Shorter Beam Tubes

[JoshGti 8]

I was re-furbishing/swapping over the beam on my brother saxo vtr the other week and it got me thinking. for a start having the tubes pressed into the beam like they are is a pain in the backside! I took 2 beams apart in a scrappy before i found one with two good tubes to put some fresh bearings too.

 

But as the beam tubes on a 205 are so long and ive read through a fair few posts that holes that go through the middle of the tubes is the reason getting them machined up is so expensive/would be so expensive.

 

Could you not put shorter tubes into the arms? Getting them made up shorter to bring the cost down? The tubes sticking out of the saxo rear beam are only around 100mm with what im assuming is a similar ammount of tube pressed into the beam as on the 205?

 

Is there any method in this madness?

[welshpug 1,658]

shorter arm shafts would lead to more force being placed on the bearings, hence why I think the 106+206 beams die far sooner than 205/306/309.

[JoshGti 8]

But isnt this the way it goes with 205 beams anway? Im only thinking out loud really, when i took my beam apart is had obviously been refurbushed at some point as both tubes were reasonable but there were NO markings on the inner bearing faces and the outers were fubar. Like the inner bearings are only there to keep the tube central.

 

I do see however what your saying about the shorter beams wearing out sooner, the saxo ones were in far worse condition than my 205 ones. But there must be a happy medium?

[Paul_13 212 1 Cars]

The bearings on a saxo/106 beam are in the trailing arms and on a 205/309/306 the bearings are in the beam tube.

 

Are you getting confused about this?

[Cameron 16]

Welshpug is right, shorter shafts would mean increased load on the bearings and a quicker death.

[JoshGti 8]

No, i know the bearings and tubes are the wrong way round in a saxo, but i was just commenting on their length. What if the material was stronger (again thinking out aloud after reading into some older threads) I.e. titanium. But making it shorter, and using sa660 bronze for the bushings, speading the load, would this not greatly reduce wear?

 

Im an engineering student so im always thinking, im just a lazy one and i dont like working out pressures and failures of items cause it involves numbers.

 

It sounds like im trying to build some kind of indestructable beam.

[welshpug 1,658]

build one without a beam tube

[JoshGti 8]

Haha, in the scheme of things and people replacing them constantly, that would be THE thing to do.

[Cameron 16]

Psst.. Titanium isn't stronger than Steel, it just has a higher strength to weight ratio. You would actually need more material if you made the shafts from Ti.

 

You could make them shorter if you used a stronger material like Cr-Mo Steel, but they would be very expensive. Besides, the point was that shorter length would cause premature bearing failure, not shaft failure.

[JoshGti 8]

But the combined point loadings of the rollers from the bearings cause the tubes to pit and fail too, as the rollers fail they create movement and play in the cage holding the bearing together destroying itself. Hence the bronze bushings being a better option, so if shorter tubes were used with a bushing rather than a roller bearing would the problem still exist?

[Anthony 1,003]

The trailing arm shafts (or "tubes" as you refer to them as) aren't really the weak point in the design in my opinion/experience.

 

The problem parts of the design is the outer crossmember seals, which fail and allow water into the beam, washing away grease and rusting the bearings and shafts, and the (outer) bearings themselves which are heavily loaded, particularly on heavier cars and/or beams with stiff torsion and anti-roll bars, and inevitably pit the shafts and begin to break up. This issue is much worse on beams built using the non-OE type bearings that had just 30 needles rather than the 45 of the original OE design, with pitting and breakup happening significantly quicker.

 

Either just replace both every few years along with regreasing, or change the outer bearing for a phospher bronze or oilon type - there is a potential performance issue with these in the form of "stiction" over the original needle bearings, so it depends what your priorities are. There are certainly a few people on here running beams using phospher bronze bearings is you do a search, and over the Xmas break I'll be finishing putting together a beam using oilon bearings for a friend of mine as an experiment.

[welshpug 1,658]

what about the stiction resulting from using bushings instead of bearings?

[JoshGti 8]

I have bought some Phosphor bronze with the aim of creating some bushes as i intend to re-build my beam in the new year, i have got grease nipples to address the grease/stiction issue also. But this material is proven in this sort of application, i think the stiction will onnly occur when the impregnated oil "runs out" as such, apparently you can solve this by putting the bronze back into boiling oil to re-impregnate them.

 

And as im aware there are a lot of members on here with significantly more experience with beams and rebuilding them than myself, but im just trying to tap into this knowledge base and your reply above seems to fulfill part of my question anthony. If the shafts (excuse my ignorance) arent the weak point and they are already shorter on the saxo. IF the other parts were improved i.e. the seals and the bearings would it be a possibility.

 

I know people dont buy into things without things being proven first so im fully up for trying something out whilst i am at university and dont have a lot of other things to worry about. But the standard shafts have the bearing surfaces ground into them with special tooling to create the correct operating surface for the needle bearings is this correct? (again, taken from reading on here)

 

Would this surface need to re-created for something like a bushing or could it be a standard machined surface? Also has anyone got the shaft dimensions and tolerances (for the press fit end that goes into the trailing arm specifically)

 

Has anyone thought to make the standard rubber seals out of a material like PU? Maybe making them slightly oversized length wise so under the compression of the beam being held together they create a better seal?

Edited December 20, 2010 by JoshGti

[Cameron 16]

Yeah the bearings are a bit of a bad choice really, using needle rollers in something that only rotates a degree or so but at a high frequency is a bit of a bad idea.

 

Someone correct me if I'm wrong, but isn't Titanium quite bad for galling?

[JoshGti 8]

Titanium is associated with galling yes, but i think its just/mainly through contact with other titantim items, for example titanium nut and bolt attached to each other (again, im only a second year student so sombody correct me if im wrong). And lubrication usually solves this, so in an application where a gease nipple can be fitted and using an oil impregnated bush this shouldnt be an issue?

 

Essentially, Ti wouldnt have to be used, if the other things can be fixed then why shell out for the cost? Only mentioned it as its lighter so you could get away with milling a smaller hole through the centre of a Ti shaft (big enough for the roll bar) instead of a steel shaft, so it would be lighter and less machining would be needed?

 

EDIT: My spelling is terrrible!

Edited December 20, 2010 by JoshGti

[welshpug 1,658]

405x4's and the BX use a much larger taper roller bearing, but less rollers so I'd guess more pressure on each contact point.

 

The trouble with making the hole through the middle smaller, is that in many instances with the higher spec cars the hole is only just large enough for the ARB, there's no scope for making it smaller unless you mount the ARB externally.

 

or run a Colin satchell chassis without ARB's at all

Edited December 20, 2010 by welshpug

[Cameron 16]

I think the increased material cost alone would make Titanium shafts more expensive than steel, even with the smaller hole.

[Rippthrough 98]

Couple of things here.

 

1. Oilite, Phosphor Bronze, and Oilon are 3 completely different materials.

 

Oilite is a sintered powdered bronze which is full of tiny holes to allow oil to flow through it, like a sponge. It's great for things like spinning shafts that can draw the oil up. It's terrible for shafts that have a tiny oscillating movement and shock loadings, the oil doesn't flow through and the pores get pounded shut. Incidentally, if you've machined the oilite to fit, chances are unless you were using razor sharp tooling for the final cut you've shut half the pores off from distortion anyway.

If you lubricate it with grease you will seal the pores shut and stop it from working.

 

Phosphor Bronze is exactly what it sounds like - a cast bar of Bronze with high Phosphorous content (and usually a bit of lead), which is what gives it the anti-galling and lubrication properties. It can work well without lubrication in low load and low speed applications, but for high loadings it needs to be lubricated with grease, that means having some means of getting the grease around the whole surface - usually by grooves, and preferably some sort of sealing system to keep the grease under some pressure - otherwise it'll just creep out any time the car is stood for a length of time, you'll end up having to re-grease fairly often.

 

Oilon is a plastic, it's a hard nylon with a high percentage of interspersed oil and lubricating compounds, it won't take the same sort of surface pressure as PB without distortion, but as it's slightly elastic it's very good at coping with shock loadings, and every time it wears a fresh layer of oil/lubricant is exposed. There is an improved version of this called Nylube which would be better for beam applications, as it contains moly-disulphide solid lubricants to reduce wear even further. They will work fine even if the grease is pushed out of them, but have less wear and friction if kept greased.

 

All 3 have friction values orders of magnitude greater than the needle bearings used in the beam, which are in the region of 0.005u when greased and installed correctly.

 

 

2. Titanium would be a waste of time unless your racing and need the weight reduction within the regs. Surface hardness is the problem, and given you can machine most commercial titanium with uncoated HSS tooling that probably gives you an idea of which is easier to harden!

Grinding the shaft finish would work out more expensive too as titanium work hardens and galls when machined/ground, so you have to run slow and take a heavy feed. More money for the material and more money for the machining too.

 

3. A new beam seems to last about 10 years or so. That's not bad going really, you'll have gone through a few bushes and dampers by then...

Edited December 20, 2010 by Rippthrough

[JoshGti 8]

Okay ripthrough, you seemed to have hit a few nails on the nead thank you, i did realised they were all different materials but i seemed to have confused phosphor and sintered bronze in my last post.

 

So titanium is a waste of time in material cost and machine time basically, unless ive got money to throw at a motorsport car basically.

 

Im going to look into getting some 1 7/8" (i know i should be working in metric, so 47.62mm) bright ground stainless steel as this will be the closest to the correct size to press fit into the trailing arm? I will be milling the bronze to size and honing to fit over the standard bright surface. I will use either a boring bar (but probably a mill) to create a 24/25mm hole through the shaft, which should be ample for an arb.

 

Would this be suitable to make shafts from? I will look into methods of removing the "lead" that will be machined into the shaft for the inner bearing faces on a lathe with either paper methods or using finishing "soaps".

 

My final query, would PU (polyurethane) be a suitable material to reproduce the end seals from instead of the standard rubber.

 

And yes, all this MAY be a complete waste of time, but i have a whole term of free machine time next term and it will be MY waste of time

[Rippthrough 98]

I think I'd* be using something along the lines of a bit of EN18/EN19T or similar.

You're still going to want a fairly hard/wear resistant surface.

 

 

 

 

 

 

 

 

 

 

 

 

 

*Well, I wouldn't, I'd find something else to make, but hey ho

Edited December 20, 2010 by Rippthrough

[JoshGti 8]

Something else to make would be an idea lol. But the only thing besides welding that is bugging me about my 205 is the rear beam, so if i can get away with just paying for materials then why not.

 

Looking at the materials EN18 has a hardness of around 490 with 304 stainless coming in at less than half that, is there a more corrosion resistant manterial or a grade of stinless close to the hardness of en18?

[Rippthrough 98]

Some 17-4 in half-hard should do, although I'm not sure why you want stainless?

Won't be cheap.

Edited December 20, 2010 by Rippthrough

[JoshGti 8]

In the eventuality is that my efforts will eventually fill up with muck and water and corrode. Id jsut like some defence before that happens lol

[Rippthrough 98]

Well in that event, mucky water = pretty good abrasive anyway.