Mounting swingarm to frame

I'm curious about the possibility of mounting the swingarm to the frame while leaving the engine and gearbox iso-mounted. I've heard the idea come up occasionally, and it seems to get shot down because of sprocket alignment issues, but it seems to me that the isolastics are designed to limit movement of the cradle to the vertical plane, which would effectively keep the sprockets aligned pretty damned well.

I've found some references to people *planning* to try it, but I can't seem to tack down any reports of people actually doing it. Perhaps those that have tried were never heard from again? Sailed off a cliff, or straight to a handling-induced nirvana state from which they never returned?

So, anybody actually done it? Seen it done? Reports please!

-Hans ('73 750 Combat, San Francisco)

hanslymoto said:

I'm curious about the possibility of mounting the swingarm to the frame while leaving the engine and gearbox iso-mounted. I've heard the idea come up occasionally, and it seems to get shot down because of sprocket alignment issues, but it seems to me that the isolastics are designed to limit movement of the cradle to the vertical plane, which would effectively keep the sprockets aligned pretty damned well.

I've found some references to people *planning* to try it, but I can't seem to tack down any reports of people actually doing it. Perhaps those that have tried were never heard from again? Sailed off a cliff, or straight to a handling-induced nirvana state from which they never returned?

So, anybody actually done it? Seen it done? Reports please!

-Hans ('73 750 Combat, San Francisco)

Click to expand...

Never seen it done, but visualized it many times. Tell us about your fabrication/machining/engineering skills....

Makes sense to me. There is only at most 1/8" fro/aft shifting allowed by the pair of iso's acting in line of drive train. Easy amount of slack for rear chain run to take up. There's are lot of cycles that use a chain tensioner like MX that have such a swing arm range chain would go too slack w/o it. Just keep the tranny sprocket from iso twisting out of line to rear. Might consider radius rod or swashplates.

Harley has one with a rubber mounted engine. I would want to see how they did it. It also has a belt final drive which is lighter than a chain. My concern would be the chain getting tight and loose at a super rapid rate as the engine vibrates forward and back while the rear sprocket does not. Most bikes with the swing arm mounted to the frame have the engine solid mounted as well.
Dan.

concours : my fabrication etc skills are minimal to nonexistent -- but my ability to come up with crazy ideas is pretty good, and I know some people who can make things happen on the realization end

hobot: thanks, I was thinking that a tensioner wouldn't be necessary, but good to keep in mind. And it seems like without the swingarm pushing on the cradle the amount of twist the gearbox sprocket will see is minimal, but I like the idea of the radius rod. You could even loosen up the isos for more extreme anti-vibration nirvana

My biggest concern is whether or not the frame could handle the load of carrying the swingarm directly, or if it would need to be reinforced. Since it wasn't designed to handle those loads, it might be too flexy and/or breaky...

thanks!
-Hans

Hm now I know why my brain flashed on Hans as Handyman. You did strike a nerve about the frame tolerating the swing arm directly on one hard point rather than spread out in the over lapping of two iso mounts. There is more shock loading jerking of tension and slack when crossing unpaved wash boards or pasture so don't think that is an issue. All this inventiveness revolves around pilot comfort and frame tolerance vs secure handling at hi loads. I know I've solved all issues experienced by others and gained some ability unknown to others while lossing all sense of motorcycle under me but patch texture and G force sensations that to me are literally breath taking. A way to absorb and store and release steering loads and conflicts of tire vectoring has stumped the best there is by their own testimony. either breaks or loses control they say. I do think making the swing arm more stable is great idea and can still retain the good parts of Commando set up. My Peel will have swash plate swing arm back up about half way to the axle. If ya tale a robust screw driver and lever in iso frame holes and tug on Z plate and brace forks and work rear tire may be eye opening as me seeing how dam elastic every assumed hard point ain't. Bob Patton's robust rear rod definitely helps tail wagging the head/forks but by accident I found more complaint-weak rods at front and top really amazing compared to sport bike antics beyond full tire grip. Someones got to find out though so wish good lost sleep pondering on it. Just know when I get Peel to max lean max fork angle and max power on tire into a decreaser radius thats just the end of ordinary fun before the sling shot frame action gets into play on higher power loads. A great handling cycle lets ya turn every turn into accelerating decrease G force orgasm. No one else seems to look forward to those states so who'd believe it.

I'm not sure there is much wrong with a Commando with good isolastics but wonder about that third 'iso reading this thread.
Would a lower rear isolastic and bracing cross tube improve what is not that bad.
(Add support to the swing arm platform while retaining some form of vibrational divorce)

(That is a word I just made up in the context of hoboTism)

Problem with 1/2 rubber the other fixed is when the bike is under heavy load and the rear chain tight,,the gearbok vibrating will cause rapid chain wear, its like a jigger pick action on the chain, i suppose a well rubber mounted rear sprocket will help..but again it's life will be short.

Harley's rear mount is at the swing arm pivot , so everything that moves stays aligned. They also have a rod link top mount. The Commando hangs from the rear ISO which allows the rear wheel to twist out of line with the vertical plane of the frame. Could be a problem or not ,depending on your point of view. A headsteady that limits side movement helps but Ludwig's method of controlling gear box cradle movement below the ISO looks interesting.

I've had long talk with head mechanic of HD that's as big as a stadium here to tell me the trick to getting their isolastic mounted models to handle really well is the addition of a low rear adjustable radius rod offered by HD or by aftermarket. Look up set up for 3rd or even 4th isolastic, whether head steady or one below cradle to see what they run into adding any extra rubber volume to engine vibration and then look up isolastic rubber stiffness softness annoyance treads too or may miss some data points to consider. The suspension motion and proper chain slack and slower going engine thumping puts more jerking length-tension loads on than tiny isolastic motion allowed for and aft. Ludwig may have solved it for his use but putting restrainers inside of cradle span ain't going to control wayward frame twist/rebounds as effectively as restrainers outside its span, both for forward and aft + up and down road and power loads. Iso gaps and iso stiffness can both be set for magical low rpm engine isolation when the iso are relieved of handling road loads too. I was most surprised how much more secure Peel was in raw off roading flings to point pavement fun seems so boring with traffic hazard dangers its not Peels main focus anymore.

hanslymoto said:

concours : my fabrication etc skills are minimal to nonexistent -- but my ability to come up with crazy ideas is pretty good, and I know some people who can make things happen on the realization end

hobot: thanks, I was thinking that a tensioner wouldn't be necessary, but good to keep in mind. And it seems like without the swingarm pushing on the cradle the amount of twist the gearbox sprocket will see is minimal, but I like the idea of the radius rod. You could even loosen up the isos for more extreme anti-vibration nirvana

My biggest concern is whether or not the frame could handle the load of carrying the swingarm directly, or if it would need to be reinforced. Since it wasn't designed to handle those loads, it might be too flexy and/or breaky...

thanks!
-Hans

Click to expand...

Keep us posted :mrgreen:

It has been done on the featherlastic. here is a link.

http://www.ntnoa.org/bobcox.htm

Yep frame mounted swingarms have been done in a number of *other* frames successfully but still begs question how can it be done successfully with the *Commando frame* and would it work better enough to really be an upgrade. All's I can say is its a continuous high when not wanting nor able to imagine any thing better than basic isolastic design that ya can't feel anything but road and wind and only blind road hazards or head sticking into opposite lane in tights slow ya down and the rougher the road the more uncannty flabbergasting secure it is over other alternative wonders. I gave up better handling on my factory Trixie Combat for the sweeter deeper isolation threshold by reducing width of the front big cushions and waist-ing about half the width of the top steady away. I definitely have to be careful of weave/wobble on lumpy / windy conditions if hanging with moderns out for a sane joy ride but no way would I attempt to hang with a rigid frame/swing arm/engine mc with decent eager pilot on vintage or modern. I take a date with about any strange woman over a ride on ordinary motorcycles any day but not on Ms Peel which is so so good I'd become celibate if I had to choose. Ms Peel pulled my testicles back to where they came from for mulitiple road orgasms I've risked some marriage bliss to get Peel's extreme pavement G-spot orgasms back in spades to work up for the jump into creek bed run to finish off with some adrenalin sense of getting away with murder. If ya live for the corner rushes > nothing does it like the zing of a rump rod for me on skinny tire. Btw a neurtal handling chassis makes fork issues disappear as can plant so much power the forks stay fully extended but on shifts and short intervals of braking well before tip ins or trip overs then send spikes of sensation that curls ya toes.

Well, hell, if it works for featherlastics, it should work for a frame-mounted swingarm in a commando frame just as well!

The more I look at my partially-disassembled bike, the more it looks like a pretty straightforward job:
- add mounting plates to the frame on the inside of the bottom rear frame loop
- modify swingarm: shorten slightly and add a wider pivot tube to reach the new mounting plates.
- modify gearbox cradle: cut off the rear section including the swingarm mount.

The real question is whether the resulting frame would be any good. There are a lot of double-cradle frames out there in the world that handle terribly, and there's no real reason to think that the commando frame would be one of the good ones. Especially since it wasn't even designed to have the swingarm mounted to the frame.

I suppose the only way to find out would be to try it -- or to find someone who's tried it and made it work

I think my best solution for the time being is to add a rear link like hobot's "rump rod" (you crack me up, man).

Thanks everyone for participating in my little thought experiment

-Hans

Hans my thot experiments have gone along your lines of thot but extended to realize from experience that ANY contact of vibrating cradle with frame will shake your fillings out so don't expect to get away with the double bracing through cradle into frame and retain Cdo isolastion. You do have to get into risky behavior to make these unsavory facts show up in all other cycles. So best wishes on proving what ya do. Lookie here for rolling your own but I suggest not to follow the dead robust rigid philosophy in the top and front links. I've tired those and consider them almost as corner crippled as un-tamed Commandos.
http://s184.photobucket.com/user/hobote ... t=3&page=2

I think I didn't explain myself clearly -- you would cut away the swingarm mount and the rear of the cradle so that the swingarm would pass behind the cradle -- no cradle to frame contact, which would of course render the whole system pointless.

Thanks for all the excellent iso mod photos -- lots of good food for thot there :mrgreen:

-Hans

Hi Hobot. Does your "rump rod' make any difference that you can tell. Also, there was an article on this forum that showed a very good looking brace for the swing arm to stop the sideways movement. Hobot looks easier to do though. My only concern is the thin wall tubing the Commando frame is made with. Will it take welding on stress lugs. [ though it must do and the engine is bolted to lugs at the front and rear.] This welding should be done by someone who knows what they are doing and the phrase DONT DO THIS AT HOME applies here.

I've covered this in spades but I'd rather have a ride on a rump rod than Dianna Riggs in her prime. Bryan Trigg in late '70's put on breast rod to solve Calif. rain groove forks hunting/wondering. Bob Patten reasoned more effective to control the leveraging of swing arm sway with the 1st low rear radius rod helm's joint. I hobot in '03 installed scabbed up top link to report on Brit Iron, INOA and NOC lists it did not transmit vibes so Dave Taylor went ahead with his nice pre-existing top steady design on my testimony. Bob sold me when he described his link allowing essentially hands off body surfing around tight Mt. roads. I found same uncanny thing, Cdo stays in what ever turn lean radius ya put it in w/o having to retrain forks much at all but to keep throttle twisted up. Its takes about same effort to fling down as pick back up but inbetween is such a secure breeze. I have learned or been forced to induce weave and wobble in modern sports bikes to restored "un-tammed" Combats but literally for the life of me i could not induce any upset what so ever on Ms Peel with just the 'rump rod'. W/o the top and breast link I could get some fork slap frame wiggles that were uncomfortable to feel pass through but by golly did not affect Peels lines, but I could not store up frame energy till the front link added in a Watt's like way so opposite eye rotations and out of horizontal plane of rump rod. Also I think it matters alot that the links be put as far away from the isolastics and front 2 allow some mm or two+ compliance. I got that by long stalks for one side of eye mount. All's Peel needed was the rump and breast control to twist up frame from forks to peg very detectably and even hold it twisted which greatly increases pressure on rear patch and release like a rubber band w/o rebound, so like a sling shot could pull it back more or less for the power level to release and also aim its release exactly where I wanted it to go. With addition of top link a whole bunch of what we, you and me, thot was just road texture though suspension and some engine sense getting through but its actually wind eddies blasting off forks and pilot and what ever. I lost sense of a motorcycle under me. Fabbergastingly Fabulous! Peel could way out handle what I'd experienced in a liter Ninja on track with heated race tires while still using same way to seer and handle, ie: counter steering on max leans under hi POwer >>> I could not get Peel to break free blasting it harder and harsher till she just pulled side ways wheelie off peg fouling leans!!!!! Then worked up insane entry speeds straight into bluff faces to twist up frame toss down with extra power/speed to wind up frame then cut power and let go of forks for real sling shot hi sides perfectly predicable and essentially effort less and no way does a human have such strength and speed to move forks as fast as needed, so just let forks do a single tank slap [as no rebound no damper desired] with R wrist action and breath forcing control the only effort needed. Ms Peel is so so good I've lost interest in sports bike spanking, some track day time events will demo that, its the raw wild off road stuff the tri-links allow that gets me off on adrenalin tremble. Peel just needs more power to do it faster as never did find her limits in public 10 mph switch backs I learned what I described. Do it!

Here's example of types Peel teased before leaving asking if I can tag along till bored! Merely the freeway like road towards Hwy 74, aka Moonshine run.
[video]https://www.youtube.com/watch?v=-oYGoE6g_PA[/video]

This is a ride down Hwy 74 to river bridge. Its hard to tell how sharp but note some sections of railings missing d/t to sharp for much a trailer to take it. On turns that came closer together Peel could enter at 55, which is too fast to keep both tires on the road but no matter to Peel to hit 65 out the 2nd in a row and almost 90 in the short opens before next G force hits. They paved over the broken up tarmac by time this video taken.
[video]https://www.youtube.com/watch?v=lE43gw08MMw[/video]