted the lower tree with crinkle finish paint. I'm really happy with how it turned out. These are stock 1988 39mm forks.

[alfajuj]

I gave up on trying to make the Evo sprocket cover work and acquired a repop 1977-78 XLCH sprocket cover (34850-77). I used a 1/2" stainless lag bolt as a plug for the kicker hole. This is also an original 1977 footrest bracket. I had to fab a longer stud to mount the bracket. The stud and two of the screws are a match with the Evo cases. The other 2 bolts plus the kicker arm stop are dummies, but it should be fine, since there's no kicker to stress it and the stud is massive.



Today was somewhat of a milestone in the project. I have mounted the tire (a Duro HF-308 4.00-18) and installed the rear wheel. For me, when at least one of the wheels goes on, it starts to feel like a motorcycle again.


I think this picture tells it all. Making this rear suspension and solo seat work on an Evo Sportster were my main goals in this project. I absolutely love the forward shocks and single-sided drum brake.


Threw the tank and rear fender on just to get an idea of how it's going to look.

[alfajuj]

This is a big milestone in the build. The front wheel is on and she's sitting on her own sidestand! It's officially a motorcycle again!
I haven't got any Champagne, but I'll find a bottle of something! Cheers everybody!

The jugs and heads are crying out to go on. I'm going to do the 883-1200 conversion, so I need to have the cylinders rebored.

The cam chest is all zipped up and the rear brake pedal operating shaft is good.

Um...I think she needs a new sprocket, ya think? It's ok, I'm going to put on a 22T to get the right final ratio anyway.

[alfajuj]

I mounted up the starter and sprocket cover, and it just fits. Actually inside the sprocket cover I needed to relieve some areas to make it fit.

I mocked it up with the oil tank and exhaust to make sure everything is going to fit.

It's a pretty tight squeeze.

I had to nip a corner out of the battery box to allow the exhaust to fit.