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Undertail install

8621 Views 15 Replies 4 Participants Last post by  lou1000
Ok guys I need your undertail install experience here. I need to know if you need to have any part of the trunk area left attached to the bike in order to install an undertail properly. My bike no longer has any part of the trunk where the electrical components were organized. The previous owner of my RC must have spent most of his time on the track or he just didn't care what the bike looked like. The undertail/fender eliminator that he had on the bike was homemade. This is fine if you are going to do a nice job of it. Essentially he just bent some aluminum and made a box to hold all of the electrical components. Then he used some Velcro to "try" to hold everything in place. I have no place to mount the license plate or taillight. I have been looking at undertails but I am a little gun shy about getting one if I find out that the means to attach it no longer exist on the bike. Maybe someone knows of a good website where they explain how to install one.
I would appreciate any input you can give me.
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Go here and it will show you what to do. Most undertails install the same way.


Thanks for the website reference. It was very helpful. Looks like I am going to have to fabricate something myself to hold the battery and some of the electronics before I put on an undertail.
I have a Hotbodies undertail I've installed.
If you look at their instructions, they want you to trim the stock fender at the line just rear of the battery box. There's a raised rib that runs cross-ways and that's their cut line.

However, I cut from that line only to either side and then back, essentially removing the the rear of the fender, but leaving the side intact. Like a square U.
Then, not only can I use the rear fender mounts for additional support, but also it leaves the relay mounts intact.
Makes for a much cleaner wiring setup. No relays flopping around or zip-tied to a frame rail.
Thanks for the website reference. It was very helpful. Looks like I am going to have to fabricate something myself to hold the battery and some of the electronics before I put on an undertail.
What was left of my fender was so butchered that I just got a new rear fender.
I was so mangled I thought he trimmed it with a chain saw.

And don't get me started on the resulting wiring job.
Had to replace the rear wire harness to correct that.
Thanks for the helpful tip. I will definitely take your advice. The wiring job on my bike is a Frankenstein job as well. I think I can salvage it, but it makes me wonder what else on the bike this guy didn't care about.
I used the scrap plastic from the fender cut to fabricate two mounting tabs to support my Hotbodies undertail near the rear mount bolt holes.

I also drilled a set of holes at the forward-most part of the undertail for support as well.
In that way the undertail is supported at the front and at the rear with the combined support at the mid-point when the rear cowl is attached.
A Dremel tool is your best friend for these projects.

As an FYI. If you're replacing the rear access panel seal (which I had to, and the OEM foam material is real crap), use the 3M closed-cell foam used for home insulation.
You can pick it up at ACE hardware. Get in the 1/4" width.
It goes on quick and easy and makes a really nice seal.
Great advice

Thanks again. You have some great tips for this project. I only have one problem. The previous owner of my bike COMPLETELY eliminated the fender. From battery box to tail. It is gone. I have been looking for a used one but haven't found one yet. Factory Price is ridiculous. From what you have said I gather that it is critical element in supporting the under tail. Oh well. I guess I will keep on searching.
Without a rear fender, how is your battery mounted?
By some fab'd brackets or what?

The previous owner of my bike did a real crappy job cutting the fender.
It looked like used a chain saw or hatchet. I mean it was ghastly and 1000% unprofessional.
Once cut there's no way back, so I just bit the bullet and bought a new fender and trimmed it.

I got practically all my parts from MrCycles.com.
The rear fender is about $119 plus S&H, less mounting hardware.
That's without the battery box cover, which is another part.

The fender holds the battery, the ECU, routes the wiring harness, mounts the relays, etc.
And the undertail mounts to it as well. So it's an important part.
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Without a rear fender, how is your battery mounted?
By some fab'd brackets or what?
He made a battery box out of alluminum that he rivited to the homemade fender eliminator. He stuffed some foam tape in the box and just laid the battery in there. He ground the rivets down a little but they still started to wear a hole in the battery. I have to do something else. The power commander and that heat sink looking part are the only other components that he actually attached to the fender. The ECU he tried to velcro on but that didn't hold well. The rest of it he just left floating around. When I first got it I only had about two months of riding before nasty weather arrived so I just zip tied things together and to the frame to secure them. But snow is flying now and I am going to try to do it right.
120 bucks for the fender! That doubles the cost of my project!
Such is life I guess.
I suspected that was the case.
Did the previous owner use this as a track bike and stripped it all down?
That's usually what they do when this arrangement is used.

I know you don't want to spend some cash, but using the rear fender is the cleanest way to go.

I wouldn't mind sending you my old bobbed rear fender, but truly, the previous owner did a horrible cut job.
The stock fender clips to the sub-frame at the front and sides, and bolts at the rear.
The idiot cut the side clips, so it had to be held by zip-ties. It's basically useless.
Yes I am pretty sure it was a track bike. There are some other clues to this conclusion. One of which is the brake light was just bolted to the rear with a couple of pieces of bent steel. There is no place for a liscense plate. Rear blinkers or any sort of mount do not exist. Most of the bolts are drilled for safety wire and some wires are still installed, but if I am not mistaken RC's came that way. The rear brake light switch was removed. The wire for the kickstand shutoff was removed, more then likely he just threw the kickstand on before he sold it and didn't even use it.

Thanks for the offer but I am sure that it would bug me just as much as you knowing that underneath it all I had a hack job of an install.

There are plenty of other cosmetic issues with the bike but the good news is it seems to be mechanically sound.
Good to hear about the mechanical condition.
Any engine can be abused to death, but these engines are way strong.

You've got all winter. Take your time, do what is affordable over time.
It'll get done eventually.

Just do a professional job, one to be proud of.
That's why it took over 4 months of actual work to finish mine.
Longer if you include the planning and parts ordering, etc.

But, I'm rather proud of the job and so far, everyone else thinks so too.
And that feels good when they give you that kind of feedback.

And I'd want you to get that happy-happy-joy-joy feeling as well.
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what are you going to do with the stock tail and lights??
i am interested
I am not sure yet. Untill I actually purchase an undertail I need to hold on to them. One of the kits that I was looking at required them.
Sorry. I will certainly let you know if I get it figuered out and I don't need them.
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