Bolt tensile strengths

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Bolt tensile strengths

Postby madbilly » Mon 03.12.2018, 21:06

Hi everyone,

As noted elsewhere, I'd like to replace all the screws and bolts I've taken out during the belts, pulleys and water pump change with nice shiny new ones. Where possible, I'd like to use stainless steel ones but am slightly concerned about making sure they're the correct tensile strength. Also, is chemical compatibility an issue? These are all the bits I'd like to replace (sizes from the manual or measured by me (in italics)):
  • Water pump (5x M8*18 flanged screw, 1.25 thread with 12mm head (Japanese standard, not normal metric) class 7)
  • Upper belt cover (5x M6x47, 28mm threaded, 1.0 thread, flanged head, class 6)
  • Lower belt cover (3x M6x20, 1.0 thread, class 8.8 ) + M6x12 washer - screw is same as for PAS fluid reservoir clamp, but different washer; NOTE that I don't think these are original screws as the parts manual shows them as flanged.
  • Engine mounting long one, M10x90, 1.5 thread, class 8.8 + M10 Nyloc + 2 washers (M10x20 I think)
  • Engine mounting mid bracket, 3x set screws M10x20, 1.5 thread, class 8.8 + M10x20 washer
  • Engine mounting to engine, 4x hex insert screw M10x30, 1.5 thread, class 10.9 + M10x20 washer
  • PAS pump pivot and adjuster bolts (size TBC)
  • Alternator pivot and adjuster bolts (size TBC)

I imagine the ones I may not be able to use stainless steel for are the engine mounting ones and for those I should use class 10.9 or better, right? All the rest can be stainless, if I can get them and there are no issues with chemical compatibility?

Cheers,
Will :)

EDITED to correct specs and add classes which I found written on the heads of the bolts.
Last edited by madbilly on Tue 11.12.2018, 22:49, edited 5 times in total.
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Re: Bolt tensile strengths

Postby Giniw » Mon 03.12.2018, 21:25

I am no specialist, but as far as I understand it, A2 and A4 stainless steel bolts may be a little weak compared to standard 8.8 bolts. Plus I think there might be galvanic corrosion with steel. I don't know about aluminium. I would just coper grease the threads and bolts heads.
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Re: Bolt tensile strengths

Postby Brit-Car-Nut » Mon 03.12.2018, 21:45

See the list in the Wiki: http://wikilec.com/view/M100_Bolts

Not all bolts are listed, but a lot are.

If going to stainless, it is best to choose the highest strength rating.

I would be inclined to use steel but zinc plated and grade 12.9 anywhere I swapped out the original bolts.

As you work on the car more, you will find a lot of yellow (gold) zinc plated hardware but be aware that the bolts that have a dab of green paint on the heads are double or triple plated for high durability and rust protection. There are a LOT of those in the suspension area.
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Re: Bolt tensile strengths

Postby dapinky » Mon 03.12.2018, 21:53

Billy,

I have replaced a lot of my bolts with stainless ones, but not on the engine, so can't comment on how good they'd be in that application.

My concerns would be for the expansion of the material with the heat generated, and keeping the torque figures correct - basically, Stainless bolts need 25% less torque applied to give the same 'stretch' as a mild steel bolt (so, if a mild bolt should be torqued to 40Nm, then a replacement Stainless one should be done to 30Nm).... with the reduced initial torque, the bolts will still be as 'tight' along their thread, but as the aluminium heats up, that figure may change and the bolts will appear too tight or too loose.

I haven't researched it at all, and it may make no difference, but it is something which may be considered.

If the original bolt is 8.8 grade, then it will need to be replaced with an A4~80 stainless bolt to give the same tensile strength (A2 and 'normal' A4 are ~70 grade).

Certainly, the engine mounting bolts and any tensioner/idler bolts may well be higher strength again. Personally, I'd re-use the old ones, or replace with new zinc plated 8.8 mild steel - I can't see any huge advantage to going stainless on the components you are swapping (maybe the waterpump ones, but only because I have M8x18 flanged bolts already!) - and the belt cover ones if I have them lying about.
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Re: Bolt tensile strengths

Postby madbilly » Mon 03.12.2018, 21:58

Yes, I need to be careful with stainless ones to get the correct strength.

Thanks for the link to the wiki, I wasn't aware of that. However, I can't see any of these bolts listed in there, unless they're some of the ones in the generic "bolts" section.

Thanks for the explanation Dave, I hadn't considered the fact that the ones in the engine bay are subject to heat which ones in the suspension etc are not.

The only really manky bolts are the water pump ones and the ones on the PAS pump and alternator. The ones on the engine mounting are average and all the ones in the belt cover are pretty fine really. The tensioner pulley one is also fine but as you know the idler one I can't see yet!

I may just try and see what I can find in town on Saturday, if I can get past the "gilet jaunes"!
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Re: Bolt tensile strengths

Postby madbilly » Mon 03.12.2018, 23:31

I did some reading. There's definitely a differential heat expansion between SS and aluminium or non-SS which may cause things to work loose, so may not be a good idea to use on a water pump unfortunately.

Also, when used with aluminium, SS can cause the Al to corrode especially in the presence of an electrolyte. So may not be a good idea to use in the cylinder head, but with ani-seize probably isn't an issue.

Anyway, what about tensile strength? I'm particular interested in the water pump bolts as those are the ones I need to replace.

Thanks BCN for the pointers on the coatings, I didn't notice any green paint yet but it doesn't mean it's not been there, I've just not had an eye out for it.
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Re: Bolt tensile strengths

Postby dapinky » Tue 04.12.2018, 12:11

If you look at the head of the bolts you took out from the waterpump (and anywhere else), it should have a specification cast into the top face of the head. If it says nothing, then it is a 'normal' steel bolt. If it has a tensile strength specification it will say '8.8', '10.9' or '12.9'.
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Re: Bolt tensile strengths

Postby madbilly » Tue 04.12.2018, 13:35

Thanks Dave, I didn't know that.

It may be a mute point - I looked online at distributors in France and couldn't find M8x18 flanged bolts, only M8x16 or M8x20. I may find something this weekend.
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Re: Bolt tensile strengths

Postby Giniw » Tue 04.12.2018, 14:19

https://www.bricovis.fr/
I've not tried them (yet) but they have a wide range. Maybe you can have a look.
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Re: Bolt tensile strengths

Postby madbilly » Tue 04.12.2018, 14:25

Thanks! :D I'll take a look!
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Re: Bolt tensile strengths

Postby Simon_P » Wed 05.12.2018, 08:59

I'll generalise and say that stainless fasteners have inferior properties to the equivalent steel fasteners. I use them where they don't do much and look pretty. As far as anything with a mechanical purpose is concerned I replace like for like.

Some input on other commitments

Tensile strength - if it is a question don't use stainless

Youngs modulus (stretch) & Torque - these are two methods of measuring clamping force. As Dave mentioned different materials have different Young's modulus so the clamping force for a given stretch is different. But stretch is only used in specific applications so you'd be mad to use anything not specified for the purpose. Torque is an empirical approximation to clamping force. If there is a torque specified I wouldn't use stainless. Also ss has a tendency to gall which would mess up a torque reading.

Sorry to disagree John, but double or triple plating isn't a process. You specify finish and hours of salt spray test resistance there are automotive norms, go outside the norms and it gets expensive. Paint dot marking is a universal method in the automotive industry for trying to ensure that the operator tightened the bolt to the correct torque. At the end of the sequence the operator gives the head a dib with a paint pen. It isn't very effective and these days is considered to look untidy.

Back to the question... Ask yourself what is the consequence of the fastener coming off or breaking?

As an aside, many of the fastnners on the engine are Japanese standard and have smaller heads.
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Re: Bolt tensile strengths

Postby Brit-Car-Nut » Wed 05.12.2018, 14:11

Simon_P wrote:Sorry to disagree John, but double or triple plating isn't a process. You specify finish and hours of salt spray test resistance there are automotive norms, go outside the norms and it gets expensive. Paint dot marking is a universal method in the automotive industry for trying to ensure that the operator tightened the bolt to the correct torque. At the end of the sequence the operator gives the head a dib with a paint pen. It isn't very effective and these days is considered to look untidy.


That info came from from the Lotus engineers while I was at Hethel.

Their description was that they were "over plated" as they didn't want the bolt's coating to be "used up" too quickly as the coating is "sacrificed" over time.

When I have the shift cable and short-shift parts plated, I pay extra for the equivalent of double the coating at the platers. The parts stay in the barrel longer than normal and a slightly heavier coating is applied.

I found it easier to refer to it as double or triple plating but regardless, the zinc coating is heavier than normal hardware.
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Re: Bolt tensile strengths

Postby madbilly » Fri 07.12.2018, 14:06

Simon_P wrote:Back to the question... Ask yourself what is the consequence of the fastener coming off or breaking?

As an aside, many of the fastnners on the engine are Japanese standard and have smaller heads.

Two excellent points! Obviously I don't want the water pump to leak coolant everywhere...

And the smaller heads is important, as I struggled to get my ring spanner on a 12mm head bolt for the water pump and if I use a metric replacement it will have a 13mm head. I think I need to find a source for these Japanese standard bolts...
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Re: Bolt tensile strengths

Postby Giniw » Fri 07.12.2018, 14:10

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Re: Bolt tensile strengths

Postby Brit-Car-Nut » Fri 07.12.2018, 14:13

madbilly wrote:
Simon_P wrote:Back to the question... Ask yourself what is the consequence of the fastener coming off or breaking?

As an aside, many of the fastnners on the engine are Japanese standard and have smaller heads.

Two excellent points! Obviously I don't want the water pump to leak coolant everywhere...

And the smaller heads is important, as I struggled to get my ring spanner on a 12mm head bolt for the water pump and if I use a metric replacement it will have a 13mm head. I think I need to find a source for these Japanese standard bolts...

SJs has the water pump bolts A100E6399S for £0.77 each.
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Re: Bolt tensile strengths

Postby madbilly » Fri 07.12.2018, 14:19

Giniw wrote:https://www.bricovissu.jp ? :lol:
At first I believed you! Doh! :lol:

€0.89 each + €15.43 deliery charges... I should have bought the water pump from them, drat.
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Re: Bolt tensile strengths

Postby Giniw » Fri 07.12.2018, 14:25

(sorry :-D )

As for SJS, once I contacted them to get a much cheaper shipping for a shaft square and round circlips I forgot to order with the CV joints boots and Steve agreed to send them in a padded envelope (up to 200g)
I would be surprised if he wouldn't agree to send your bolts for cheaper than £15 ^^
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Re: Bolt tensile strengths

Postby Brit-Car-Nut » Fri 07.12.2018, 14:38

If you make a decent sized order, the "per item" shipping cost is significantly less.

That is why it is usually best to make your list and then buy all the parts from one supplier.

In the past, I have also arranged with SJs to place an order and have a courier collect the package and get it to me at a huge shipping saving. (I was ordering a lot of parts and his site didn't do well calculating the postage).

One small item is never economical to ship.
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Re: Bolt tensile strengths

Postby madbilly » Sun 09.12.2018, 16:17

After going to several places in Manosque I finally found a Honda motorcycle garage who knew what I was talking about and they've ordered the water pump bolts for delivery later this week (gilet jaunes dependant).

I got most other bolts except the hex key ones as I couldn't find anyone selling them in class 10.9. However, I can get these online.
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