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MG Midget and Sprite Technical - Bronze bushing life



"I suspect longevity is more related to maintainance than initial set up unless you get it miles out, and those BBS contributors suggesting heavy oil not grease may have a point, that's what I use now."


This comment in the king pin reamer thread got me to thinking about bushing wear and I wanted to pass along something that I've seen in my job when using bronze bushings. I found that using any lubricant that contains bits of teflon such as Tri-Flow or some greases would actually clog the pores in the bronze and prevent proper lubrication resulting in rapid wear. I now only use standard oils or grease without any additives on bronze bushings with good results. I wonder if modern chassis grease that we're using is actually doing more harm than good for our kingpin bushings? Anyone else have similar experience?
Bill Young


How to tell which grease/oil has teflon in it?

Andy
a borris

Bill,

All the bushes I have used for the kingpins were steel backed bronze bushes which had a solid bronze surface so no pores, these came with the kingpin kits. I have used porous bronze bushes (Oilite) for some suspension components but didn't use a ptfe containing grease just a standard grease like Castrol LM IIRC, if not relying solely on the oil charge in the oilites..

Regarding ptfe and kingpins an engineering lecturer of mine mentioned he had started to use ptfe tape for the trunnions on his wifes Morris Marina and didn't suffer from wear after. I have tried this on slightly worn kingpins and it has the benefit over grease of not being expelled as the ptfe tape is a solid lubricant.
David Billington


Is that the type used by plumbers?

Wondering because I'll shortly be fitting some neg camber top trunnions which are brass.....

Andy
a borris

Andy,

Yes, it serves 2 purposes, one is to help seal but another is as a very effective solid lubricant on the likes of taper threads to allow them to be done up tight to the point that the threads themselves seal. Worked well on the likes of the kingpins which are slow speed rubbing bearings. The trunnion would see more movement so not sure how well it would work.

Not sure about use on the trunnions, you have to have clearance to get the tape in although it is very thin unless you get the thick stuff. Depending on the use I might look at fitting DU bushes in the brass bushes but it depends on whether the brass bushes turn in the trunnion or rotate on the pin in the end of the damper. If the rotation occurs on the damper pin I would be inclined to fit replaceable bushes if space allows. This would of course also assume you were doing enough mileage to make wear concerns an issue.
David Billington

OK, showing my lack of engineering knowledge now, DU bushes?

The trunnion has a grease nipple and rotates on the pin, what sort of mileage are we talking? Will probably put 6000 miles a year on the car.

Andy
a borris

I find it interesting that in the first two (1961) editions of the midget owners handbook 140 gear oil or grease are the recommended lubricants for the front suspension, and 1000 miles is the recommended interval. Then, in 1962, the 140 oil disappears from the lubricants list, and in 1963 the intervals are suddenly increased to every 3000 miles.

I would think that the only reason for this was the general pressure to make maintenance simpler, with longer intervals. As we know nothing important was changed in the suspension design. It makes me wonder if oil is really the best lubrication here. If not, why would the factory bother to mention 140 oil as an alternative to grease?

Tore


Tore

Andy,

A DU bush is a self lubricating bush. It is steel backed with a PTFE impregnated sintered bronze surface. Have a look here for further details http://www.ahrinternational.com/Glacier_DU_DU-B_DP4_summary.htm

David Billington

What is the normal life to be expected from kingpin bushes that are greased every 500 miles or so?

Tore
Tore

Tore,

With regular service, I replaced my original kingpins at 44K. Wear at the wishbone spring pan, and bottom fulcrum pin more so than the swivel axle bush being the main concern (for me). At the time I sourced new spring pans, and rebuilt pin units from my MOSS rep who I believe had them done at a local machine shop.

Don't know how much this may matter, but most of these miles were on-road with no real competition driving, save a few sprints around the course at local club auto-cross events. I do not drive that many miles per year now, and try to keep this higher on my maintenance list.

Regards,

Larry C.
Larry C '69 Midget

When I replaced my kingpins and bushes after about 8 years of use, maybe 50k miles, and lack of regular greasing I found the old bushes were a better fit on the new kingpins than the newly reamed bushes. That was annoying but does go along with some comments I have seen that the bushes often fair better than the kingpins regarding wear. Next time I do them I'll do the job myself like I did for the first set of bushes.
David Billington

I have wrapped plumbers' Teflon tape around the threaded bottom fulcrum pin, with good results. After 5000 miles I striped it down and considering how much of a pounding those pins get I was very surprised to find that the Teflon tape wrapping was still intact!
Guy Weller

When I try my new kingpins in the old stub axles (drum braked ´61 Midget) I can feel no sideways movement in the upper bushes. In the lower bushes a little wear can be felt, sufficient to make a little clicking sound when I move it.

I am tempted now to try ptfe tape in the lower bushes, if I can get it in, and save the new bushes for a later date when the upper ones are a little more worn, too.

How much clearance is regarded as acceptable before you have to change the bushes?

David,

How long did the ptfe tape last when you used it on your slightly worn kingpins?

Tore


Tore

Tore,

IIRC the PTFE tape lasted quite well from one year to the next. I tended to pull the outer suspension apart every couple of years to inspect my non standard lower trunnions so the kingpins got looked at as well.

The PTFE tape is quite thin so can fill small clearances. I tended to put a thin wrap around the journal and try it. If too much then remove some, too little then remove and add another longer section for more build up. I would smear some grease over the surface prior to fitting.
David Billington

Maybe one thing not to do as related to me by a local garage I used to use. They had failed an old car on excessive kingpin play and the owner took the car away for repair. He returned a few hours later proclaiming the kingpin issue sorted and wanted a retest, it was failed after a quick examination and he was told to go elsewhere and not come back. I was told that it was apparent to the tester that the fault could not have been properly repaired in the time as you could not disassemble and reassemble the parts in the time and the evidence showed the use of body filler for kingpin repair.

It seems the owner had mixed body filler and used a grease gun to inject it into the bushes to cure the problem. The garage said this could have worked as a ploy except for that fact that he returned too quickly, should have waited a day or 2 to allow time for a proper repair, and he had not wiped the excess filler away that exuded from the bushings and nipples.

Having just written this recount I wonder if something like Moglice ( http://moglice.de/ ) would actually be quite valid for the purpose and used as the dodgy bodger did. Apologies to true bodgers whose trade has has been befamed due to the change in use of the word.
David Billington

This thread was discussed between 06/11/2008 and 14/11/2008

MG Midget and Sprite Technical index

This thread is from the archive. The Live MG Midget and Sprite Technical BBS is active now.