Chip's '72 Combat project

I guess I'd wonder if it is a Norton expert checking the swingarm looseness? The reason is that, if I recall correctly, on my old Commandos one could alsways move the swing arm and engine assembly in what would be an alarming manner on one of my Hondas.
I recall thinking that given the amount of movement here I'm amazed that this bikes works as well as it does, and it did. I remember giving ride after ride to friends over the ton with that bike, and she was quite predictable on corners.

I notice the same thing and being a one Norton guy it had me worried. Why would a new MkIII cradle, with a new spindle, new bushings, new cotters, new Iso's and a Taylor headsteady move around a bit? Guess it's just part of the package.

Its positively mushy compared to my CBR, but that's to be expected. Nevertheless, it does track predictably enough for me to scrape the pegs on the rearsets from time to time.

I used to load the Commando in the corner, applying force until it seemed to take a set, then it seemed to stay where you put it. It was a pretty pleasant bike to ride.

Norton's squishy suspension was not made for handling; instead it was designed to quell vibration.

If you tighten up the isos, you tighten up the handling a bit but at the expense of increased vibration. The increase in vibration often means metal fatigue, such as broken oil tank and gas tank brackets.

Nortons and razor-sharp-handling should not be mentioned in the same sentence.

I would just check to see that that iso's were still set, Maybe they just took a bit to bed in and now need to be readjusted. As sometimes new parts will do.

Its hard to evaluate the handling of the Commando if one is using current technology as a reference.
But...when you look at the fact that the entire powertrain is separated from the body by a heim joint, two shocks, and a handful of rubber discs mounted on 2 steel rods, its amazing the thing works at all.

When I first put mine on the road, it was pretty unstable over 85 on the throttle, and didn't settle down on trailing throttle until it dropped below 75.
The swing arm bushes seemed OK when I assembled the bike, but I went ahead and changed the bushes, spindle and seals. - little change
Shocks were original, as far as I know, so I changed them for the Emgo lookalikes. - little change
Isolastics are MkIII style, so I played with them. - no change
Changed the headsteady to the Dave Taylor style, with the MkIII helper springs. - pretty solid up past 6000 RPM in top gear. Still need to dial in the helper springs to fine tune the secondary vibrations, but what a difference!
Every time I ride it, I get a little more comfortable with its idiosyncrasies.
Even with all this, the Norton is less stable at 65 than the Speed Triple at 130.

The isos were properly adjusted and it hasn't got 100 miles on it yet.

Just danged wierd...

The niggling problems mentioned after delivery are to be expected after a complete restoration and I find it normally takes a few hundred miles before things start to settle down, after several trips round the bike with a set of spanners to retighten the various things that predictably come loose. Regarding swingarm play I noticed what I consider to be excessive play at the swingarm after only a few hundred miles on a newly restored bike. I had replaced the pin and bushes and set the isolastics correctly. It turned out to be the pin moving in a very slightly oval bore in the swingarm/gearbox carrier. This was not evident when I put it all together as the movement was tiny and there was insufficient leverage with the sub assembly off the bike to notice anything - in fact the swingarm felt quite tight. Once the rear wheel was on the bike the movement when checked was increased to at least a couple of mm at the outer edge of the tire. I dismantled the whole thing and rebored the carrier tube and fitted an oversize spindle, which cured the problem.

Just a small but important point for re-builds if a '71 750 is the project. That series of frame, with the front lower cross brace incorporating the side stand gusset and down facing mounting pin, - it had its own particular steering top and bottom yokes. If you fit later yokes, its is very common to find a speed weave around 60- 70mph (100-120kph).

Apparently there was a minor degree change in the steering geometry in 71 and the factory rectified this soon after. The yokes look identical to later 750 and 850's but there is a different angle. Beware it is potential problem.

Mick

Nope, this is all '72 stuff, and the swingarm bores were perfect, as was the tranny cradle bore.

Still scratching my brain...

Paul,

Once you've exhausted everything else try changing to a different rear tire. I say this having gone through essentially the same as you're experiencing. Changing rear tires, same brand/size completely eliminated the problem. Now, it's possible, it may have just been a mounting problem.

That series of frame, with the front lower cross brace incorporating the side stand gusset and down facing mounting pin, - it had its own particular steering top and bottom yokes.

Click to expand...

Really?
The '71-'73 750 yokes have the same part number (061915/061916) changing with the 850 (064080/064078) when the steering head angle was changed in the frame (yokes were re-angled to maintain wheelbase). And of course the earlier models (061133/061131) with loose ball bearing were different to allow for bearing adjustment.
I was under the impression that the steering head angle on all 750 frames was the same, as was the wheelbase.
How can you distinguish '71 yokes from '72-73 750 yokes? I have a couple sets of 061915/061916 yokes and would like to know what they are.

GrandPaul,
If there is rear end "looseness" how can it be anywhere but iso's or spindle/bushes/spindle tube? If you can't feel movement by placing a finger at the swingarm and moving the wheel side to side, can you adjust the vernier iso's to zero free movement and still detect looseness? Could it be in the rear hub and/or bearings?
Is this a handling perception or actual visual or measurable looseness? If it is a handling issue then perhaps it is an alignment issue? Tweaked swingarm or forks or steering head?

The problem is that it's 1500 miles away in Florida.

And it's not in RIDING the bike, so rule out tire; it's when sitting on the centerstand. The guy handling the warranty issues can jiggle the rear wheel "about an inch".

All new wheel bearings in excellent condition hubs, by the way...

As Bill T indicated - Head steady!!! I also have a Dave Taylor and had the same great results. The springs are not necessary so for $129 it is hard to beat. Or make your own just to prove it to yourself.

Get rid of those squishy rrrrrubber biscuits.

Russ

Taylor head steady installed and properly adjusted.

Next?

it's when sitting on the centerstand. The guy handling the warranty issues can jiggle the rear wheel "about an inch".

Click to expand...

That IS weird!
If it is moving "about an inch" you would have to see it moving at the swing arm, the rear iso, or the front iso!
Actually an inch of movement would make it totally unrideable, so I'm sure we are dealing with a quarter-inch or less.

Does the cradle have the Heinz Kegler style clamps or welded nut/bolt arrangement to fix the spindle? If so, could the fixing bolts have backed out?

Stock captive nut w/ bolt arrangement.

The guy says it's all at the spindle, so I'm sending him TWO freshly powdercoated cradles to pick from, and a new spindle. If that doesn't cure it, I give up!

As the owner of the bike, I have a vested interest in this discussion and I've been following it very closely. The fact that I don't have a lot of experience with the mechanics of my machine delegates me to the sidelines when it gets down to probable causes and/or fixes.

I feel the need to weigh in at this time, however, since I'm the only one here who has seen the "play" in the swingarm. When the tire is grasped and moved in a side-to-side motion, the tire does not simply "jiggle" back and forth. When moved with some authority however, the tire does flex side-to-side and the movement is approximately 1/2 inch (or greater) in either direction. While flexing the tire, it's easy to see that the spindle is also flexing as well. In any event, the fact that the tire movement is more than 1/8 or 3/16 of an inch is cause for concern.

Paul is an expert when it comes to restoring vintage bikes and his integrity is unquestionable. Paul has been in constant communication with me ever since the bike was delivered. His operation is completely transparent as evident by his numerous project contributions to several forums on the web. I have 100% confidence in Paul's ability to work with my local Norton mechanic to resolve this issue and I would highly recommend Paul to anyone in need of restoration services.

Chip

I just received a backup call from Bill mentioning something I had considered ion the back of my mind: the drill & bolt-on clamping fix that once and for all time does away with the potential of the swingarm pivot pin to move about in it's bore on the transmission cradle.

I'll be talking to the guy that's got the bike in his shop and see if he's got any valid argumnets against using this known quantity to cure the problem, IF IN FACT it is play in the swingarm pivot pin.

Chip, I appreciate your candor & confidence. I hope it is justified and rewarded presently.

Paul I have installed one on my project bike and can tell you that the one from Heinz makes for a rock solid permanent fix. His kit is first class quality thats for sure. Chuck.