Potentially Dumb Question

Can someone explain why it's necessary to remove the swing arm assembly when removing the power unit on a MarkIII? I am reviewing the manual and this one of the last steps in the procedure. Does it have to do with th Z plates?

Thank for your indulgence in advance!

The swing arm is attached to the engine plate, not the frame.

illf8ed said:

The swing arm is attached to the engine plate, not the frame.

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Ahhh - I see! I guess I could have taken a closer look before asking here. I am almost ready to start with this, but I've been staring at the mounts more than anything else.

I suppose this is a good opportunity to replace the swing arm bushes, too?

Thanks much.

contours said:

I suppose this is a good opportunity to replace the swing arm bushes, too?

Thanks much.

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Only if they need replacing... If you have a handling issue, you should analyze to see where it's coming from rather than just throw new parts at your machine. Early bikes, (not yours, but mine) had only one bolt on the cradle swingarm tube so when I replace the bushings I got no improvement. Later when I added a swingarm tube modification my handling vastly improved... and a little later I added a comstock headsteady which improved handling even more...

If your swingarm bushes feel solid, and don't have a lot of mileage on them, I wouldn't waste money and time on them...

**** Also, if you have a particular issue, the search funtion here is great. You'll find threads that have answers to questions before you ask them. Sometimes in cases like my swingarm tube, I found out the answer to my handling issue and learned that the problem I was experiencing was not what I thought it was.

Points well taken. Things do feel loose ... mostly at the steering head. But I will have a chance to examine the bushes after the swing arm is removed, correct?

If you're working on the machine in your avatar, it looks pretty complete and a Corbin seat. Why are you taking it apart?

illf8ed said:

If you're working on the machine in your avatar, it looks pretty complete and a Corbin seat. Why are you taking it apart?

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The isolastic mounts are original, the rubbers are dry and cracked. Before I go to adjust them I figured I would start with new ones. I already replaced the head steady with a Dave Taylor unit. There was an improvement, but I really want more if I'm going to ride this machine with any regularity.

For now I have two other bikes to get my thrills from. Ultimately, I want to work this baby into the mix.

contours said:

Points well taken. Things do feel loose ... mostly at the steering head. But I will have a chance to examine the bushes after the swing arm is removed, correct?

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IMO,...... I would pull the rear wheel off, with the rest of the cradle and engine all connected, then look towards the back of the cradle where the swing arm mounts and flex the swing arm from side to side and see if you get any shifting of the swingarm. If it shifts a bit, I would try tightening up the swingarm tube set screw bolts to see if that's the cause of your play issue...

IF your swingarm is rock solid and the play that you feel is the whole cradle and engine moving, then you are on to the isolastic spacing to eliminate play.... One good way to know if it's your isolastics that are sloppy is just to tighten them up temporarily. You'll feel a noticeable buzzing in your footpegs and your handlebars. If your handling is still sloppy, then you are looking elswhere like your steering head or maybe the swingarm/cradle interface....

I've gotten my bike to handle really well now. Prior to my swingarm tube modification and the headsteady mod, my bike was like riding a snake down the road at 80 mph. I see on Jim comstock's (and some other bikes) the addition of rose joint steadies being added to the front and rear isolastics too... Needless to say they have taken their handling to the next level to improve frame rigidity without eliminating isolastic engine mounting....

If I was you, do the inspection and determin what you need to do, then ride the bike and determin if what you did had the effect you wanted.. IF NOT, then do more homework and take it to the next level.... HTH

Good advice. I will take it under consideration while I'm still assessing the problem.

Thanks!

Besides watching the rear area one is tugging on also watch what happens at front iso gap/slop. Now do it with a jiggle action such as wind gusts or road texture might do. Also before rear tire off stand next to bike and turn forks lock to lock and watch the snake actions at tire patches which does similar as rear imputs but induced from front loads as well. Also might grab the Z plates to tug on and see some frame deflection near rear iso mounts. Add these together is splashes and all hell can break loose. usually w/o much warning of crossing threshold into positive feedback wobble weave til tires can leap off surface. No sane pilot should risk satisfying suicide wish like me to find out the effects of various links signally or in combos to state just front and headsteady are plenty enough to stabliize to equal other bikes handling loads but *only* single rear low far away from isolastic mount link prevented me from ever hitting a threshold of wobble/weave/hinged frame and rubber isolastic/forks rebounds.

What I did find out to alert you lessor hot shots is the front + head link really upped the handling threshold loads and smooth stable sense BUT when I crossed their limited tolerance to prevent the frame/iso rebounds All HELL broke lose with frame forks wipping so fast hard no way can human act that fast nor strong so only picking right place w/o oncomming saved me, no skill not links not tires > pure LUCK as a number of almost crashes on THE Gravel or Mud. But I know what lies just beyond what feels so secure on rails so beware how close to crashing you are getting w/o realizing it. Rigid moderns are like this to me too all seems so fine right up till NOT. I was never able to induce any upsets on Peel w 3 links all set loose for going in/out rather harsher than moderns let me down.

On the other hand I can hang with elite moderns out for serious joys rides thats not competition track racing level, on my plain jane Trixie, taking care not to get too hi rpm -too long- and good caution into/out of turns, almost as fast as they do. This worked/scared the snot out of me, as required resisting some hingling just short of loss of control - so proved to myself what factory Combat limits are and not worth the risks. I hope ya do not experience what I did to make such a firm decision w/o some sort of rear link > for ever more. Pure luck I am still here after ordinary Commando and modern upsets did not end up a wad of scrap to learn how close they all get to out of control. No one yet knows the optimal combo of swash plate or radius rod links. I just know I seek no more smooth power handling capacity in Peel so moved on to power/mass ratio + Mad Max crash features and sticking to my story in face of rejection and disbelief.

Btw some claim to be able to remove bare cradle with sa attached but likely they are powder coating frame later to cover up the dings doing so.

How refreshing. I haven't had a good dose of Hobot-speak in a long while!

hobot said:

Btw some claim to be able to remove bare cradle with sa attached but likely they are powder coating frame later to cover up the dings doing so.

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Now that's good advice for sure.

o0norton0o said:

IMO,...... I would pull the rear wheel off, with the rest of the cradle and engine all connected, then look towards the back of the cradle where the swing arm mounts and flex the swing arm from side to side and see if you get any shifting of the swingarm. If it shifts a bit, I would try tightening up the swingarm tube set screw bolts to see if that's the cause of your play issue...

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I can do this sooner than later. I have the bike on a lift right now, but it shouldn't be a problem to check this out ... thanks!

contours said:

o0norton0o said:

IMO,...... I would pull the rear wheel off, with the rest of the cradle and engine all connected, then look towards the back of the cradle where the swing arm mounts and flex the swing arm from side to side and see if you get any shifting of the swingarm. If it shifts a bit, I would try tightening up the swingarm tube set screw bolts to see if that's the cause of your play issue...

Click to expand...

I can do this sooner than later. I have the bike on a lift right now, but it shouldn't be a problem to check this out ... thanks!

Click to expand...

The swing arm does indeed seem solid. Pointing the blame back t the Iso mounts and/or steering head. I am about to go forward with replacing the mounts now that I have everything stripped down. I will do a simple check on the steering head bearings once the Iso's are done. Also changing the fork oil and dropping in my new Landsdowne dampers (finally).

Give me a few weeks to report back. I'm kind of slow with this stuff. :wink: