E34Croak’s 1974 CB750 Chopper

[e34croak]

Hello.
I picked this old school chopper up to build and I’m wondering if anyone can help identify the front end? Thank you in advance!

[TriNortchopz]

nice chop.looks like somebody stretched, raked and hardtailed a stock frame.

That frontend is similar to the Harman internally sprung girder, but is not;

it is an American Choppers Enterprises torsion bar frontend





American Chopper Enterprises Inc., Company Number 0591140, was incorporated on Feb. 3, 1970 in CONCORD, CA, suspended in March 1979.

[TriNortchopz]

from CBH:

"...First of all John Harman didn’t really invent the internal suspension girder as there were already several very old ‘Sprung leg’ type designs you can find by doing some simple patent searches. The man was a creative genius but he was also a chopper builder so like most of us he did his research when he was trying to develop his ideas. There is nothing wrong with that. In fact I'd be worried if I was going to buy something from somebody who didn't do any research.

Most people actually credit H-D with the ‘Internal Suspension Fork’ System patented in 1907 as being the first successful commercial rendition of the concept but J.W. Gates was building a much-improved version back in 1905. Unfortunately he did not receive a patent until 1910.

The design that most closely resembles the Harman however is that fork system used on the 1912 Thor racing cycle as shown below. I've talked about these forks and the Thor bikes in other parts of the site. I'm very surprised more builders haven't tried to bring a modern version of these forks back into production.



A lot of people don’t realize that Harman’s forks were actually an evolution of a design he used to build in the sixties that were just conventional Girders. Later he dropped the traditional Girder spring and started to experiment with’ Leaf Springs’ but still kept the girder links. Harman was building these forks while he was still in High School in 65 and his shop teacher did the welding work...



John did however have competition for that ‘style’.
Most notably was American Chopper Enterprises who made the ‘torsion’ bar forks shown in the old magazine shot below.


In many ways this was a pretty slick fork design. It utilizes small torsion bars as seen in the photo below.
You can just barely see them running between the ends of the Girder links.
The spring rods run all the way down through the rear legs to the rocker and terminates in a clevis on the rocker like Harman's.



Both Harman and ACE forks were also often customized and modified by Bob Dorn who also sold his own variations of the ISG during the early seventies. Dorn was a very talented Designer/Builder in his own right but you don't hear a lot about him. The picture below illustrates the lower end of his fork design. Note that he utilized a single rocker with a large clevis at the main pivot point and also used torsion bar suspension. He built several different variations of his version of the 'Spirder' over the years.

https://chopperbuildershandbook.com/har2.html

[e34croak]

Awesome! Thank you so much for the information. It seems like there is some damage to it or it is missing a component up at the neck area. There’s some grinding marks but I’m not sure if some part of it was cut off or what exactly the deal is.

[TriNortchopz]

that is so cool, love that ACE internal suspension girder.

what I see from yours, compared to the others I see from the CBH page, is the angle of the linkages; note how yours are less than 90 degrees from the front leg, kinda pointing down, while the CBH images show the linkages pointing up higher... there is more of the upper spring rods showing.
from your photos, I can't see anything missing - at least compared to the couple closeup photos from the CBH.

Can you share a couple more close up photos that show the upper and lower trees, from above and from below, and another straight on from the front at the top and at the bottom.

It looks like the ends of the torsion springs have been welded - wonder if they broke away and spun, or the ends of the torsion rods that were welded, had the welds cut, the torsion rods turned, then re-welded so the spring rods are further into the forklegs at the top, which would cause the spring rod at the rocker end to be further out at the bottom - raising the axle end of the rocker, which would raise the axle - and drop the front of the bike down... hhnmmmm.
The other difference I see between the CBH images are the linkages - yours, and the lower image showing Bob Dorn's, are two straight pieces with rounded ends, yet the one from the magazine article has linkages that are a bit of 'dogbone' shape.
Also, the bottom where the back leg joins the front - one has a gusset - like yours, while the one by Dorn doesn't have a gusset.
is the CBH gusset and yours the same- with a slot and three holes?

not sure what is going on at the bottom of the fork legs...perhaps it had been damaged then repaired... is it painted or powder coated... it's not chrome like when new...maybe it got rusty and they painted/coated it... can you sand off that coating to have a good look at the bottom of the legs where they bend, was it welded, or heated and straightened... is it straight, not tweaked, the tire at 90 degrees to the legs, bottom of legs at mid-point of rocker is even on each side.

How does the suspension feel - have you ridden it? can you just push/pull/bounce it to determine how well it works.

in my research I saw there are two ACE facebook pages... I can't get there from this old clunker laptop on satellite internet, deep in the woods of remote northern Canada... take a look there for more info - it would be cool to see an original ad, or a parts image, and find more history;

AMERICAN CHOPPER ENTERPRISES | Concord CA - Facebook
www.facebook.com › profile
AMERICAN CHOPPER ENTERPRISES, Concord, California. 806 likes · 30 talking about this. FOUNDED BY BOB DRON 1970.

AMERICAN CHOPPER ENTERPRISES | Concord CA - Facebook
fo-fo.facebook.com › people › AMERICAN-CHOPPER-ENTERPRISES
AMERICAN CHOPPER ENTERPRISES. 774 mær dámar. ��. 838 followers.

let me know if you find more info and can share it here.

[e34croak]

[e34croak]

I’m not sure why all these photos are sideways.
Here’s some more shots of the damage/repair? As well as some from above.

[TriNortchopz]

looks like the welds holding the ends of the torsion bars broke and were re-welded...could have been welded nicer.

In photo 2 it looks like there needs to be a bushing around the torsion bar - it's sloppy in that hole.

Are the linkage arms bolted to the end of the torsion bars? that would be the way to get new bushings in there... and maybe they are indexed by teeth or key, and could be moved to closer to the angle of the others seen in photos from CBH (above) if needed.