Extended swingarm modification

[Grewth]

I bought my second 650 Special about 18 years ago, mainly because all the good parts present seemed to match up exactly with all the bad parts on my first Special, bought a few months earlier.
The second bike was more or less standard apart from one strange modification.
The owner had extended the swingarm by about 6", by means of cutting the tubes and welding in extra pieces of tube.
Because the lower rear shock mounts had also moved rearwards 6" or so, obviously the standard shocks were now much too short for the job.
So a set of long bright red motocrosser type shocks had been substituted, which were raked back at about 45° maybe.
A sort of bodged up flat mudguard completed the job, the bike looked sort of freakishly disjointed to me.
The vendor seemed very proud of his handywork, and insisted that the extended bike handled so much better than his brothers standard XS.
I was thinking that the freakish appearance of the bike was probably the reason that he was struggling to sell it.
However, there were two standard swingarms included with the sale, and a knackered set of standard shocks, so I made an offer and a deal was struck.
I never did ride it with that long swingarm.
Both the spare standard swingarms had decent bearings, so I fitted one with some good shocks.
About six months later on, the vendor phoned me, out of the blue, and said that the swingarm bushes on his brothers bike had failed, and that I could sell him back one of the spare swingarms.
I replied that I was quite happy to keep the swingarms, thanks, that I was not operating a free parts storage service, and his brother could go whistle.
He swore at me a bit, I never heard from him again.
I've always sort of regretted not trying the bike when it had the extended wheelbase.
It looked well engineered enough, aligned properly at the very least.
The drive chain made up of two lengths joined together put me off quite a bit.
I think I slung the extended swingarm in a scrap skip at work.
Would it/could it of handled much better than standard ?
I believe that Yamaha extended the XS2 swingarm compared to the XS1, and Percy Tait had it extended further still.
But only a few mm not that sort of extension.
Surely it would have impacted the handling negatively in some way too ?

 

[AUTOMAN]

Should have tried it.

 

[Grewth]

To be fair, it looked like it had done some serious milage since being modified, so virtually no chance of it breaking at the welds etc.
But I still didn't fancy it.
It looked really freakish

 

[timbeck]

One of my XS's has a 4 inch extended swingarm and I feel that it rides like a hardtail . It also has a Brat kit so between the two the shock angle is pretty much useless. It works for me as an around town take it for a blast bike.....

tim

 

[Grewth]

TBH, I've never really understood the mechanics of what makes a motorcycle handle well or not.
I understand what makes a frame stiff or flexible because I understand structural design and the design of welded joints, but frame geometry is something of a mystery to me.
When Percy Tait helped Yamaha sort out the dubious handling in 1973, most of the changes were to stiffen up the frame and stop it flexing.
But he also extended the swing arm by about 3".
The most obvious effect of this is to alter the weight distribution, putting more weight on the front wheel, less on the rear.
Now just because that improved the handling, doesn't mean that extending even further back will improve things even more.
I haven't had the pleasure of riding my XS1B yet, all my previous bikes were post '74, so I really don't know how bad the "problem" is.
Having said that, my first "real" motorcycle was a Suzuki GT750 back in 1978, people told me they didn't handle well, not in a sort of "widowmaker" way, but not good either.
But I just thrashed it, the suspect handling didn't bother me much at all.

 

[gggGary]

But he also extended the swing arm by about 3".

2" but I quibble



The OD of the swing arm tubing also increased from 33 to 35mm
The width at pivot and axle also increased but I don't have the number handy 10mm?
Having ridden many later XS650s and 3 different 70-71 bikes now, I don't find "day and night" handling differences.
I'm no longer a road racer but probably still ride in the upper quartile of riders.
Have pushed two different 70's "pretty good" on local backroads and with the boys at the Ozarks rally two years ago.
Both bikes were sorted with fresh tires and tapered steering bearings.
I did get myself into a tankslapper on an XS1B, 45 years ago! In it's defense I knew NOTHING, it was a used bike I dragged out of a snow bank, got running and took on a 2,000 mile road trip with a bunch of gear lashed on the rear! After cranking down the steering damper (so THAT's why it was there) the bike completed the trip in fine style. (After shaking off anything not bolted firmly in place over the first couple days).
I do keep a bit of tension on the damper these days but not enough to notice slow steering.
So yeah they are a bit more flexy, but it's not night and day.
Probably the biggest handling difference came from the reduced trail when Yamaha took about 15mm out of the triple's neck, fork tube offset in the 73-74 chassis revisions. Especially at lower speeds I can FEEL that deeper early offset.
A special triple atop a 70 triple


quick list of changes through the years
Stiffer frame, engine mounts
longer wider thicker tubing swing arm
thicker fork tubes
reduced trail triples.
I've also ridden XS650 and Norton Commandos back to back and don't find major differences in handling.
IMHO the Norton's rear swing arm/mounts are rather noodly.

 

[Grewth]

The width at pivot and axle also increased but I don't have the number handy 10mm?

Now here's a funny thing.
The early swing arm pivot bolt is indeed shorter, it's impossible to tell just how much from these two, because the shorter XS1 item is a pattern replacement, and may not be exactly to Yamahas OE specs.
But I'm measuring about 18mm difference.
Now compare the width of the swing arm itself, at the pivot end.
Pre '74 and post '74 are exactly the same width, as far as I can make out.
I'm planning on using a late type single piece bearing shaft in my XS1B, if the side play works out right (feels like it is).
I'm using a genuine Yamaha bearing tube, but with pattern bronze bushings from Germany, and pattern end cap washers from Yambits which are probably made in China, so there's still a possibility that things may go horribly wrong.

 

[gggGary]

Good catch, I concede the front width, seems like @GLJ found he could sub late model one piece bits into his 72 arm.
They did get wider at axle and shock mounts, the later frames all have a jog out on the left rear angled tube to create the wider shock mount spacing.

 

[GLJ]

The aftermarket bronze bushing and tube/bushing are the same for all years. The pivot bolt is different between early and later frames.