roller bearing vs. swinging arm bushes?

[Phil]

Hi - has anyone experience of using roller bearings in place of swinging arm bushes? Would they be of benefit to a race bike? Any advice welcome!

[Voxonda]

Hey Phil,

In my, humble, opinion based on a few experiences a bronze bushing is as good as, or even better, then a roller/needle bearing. 1st of all roller/needle bearings need to roll, they are not designed to operate in just a few degrees of motion. Second a roll bearing has a point contact area and a needle bearing a small line contact area. A bronze bushing, even with the same dimensions as the original bushing has a bigger contact area. The main problem, from all the swingarms I've seen is, the lack of, lubrication. Most of us don't bother to lubricate at all, or too little, the swingarm pivot. On my own, homemade, swingarm I have 2 nipples(?) directly placed on the bearings, so I am sure that they get grease.
If you service the pivot make sure you put in enough grease, watch the old grease being pushed out by the new grease. Use a good lithium based grease.

Cheers, Rob

[Phil]

Thanks Rob - that certainly makes sense. M3 say that their "special bush" eliminates the "high speed death wobble" that CB750 are famous for! They can't supply and I wondered if the roller bearing might be a substitute. I have experienced the famous wobble (and survived to tell the tale!) and want to try to prevent it on this CR replica (I am too old to experience it again)! I have two frames - neither of which has any play that I can feel when the bile is stationary but since they are being blasted, welded-up, strengthened and   painted, I thought I would do what I could. Thanks again!
Cheers

Phil

[SteveD CB500K0]

when the bile is stationary

You need to see a doctor about that Phil...

[Voxonda]

Hey Phil,

I have looked at the 'special'bushes from M3 racing, but these are a standard replacement for the original one's. I happen to provide a CB four specialist, http://www.fourdeel.com/, with these items. I make them out of a high(er) grade bronze.


Cheers, Rob

[Phil]

Thanks - all this information is very helpful. I was puzzled by the M3/ Adam Pop claims. It is scary at speed though! I am having a titanium swinging arm pivot machined, would increasing the i/d of a high grade bush help? Why is the bush not longer? Why not drill the centre of the pivot and put grease nipples on the ends? Can you custom produce? Sorry for all these questions...

Phil

[Voxonda]

Hey Phil, no worries about the questions, always willing to share what I (think I) know. In my opinion the way to go is increase the diametre of the pivot/bearing assy, but then you have to inline drill the holes in the frame and change the swingarm. But the space behind the engine is limited. I have build a box swingarm, which is approx. 1" longer than the original and a lot stiffer. Think that is basically all you can do without going ballistic about it and replace the frame for whatever Spondon, Egli, Dresda etc. The length of the bushes is limited by the depth of the drilling in the swingarm. Making the bushes longer with this diametre brings nothing, they are long enough.
I can make the bushes by drawing. I will not drill in the pivot, because you also have to drill square to the pivot-axle and makes it a weakened area.
This is one of my bikes, almost ready for paint. Replica of a 1973 JAPAUTO Endurance racer.


Cheers, Rob

[Phil]

Thanks again. I have to keep the standard swinging arm in order to comply with the CRMC rules. I think I will go for high quality bushes and keep the pivot bolt standard except replicate in titanium. Love the Japauto! I raced a 960cc Japauto in a six hour endurance race in Belgium back in the early 1970s - quite a beast then!

[Voxonda]

Thanks again. I have to keep the standard swinging arm in order to comply with the CRMC rules. I think I will go for high quality bushes and keep the pivot bolt standard except replicate in titanium. Love the Japauto! I raced a 960cc Japauto in a six hour endurance race in Belgium back in the early 1970s - quite a beast then!

Any pic's dare I ask from the 70's?
What you can do to further stiffen up (is that english?) the overall 'feel' of the bike is looking at both the engine mountings right front and back. I will make pictures of my 'solution'. Made the front plate in Aluminium 7075 (high tensile) and doubled the back one, meaning made a new one from two, integrating a threathbushing for the top rear engine mount, instead of the nut. Have to get some new batteries for the camera.

Cheers, Rob

[Voxonda]

Found a pic but here the rear one is not ready yet. The front one wasn't polished then.

Can work with the original oiltank but then you have to space the tank outwards a bit.
works for me.

Cheers.

[Phil]

That brings back memories! Regret no pictures - all I have is a front sprocket! I like your Japauto and some of your ideas are great. Strengthening the frame around the engine mountings is a good idea. In the early days we used to think the flexing was the swinging arm - hence people fitting Dresda box section ones. Now they know the original swinging arm is fine in terms of flex. The factory heavily braced the top two tubes between the shock top mountings. The metal quality of these frames was/is terrible. I have a K7 frame which I have cut up and the wall diameter is paper thin in places and not through rust. It is also rusted right through in other places because condensation forms inside these tubes and they rust from the inside. The welding around the headstock is also terrible. Tubes are rammed into other tubes and held in place with a couple of spot-welds! Some of the serious CB750 racers had new frames made to the exact dimensions of the originals - but made of top quality tubing. The frame design/ dimensions are fine, it's just the crap materials I think! I would love to see more pictures.

Phil

[Voxonda]

One point of consideration might be, what people expect from a surtain design, and what they want to do with it.
In my opinion, the CB750 was never really intended to be a all out racer! In those days from a marketing point of view, it had to be! But it could never really live up to the expectations. Though fast, it was a bit unreliable when "highly" tuned. In endurance, with milder tuning, it was top of the bill. Even when fitted with big-bore kits. One of the weakest links was, and still is, the camdrive when fitted with race-camshaft.
In present days people tend to overdo tuning while only 'parade' or so of and on a classic trackday! Really think that for these purpose a standard engine with good (total loss) ignition, exhaust, loose the heavy dynamo and fine tuned carb's will do the trick! Bonus is that everything will stay in one piece. Personally I focus on getting it round the corners, though I am no #1 racer.

Cheers, Rob

PS.Will show some pictures shortly.

[Voxonda]

Hey Phil,

Here is a picture of the rear top engine mounting. Makes it a lot more rigid. just have to give it a blast and a paint.

Am just starting up a little business in developing and producing some hard(er) to get items for our beloved bike(s).
Cheers, Rob

[Voxonda]

This is the front engine mount, made of 7075 Aluminium.

Please let me hear what you think.

Cheers, Rob

[Phil]

Your stronger engine mountings look much better than the originals - this is a real area of weakness! I wanted some made in 7mm titanium (I have the plate) but am struggling to find a machine shop that can do the job - same story trying to get Ti engine bolts, wheel spindles, swinging arm spindles etc. Nobody wants to work with the stuff! I am interested in your swinging arm bushes - what is the price? Also, your spin-on oil filter is pretty neat - did you make the holder? Do you make a blanking plug for the kick-shaft spindle? Phil