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Thread: 71 OIF Build

  1. #1
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    Default 71 OIF Build

    This is my first post on here. I've owned a basket case Trump for 15 years and finally decided to put it together. The plan is to hardtail it. So far, I have fitted a late 90's sporty front end and 21" wheel. I will post pics as I progress.
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    Progress. Started tearing the motor down, got the rear wheel assembles and bars mounted.

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    Last edited by skankr1; 09-06-2016 at 1:42 PM.

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    Let us know how the hard tail goes. I've got a 71 myself and was thinking going the hard tail route

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    The hardtail is being built. The cylinders and head are at the machine shop getting honed and resurfaced. I haven't done much to it except gather missing parts and wait. I will post more as I progress though.

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    I did get my tail light built. Repurposed old Turner microphone.

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    Hey man, me and a pal finished a 72 OIF bonnie this past fall. except we ran into running issues after we finished i think we screwed up the piston rings. we put a david bird hardtail on it. and an early evo 35mm front end.

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    That microphone tail light is killer...I'll be following your progress , keep the pics coming

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    Update. Cylinders and head are back on. I have most of the electronic parts (minus battery, ignition switch and wiring) to finish. I just need the hardtail to come in and she'll finally start coming together.

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    Just a note of caution, It used to be uncommon to see OIF bikes hardtailed, but clearly more and more being done. Theres a few kinks in using them. The factory experienced cracking of the frames on some early models. The reason is the main spine (Oil tube) is rather thin. Some cases of cracking at the headstock but not often as its well braced and they changed it slightly post 73, But the most common problem was cracking and oil leaks where the oil tube joins the plate at the rear of the engine (Top side of the sump) If you look, many have cobbly welds and a lot of splatter. My advice is make a collar split in 2 that extends up the spine (oil tube) and drill some 1/4" holes in the collar, Fit both halves around the spine where it joins the bottom plate, tack in place both halves then weld in the holes spreading the weld contacts around the whole collar and then weld in the split and tops and bottoms of the collar. Best to use TIG and done in a JIG. dont warp anything and control heat. A Wire feed will work if you know what you are doing but again control heat.
    This reinforces the area considerably. Keep in mind you are re-purposing the frame in a way the factory never intended.
    #2) Again, this is REALLY thin tubing you are welding too and expecting it to support a lot of weight and stress. The pix SAMTHEMAN posted show this problem. I would seriously consider reinforcing and spreading out stress and loading by using a triangle plate and welding it across the tops of both tubes and spreading out the load and welding to the Oil Spine in a much larger area. After a lot of riding you will find that metal fatigue will fracture the oil spine the way its currently done in those pics. Sure suck to have your frame crack or break.
    #3) Most of these Hdtails come too far fwd, I have a frame here someone did years ago, I am redoing the hardtail because the stock type Triumph tank wont fit. It hits those top tubes. While the pix of the little peanut tank might appeal to some, the big complaint about OIF frames is they look bulky. The stock gas tanks cover up this part very well. Perching a little wassell tank on top again might look cool to some, but to me looks like a tiny hat on top of a fat guy. (Think tiny top hat on a sumo wrestler) I LIKE the big 1971 tanks and they look good on this kind of build. Feel free to disagee but regardless you guys are gonna have a hard time finding ANY tank that will have a wide enough tunnel for that fat spine. The stock type Triumph tanks look good and are easily sourced. Plus,, you can modify those to suit. I like the 50s style and have fit the package racks on them as well. (look cool, and you can carry a 6 pack there at bike rallys or really tiny strippers)
    My unsolicited $0.02

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    Thanks for the info Doug. My pops is doing the welding. He's a CWI and used to build drag bike frames. He's knowledgeable and doesn't cut corners. It will be all jigged & TIGed, and we are going to gusset the bejesus out of her. The tank I have is a narrow tank from a later OIF. I'm going for a very skinny look. I am going to make the tank bottom sit flush with the bottom of the tube. Here's a pic of how I want the tank to sit. Feel free to criticize, but I dig it.

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    Sounds like you got a handle on it. I was pinged earlier by another guy seeking advice on a OIF build so I thought i would throw out some input and kill 2 birds with one stone so to speak.
    Many people are unaware of the cracking issue, especially the rear spine. It starts as oil leakage and people assume its all coming from the motor when its small cracks in the frame. If your pops has the skills, Im sure you will see what I mean soon enough.
    Your tank is fine.. If it covers the Oil tube/spine that will do the trick. Again, I am just expressing an opinion and I realize many people really like the tiny tank look, I like bigger tanks as well as balancing the look.
    That one pictured is a smooth top later T140 tank, I am sure it will be fine. Be advised though they ARE prone to their own cracking. Make sure you retain the bottom reinforcement strap and if yours is missing or no bosses, ADD THEM. The tanks tend to bow and spread and then crack. Common problem, also be sure you use lots of good rubber donuts on the underside to properly support and cushion it. When people neglect that they distort and metal fatigue and then crack.
    The important thing is its cool you guys are wrenching on the old iron and keeping them on the road. Motor on!

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    Progress.
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    So I have a question for a sanity check. Right now the hardtail is just tacked in. The front hoop is centered, neck is leveled vertically, the lower tubes are leveled horizontally front to back and side to side. We measured and squared from the center of the neck to the front of the axle plate slots. Does anyone disagree with this method? Is there a better way to square it up?

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    Sounds reasonable to me. Just for grins, run a plumb bob on the neck and then run a string as far as you can and then measure at the ends to see if truly square as the building and construction mantra is the same. A 1/16th off here is 12 inches at the end of a wall. But all in all looks good. Last thing to check is did you verify your ride height? Witha 16 or 18 in the back is the frame gonna sit level? (While it might seem like it little difference between a 16 and 18.) Is the height where you want it? Once the axles height is fixed not much you can do. Low is cool but too low is not fun at all unless you never go into parking lots, speed bumps, Gopher or mole mounds....

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