Clutch bearing collapse

[John Miller]

@John Miller

The reason I would use high tensile is to ensure they had sufficient tensile strength in shear but also in tension as they are under constant load. Bit like insurance, fatigue plays its part over time.

 

[R-III-R Turbo]

The reason I would use high tensile is to ensure they had sufficient tensile strength in shear but also in tension as they are under constant load. Bit like insurance, fatigue plays its part over time.

Do you know what tensile strength the stock bolts are?

Curious about the stock bolts strength, they have an embossed 7 on the head. It could be a fancy L too, but i think it's a 7.

 

[John Miller]

I don't have a spec for the stock bolts, I know if I was to replace them what I would use to be sure I could rely on them. Just my 2C from my own experiences.

 

[Tripps]

Grade 8 are the real good ones, so I'm guessing one grade below that?

 

[John Miller]

Bolt specs for reference.

Diameter Range Metric Grade Approximate ASTM Equivalent Description Tensile, min Yield, min
Mpa ksi Mpa ksi
All 4.6 A307A Low or medium carbon steel 400 58 240 35
through 1" (M24) 5.8 - Cold worked low or medium carbon steel 520 75 420 61
through 1" (M24) 8.8 A449 Heat treated medium carbon steel 830 120 660 96
above 1" (M24) 8.8 A193B7/A354BC or F1554G105 Heat treated medium carbon steel 830 120 660 96
through 1-1/2" (M36) 8.8.3 A325 Type 3 / A449 Type 3 Heat treated medium carbon weathering steel 830 120 660 96
All 10.9 A490/A354BD Heat treated medium carbon alloy steel 1040 151 940 136
through 1-1/2" (M36) 10.9.3 A490 Type 3 Heat treated medium carbon alloy weathering steel 1040 151 940 136
All 12.9 A574 Heat treated alloy steel 1220 177 1100 160

 

[R-III-R Turbo]

I don't have a spec for the stock bolts, I know if I was to replace them what I would use to be sure I could rely on them. Just my 2C from my own experiences.

At the risk of being inflammatory - if you don't know what strength the stock bolts are, how can you decree with such authority that 8.8 high tensile carbon steel bolts are the minimum required?
And that stainless bolts are no good?

If the stock bolts were 10.9s or 12.9s, then those 8.8s would be no good.


Having sought out a few professional opinions (e.g. Pro Bolt and others who sell bolts for a living), the general consensus was that the stock bolts pictured are not likely to be high tensile given the cut of the head and the lack of a grade marking.

The most solid answer (from a 50 year career fitter across many industries e.g. auto mechanic, plant maintenance, machine shops) was that the 7 on the stock bolt more than likely means 700 tensiles or somewhere near it.
Which is what the stainless A2-70 bolts (that I used) are too.

In any case it appears that the stock bolts are sufficient, strength wise.
We're looking at a probable strengthening of the towers by using longer bolts (not stronger bolts), because, well it costs a few cents, so why not. While you're in there.

 

[John Miller]

A2-70 = 600mpa min yield Gr:304 Stainless Steel as per spec.

Don't get me wrong its just that "GR 8.8 or better" as I stated, will have a known and tested spec whilst stainless bolts can come from anywhere from places where Quality control around tensile strength might not be managed as it should be.

If your happy using those bolts good luck to you.

 

[barbagris]

The most solid answer (from a 50 year career fitter across many industries e.g. auto mechanic, plant maintenance, machine shops) was that the 7 on the stock bolt more than likely means 700 tensiles or somewhere near it.

If they're 700 then I am suddenly grown strong. It is a piece of cake to twist those heads off

 

[R-III-R Turbo]

A2-70 = 600mpa min yield Gr:304 Stainless Steel as per spec.

Don't get me wrong its just that "GR 8.8 or better" as I stated, will have a known and tested spec whilst stainless bolts can come from anywhere from places where Quality control around tensile strength might not be managed as it should be.

If your happy using those bolts good luck to you.

No need to be like that now, we all make mistakes. Hell I wrote down 1.25mm as the thread pitch instead of 1.0mm.

Hell if someone can educate me on what the 7 means / what the stock bolts' tensile strength is for certain, I'd be grateful and willing to learn. As you should too bro.


Going off the original point, but Google 'stainless steel bolt A2-70 tensile' and you will see that it is 700 Mpa tensile, everywhere. Not 600.

If you're (not your) going to use yield strength numbers (I'd imagine in an attempt to defame stainless in the eyes of the audience here), then you need to use the same property to rate your 8.8s, where the yield strength is also much lower than the tensile strength.

Also, if a stainless bolt is marked A2-70, then it has every bit as much of a chance of its tensile strength being 700Mpa as indicated, as a steel bolt marked 8.8 has of being 800MPa as indicated too.

Nobody said the stainless bolts were not marked.
If any bolt is NOT marked, then yes, as you say, their strength cannot be relied on, but the same goes for any bolt.

If they're 700 then I am suddenly grown strong. It is a piece of cake to twist those heads off

Exactly... and they have appeared to stand up to high power bikes, which is why one cannot say 8.8 bolts are the "minimum" spec to replace them with.

 

[barbagris]

Exactly...

Mind you - I seem not to be "noticing" things these day. For example? - well this last bottle of rum prooved to be 130-proof - Yup 65%b/v - No wonder I was happy!.