Stainless bolts

My restored 140D has a set of stainless steel bolts and motor mount bolts. I've been told by a restorer, they sure look purdy, but stretch and should change them out. True? Few thousand miles with no problems yet. Not doubting the guy. Just getting opinions.

From my experience the answer to whether you should change them out is - it depends.
Not all stainless bolts are the same.
The two ends of the spectrum are the "soft as butter" 316 bolts you can buy at your local hardware through to the high tensile SS bolts supplied my people such as ARP.
I think you definitely need structural grade bolts for those locations - at least Grade 8.8, in Australian speak, which has a yield of 640MPa.
Look for markings on the heads of your bolts - if any are there they will indicate the grade of the bolt.
If there are no markings I would probably do as your friend advises and change them to a bolt of known quality.
Cheers
Rob

Some restorers do get their knickers in a twist over stainless steel!

Yes... Cheap / ‘wrong’ stainless does indeed stretch, in fact they feel kinda ‘spongey’ when torquing up.

But... Good / expensive / ‘correct’ grade stainless is perfectly fine. Just look at ARP offerings for example.

The other issue with stainless is it’s ability to self weld. Stainless nuts WILL weld onto stainless bolts solidly, the only way to avoid this is to put something on the threads. Copper Slip is commonly used for this.

Copper Slipped bolts on a T140 however will soon end up on the highway! So you then either need self locking nuts or at least spring washers.

But... being pragmatic, if they’ve been trouble for a few thousand miles already then I think you’re probably fine leaving them be.

I use stainless bolts on engine mounts but apply copaslip and check regularly, if they are going to be an issue it will show up in the first few rides.

The two grades of stainless steel fastners commonly available are A2 & A4 grades. A2 is 304 & suitable for general cycle part fixings. A4 is 316, sometimes called marine grade due to its corrosion resistance, & roughly equivalent to a 8.8 grade bolt. These are a better choice for more highly stressed areas. For anything stronger than this you would be looking for fastners made from 431 grade material.
Also remember that powder coat tends to compress & bolts need to be checked for tighness for the first few thousand miles after a rebuild.

Martyn.

Britfan - I concur with those above who have used good quality SS fasteners, and when buying, look for the grade. When I inherited my Commando, it was littered with stainless bolts. Some of these had no grade stampings, and some of these indeed stretched and self-welded. I replaced all such fasteners with good quality SS fasteners. Be careful at shows and autojumbles, where there are boxes of shiny SS fasteners on display - all that glitters is not 'gold'.

I have used good quality SS fasteners for decades on a range of classic machinery, without any problems. Even before I learnt that one should use copper grease on the threads, I never had any of these fasteners self-weld or stretch permanently. I will buy from engineers suppliers, or if online, I look for the grade. One might be cautious about using SS for wheel spindles (especially on Commandos where the spindle fastens to a stub axle) and other highly-stressed parts but I have never heard of any failures due to a spindle being stainless. If I was confident of the grade and the alloy and if the threads were rolled, I would use SS for spindles.

Thanks. Although I hadn't had problems with them, yet, I swapped them out. I kept the SS hex bolts on the side primary and ignition covers. Nothing weight bearing there.

Matchless said:

The two grades of stainless steel fastners commonly available are A2 & A4 grades. A2 is 304 & suitable for general cycle part fixings. A4 is 316, sometimes called marine grade due to its corrosion resistance, & roughly equivalent to a 8.8 grade bolt. These are a better choice for more highly stressed areas. For anything stronger than this you would be looking for fastners made from 431 grade material.
Also remember that powder coat tends to compress & bolts need to be checked for tighness for the first few thousand miles after a rebuild.

Martyn.

Click to expand...

Never use a 400 series ss fastener in an aluminum or aluminum alloy base material.

A simple to use material compatibility chart is here:

https://www.engineersedge.com/hardware/fastener_material_galvanic_13354.htm

Slick

Whilst this is true, in practise it is not really a problem, as the only place 431 is required is wheel & swing arm spindles. The only aluminium contact is with fork sliders. I have made & fitted spindles from this grade of material to many bikes, none of which has had a problem with galvanic corrosion. On a yacht it would be a different matter. What really makes me shudder are wheel spindles made from 303/304 grade.