Finally got around to modifying my frame. (update 1.7.13)

Here's the album.

I scooted up to my buddy's house this past weekend and finally did some substantial work on my maxim bobber project.

I don't like how the stock frame looks when the bike is bobbed. The frame rails beneith the seat don't flow with the tank. So I found a set of harley springs which allowed me to relocate the upper spring bracket downaward.

I am going to need to find smaller I.D. bushings for the shocks. That or some sleeves, but they worked out pretty well otherwise.

I still need to weld in the frame cross members but I ran out of time.

Overall, I'm happy with how it's coming out. What do y'all think so far?

~Rev

 

Re: Finally got around to modifying my frame.

The photo looks like you're keeping it secret.

Use a flash or turn-on a light!

 

Re: Finally got around to modifying my frame.

Haha, sorry about that. I finished up at 10 pm sunday night and only had my cell phone.



There are some better lit pictures in the album I linked.

 

Re: Finally got around to modifying my frame.

looks great man.....how did you decide and finally dial in your angle and what size tube did you use?

 

Re: Finally got around to modifying my frame.

Thanks bud.

To be honest, I just chopped off the factory upper spring mounts, bolted the shorter shocks in the lowers and played around with it until I liked how it looked. After I had one side dialed in and welded out, I used a combination of an angle-finder, a bit of wood, and a level to match up the other side.

The tubing I used is 1" O.D. I can't recall the wall thickness off the top of my head, but I do know it was a bit thicker than the factory frame.

I drove up to work on it this past weekend, but somehow I managed to forget my welding hood... That was a bit frustrating. Though I did bring my camera and snapped a couple pictures of the bike with the tank on.

Sorry about the giant picture size.

(Resize the photographs please)
Rick

Use PHOTOBUCKET.COM

Sorry about that Rick. I'll try this again.

 

Re: Finally got around to modifying my frame. (update 1.7.13




As of 1.7.13: New seat, welded upper rear x-member, fender mocked-up, rear tank mount installed, and slight tank mod.

Album updated with recent pictures.

 

IMHO you should re-think that Rear Fender placement.

That partial Rear Fender is going to be useless.

If you get caught in a shower, ... the rear wheel is going to sling moisture right at your butt, up your back and up-under the back of your helmet.

 

Aww, c'mon Rick. At least it's there. The original plan was to go completely fenderless...

Truthfully though, you're probably right. I just want to try it out like this and if need be, I can always change it.

Good lookin' out Sir.

 

will you be running pods or stock airbox

 

Neither. I'm just going to fab a custom airbox with a filter on either side. I don't much care for the way pods look (tuning issues aside) and I don't think the stock box is even an option now that I've chopped up the frame.

 

I hate to be the bearer of bad news but that geometry doesn't look kosher. When that shock compresses, the swingarm is just going to go up and past where it was meant to travel. Or maybe not. Looks pretty sweet though.

 

No worries, you're not the first to suggest this. I know it's a fair deal lower than most configurations, but I don't see how this is a possibility. The upper spring mount is a fixed pivot. There's no way for the spring/swingarm to invert.

Admittedly, the ride will be substantially stiffer than it would be had I kept factory geometry but I don't see a possibility of failure arising from the angle I used.

 

I think the concern is twofold.

First, the shaft drive can only tolerate a certain range of motion (much less than the swingarm allows when not restricted to the range of the stock shocks). So if the bike is lower, it MUST have less travel to not go out of those bounds.

Second, slanting the top of the spring forward increases the leverage ratio (the amount the shock compresses for a given force pushing the wheel up / seat down). As you say the ride will be substantially stiffer, I assume your springs are much stronger than stock (100lbs per inch by my measure); from what I gather the spring strength needed rises as the square of the leverage ratio.

Put those together, and you may (or may not, depending on springs and shock throw) have a situation where bumps can push the swingarm up far enough to damage the u-joint.

If you can pull the springs off those shocks and the bike rolls OK with the suspension fully compressed, then you should be good. If that's not an option, maybe figure out how far they will compress and cut some blanks from wood that are the length they would be when fully compressed, and mount those. Its a good call for safety's sake, I'd think. I know I'll be doing it; the rear I'm setting up will allow me to tweak ride height to address this exact concern.

 

Thanks for the input Sebwiers. The springs are significantly stiffer than stock and no amount of jumping on the bike (super technical testing, haha) has put the CV joint at a dangerous angle. I do think I'll take your advise and check the struts' travel limit just in case though.

 

I don't think travel limit or going "over center" will be an issue. With the geometry of the angle they're at, they aren't going to move much going over bumps. "Substantially stiffer" will turn out to be an understatement in terms of suspension compliance.

Unless it just bends them or breaks the frame instead.

 

With the geometry of the angle they're at, they aren't going to move much going over bumps.

My impression is that leaning the shock forward increases the leverage ratio, which effectively makes the spring response "softer". If I'm wrong, there is something very odd about my (use of) ruler and caliper.

The triangulation in the direction of the shock force looks good to me, but it is hard to tell from the photos whether there is anything of substance joining the left and right sides to prevent them from spreading out / folding in. There certainly should be. Ideally it should also provide enough bracing to prevent them both from skewing to the same side. A pipe of the same diam & wall thickness as the other members going straight from one side to the other between the upper shock mounts would probably do, maybe with small gussets.

It is worth noting that all of the shock mounting points will be taking more stress than in the original system. That's what "increased shock leverage" means, after all.

 

There is a x-member going between the upper shock mounts and I gussetted the upper shock mounts. The only way this frame is buckling is if it goes under a suburban.

 

Just making sure you thought of testing it! The old jump up and down method is the industry standard, I believe. Keep up the good work and the pictures!

 

Agreed - and the "limit" will be further into the travel,

FYI someone on this site hard-tailed an XJ at a claimed 5" drop, and the "U" joint lived (can't remember who)

 

Its possible, depending how they did it and how they measured. If you put the bike on the center stand, you can probably raise the wheel 5" relative to it's 0 load position. That's your 5" drop right there.

Or, you can raise the back of the engine so the u joint is straight. Not much extra work when you are already doing a custom hardtail. That's what I would do if doing a HT shafty with that much drop.