building a frame for a Twin Cam A...

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Prof
Founder, Choppers Australia
Posts: 5936
Joined: Sat Oct 22, 2005 3:54 pm
Location: Willunga, South Australia
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building a frame for a Twin Cam A...

Post by Prof » Tue May 14, 2019 9:35 am

Garry dropped in his twin cam recently purchased from NSW (writeoff). NSW does not alow repairable writeoffs, so although this only has bent forks and and broken indicators, it has to have a new non Harley frame. Ridiculous, but due to bike laws being tied in with car rules and done to reduce rebirthing...
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I have learnt a bit about modern HD's so far in this exercise. Garry 's FXR is a twin cam A motor which is rubber mounted. Twin Cam B's were introduced with twin balance shafts a couple of years later and were solid mounted in response to buyer feedback. Plenty of custom frames exist for the B motors, but we have so far found only the Rolling Thunder frame below that does a rubber mount twin cam frame...
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If the motor was a solid mount B, we could use a soft tail design, but that is ruled out because the rear of the motor has to be attached to a flexible rear swing arm.

I spent some time talking to a Harley shop and chasing info on the net and all advise against solid mounting the A motor; apparently frame cracking issues.

We have another alternative and that is building a new frame in house. I'm just waiting on my engineer to get back to me on a question about this approach, and we can get on with the project.

Garry wants the bike to be fairly standard but with a springer. We'll use a Meatballs springer and add some rake to retain stock trail, plus add another inch or so for better highway handling... Garry lives out in the sticks.

More soon as I know something...
Chopit'nrideit... Prof

Prof
Founder, Choppers Australia
Posts: 5936
Joined: Sat Oct 22, 2005 3:54 pm
Location: Willunga, South Australia
Contact:

Re: Twin Cam needs new frame

Post by Prof » Sat Feb 22, 2020 10:28 pm

Finally have a fast computer and access to all my picture files. I've been able to begin catching up on work as a result of a variety of family and other set backs, so at last we can show you Garry's build.

Quite a few hours went into researching frames. We found two possibilities claiming to suit the rubber mounted Twin Cam A, but some things just did not seem right, so I decided our safest bet was a new in house TCS frame.

Because the bike is a statutory write-off it has to be engineered as a current independent build known as an ICV (Individually Constructed Vehicle.

Step one... engineer comes here and we discuss construction of the frame, shape and tube size and type, gussetting etc. Then materials are ordered and I build the frame.

Step two... Engineer comes again to check that is what we decided, weld quality etc and takes a bunch of photos. He then sends in application for VIN.

Step three... frame is completed, moulded and painted and entire chopper is assembled. It has to comply with ADR's and current regs (as with any new bike entering Australia) therefore indicators, e marked lens, mirror size, handlebar height, width, lighting, labelling on switches etc etc etc!

Step four... Engineer does final inspection including brake and noise tests. Takes heaps more photos and does a big writeup for the road traffic blokes (oh sorry! and sheilas).

Step five... They say "Oo how cool!" and arrange an inspection time, which of course we will pass and they then hand us a form that allows the owner trot into the nearest Service SA centre to register the machine.

Step one was completed last year and I am now building the frame. To keep things as easy as possible, we will run original (stock) brakes, wiring loom and exhausts.

At this stage Garry wanted the bike close to stock but with a springer. A benefit of the time lapse between him bringing the bike in and starting on the frame has meant he has decided to be a little less traditional and wants a King'Queen seat, medium height sissy bar, bobbed rear guard, custom tail light and head light and forward controls. With some advice from this ol chopper jock, he agrees to a bit of extra rake and some stretch in the frame. Result is at this stage nice looking machine that appears to be moving fast just standing still. I think he'll love the result. It will definitely be much nicer to ride than the stock machine.

So with out further ado, let's get into it...

My new worker, Lionell, is taksed with dismantling the bike. We will be using the motor/gearbox, swingarm, both brakes, rear shocks and the front wheel (with new rim and stainless spokes) hand controls plus the other parts mentioned...
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Now for rake and trail and adherance to the Ridikulous Rool. Working this out will give us the height of the steering head, the first thing we need to begin setting up for our new frame. I have calculated that with a moderate increase in rake a 2" over Meatballs springer will be about right and got that sent over from Bendigo. Four over would have been nice, but Garry has not ridden choppers before and began wanting something near stock so the 2" over is a bit of a compromise.

This contraption allows us to work all this out because we can move the steering head up and down and adjust the rake...
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First the 550 Rool. I set up the springer up on a 19" wheel and set the RR at 500mm. This is the horizontal distance between the centre of the steering head and the bottom centre of the forks (the axle on telescopics). Because this is a springer and I haven't tried to get one past regio arguing that on a springer it should be the centre of the bottom of the back legs not the actual axle, we will play safe and use the axle as our measuring point...
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What rake do we end up with? 37.5 degrees. 9.5 degrees over stock. That's quite manageable.
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Now check for trail. Stock rake on this model HD is 4.1" I want to go to between 5" and 6". Any more and a less than died in the wool chopper jock would not like the heavier low speed feeling. Comes out to just over 5"...
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Play around a bit more increasing rake and checking figures. Decide on the 500 RR, 37.5 degree rake and just over 5" trail.Gives us a steering head height of 900mm, about an inch lower that stock. I like this because we can achieve a cool rakish frame with the steering head dropped a bit... will have a slight digger look...
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Rake is now dialled into the frame jig...
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Stock ground clearance is 6.5" and I will keep to that. Set up a bunch of wooden blocks on which to initially rest the motor...
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Now have to do a myriad (and I do mean a myriad of measurements) so I can build the front and rear mounts for the motor on the jig. Finding places to secure the motor/gearbox that would not interfere with the frame mounts can be a bit of a challenge and was here, as eventually I had to modify both. Just a few pics of the dozens of measurements made). Rear of garbox...
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Front engine mounting needed spacers...
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Numerous checks on original frame eg front engine mount is off centre...
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Turning up some spacers...
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First mount being set up...
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More checks for squareness...
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Engine is hoisted up with block and tackle and st on the blocks. Here, rear mount has been made and attached...
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Front mount done. Swing arm now attached to rear of gearbox...
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Jig is checked for level. Engine is double checked for level and centred at the front with a plumbob and the rear to the centre of the tyre...
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Distance of stock steering head from a known points (bottom engine mount) is measured...
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Four inches of stretch is added and steering head height and rake checked.

Why the 4" of stretch? 1. The extra rake throws the handle bars back towards the rider so the steering head needs to move forwards. Garry lives a few hundred miles out of the city with mostly straight roads. The extra wheel base will make for a more stable bike on the highway.

It will make it a little slower in really tight corners like small roundabouts and T junctions, but most riding will be on the highway so let's make sure it is a good highway bike. He'll be laughing when out with his mates, as it will be so much more relaxing to ride...
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Next machine up a steering head. Although the modern HD's have bearing cups integral with the steering head, I prefer those used on earlier frames that have removable bearing cups. It allows us if needed to use 3 degree raked cups to increase of decrease rake if different forks get used down the track. I use a heavy walled pipe for steering head...
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Steering head and bearing cups installed...
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Now back the the rear end. Swing arm has 3.5" travel so we need to know highest and lowest points of swing arm, tyre, and drive belt. One inch flat bar and 1/4" round is used to make up some guides so we don't stick a frame member in the wrong place!...
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Curved flat bar yo see here is the highest point of the tyre (plus 3/4" clearance) to allow for when it hits one of our many SA road bumps. I am planning a traditional style frame, but with rails behind the seat that follow the highest point of the wheel. Let's see how the standard shocker will fit. The stock mounting point is well forwards of the axle which creates a problem for the top mount. It would be way above the curved rail. So we cut off the bottom mounts and move them back a couple of inches. Shocker now fits. For strength, because we are dropping the seat rail lower than stock, we will slope the shocker a little extra. This will harden the ride slightly but be hardly noticeable...
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OK. So that's the basic set up. Now to build the frame around what we have set up. Heaps more measuring to clear everything, but still keep a rakish look. That will be for our next post shortly...
Chopit'nrideit... Prof

Prof
Founder, Choppers Australia
Posts: 5936
Joined: Sat Oct 22, 2005 3:54 pm
Location: Willunga, South Australia
Contact:

Re: building a frame for a Twin Cam A...

Post by Prof » Mon Feb 24, 2020 12:08 pm

Now ready to build the frame. Just one pic missed off last post. To locate top shocker mount we cut and drill a piece of 20 square tube with full length and collapsed length of rear shocker...
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Tubing...
Discussions with the engineer resulted in main tubing to be 32mm DOM x 3mm wall. Backbone 50 x 50 x 4 square tube. Square backbone is to keep it simialar to the original frame. Wall thickness is greater. Rest is up to my discretion.

Tubing suitable for motorcycle frames is 1. ERW which is the normal tube you would buy at ans steel supply place. It can be identified by an inner weld seam running the length of the tube. 2. DOM which is ERW that has been resized over a mandrel to remove the weld seam and create a uniform wall thickness. DOM is also more rigid than ERW because the steel has been slightly compressed squeezing it between the mandrel and the outer former.

I use 25mm x 3mm ERW for frames on up to 90's choppers, but go to the larger DOM on the big inch motors as they develop more power and expecially more torque (twisting of the frame). Steam pipe which is similar to DOM but softer for easy bending is not suitable as frame tubing. Ordinary pipe in smaller diameters very definitely a no no expecially 'water pipe'.

Pipe (not water pipe) is suitable for backbones if at least 2" diameter and 4-5mm wall thickness.

Note that tube size is quoted as Outer Diameter and wall thickness whereas pipe is quoted as Inner Diameter and wall thickness.

Because we are now gong to be cutting and welding tubing is is time for a check on alignments. My laser guide is put into the steering head. You can align steering head fairly accurately if you machine up a piece of tube to exactly fit in the steering head with a centralised pointer at the other end. A quarter of a mil out in the steering head will be magnified 8 or so times by the time the error is transmitted to ground level = 4mm; .5mm = 8mm!

That said I figure that alignment up to 3mm error would not be noticed on a chopper, but do my best to keep it within 1mm. Frame flex in hard cornering will most likely cause more misalignment than that remembering also that tyres flex as well... and frames do need a certain amount of flex to reduce stress points breaking. That said keep alignment of steering head within 3mm...
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Laser pointer mark...
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Steering head is also checked for centre...
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... and rake rechecked...
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A metre rule is used to mock up backbone and this allows me to then use my 'angleometer' to establish angle of cut in backbone...
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Angle cut and bottom and top curved to match steering head. Still needs a bit more shaping. Very, very important to have all tubing joins a very exact fit to prevent pulling and twisting out of alignment when welded. As a weld cools it contracts and will pull tubing to one side quite dramatically...
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Backbone needs to be curved over the rear cylinder for clearance and so we can have the correct steering head height and the lowest possible seat height. A series of very precise cuts are made. Lines of cutting are drawn with a square. If the cuts are out of square you can end up with a bend and twist to the right or left...
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Backbone set up on our chopper. The motor has to be able to be removed from the frame so the bottom of the 32mm bottom frame tubing will be level with the bottom of the motor. That means I need to allow 40mm clearance above the motor, the main clearance being the rear cylinder. Wooden blocks in the photo are the spacers needed to accomplish this...
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Next is the rear vertical that carries the rear rubber mount at the bottom rear of the gearbox. Here I use 75 x 30 x 4 rectangular tube...
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We need reinforcement so the bolts don't crush the tubing. I cut up two pieces of solid bar to fit...
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One piece has to be grooved to clear the welding seam...
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A couple of holes are drilled to plug weld the bar in place...
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Holes for the rubber mount are now marked and drilled...
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Bolted in place. Now to work out a backwards sweep to keep it close the the guard and allow as much seating space as possible...
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Angle is established and a pattern cut out. Location of bend is marked with square. Pattern is used to work out how much metal has to be removed...
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This is then marked out of tube...
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Very carefully cut and bent...
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Perfect...
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Battery needs to fit in under 25mm frame rail. Lines up nicely with end of backbone...
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Squared up ready for welding...
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As previously mentioned, welds pull as they cool and shrink. A piece of tube is tacked across the cuts to be welded to keep the correct angle...
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Cuts chamfered...
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Tacks across bottom edge then tube turned over...
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... and second set of tacks done. They are then left to cool before removing the tacked on tube...
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Steering head tacked. Because weld pulls on cooling (have you got that message yet!!?) I do a quick tack at top left then around the other side and bottom right, then bottom left and top right. Same for the rear...
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Lower tubes next... and that requires lots of measuring. Our next post.
Chopit'nrideit... Prof

Prof
Founder, Choppers Australia
Posts: 5936
Joined: Sat Oct 22, 2005 3:54 pm
Location: Willunga, South Australia
Contact:

Re: building a frame for a Twin Cam A...

Post by Prof » Tue Feb 25, 2020 11:37 pm

Lower frame tubes right side...

The lower frame tubes start at the steering head sweep under the motor on both sides turn up behind the clutch/gearbox and when they get close to the shocker top mount curve around to line up with the top of the rear guard.

Each side needs to be identical. The bottom of the lower tubes will be level with the bottom of the motor. they also need to keep as close to the crankcase/primary cover for greatest strength and good looks. The right side needs to clear the stock exhaust which will be mounted to pass inspection.

The front right down tube could easily get in the way of the exhaust as it exits the front head. Both down tubes need to be in a good position so we don't end up with an ugly front rubber mount set up. We also need to think of how forward controls will be mounted off the down tubes.

To the rear, the left side has to clear the primary cover, the belt drive when under full shocker compression and end up in front of the shocker top mount, then swing in towards the guard so we don't end up with an ugly fat rear end.

The right side has to clear the exhaust, allow the swing arm bolt to be retracted and also end up in front of the shocker top mount.

Measure, measure, test, test. We will need to use tight curves to accomplish all this. I have two different radius formers on my bender so the smaller radius one will need to be used.

Now we want some supports for the tubes as they pass under the chopper. I use a couple of scissor jacks, square tube of angle iron and level them with wedges...
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Lay a piece of tube so I can mark where bends and cuts will be...
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To make bending simpler, I will fabricate each side in two pieces, joined in a spot where they will later be joined across the bottom by the sidestand set up. Turn up a pair of slugs and will drill holes in frames for plug welding. Length slugs should extend into each tube is 1.5 x ID of tube...
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Now for the angle of the down tube sections keeping in mind clearances with exhaust and positioning for front engine mount...
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Bends are marked from where they start and an arrow shows the part of the tube that will be in the bend...
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First one bent and tested for fit. Spot on first time. Bender former is marked so it can be brought to same position for second bend; this needs to be done because the tube springs back when the bender is released...
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Tubes laid side by side to ensure they are exact same bend. Arrow shows we need a little more on the second tube...
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This can be tweaked in the vice with a long piece of pipe...
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Angle correct and second tube cut to exact same length from bend. Set squares or a high long block of wood will keep the two tubes in proper alignment for measuring...
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Plan for rear section of tubes. Measure twice and bend once! This is checked that it works for both sides. Again direction and start of bend is marked clearly...
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My long 'angleometer' is used to get the correct angle...
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Both rear sections bent and joined temporarily to front sections with slugs. You'll notice that the front tubes start bending a little later than normal.
This is so the rubber mount bracket doesn't poke out forwards too far...
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Next post we will curve the rear tubes using heat. When doing this work I've just desribed you can't be too patient and careful...
Chopit'nrideit... Prof

Prof
Founder, Choppers Australia
Posts: 5936
Joined: Sat Oct 22, 2005 3:54 pm
Location: Willunga, South Australia
Contact:

Re: building a frame for a Twin Cam A...

Post by Prof » Fri Mar 13, 2020 10:46 pm

Sorry for the delay. I've been trying against the odds to get this thread up to the current situation, and at last finally can get some done tonight...

My favourite treatment on the rear of swing arm chopper frames is a curve that matches the top of the guard. This requires bending a wide curve in the tube. Years ago, I bought a tube roller to do this job, but it is too inaccurate and wastes a lot of tube, so frame has to be curved using heat...
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Tube is progressively pulled around a former. Trick to an even curve is slowly progressing the heat as pressure is placed on the tube. An extension (arrow) is usually needed especially in the case of 32mm DOM...
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First curved frame set up. Not shown here are a couple of photos I lost that show the wheel raised to its maximum height plus safety gap of 5/8" (16mm). Tube needs a bit of a recurve to get it just right and final shape shown here...
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Backbone is now completely welded up at curve...
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Tack welded to steering head. The four tacks are done in a set sequence to minimise twisting. Bottom left, top right, bottom right top left as quick as possible... then laser used to check alignment once welds have cooled. Backbone is attached so that there is about 10mm clearance to top of steering head to allow for weld to be kept a little way away from the bearing mount. This is because welding will tend to distort the tube if it is done too near to the edge. I also prefer where possible to weld the steering head to back bone before I weld the rear of the backbone. Less chance of steering head coming out of alignment that way, but not always possible...
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Backbone now tacked at rear...
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Second rear rail is now curved and checked against first one. Again a couple of goes are needed to get them matching exactly. Levelled then...
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...end checked for vertical. If vertical it means the two are the exact same length...
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Arrow shows some heat being applied again to a spot to even up end of curves...
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A final couple of cold tweeks are done using a long piece of pipe in the vice...
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NOW LOTS OF MEASURING! Rear rails have to clear a whole lot of parts. Must clear swing arm as it moves up and down (bottom red arrow). Must clear drive belt as it moves up and down (top red arrow). Needs to clear motor sump and primary drive inner case. With these parameters established a wooden guide block is clamped to keep it at the right location (green arrow). Of course...
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... the right side has to also clear everything... including the exhausts (green arrow). Also has to allow a socket to get to the swing arm shaft...
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Both frame bottom rails need to be the same distance from the rear upright. You need to be patient at this point. It is important to get everything lining up and clearing everything. If you don't take much care at this point frame will be out of alignment which can cause all kinds of nightmares later on. I've had frames come into the workshop with seat rails different lengths, out of level (leaving the seat on an angle) and even the shocker mounts in one case a full inch out and different heights!..
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An angle is tacked to the rear post to ensure the rear frame rails are even. Bike is checked for level and tacked angle levelled...
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Measurements to each side are taken from a central point in this case the steering head...
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Frame angle has to match on each side. Again, a whole pile of measuring and finally another guide block clamped in place...
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With all this done, we can now fabricate lower and upper rectangular sections that join the two rails to the rear post. That will be the subject of the next post. Thanks for your patience.
Chopit'nrideit... Prof

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