high tensile v stainless

Gidday. How critical is using high tensile bolts for disc rotors and caliper mounts vs stainless steel allun key bolts for example?
will the s/s bolts sheer off under load on an average road bike?

thanks Hillbone

In my experience using the type of stainless which seems to be available from aftermarket suppliers for any critical union is a bad idea. After installing a SS head bolt kit on my bike I was surprised to discover my head gasket was leaking upon re-torquing. When I removed one of the head bolts I discovered the thread pitch was elongated and the diameter above the thread narrowed to the point of snapping. I called the supplier and he could not verify the grade of SS. I suspect most of the SS fasteners offered by suppliers is a low carbon variety most likely 300 series SS. I understand your brake rotor is more of a sheer than tensile application but for my money I would stick with the high carbon steel unless you can verify the grade of SS.

domiracer66 said:

In my experience using the type of stainless which seems to be available from aftermarket suppliers for any critical union is a bad idea. After installing a SS head bolt kit on my bike I was surprised to discover my head gasket was leaking upon re-torquing. When I removed one of the head bolts I discovered the thread pitch was elongated and the diameter above the thread narrowed to the point of snapping. I called the supplier and he could not verify the grade of SS. I suspect most of the SS fasteners offered by suppliers is a low carbon variety most likely 300 series SS. I understand your brake rotor is more of a sheer than tensile application but for my money I would stick with the high carbon steel unless you can verify the grade of SS.

Click to expand...

Is 18-8 more acceptable?

I used 316 and 304 stainless bolts and nuts on my calipers for ever, from memory the shear strength is adiquate, for heads etc the tensile strength can be poor.

Cash

I would say that it's not a good idea to replace the standard disc rotor studs with screws of any description as sooner or later the threads in the hub will deteriorate. It's also unlikely that you'll find a plain shank shorter than the mounting thickness so you'd have the disc bearing against a threaded section. I use stainless dome nuts on the standard studs.

I've long used stainless bolts for caliper mounting (supplied by Middletons in the UK).

When I crashed the bike heavily, one fork slider broke and the top mount lug was torn from the caliper (the wheel spindle sat in the timing cover so it was a fair old whack). There was no visible damage to the SS fasteners on the forks, nor to the isolastic studs and bolts further back. I replaced them as a matter of course and in fact the rear iso stud now does service inside my 16H footrests.

I've always steered clear of SS wheel spindles but have never had any problems with other fasteners.

18-8 is 300 series 304 to be exact... The 18 in 18/8 is the % amount of chromium with the 8 being the percent of nickel. 304 SS is considered a formable or deep drawn SS so I doubt it would be good for anything beyond holding your license plate on.

In the UK they supply coloured nylon screws for holding the licence plates on. Perhaps we just like living dangerously ?

These casting are so soft that anything other than the original screws tend to have issue. There seems to be more and more threads on stripped threads after someone goes stainless. Some may feel that now that they have these tough screw they can now torque them a bit beyond specs. SS screws are good in educated hands and as long as the pitch is perfect.
FWIW, A running Norton is a rust free Norton, except for maybe along the coast.

You can get SS fasteners in rated grades, there should be two sets of characters; A2-50 etc
Now the first part identifies the material (steel grade)
A2 = 304
A4 = 316

The second number indicates the tensile strength (property class)
50 = 500MPa
70 = 700MPA
80 = 800MPa

So with this it appears that either an A2-80 or A4-80 will be similar to a 8.8 grade carbon steel bolt, this however is not the case as the SS bolt has a much lower yeild than the carbon steel bolt

0.2 yield
50 = 210MPa
70 = 450MPa
80 = 600MPa

An A2-80 would be equivalent to an 8.6 carbon steel bolt if there was such a thing.

Hillbone, depending on where you are located, you might or might not find high tensile strength SS fasteners readily available. 17-4 Ph steel is used for stainless fasteners in a lot of applications, particularly marine use. It has an ultimate tensile strength of over 1000 MPa, and up to something like 1300 MPa in some heat treats. It's yield strength is also over 1000 MPa in most heat treats. It's not too hard to find very high strength stainless fasteners in aircraft applications (some of the NAS series bolts come to mind). If you hunt around enough, you can find aerospace supply houses with almost any kind of fastener you can imagine, but they frequently don't come cheap. They come in both metric and standard, but the metric ones are a bit harder to find in the US.

Ken

Is't it rather a moot point knowing you are screwing these into material that you can almost scatch with your finger nail. I will add, a bolt or stud not being able to shear can be a bad thing in curtain applications. Although shearing a bolt does not sound good, blowing out a hub seems much less inviting.

304 sucks to machine

lcrken said:

Hillbone, depending on where you are located, you might or might not find high tensile strength SS fasteners readily available. 17-4 Ph steel is used for stainless fasteners in a lot of applications, particularly marine use. It has an ultimate tensile strength of over 1000 MPa, and up to something like 1300 MPa in some heat treats. It's yield strength is also over 1000 MPa in most heat treats. It's not too hard to find very high strength stainless fasteners in aircraft applications (some of the NAS series bolts come to mind). If you hunt around enough, you can find aerospace supply houses with almost any kind of fastener you can imagine, but they frequently don't come cheap. They come in both metric and standard, but the metric ones are a bit harder to find in the US.

Ken

Click to expand...

+ 1 on the 17-4 PH. I recently mounted a TD3 260mm 4LS in between my Roadholders. The brakes bearing I.D. was 15mm which seemed a little on the small side for an axle. 17-4 PH was the only grade I trusted to turn the axle out of.

I suppose little horror stories will always be passed around regarding the use of stainless, have worked with loads of it .all i can say is respect the material!
It as a great tendancy to" pick up" over tightening will distort the thread,Then removal can be a problem, I called on a motorcyle repairers a few years ago. they had spent hours trying to remove a standstand spindle, the nut had picked up and this resulted in hacksawing it in half...which under a bike with lots in the way proved tricky...Much swearing and cursing :!: Always lube the threads, Copperslip is good,and tighten with care.
Biggest problen is the size of threads cheap grade mass produced " far east" items are well below the din spec. and nuts allso.
Its better to use quaility machined high tensile fastners with a plated finnish. but in the right place used properly stainless is great...Timing covers etc...just remember...RESPECT the stuff and lube all threads!. Cummin's diesel engine's on hi stress parts use only rolled 10.9 carbon steel ..No stainless!'

I have heard that nickel anti-seize is best for SS.



Dave
69S