Cafe Racer Forum banner

41 - 60 of 461 Posts

·
Registered
Joined
·
1,295 Posts
I have great luck with bimetal hole saws. Even with my less than perfect drill press things come out OK. Not to ask a dumb question but,did you remove the pilot drill from the saw for the picture, or did you saw with out one?
 

·
Registered
Joined
·
1,828 Posts
Discussion Starter #43 (Edited)
I'm starting to get excited; things are moving from the drafting table to the workshop, if ever so slowly. I actually mocked up the swingarm position this morning, if only temporarily.



I am not going to use my mounting plates, because a kind soul over on the Garage Journal took pity on me and volunteered to make up a pair using proper machine tools. And of course, it will have to then all be welded together.



I decided that I am going to weld in the tube and swingarm mounts first, then cut out the center of the cross tube later on to make the rear engine hanger. I want to make absolutely sure the swingarm is mounted as true as possible. The rear engine mount is not as critical. And this way I can finalize the two steps separately.



As much as I've bellyached about the YZ125C swingarm being less than ideal, I have to say that width-wise, it is remarkably spot-on, even with the pivot offset to the left. If I butt the left mounting plate against the frame, the swingarm is centered nicely within the frame.
 

·
Registered
Joined
·
1,828 Posts
Discussion Starter #44 (Edited)
With the swingarm clamped in place, I briefly played around with the rear axle.



All sorts of finagling will be needed to align the rear rim and rear sprocket, both of which are wildly off in stock GS450T configuration, but we're not ready to go there quite yet. I'm taking one baby step at a time.



Since the side plates on the Yamaha swingarm are thinner than those on a GS450, I have to make plates to widen the swingarm to match the Suzuki adjusters. The photo above shows them mid-fab. I need to remove the red shaded areas and round the jagged outside edges into smooth curves. These will be welded onto the outside of the swingarm axle slots.
 

·
Registered
Joined
·
1,828 Posts
Discussion Starter #46 (Edited)
And finally, even though I am nowhere near this point in the project, I used some cardboard scraps to figure out the dimensions of the seat pan.



It's a very funky, odd-sized shape to start with, and having the rear wheel extend so far beyond the rear loop makes it even goofier to fit. A careful examination of the Airtech product line has convinced me that there's nothing out there that will fit this easily. I will have to either custom mold a seat shell from fiberglass, or modify the rear part of the frame to fit something I like. But for right now, I am just going to concentrate on getting the chassis in one piece and rolling around on two wheels. One baby step at a time...
 

·
Registered
Joined
·
1,828 Posts
Discussion Starter #47 (Edited)
Finished shaping the rear axle reinforcement plates I showed in rough form earlier. They are certainly not show quality, but they look a lot better than they did earlier, and more importantly, they'll be functional enough to solve the issue at hand.



Sure, they're basically two over-glorified washers, but with just a hack saw, a flat file, a round file and a dremel tool, I'm happy to have created any sort of part at all.



And here's where they'll be welded onto the swingarm. I've got some welding training and a Clarke spoolgun MIG, but I've been hesitant to do my own welding on a motorcycle. This is a good prospect to test my skills, because in use the plate is clamped in place, and even if loose would remain fully captured by the axle. The welds' only purpose will be really just to keep the place aligned around the slot and in place when the axle is removed.
 

·
Registered
Joined
·
681 Posts
Are you going to just drill a couple spots in the plate and tack weld, or draw a full bead all the way around the perimeter?
 

·
Registered
Joined
·
681 Posts
Come to think of it, I think my dirtbike runs plates just like those on the inside of the swingarm. It's a cast/welded aluminum swingarm, the plates are screwed on with flush countersunk cheese head screws to provide a harder surface for the spacers to butt up against. So, the precedent is there to just screw them in place if you wanted an easy out.
 

·
Registered
Joined
·
1,828 Posts
Discussion Starter #51 (Edited)
Well, I thought I was making real progress, but now I'm not at all sure. I'm taking a huge step back and rethinking my idea of moving the swingarm pivot rearward from the rear engine mount. I'm afraid it's not going to work. Look at this photo:


Look at the distances from the countershaft to the swingarm pivot to the rear sprocket. I'm thinking that the distance between the front sprocket and the swingarm pivot is too much of the total percentage of the sprocket-to-sprocket distance, so that the chain tension is going to change too drastically as the suspension moves. The Bultaco motor already has the countershaft pretty far forward from the rear of the crankcases. By voluntarily increasing it further, I'd just be making an already less-than-ideal situation more unworkable.

Time to rotate my thoughts and take another run at this.
 

·
Registered
Joined
·
1,828 Posts
Discussion Starter #52
Hey, guess what? I've wasted a whole year!

Okay, so not totally. I've collected more parts, scrubbed and sanded parts, and completed a few other minor bits of fabrication.

But as far as the swingarm mounting issue goes, I've decided to go back to the design I originally posted here on Nov 03 2011 — nine days after I started this thread. Every design I've come up since presents too many other functional or fabrication issues, or would require excessive cost.

After spending a year sketching, calculating, and pouring over fastener/bearing/bushing/tubing specs, I've concluded that going back to one of my earliest solutions is the only way to get off what has turned out to be an unending merry-go-round of "this-fixes-this-but-complicates-that" pretzel logic. I bought three different pivot bolts, frame tubing, and was about to sink money into high-end needle bearings and having a pro welder modify my swingarm to fit them. At that point I came to the conclusion that there isn't an ideal solution.

Besides, with the exception of having a shaft turned down on a lathe, I'm back to do being able to do all the work myself. That's what this whole project is about. Paying a welder to build a swingarm doesn't teach me what I want to know.

I keep reminding myself not to think of this as my first custom build: it's only an educational simulation, a dress rehearsal for maybe building a real custom bike someday. I am going through this process to learn what it takes.
 

·
Registered
Joined
·
1,828 Posts
Discussion Starter #53 (Edited)
Remember this?

I've started working on this configuration, minus welding the second washer to the inside of the frame. (Turns out, there isn't room.)

SO, I reamed the right side pivot mounting hole from 14.3mm to 15mm...

Which allowed the hole to accept the 15mm Suzuki front axle I'm re-purposing as my pivot bolt.

The axle necks down to 12mm threads, which can pass through the existing 14mm hole on the left side of the frame, but the shoulder behind the threads can't.

Fortunately, when pushed against the hole, the bolt shoulder's taper forces the 12mm threaded portion to center itself within the hole...

Which allows me to locate a 1/4"-thick washer's 12mm bore concentric to the original 14mm hole in the frame.
[EDIT: I guess I didn't make clear that I am doing this only to position the outside washer for welding; the shoulder will eventually be turned down and pass completely through the hole.]

Snug it up with the axle nut and it's locked securely in position. Now I just need to sand everything down to bare metal in order to accurately weld the washer plate into position.


And while I'm doing that, my spare Suzuki axle is back in the hands of a lathe-owning co-worker...
 

·
Registered
Joined
·
2,047 Posts
Relying on the shoulder to locate one side of your swingarm is a bad idea. Hell, threading some stainless rod stock should be cake for you, make your own pivot bolt.....really.
 

·
Registered
Joined
·
2,047 Posts
Relying on the shoulder to locate one side of your swingarm is a bad idea. Hell, threading some stainless rod stock should be cake for you, make your own pivot bolt.....really.
 

·
Registered
Joined
·
1,828 Posts
Discussion Starter #56
quote:Originally posted by Swagger

Relying on the shoulder to locate one side of your swingarm is a bad idea. Hell, threading some stainless rod stock should be cake for you, make your own pivot bolt.....really.
What makes that a bad idea? I'm only using the shoulder to temporarily center the new washer, long enough to weld it onto the frame. The shoulder will eventually be turned down (along with most of the length of the pivot bolt) and pass fully through the new, welded-on plate when it's all properly assembled.
 

·
Registered
Joined
·
2,047 Posts
Ok, for starters that washer is likely a very soft alloyed steel, they generally are since they offer that last quarter turn of tension. However that aside, if all you're doing is locating the washer to weld then it's not a big deal other than a likely propensity to egg out down the road.
 

·
Registered
Joined
·
2,047 Posts
Ok, for starters that washer is likely a very soft alloyed steel, they generally are since they offer that last quarter turn of tension. However that aside, if all you're doing is locating the washer to weld then it's not a big deal other than a likely propensity to egg out down the road.
 

·
Registered
Joined
·
1,828 Posts
Discussion Starter #60 (Edited)
How long does it take to turn down an axle?

Well, when you don't have access to a lathe, and you're trying to get it done inexpensively, and you aren't even sure you want it done, the answer is 358 days.

But here, finally —*after passing through the hands of four different machinists and more than a little hesitation on my part — is the secret ingredient to my swingarm installation.


It turned out great, it's a nice, snug slip fit within the bearing sleeve, and it doesn't look nearly as spindly as I expected it to. And even though I was willing to pay to have the work done, I ended up having it turned for free.

Before I can mount the swingarm, I still need to make up some sort of escutcheon plate for the left side pivot hole and the spacer that's needed to go over the right-side end of the pivot shaft. But hey, it's one roadblock I've gotten beyond. On to the next of a hundred thousand things that need to be accomplished...
 
41 - 60 of 461 Posts
Top