Modifying a Phosphor Bronze Bush

[Shox Dr]

I need to replace the bushes in the Sunbeam forks. The upper bush is no longer available...

I've bought some bushes for leaf springs, I can machine down to suit. However they have grease groves, and the ID is just about where it needs to be so I can't machine them out.

I was thinking of loading the groves with either lead or soft solder, and machining back.

Whats everyone think, would that work. Would the solder ahdere to the PB well enough to stay put?

 

[Pete.]

What's the basic problem with leaving the grooves there Dave?

 

[Rannsachair]

I would not take the risk and just look for another piece of phosphor bronze and make from scratch unless you can live with the grooves and shorter bush life?

 

[MCKDAVID]

not sure never tried, but I would think so, as long as it was well fluxed, clean, and hot enough to get it to flow down into the "pores" to lock it into place, but my concern would it maintain enough porosity in the surrounding area to retain oil to maintain it's lubrification ...

was going to ask the same question, can't you just leave the grooves in place? what impact they would have? , suppose it depends on how much surface area you'd lose??

 

[Gritineye]

As the inner bearing surface was designed to support the expected load on that size pin with the groves there, unless you are over loading the pins what's the problem with leaving them there?

If in doubt install them with the groves in a low load orientation, if that makes sense..

 

[Shox Dr]

What's the basic problem with leaving the grooves there Dave?

The groves are in a spiral... The inner Stanchion has 3 top out ports. If the groves are left in it may allow oil to blow past the fork seals. In the original bushes their are 6 radial groves to stop this while holding a bit of oil for lub



bush dims are 1.25x1.5x4" so not a small bit nor cheap. The leaf spring bushes were a fiver each

 

[Seadog]

Aren't they the same as BSA heavyweight forks?

 

[Shox Dr]

Aren't they the same as BSA heavyweight forks?

No. BSA bushes do fit though are shorter so the fork will have a harsh topout.

 

[Seadog]

That's a bugger. And I bet that there's not a great deal of difference, either?

 

[Munkul]

The groves are in a spiral... The inner Stanchion has 3 top out ports. If the groves are left in it may allow oil to blow past the fork seals.

That's what oil seals are for... bushes are designed with clearance and to carry oil... I think I'd be calling it good and using them as-they-are.

 

[dobbslc]

Will whatever you load the grove up with wear out the pin quicker that PB? And if whatever you use manages to break free it'll damage / seize the pin surely.

 

[Shox Dr]

Will whatever you load the grove up with wear out the pin quicker that PB? And if whatever you use manages to break free it'll damage / seize the pin surely.

I dont think so. Lead is a lubricant.

 

[dobbslc]

Tell that to the missus!

 

[slim_boy_fat]

bush dims are 1.25x1.5x4" so not a small bit nor cheap. The leaf spring bushes were a fiver each

What would be the cost of buying material to machine to size [properly]?

"Spoiling the ship [sheep] for a ha'p'orth o' tar" springs to mind. Sorry, not what you want to hear....

 

[Shox Dr]

What would be the cost of buying material to machine to size [properly]?

"Spoiling the ship [sheep] for a ha'p'orth o' tar" springs to mind. Sorry, not what you want to hear....

Far too much. I could give Locate Supplies a call, they are good for off cuts, but still be well north of 75quid.
BSA full set of top and bottom can be had for 40quid. But too short. These cost me a tenner. Probably worth more in scrap

 

[Shox Dr]

No worries Slim. I bought 3 (just in case) one I will make up a loose fit wood dowel as a core and cast a lead liner, machine back. See how that pans out

 

[MCKDAVID]

just an off the wall thought,
presuming one single groove in a spiral from bottom to top, and your concern about oil pushing past, could you "break / block" the oil passage groove with something, like drilling / tapping a hole through at the spiral point, and plugging from outside with a brass bolt, then machine that down to the final bore size? basically interupting the path for the rising oil in the fork at several points?, maybe more than one to avoid any passage, or at least limit it?.
might avoid the need to lead line the whole bushing..

 

[Shox Dr]

just an off the wall thought,
presuming one single groove in a spiral from bottom to top, and your concern about oil pushing past, could you "break / block" the oil passage groove with something, like drilling / tapping a hole through at the spiral point, and plugging from outside with a brass bolt, then machine that down to the final bore size? basically interupting the path for the rising oil in the fork at several points?, maybe more than one to avoid any passage, or at least limit it?.
might avoid the need to lead line the whole bushing..

Not as daft as it sounds, you could tap the bush and use brass machine screws, loctited in.

edit; wot you said

 

[MCKDAVID]

aye kinda what I was thinking, or peened over / centre dabbed over from outside to lock the set screw in place. I'm thinking it would be a fairly slow moving / rotating part, so wouldn't expect much chance of it falling out?. can't really tell from the photo, how thick is it?

 

[Shox Dr]

aye kinda what I was thinking, or peened over / centre dabbed over from outside to lock the set screw in place. I'm thinking it would be a fairly slow moving / rotating part, so wouldn't expect much chance of it falling out?. can't really tell from the photo, how thick is it?

Its the top bush from a 1950s motorcycle fork. No rotation just linear with side force. 7/64 wall thickness so not a lot