Bronze bushing question

[alien]

I have a Nordic track stair stepper. I am a big guy (working on getting smaller). This is my third one (I have worn them all out) over the course of 3-5 years. The part that wears out is small bronze bushings that are pressed into the arms the foot rests/peddles bolt to.

The factory bushings only go in about a 1/2 -5/8 of an inch on each side and there is a gap of about an inch in the middle between the bushings that are pressed in from each side.

I am thinking of getting some bronze rod (open to ideas on material or options) and having it drilled the bolt diameter with a press fit for the full length of the bolt hole.

Any ideas or suggestions? I don't have time to go to a gym and I don't mind the 45-60 minutes I use this most days.

 

[larry_g]

a coupld of questions

1. Is this a full rotary joint or oscillating?
2. You say this has a bolt in it, is it just a plain bolt or does it have a machined bearing surface on it? Can you replace this bolt with a hardened , finished pin? When newly assembled is bearing to bolt a good fit or a bit sloppy?

3. Do you lubricate this joint/bearing periodically?

4. Are you willing to spend some money to modify this arm to hold a different bearing?

lg
no neat sig line

 

[bwringer]

Order up a bunch of flanged sleeve bearings from McMaster-Carr, replace as needed?
https://www.mcmaster.com/#standard-sleeve-bearings/=47j9fbcfe9iz2y12oa

They also sell high loan versions -- maybe these would take the pounding better:
https://www.mcmaster.com/#standard-sleeve-bearings/=47j9fbcfe9iz2y2ye1

 

[alien]

a coupld of questions

1. Is this a full rotary joint or oscillating? Oscillating, up and down with each step.
2. You say this has a bolt in it, is it just a plain bolt or does it have a machined bearing surface on it? Can you replace this bolt with a hardened , finished pin? When newly assembled is bearing to bolt a good fit or a bit sloppy? Its just a hardened bolt about 3/8 inch. The bolts don't wear, just the bushing. It is a good fit, you don't have to hammer it in but it's not sloppy?

3. Do you lubricate this joint/bearing periodically? Yes I have lubricated it. You have to disassemble it to lubricate it.

4. Are you willing to spend some money to modify this arm to hold a different bearing? I'm not willing to spend $500-1000, I paid less for the machine. There really isn't a lot of room in the area to install a bearing even if it was reworked. I figured a full length bronze sleeve would be twice the length than original and hopefully at least twice as durable? I am willing to spend some money before I just replace the whole unit.

lg
no neat sig line

I get bored on a treadmill, bicycle, and don't like elipticals. I get a great workout in 45-60 minutes and have done 90+ minutes a few times. I am down 30 pounds (down to 280 at 6'2").

I can post some additional pictures if needed?

 

[alien]

Order up a bunch of flanged sleeve bearings from McMaster-Carr, replace as needed?
https://www.mcmaster.com/#standard-sleeve-bearings/=47j9fbcfe9iz2y12oa

They also sell high loan versions -- maybe these would take the pounding better:
https://www.mcmaster.com/#standard-sleeve-bearings/=47j9fbcfe9iz2y2ye1

These ones are odd sizes or I would be willing to go that route. They don't have an exact fit

 

[e36jon]

Looking at the way that bushing failed my take is that the part was designed incorrectly. That joint wants the loads to be happening inside the steel tube that is the bottom of the arm. The way it's designed now, with the bushings having such a thick flange, the flange is seeing the loads where it isn't supported by the steel tube, so it's cracking. You could 'fix' it by getting another set of stock bushings and a tapered reamer of the right diameter, then using the reamer to introduce a shallow countersink such that the loaded area is entirely within the bore.

Just one guys two cents.

Bravo on losing the weight by the way.

Jon

 

[LS6 Tommy]

Looking at the way that bushing failed my take is that the part was designed incorrectly. That joint wants the loads to be happening inside the steel tube that is the bottom of the arm. The way it's designed now, with the bushings having such a thick flange, the flange is seeing the loads where it isn't supported by the steel tube, so it's cracking. You could 'fix' it by getting another set of stock bushings and a tapered reamer of the right diameter, then using the reamer to introduce a shallow countersink such that the loaded area is entirely within the bore.

Just one guys two cents.

Bravo on losing the weight by the way.

Jon

I agree. I'd try a bushing without the flange (or machine off the flange if the bushings are that hard to find) and use a spacer or washers to make a new thrust surface to relieve the side-to-side play.

Tommy

 

[alien]

I took some pictures, sorry some are a little blurry but you get the idea (I hope).

First is the bolt at .383 inches or 9.7mm

next is the bushing ID at .398 inches or 10.15mm

and the OD of the bushing at .518 or 13.17mm

the over all bushing length at .476 inches or 12.12mm

And the over all length of what the bushing length could be at 1.73 inches or 43.95mm

This is the end the foot rest/pedal goes on. The two bolts are in the bushings with the extra bushing on the bolt for reference.

A look up with the pedal installed. Not much room to add bearings or re engineer?

And the whole arm assembly.

 

[alien]

I agree. I'd try a bushing without the flange (or machine off the flange if the bushings are that hard to find) and use a spacer or washers to make a new thrust surface to relieve the side-to-side play.

Tommy

My thought and I agree to a point. If I found some round stock (bronze or whatever is recommended) the diameter of the steel tube drilled out to accept the bolt. Only about 3/8 of an inch on that flange gets inserted into the steel tube. That tube is 1 1/2 inches long leaving 3/4 of an inch gap between the two bushings. By making a solid bushing without the flanges (with washers to make up for the flange lip) I would be basically doubling the surface area from 3/4 total to the full 1 1/2"?

Thoughts? Material/grade to use? Any machinists want to make me 4 or 8 of these?

 

[alwaysFlOoReD]

In my city of 100,000 people, there are numerous industrial areas and I can think of 3 bearing supply houses off the top of my head. I'm sure they could find a bushing appropriate for your needs. Perhaps put your location in your post and someone local could suggest a place.

 

[alien]

Brockton MA 02302. None close. NH about an hour away and I doubt they would have anything. It seems a lot of Nordic Trac stuff is proprietary and no longer available. Tried buying a bunch?

 

[matt_i]

My take is the oilite bushing (SAE 841) is sintered and prone to fracture and or explode as you have there. The upside is that nobody ever has to lubricate it because the sintered (porous) piece is vacuum impregnated with some type of oil.

If I were you I would buy the same exact flanged bushing except in SAE 660 which is a cast bronze. It will not fracture and explode, but it will wear egg-shaped if it is never lubricated. And so, if you were willing to give it a drop of oil ~4 times a year I think your problems would go down significantly.

Biggest manufacturer I know of is Bunting Bearings.

http://www.buntingbearings.com/pdf/Bunting Product Catalog 040610.pdf

Pages 28+ have the metric flanged series. Its likely a nominal size. You probably can't buy from them but can try Amazon, Motion Industries, or Applied Industrial Technologies or any other "industrial power transmission" supplier locally.

Also, the SAE 660 alloy is same as CDA 932 (which is Copper Development Association...they have their own standard for alloys for whatever reason). There are more exotic and expensive "aluminum" bronzes that get much harder with higher P*V ratings (pressure * velocity) but are less sacrificial and will put more wear on the shaft.

 

[alien]

I ordered a couple of variations from ZORO and ebay using the bunting numbers, thanks for the link. I have no problem oiling 4 times a year. I'm lucky to get 3 months before one of the bushing eggs and or breaks now? Do you think an oil like kroil or a grease would work better? I don't have a problem removing 4 bolts to grease or oil?

I'll update how things work out.

Thanks

Still open to further suggestions.

 

[kbs2244]

The only critical dimension is the OD of the bearing so it fits in the tube.
And that can be fixed with sandpaper.
Replace both the bolt and bearing.

 

[marineengineer]

For a source of a bushing local to brockton ma try capeway
Bearing and machine in plymouth. Great people to do business with and have most stuff in stock. I went to college by cape cod and have gone back there a few times to use them even living 4 hours away.

 

[manwithtools]

If you have the time and inclination, look into Igus polymer bushings. They make some very serious bushings in just about any configuration you can imagine; no lubrication necessary. The cool part is they will give you samples (if they won't because you are and individual, PM me and I'll get them for you)

 

[pancho400cid]

Not sure if that is a 10 mm or 3/8" bolt - common either way.

All the above is good, but just as a check, Lowes and Home depot DO stock assorted similar bushings in the hardware section. I was pretty impressed with what my local Lowes had available last time I needed similar. I'd take the bushing to one and see if they stocked one that would work before moving to other options.

 

[larry_g]

Your running a bushing on a black oxide bolt. That is an abrasive surface, no wonder your tearing up bushings. I would suggest that you get a 3/8" shoulder bolt to put in there so you have a bearing surface for the bushing to run on. I would also suggest that you get a 3/8 x 5/8" bushing and turn down the outside to fit in your bore in the arm. Then drill a small hole between the bushings in the arm so that you can oil it regularly.

lg
no neat sig line

 

[alien]

Your running a bushing on a black oxide bolt. That is an abrasive surface, no wonder your tearing up bushings. I would suggest that you get a 3/8" shoulder bolt to put in there so you have a bearing surface for the bushing to run on. I would also suggest that you get a 3/8 x 5/8" bushing and turn down the outside to fit in your bore in the arm. Then drill a small hole between the bushings in the arm so that you can oil it regularly.

lg
no neat sig line

Factory bolt, but I agree. Might try and polish it?

I don't have a lathe?

 

[alien]

If you have the time and inclination, look into Igus polymer bushings. They make some very serious bushings in just about any configuration you can imagine; no lubrication necessary. The cool part is they will give you samples (if they won't because you are and individual, PM me and I'll get them for you)

I'll look into that this week. I "may" take you up on that.

Thanks

 

[matt_i]

I ordered a couple of variations from ZORO and ebay using the bunting numbers, thanks for the link. I have no problem oiling 4 times a year. I'm lucky to get 3 months before one of the bushing eggs and or breaks now? Do you think an oil like kroil or a grease would work better? I don't have a problem removing 4 bolts to grease or oil?

My personal take is that oil is best. Kroil is not a long term lubricant imo and grease does not flow to the problem area like oil will.

So that said, I would use either something like engine oil or chainsaw bar oil. My caution is don't use "rear axle lube" like 85W140 because it contains EP- (extreme pressure) additives for steel on steel (like a ring & pinion set). The EP additives have a long and well known history of chemically attacking bronze-based products.

 

[dffay]

I tend to overkill but here's the fix I might attempt on my equipment: drill and tap for 1/8npt and tap for a zerk fitting. Replace the bronze bushings but use a shoulder bolt that is smooth along its shank (McMaster-Carr source comes to mind) and reassemble with a grease gun lube to finalize the work. Bona fide chassis lube might just be the long term fix. It's the proper stuff for king pin front ends and those have bushings.

 

[gungatim]

just a suggestion, have you tried contacting NordicTrack to see if they are aware of the problem? my hunch is they are, and probably re-designed that area on a revision somewhere along the lines. even if parts are NLA, they may help you by sending a copy of the revision drawings, or at least explaining what they did to fix it. you'd be surprised at how many company's are willing to help out a customer in that way. not all, but many will if you get to the right person...never know, they may have spec'd a different bushing and a polished bolt or something you could copy...

 

[alien]

just a suggestion, have you tried contacting NordicTrack to see if they are aware of the problem? my hunch is they are, and probably re-designed that area on a revision somewhere along the lines. even if parts are NLA, they may help you by sending a copy of the revision drawings, or at least explaining what they did to fix it. you'd be surprised at how many company's are willing to help out a customer in that way. not all, but many will if you get to the right person...never know, they may have spec'd a different bushing and a polished bolt or something you could copy...

Sad to say they don't make or care about these anymore. I've tried calling, emailing and on the one occasion I spoke with someone they just said that is discontinued?