81 xj750 rigid project pics

After seeing some of the rigids in the galleries, I couldn't resist... any suggestions/comments welcome

 

Re: 81 xj750 rigid

i have uploaded several pictures in the gallery

 

Re: 81 xj750 rigid

more pics... more rake and different backbone

 

Re: 81 xj750 rigid (new pics of backbone and added rake)

is that the stock front end in the last picture? looks pretty wicked

 

Re: 81 xj750 rigid (new pics of backbone and added rake)

yes. stock front end and wheelbase is 2 inches longer after rake change

 

Re: 81 xj750 rigid (new pics of backbone and added rake)

Looks terrible! Can I have it?!

 

Re: 81 xj750 rigid (new pics of backbone and added rake)

i take it you added to the bottom frame rails? do you have any "in the making" pictures?

 

Re: 81 xj750 rigid (new pics of backbone and added rake)

i removed the entire backbone and replaced the triple configuration with one piece of pipe. I have several pics in my gallery of "before" and "after". The bottom frame rails have not been altered.

 

Re: 81 xj750 rigid (new pics of backbone and added rake)

Looks to me like you should add a couple of gussets in the rear.
Some extra load-bearing won't hurt the cause.

 

Re: 81 xj750 rigid (new pics of backbone and added rake)

Don't put up too many pics, Hillsy will steal them and post them all over other forums "for your own good". Without so much as a peep in regards to asking permission.

 

Re: 81 xj750 rigid (new pics of backbone and added rake)

far from being done with the frame, I intend to gusset where necessary for safety. Hillsy? will keep that in mind. Thanks rick and kevin

 

Re: 81 xj750 rigid (new pics of backbone and added rake)

I don't know if you've done this, but welding the swingarm to the frame will strengthen it quite a bit. Overkill is a good thing in this circumstance. Watch the grease in the bearings when you do it though.

 

Re: 81 xj750 rigid (new pics of backbone and added rake)

much appreciated, thanks kevin

 

Re: 81 xj750 rigid (new pics of backbone and added rake)

You're doing a sweet job of it for sure. Just curious about the rake and stuff...I chopped my X and after considerable research, learned all about altering frames and trail. Have you calculated your trail measurement yet? In order for your bike to handle properly after such a drastic modification, your trail must fall between 4 and 6 inches, depending on your bike. My model's trail was supposed to be 4.7" and after the front end was installed, the trail remained the same. This measurement is key to good handling, just like a front end alignment is crucial to a car. Just curious dude, and safety conscious as well.

 

Re: 81 xj750 rigid (new pics of backbone and added rake)

Johno, out of curiosity, how does go about calculating the trail measurement?

 

Re: 81 xj750 rigid (new pics of backbone and added rake)

here is how the rake was achieved: after i removed the original backbone i took the overall measurement and left the new backbone one half inch (1/2") short. After spot welding the bottom of the new backbone to the hardtail section, I heated the down tubes below the neck brace and let the headtube fall into the cope of the new backbone. After tacking the backbone to the neck I checked to make sure the axles were parallel. They are within 1 degree of each other. As far as the trail measurement, I am unsure. Wheelbase did increase by one and one half inch (1 1/2").

 

Re: 81 xj750 rigid (new pics of backbone and added rake)

Ok...here is a good writeup from Frames and Frames Geometry
It has pictures and even points you to a couple of sites with Trail Calculators so you can punch in your numbers and get an instant readout of what the trail is for your particular setup. There is a lot more on this topic if someone really wants to get into it. IMHO, this is an important topic for anyone wanting to alter their ride's frame.



Trail is the distance between the front tire’s contact patch and the point where the centerline of the bike’s steering axis meets the ground (see the illustrations).

Motorcycles have positive trail. Much like the caster angle of an automobile, positive trail provides the straight line stability that allows us to take our hands off the bars while rolling down the road. The more trail the more straight-line stability.



Trail checking tool kit. The carpenter’s square and protractor came from the lumber store, the rest of the tool was fabricated from various pieces of aluminum stock.
Most motorcycle designers and builders like trail figures in the 4 to 6 inch range. Most factory bikes fall into this same range. In fact, the chart for the current model line up from Milwaukee lists trail figures from 4.1 to 6.2 inches. In general, sport bikes run less trail which tends to make them quicker to change direction (some would call it twitchy), while cruisers and factory customs run more.



This is the basic set up. The small cross shaft bolts to the bottom of the lower triple tree. Aluminum tubing (the pointer) slides over a slightly smaller piece of aluminum stock.
With most standard-issue front fork assemblies and standard triple trees an increase in rake will result in an increase in positive trail. With choppers this means a rake angle of 45 degrees can result in a trail dimension of 8 or more inches. Too much trail means great straight line stability, but a lot of what’s called “flop” at slow speeds, shaky off the line. The more straight line stability the less a bike wants to turn. At speeds the bike wants to stay straight and you’ll need a larger turning radius and more pull to handle corners. That’s why a balance is important unless you’re building a bike for Bonneville or the drags.



The trail dimension can be altered without altering the frame, with the use of “raked trees.” (Check the illustrations here for clarification.) In fact, some of the factory bikes from Milwaukee use raked trees to help them achieve what the engineers consider an ideal trail figure. Before bolting a set of raked trees on your bike remember that raked trees reduce trail. Exactly how much depends on the angle and height of the neck, the size of the front wheel and where the triple trees position the fork tubes relative to the neck.


Don’t skip ahead here - this is important stuff.

Because raked trees reduce trail you can’t just bolt a set of seven-degree trees to a stock Sportster to give it that long raked look. Raked trees on a stock bike can easily move the machine into a negative trail situation. This means you’ve lost all straight-line stability and your bike will be prone to high-speed wobbles. We’re talking major instability here.

Experienced chopper builders might buy a frame with 40 degrees of rake and then use a set of “five-degree trees” (this is an example, don’t duplicate these numbers) for a total of 45 degrees of rake. By using the five-degree trees they reduce the trail to a more manageable level (approximately 4 inches) and get rid of that really heavy feeling, most noticeable on slow speed turns, that results from extreme trail dimensions.

The best way to know for sure what the trail is on that new chassis you just purchased is to check it. Option number two (and a good aid to planning a chassis) is to use the very slick trail calculator at perseperformance.com. RB Racing also has a calculator at: www.rbracing-rsr.com/rakeandtrail.html. And if that’s not enough, there’s a rake/trail/tube length chart in the Drag Specialties catalog. Back to the photos. The shop images come from American Thunder in Prior Lake, Minnesota (a certified Wolfgang Publications affiliate shop). The trail-checking tool is a simple tool that Neal and crew assembled from aluminum stock - designed to screw into the threaded hole found in the bottom of most triple trees.



As you can see, there’s lot of difference between a bike with a 33-degree neck and another with a 40-degree neck. Vince from Redneck Engineering likes to see the trail between three and five inches, the Perse Website uses a figure of 3.5 to 5 inches. Some stock Harley-Davidsons come with 6 inches, so maybe that should be the upper limit.

The important thing is to be aware of the impact that trail has on the bike’s handling, and avoid building a bike that falls outside what most chassis experts and professionals consider to be the acceptable range.

 

Re: 81 xj750 rigid (new pics of backbone and added rake)

Thanks Phil, that was an excellent article. I will be sure to take some measurements and adjust accordingly.

 

Re: 81 xj750 rigid (new pics of backbone and added rake)

No problem...just want to promote safety. Good luck with your build, if I can help out in any way, pm me.

 

Re: 81 xj750 rigid (new pics of backbone and added rake)

The thing that really worries me is that people who have no idea how to build or modify a frame see all this DIY hardtailing and neck chopping on the internet and think "that can't be too hard - I might have a go at that myself" and end up getting hurt or killed.

I could write a whole lot of other stuff here but that's all I really want to say.

 

Re: 81 xj750 rigid (new pics of backbone and added rake)

It's not your intentions that are in question here, it's your methods. Simply asking permission to post in another forum, or even pointing others to an existing topic here would have been better. Then all concerns could be addressed by the bikes owner, not channeled through you, a "worried" bystander. <sarcasm> Noone would have ever thought to hardtail a bike before reading it here. </sarcasm>

 

Re: 81 xj750 rigid (new pics of backbone and added rake)

I actually PM'd you about this in April - did you not get that???

PS: Sorry to hijack your thread 81rigid - your bikes looking good.

 

Re: 81 xj750 rigid (new pics of backbone and added rake)

I have never recieved a PM from you. Besides, if you did PM me, I never granted you permission to... Whatever, man, I'm over you and your good intentions.

 

Re: 81 xj750 rigid (new pics of backbone and added rake)

Maybe you should've asked permission to hijack this thread...

Glad you're over me Hans.

Once again - sorry about the thread hijack 81rigid

 

Re: 81 xj750 rigid (new pics of backbone and added rake)

I didnt hijack it and take it to another forum in a community he's not even a member of. I have more respect for others than that.

 

Re: 81 xj750 rigid (new pics of backbone and added rake)

now.. im not a mod or anything but.... shouldn't this be kept to pm's?

 

Re: 81 xj750 rigid (new tins arrived) pics

new tins, mustang single cap tank, 3 gallon capacity and 6" rear fender that needs to be shortened...

 

Re: 81 xj750 rigid (new tins arrived) pics

Hey there crew, Deathmetaldan is right. If you two have a beef, take it outside. And I'm certain you two can do the right thing.
Any more sniping and I'm locking the thread.
All else aside, while I'm a purist at heart, your work is very nicely layed out 81rigid. I'm with Johno8, please be very careful in your efforts, I'd hate to hear of a mishap down the road. I'm looking forward to your finished work.

 

Re: 81 xj750 rigid (new tins arrived) pics

Looks awesome with th new tins.

Get a better pic!!

 

Re: 81 xj750 rigid (new tins arrived) pics

thanks Robert and Ease... Operator error on the pic, will try to get more and better pics posted tomorrow.

 

Re: 81 xj750 rigid (new tins arrived) better pics

better pics of tins

 

Re: 81 xj750 rigid (new tins arrived) better pics

looking good

 

Re: 81 xj750 rigid (new tins arrived) better pics

I noticed you didn't cross brace the framing from the backbone down to the rear wheels. I was curious if the frame is strong enough without the bracing? I am going to start chopping up my maxim when I get some good information from all of you.

 

Re: 81 xj750 rigid (new tins arrived) better pics

mike, i am not done with the frame yet. i still have alot of work left to do to make the bike safe to ride. i was just mocking up the tins to see if everything fit.

 

Re: 81 xj750 rigid (new tins arrived) better pics

Like Rick I'm a bit of a purist but I have to say I really like the way that bike sits,looks tough.
The wheels look like they will work with the look as well.

 

Re: 81 xj750 rigid (new tins arrived) better pics

more pics of fender after i cut 14" off of it

 

Re: 81 xj750 rigid (new tins arrived) better pics

Lookin great!!

 

Re: 81 xj750 rigid (new tins arrived) better pics

thanks gunnabuild and ease for the positive comments... more pics of possible running of front fender and of the final tear down.

 

Re: 81 xj750 rigid (new tins arrived) better pics

Lookin good you do good work for sure!!! that already is one sharp bike ti is gonna be killer once the paint is on.

 

Re: 81 xj750 rigid (new tins arrived) better pics

Looks good, but ugh to the bars...

 

Re: 81 xj750 rigid (new tins arrived) better pics

I think the Rear-end needs a Gusset on either side or some other form of support to keep the whole Rear-end from bending or stress fractures occuring to the Upper trailing section.

A few nasty bumps in the road and that Rear-end will probably bend right up.
Somethings missing.

 

Re: 81 xj750 rigid (new tins arrived) better pics

Thanks 85maxim, Kevin and Rick for the comments. Kevin, I agree the bars don't work for this project, but I have decided to upgrade to 1" risers and bar. So I drilled out the top triple tree to fit, cut the top riser plate (off of a sporster) and found some stock bars ( off a dyna lo-rider). Let me know what you think. Rick, I am still in the process of gusseting the frame for strength and this picture was before I began that process. I will post some pics of the finished frame as soon as I am ready for paint. Thanks again for the comments and suggestions.

 

You're going to want to weld your swingarm to the frame. Otherwise, as Rick stated, it's going to bend. You want as little motion as possible back there or eventually your hardtail will fail and bend/break.

 

great lookin bike...this is the direction i would like to take mine soon (enrolled in community college welding class!)

what kind of welder did you use for the frame work?

also what else do you plan on doing to the frame?gussets or other support?

 

oksooner, i am using a maxxis welder 140 amp (120 volt) and i have started the gusset phase now. progress has been slow with the holidays and all. i have a newer picture i will add to this post. good luck with your class and your project.

 

that bike has perfect stance...awesome.