Stainless shortcomings

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This failure of a Stainless banjo bolt for the rocker oil lines (double line), occurred at about 1/2 the recommended 180"/lbs. It had been in use, removed without undue force and upon refitting snapped with little effort. The fitting also had never been struck/abused. A reminder that some "upgrades" especially those in Stainless may not be up to original engineering standards.
Any other S/S disappointments to share?
WOJ6gx8.jpg


Cheers
 
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Too sharp a corner in the root of the thread will do this, luckily for stainless spokes the thread is rolled not cut.
 

Onder

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That threads into aluminium. Hard to believe it failed first. But it did.
 
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I have a stainless Goodridge single banjo line sold by Fair Spares many years ago. Probably made with decent/quality material from a civilised country. I've never had a break like you... Too bad that your bolt failed, it means that we must be aware of the non benefit of free trade environment we live in
 

xbacksideslider

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Many of the hardware kits, sold in stainless, consist of bolts and nuts where the thread is too coarse. That is the original British threads are finer and generally resist vibration better. I suspect that stainless is just too difficult to cut fine threads in. The manufacturers and the sellers of those kits find it difficult to supply them in original fine thread pitches. The fasteners then tend to loosen and fall off at a greater rate than the original.
 

MikeG

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Not the same failure mode, but my 2017 Triumph T100 has lots of stainless hardware on it. Problem is a lot of it is threaded into aluminum and no type of treatment was put on the threads to keep things from seizing. This bike is 3 yeras old, garage kept, only seen rain once or twice, but it can be as miserable to take things apart as the rustiest old saltbelt Chevy out there.
 

ntst8

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I recently had a stainless mirror stem fatigue through the threads, the threads had been very roughly cut so it was a prime candidate for that in hindsight.
The replacement chrome ones from Andover look much more durable.
 

concours

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Not the same failure mode, but my 2017 Triumph T100 has lots of stainless hardware on it. Problem is a lot of it is threaded into aluminum and no type of treatment was put on the threads to keep things from seizing. This bike is 3 yeras old, garage kept, only seen rain once or twice, but it can be as miserable to take things apart as the rustiest old saltbelt Chevy out there.
Thaiumph
 

RoadScholar

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Do you take issue with the material or its maker? My eyes aren't what they used to be, but the break on the banjo bolt appears to be crystallized?

All fasteners regardless of the material they are made from should be hand fit first and go in to the correct depth before applying torque. That this part failed before the aluminum threads stripped amazes me; clearly the part was made defective material, not that the buyer could have pre-determined the condition.

Another question: Are these parts made by modifying a bolt or do they begin life as bar stock?

Best.
 

Richard Tool

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I recently had a Stainless center stand spring fail . Fractured just behind the coils where the tang for the stand begins . Stand dropped while riding . The spring was less than a year old and under 1k miles and was purchased from a very reputable supplier.
 

ashman

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I am still using all the original bits, studs and engine mount bolts on my motor after 46 yrs they are still good even with solid mounts engine in the featherbed frame, not a fan of SS bolts and nuts.

Ashley
 

marshg246

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This failure of a Stainless banjo bolt for the rocker oil lines (double line), occurred at about 1/2 the recommended 180"/lbs. It had been in use, removed without undue force and upon refitting snapped with little effort. The fitting also had never been struck/abused. A reminder that some "upgrades" especially those in Stainless may not be up to original engineering standards.
Any other S/S disappointments to share?


Cheers
Where did you find the torque spec. 15 foot pounds seems like too much to me.

SS is more brittle and the bolt has a hole down the center.

IMHO:

That size fastener made in steel and screwed into steel should be around 20ft lbs.
With a hole reducing the area by about 1/3 I'm guessing steel into steel about 13ft lb.
It has relatively fine threads so unless helicoiled I would be nervous above 10 ft lbs and that seems like about the limit for that bolt.
I've never used a torque wrench there but I think I make them about 8 ft lbs.

Still as someone earlier said, it should have stripped the threads out of the case before breaking!
 
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Looks almost like the bolt bottomed out and then twisted apart at the top of the threads. Maybe too long? I'd check the thread depth and length of the replacement bolt.
 

Time Warp

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The stock steel banjo bolts are torqued to 15 ft/lbs - 180 in/lbs but a decent grade stainless steel should be able to use that figure also Shirley.
 
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Definitely poor quality S/S alloy. I'm sure there are some specifications that would be suitable but obviously not in this case.
180"/lbs comes right from the service manual. No binding at all, the remains easily threaded out & threads in head ok.
Cheers
 

Derek Wilson

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Where did you find the torque spec. 15 foot pounds seems like too much to me.

SS is more brittle and the bolt has a hole down the center.

IMHO:

That size fastener made in steel and screwed into steel should be around 20ft lbs.
With a hole reducing the area by about 1/3 I'm guessing steel into steel about 13ft lb.
It has relatively fine threads so unless helicoiled I would be nervous above 10 ft lbs and that seems like about the limit for that bolt.
I've never used a torque wrench there but I think I make them about 8 ft lbs.

Still as someone earlier said, it should have stripped the threads out of the case before breaking!
I thought it seemed a bit high as well, pulled out my trusty circa 1972 factory service manual - sure enough - 180 in.lb is specified.

I have made my own SS rocker banjo bolts from 303 SS hex bar - never had one break.
 

marshg246

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Definitely poor quality S/S alloy. I'm sure there are some specifications that would be suitable but obviously not in this case.
180"/lbs comes right from the service manual. No binding at all, the remains easily threaded out & threads in head ok.
Cheers
Agreed on the SS quality.

See page 18 of the MKIII Workshop manual (00.4224) The table and notes on that page explain that torque settings are specified for plain fasteners with no lubrication - I wish they made that clear with the other tables - I'm pretty tired of removing broken SS bolts and replacing stripped threads for people.

Here is a generalized (medium strength bolts) version you'll find on the OldBritts site:

GENERAL:
  • 1/4" Bolt 8 ft lb.
  • 5/16" Bolt 15 ft lb.
  • 3/8" Bolt 25 ft lb.
  • 7/16" Bolt 40 ft lb.
  • 1/2" Bolt 60 ft lb.
  • 9/16" Bolt 80 ft lb.
Note: The above figures are for plated bolts. Lubrication makes bolts easier to turn and therefore lower torque should be used.

Since SS always must be lubricated when screwed into AL alloy, that alone says that the book specification is not right and too high for the SS banjo bolts.

The table here makes it clear that 180 in lbs is too much for SS when dry and therefore way too much when lubricated: https://www.engineersedge.com/material_science/torque_values_stainless_steel_13353.htm

Finally, in the last two sections of this page I try to combine the data more. As always, I'm happy to discuss any of it and to make changes that make sense - it is an attempt to help only - most of it comes from others: https://www.gregmarsh.com/MC/Norton/Norton Commando Torque.pdf
 
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