Cradle wear - Newbie posting

Been a lurker for a while but have only recently undertaken a complete rebuild of a '73 Commando - so please be gentle with me

So I've just had all the frame components back from the powder coaters and am looking at the rebuild process. On close (or i should say initial inspection having already had the thing powder coated :roll: ) i have some very pronounced wear on the cradle on the RH side where the swings arm locates. The swing arm itself is a TIGHT fit on the cradle and the spindle and bushes look to be in good 'servicable' condition. So my questions are a) what causes this wear and b) is the cradle scrap?

Many thanks - Nabbott

the cradle is made that way. it is machined to arrive at the proper dimension for the swingarm to fit the cradle. the wear issue is the fit of the pin in the cradle. if it is a loose fit I have an economical bolt on fix.

+1

Thanks gentlemen. As I mentioned the swing arm is a very close fit (even more so with the additional thickness of the powder coat)

That's one less thing to worry about/shell cash out upon

The cradle really shouldn't be powder coated or even painted around that area where the bronze bushing and the 0-rings attempt to seal the oil inside the pin and bushing. See the Old Britts article on masking for powder coat. I even masked the transmission mounting points.



Dave
69S

Dave hit it right on - you need to carefully scrape the powdercoating off the recessed swingarm spindle area, and all the bolt holes (both sides). If the inside of the isolastic tube got powdercoated you may or may not have a fun time getting the rubber isolastic mounts in there (front one is typically harder than the rear to install); either way, the face needs to be cleaned to allow the isolastic end caps to fully seat.

Otherwise, the engine will keep rattling loose and you'll likely break mounting bolts frequently.

AFTER powdercoating is removed, you can touch up all the bare spots with Rust-O-Leum gloss black (not too much).

Modification.
http://www.doov.com/apps/nortoncompanio ... s&Itemid=8

Yeah, do a search for "swing arm spindle" fix and the like. At this stage of your project, worthwhile stuff to know.

The spindle to cradle is one of the designs weak points . Bleedy great clamps arnt a bad idea , for spirited rideing on irregular surfaces , clamped up tight
is likelyer to clamp it up tight , in the cradle . Unless you go for a interfearance fit & a 10 or 20 ton press . Critical fit is the ends ( sides ) of cradle . So that no logitudeinal creep at the spindle creates laterl slop at the rear axle . let alone vertical creep / insecurity at the spindle . Wants to be firmly held in place .

I will post my two cents here and then slink away since it doesn't follow conventional wisdom. I agree that you shouldn't have a heavy, thick coating of plastic or paint at swing arm bushes or under bolts, but I don't think it needs to be bare. There are stories that tell us that mounting bolts break when snugged up against thick powder coat. It is my view that the vibration effectively attacks the joint until it becomes loose and then the bolts break. That and most of the full length bolts thru the engine or gearbox are threaded a bit too long so the bearing surface of the bolt is threaded.

What I did was to paint my cradle with two part paint. Then I made up a set of tools to allow me to sand down the bearing areas. For the swing arm pivot I made a disc from plexiglass using a hole saw the same diameter as the bush. I drilled out the center hole to accept a length of 1/2" PVC pipe. It is really close to the correct diameter for the spindle. I slid the disc on to the tubing a couple of inches and glued it into place with 5-minute epoxy. I cut a donut the correct size for the disc from some cloth backed sand paper and glued it to the face. It to longer to type this than make the tool. The tool is simply dropped into the spindle tube and rotated between the palms until a smooth and thin surface coat is all that remains.

I made similar tools to match the size of washers on other fasteners and dropped the whole bunch into my specialty tool box. It just takes a few moments to reduce the thick coating to a thin one. Time will tell if this was another stupid idea. I would post a photo but I am traveling and don't have access to the tool.

I think it is pretty important to check those cradle bolts for tight, often after a new build until you get that stuff settled into place. Again,just an opinion that might be wrong.

Good luck,
Russ

It looks like you and I are in the same position. I've just dismantled a basket-case and have begun the rebuild process. I have not gone with a powdercoat on this bike but have opted for a standard prime/topcoat/clear process. Currently the frame etc. are all in primer.

It looks like you and I will get to learn together...but there's a lot of very helpful advice out here.