I want to replace the top shock mounting bolt on my R100GS with an M55 x10mm stainless steel item. The ones I've seen advertised on ebay all seem to be A2 quality. Is this standard strong enough?
stainless steel bolts
- Thread starter FatAl
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Mikeyboy used these people for the stainless on my 80gs and it is superb quality.
www.shawstainless.co.uk/
www.shawstainless.co.uk/
Thanks for that Garry, some nice stuff there. My bike is mostly stainless fasteners, I just need to get the rear shock mount bolt sorted. I've seen plenty on ebay, but there appears to be different levels of DIN standards, and I'm wondering about the quality of A2 stainless. I want to be sure the bolt won't shear, especially as I'm a heavy fat fecker.
Stainless steel bolts do not have the same strength as HT bolts, I would never use a St St bolt on any application where torsional strength is important, such as frame, brakes, suspension, steering.
They are fine for cosmetic applications.
Personally I use Gr 8.8 BZP unless a higher grade is required.
They are fine for cosmetic applications.
Personally I use Gr 8.8 BZP unless a higher grade is required.
I've seen 8.8 on bolt heads before, whats the BZP part of it? Would Titanium bolts be suitable?
All I can say is that A2 woodscrews are crap, A4 seems about the same as ordinary mild steel. I’d avoid using anything other than the original spec parts for the rear shock mounting as it seems to be subject to heavy loads (there being only one).
Beemerboff
Registered user
The shock bolt should have the grade on the head, and if it is higher than 8-8 I wouldn't replace it with a A2 stainless bolt.
The difference between A2-70 SS bolts and stock 8-8 auto grade bolts is minor and there is no problem changing - bolt sizes are usually determined using a factor of safety of four or five so 10% is neither here nor there, but where the OEM bolt is something other than a stock 8.8 bolt I would attempt to find the equivalent grade of stainless - the info you need isn't hard to find!
The difference between A2-70 SS bolts and stock 8-8 auto grade bolts is minor and there is no problem changing - bolt sizes are usually determined using a factor of safety of four or five so 10% is neither here nor there, but where the OEM bolt is something other than a stock 8.8 bolt I would attempt to find the equivalent grade of stainless - the info you need isn't hard to find!
Stainless steel is inherently weaker than Gr 8.8 as it flows under stress.
BZP is bright zinc plate, they do go dull but unless damaged they don’t go rusty, most structural steel and pipe work joints use them. Gr 8.8 had a higher tensile strength than stainless or standard mild steel.
I’m fairly sure A2 is 304 stainless and a4 316 stainless, it still offers no more tensile strength but has a greater corrosion resistance. Typically 304 is used where chemical attack is less harsh, 316 is more common in food and medical applications.
BZP is bright zinc plate, they do go dull but unless damaged they don’t go rusty, most structural steel and pipe work joints use them. Gr 8.8 had a higher tensile strength than stainless or standard mild steel.
I’m fairly sure A2 is 304 stainless and a4 316 stainless, it still offers no more tensile strength but has a greater corrosion resistance. Typically 304 is used where chemical attack is less harsh, 316 is more common in food and medical applications.
I'd use only the original OEM bolt there.
IIRC the difference between A2 and A4 stainless is more about corrosion resistance than anything else.
IIRC the difference between A2 and A4 stainless is more about corrosion resistance than anything else.
The bolt fitted isn't the original one (done by previous owner) it doesn't have any markings on it. I've ordered a BZP high tensile grade 8.8 DIN 931. Hopefully that will be OK.
Thanks for the comments lads.
Thanks for the comments lads.
Another vote for Chris Shaw https://www.shawstainless.co.uk/
He does full kits for BMW's - I had them on my K1100RS and K1200RS...
He also has the BWM-specific stuff like drain and fill plugs for gearox and bevel ox...
For my Defender, I use Stigs https://www.a2stainless.co.uk/ - they do Defender kits
Both these guys do top service
He does full kits for BMW's - I had them on my K1100RS and K1200RS...
He also has the BWM-specific stuff like drain and fill plugs for gearox and bevel ox...
For my Defender, I use Stigs https://www.a2stainless.co.uk/ - they do Defender kits
Both these guys do top service
Steel bolts. Around 20,000 psi in tension. Half in shear. Do the sums.
8.8 or dot marking is the industry standards for tensile strength of bolts
If i recall most bolts used for certain automotive applications must meet 8.8 or higher
I'll see if i have the spec sheets flaoting around some where
I seem to recall there are certain applications where you can & cant use SS bolts
This should help
https://www.boltdepot.com/fastener-information/materials-and-grades/bolt-grade-chart.aspx
As you can see SS falls some way below the strength of 8.8 bolts
Very useful information, thanks. The stainless bolt that I've replaced has been in place for at least 15 years. I'm happy in the knowledge that the 8.8 BZP is a lot stronger.
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Never had a stainless steel suspension bolt sheer in all my years ? ( Then again Fatal is a tad larger, cough, than me ! )
Beemerboff
Registered user
The shock bolts on my Funduro should be 10.9 but mine have been A2-70 for at least the last 80,000 km.
All fasteners will have a large factor of safety, and part of this calculation will include the bolts strength throughout its life.
As carbon steel bolts loose a considerable part of their strength when corroded this will be taken into account when the factor of safety is calculated, but of course this allowance is not required with a stainless bolt , which might be why the dont have to be as strong when new.
Most of the tables around are pretty basic and obsolete too - auto grade bolts have been cold forged with rolled threads for years, but the tables still talk of quenched and tempered, which would apply to hot formed bolts, so their current applicability is uncertain , to say the least.
All fasteners will have a large factor of safety, and part of this calculation will include the bolts strength throughout its life.
As carbon steel bolts loose a considerable part of their strength when corroded this will be taken into account when the factor of safety is calculated, but of course this allowance is not required with a stainless bolt , which might be why the dont have to be as strong when new.
Most of the tables around are pretty basic and obsolete too - auto grade bolts have been cold forged with rolled threads for years, but the tables still talk of quenched and tempered, which would apply to hot formed bolts, so their current applicability is uncertain , to say the least.
I found this old photo of us back in the day. Smithdown lane nick circa 1990
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