No. 3 build ready to kick off...

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Jun 25, 2017
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The parts stash for my No. 3 motorized bicycle build has begun to grow. I just bid on and won a suitable 'vintage' motor for the project on eBay - a spiffy 1946 Gnome et Rhone 2 stroke featuring hand change gears - which I bagged for the unbelievably stingy sum of 19 pounds, way less than the maximum bid I allowed for. Hard to believe really when you consider the same seller auctioned off an all but identical - but nowhere near so nice and with a couple of broken fins - motor a couple of weeks previously which sold for 197 pounds.

I'm delighted with this purchase, not least because of the hand change gear arrangement. That'll suit this upcoming 'vintage' inspired build perfectly. The motor appears in amazingly well preserved condition. Has excellent compression, all gears select smoothly and the piston/rings look like new. I'm in the process of hunting down a suitable carb and replacement plug lead.



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Anyone else having trouble uploading a post and/or pics?
Yesterday I spent several hours typing and re-typing the above new thread message and trying to upload the associated pics - and every time I hit the 'post message' button, an 'internal server error' message flagged up saying my request couldn't be completed. Worse, everything I typed apart from the first third of my message was repeatedly deleted. After retyping the message again and again, I finally gave up round midnight and went to bed.
This morning I tried again and it let me upload the pics - but when I went into 'edit message' format to add the missing two thirds of my new thread text, the same server error message flagged up repeatedly and I've againb given up trying to add this after typing and losing the text half a dozen times.
Let's see if the same will happen when I try posting this message.
Thanks for the heads-up re the server error issue. At least it let me post a new message, so here goes another attempt to add the missing portion of text from my original first posting in this new build thread. Assume the following reads on from the first message...

...Those superb heavy duty sprung girder forks I purchased for this build came from cnolmotorsport, the same China outfit I bought the frame/forks/tank from for my Indian board tracker tribute bike build. Yesterday I mated them to a 26" rim shod with a Schwalbe 2.35 Crazy Bob skin. Instead of my usual preferred arrangement of a Sturmey Archer 70mm drum brake up front as used on my two previous builds, this time round I opted to go with a SRAM roller brake. Was unsure if the SRAM unit would look too modern on what will essentially be a 'vintage' inspired build but once it was in place I was happy how right at home it looked. I'm particularly fond of the cooling fins on the rear of the SRAM unit's cover plate. Cool set-up.
Frame-wise, this build will be a complex, not to say ambitious affair - at least for me. I've purchased a new suspension frame for a bargain price which will donate its rear portion to the project. This will be mated to an entirely new scratch-built front frame designed and fabricated to accommodate my Gnome & Rhone motor. A hand-shifter will mount to the right side of a scratch-built flat tank I'll knock-up, connected to the small cam lever protruding from the right side of the alloy casing atop the motor's gearbox as shown in the pic of an original Gnome & Rhone R4 below.
Pics posted in this thread's introductory post show the as yet uncut donor frame. Just imagine everything forward of the seat tube, with the exception of the shock, will be dispensed with and consigned to the parts bin. Plan is for a long, low frame sporting a 24" rear wheel and with the front forks raked-out accordingly.

gnone et rhone.jpg
Season's greetings to everyone.
Having polished off the last of the cold turkey, I felt the urge to resume work on build No. 3.
After buying myself a 26mm flat slide carb for Christmas, I needed to figure out how best to fit this to my vintage Gnome & Rhone 125cc motor. All the 26mm intakes I looked at online over the last couple of weeks were no good. They featured a 90 degree bend and had fixing stud centres 45mm apart on one flange and 48mm apart on the other flange. I needed an intake with a bend of approximately 45 degrees and 48mm fixing stud centres on both flanges. Nothing else to do but fabricate the intake manifold I was after. So I purchased two different 26mm manifolds, cut off the portions I needed and discarded the off-cuts.
I'd had great success building my own alloy gas tank on my previous DECOLINER project using Alubuild 300 brazing rods, so I figured the same process would work when 'welding' this alloy cut-n-shut manifold. Worked a treat. Using a butane torch, I first pre-tinned the joint surfaces of both intake pieces. The parts were then positioned correctly together and the torch waved over them till the molten Alubuild 300 flowed, neatly making the join. All very low tech and very straightforward. The first pic shows the newly modified intake manifold posed alongside the unwanted off-cuts. Look hard and you'll notice the joint securing the flange shown at the right side of the pic.
The remaining pics show the carb and modified intake manifold bolted up to the motor. The new manifold was designed specifically to locate the carb offset to the left for two reasons. Firstly, the underside of the carb's float bowl had to avoid contact with the alloy gear cover atop the motor's crankcase. Secondly, the carb's air cleaner must be located sufficiently off-centre to avoid contact with the frame's vertically mounted suspension coil-over spring. Mission accomplished.
For the time being, the air cleaner's cover is sprayed in grey primer awaiting a top coat of whatever colour this project will be finished in...

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Looks good.
Where the two parts simply butted together? If so, I'm thinking that some type of support bracket further down the line might be a good idea to prevent the weight of the carb from putting leverage on the welded joint. The leverage along with the engine vibrations could possibly cause it to break at the weld.:39:
Looks good.
Where the two parts simply butted together? If so, I'm thinking that some type of support bracket further down the line might be a good idea to prevent the weight of the carb from putting leverage on the welded joint. The leverage along with the engine vibrations could possibly cause it to break at the weld.:39:

Hey Jim,
Yeah, in view of what you said, maybe it's sensible for me to run a test just to establish the joint strength on my modified intake manifold. Best way is probably for me to braze together the two discarded intake parts and test that joint to destruction. I'll do that asap and report my findings.
(FYI: Alubuild's tech blurb says any joint performed should be at least as strong as the alloy component material. I guess we'll put that claim to the test...)
OK, so yesterday I went ahead and carried out a weld strength test using the unwanted off-cuts left over after I fabricated my new intake manifold.
Once again I used Alubuild 300 brazing rods to 'weld' the pair of off-cuts together. As before, I made sure the work-piece was thoroughly heated and both joint surfaces were pre-tinned with a generous coating of molten Alubuild rod. I reckon this is the most important factor, ensuring maximum weld penetration of the joint. I wouldn't simply place the parts being joined together and rely on wiping a brazing rod round the exterior of the joint till it melts.
After performing the joint and letting the test piece cool down, I attempted to manually break the joint using all my strength. No joy. I tried again using brute strength and a broom handle inserted into one end of the test piece for extra leverage. No luck - so I set about whacking the test piece firmly with a mallet and the joint began failing after five blows and finally separated after eight.
I re-welded the test piece together a second time and repeated the process with pretty much the same result. Good enough for me to feel I can rely on my 'welded' intake manifold to hold up. But I may just take Jim's advice and rig up some kind of carb support as a belt-n-braces approach.
Finally - a little later than planned - work has begun to create this build's new frame. Sub zero temps and heavy snow have delayed delivery of the hydraulic tube bender I ordered, but I doubt I'd have gee'd myself up to go do some work in a freezing unheated garage anyway, so no worries.
I've already cut off the unwanted parts of the aluminium bike frame I purchased for this project, leaving me with the aluminium seat tube and the steel rear triangle with coil suspension. I'm loving the look of this set-up.
After several attempts doodling frame plans, I eventually came up with a layout that works for me. See pics. First pic shows the frame layout drawing. The other two pics show components laid over the drawing to hopefully give an impression of how she'll look. Not sure yet if I'll make the upper two frame bends a little more curvacious - I'll figure that out after my tube bender shows up and I've had a chance to play with it.
I've found a guy at a local tractor repair shop who's certified to weld aluminium. Already bought the 25.4mm (1") diameter 6061 alloy tube for the new frame. So now I need to fab a jig from 1" square alloy tube to hold the new frame parts in alignment for welding. It's all good....

Update....Ten minutes after posting the above message, the delivery guy struggled to my door in foot deep snow hauling my tube bender on a sack trolley. No excuses now. Freezing or not I'll be in the garage giving my bender a workout tomorrow. (No, that's not a euphemism...) lol.
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You need to check the articulation. I don't think it will work as it is drawn on the cardboard.

... I'll be in the garage giving my bender a workout tomorrow. (No, that's not a euphemism...) lol.
OK, you got my attention. What have you spotted that I've maybe overlooked?
Move along, nothing to see here.

I was in a hurry and didn't look at the other photos. At a glance the drawing looked off, but I didn't realize that it was just a sketch of the actual working part. I thought you were going to make it yourself based on this drawing. :doh:

Just for clarification, this is the problem that I saw. The triangle is pushing into the pivot arm. I was going to suggest additional pivots in the rear triangle. but I see now that it has them. :21:
frame articulation.jpg
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Phew! Glad it was a false alarm. I thought it was going to be a case of "back to the drawing board" - or in my case, "back to another flattened cardboard carton". :thumbsup:
Sorry for the false alarm. I was just about to leave for lunch when I saw it. Like I said, I didn't take the time to look closer, just knew that the drawing wouldn't work as shown. So I quickly posted a message before I walked out.

Looks great!
Well, I finally, managed to bend-up the new frame's downtube after a couple of false starts. It took a few practice bends using my new bender to both familiarize myself with how the tool works best and to learn the limitations of how much stress the 1" dia, 12-gauge aluminium would tolerate before fracturing.
I soon discovered the tube would fail, ie fracture, on the outside radius of the bend being formed - even on a relatively modest bend. The secret was to form the bend incrementally and with care, - which took a couple of hours sliding the tube in and out of the bender umpteen times. No complaints - my time comes free.
First attempt, the tube fractured just short of me completing the frame's lower bend. SH-T!!! That was almost and hour wasted. First pic shows where I got to before the bend failed. Second attempt, I didn't get much further before the tube cracked again. Oh well, the bender's instructions said practice making a few bends on scrap material before getting down to the real thing....
Third attempt, I decided to ease the lower frame bend's radius a fraction and I knew now from experience I'd have to make the downtube's upper bend gentler, rather than as drawn on my plan. So that's what I did, and this time everything worked out fine. Second pic shows the formed downtube overlaid on the drawing. Not much of a difference in shape - but it made a world of difference when it came to forming the bend without the alloy tube fracturing.