Hoping this is not a repeat question, did have a look through some of the posts but hoping someone will be able to help me here.

Looking for replacement stretch bolts for the rocker ladder/cage but hitting a brick wall in finding them. I assume I can't use standard M8 bolts or Ford would have used them in the first place so hoping someone will be able to advise or link where I can get these. 

Thanks in advance.

'Stretch bolt' and 'torque to yield bolt' are misnomers, there's no such thing as special bolts with such names. All bolts are stretched to some degree when they're tightened down. The greater the force, the greater the stretch. Every bolt, depending upon its properties like size and material, has a point up to which you can stretch them where they will relax back into their original shape/length once undone; beyond that there's a 'yield point' from which they won't fully do so (they yield somewhat to the force of the strain, becoming somewhat permanently deformed - if you measured them afterwards you'd find them to be ever so slightly longer); and of course beyond that a point where they'll just snap. A bolt that's never been pushed beyond its yield point can be reused as many times as you like. A bolt that's been pushed beyond it's yield point will have essentially become somewhat weakened, and each time you reuse it you're pushing it closer and closer to snapping.

Bolts in your vehicle that are described as 'single use', 'stretch bolts', or 'torque to yield', are simply those where the bolts have to be tightened down so tightly to achieve the required clamping force, that the bolts are pushed to some degree beyond their yield points. Technically this doesn't mean you can't necessarily get some additional use out of them, but unless you have the engineering information to determine that an additional use can be successfully achieved without them being at risk of snapping, either when installing or when under additional strain during use, you're taking a blind gamble with your expensive vehicle and perhaps your life and the lives of others if you choose to reuse them rather than get replacements.

However, NO, you can't just use any odd random M8 bolts. The physical size and shape of the bolt and its threads are only one aspect that you need to consider when finding a suitable replacement for a bolt. Another hugely important aspect is the strength, or metric 'grade'. On a bog standard bolt you might not find any strength marking, but on 'high tensile' (high strength) bolts, as many bolts in a vehicle will be, you'll find a marking like '8.8', '10.9', 12.9' or '14.9'. These two numbers, separated by a decimal point, are its grade, and are indicators of 'tensile strength' and 'yield strength' respectively, i.e. how much force it can be subjected to before snapping, and the percentage of that force where its yield point lies. An 8.8 grade bolt for instance has a tensile strength of 800MPa and its yield point is at around 80% of that (not that you need to know as much detail as this, but you might find it interesting). The bolts that you need to replace should have a marking like one of those just listed. You'll want to find replacements with the same marking. You might be tempted to go for replacements with a higher strength marking, but there can actually be negatives to doing so, so you should avoid that.

Another detail to consider is differences in surface friction. Torque is simply a measure of how much turning force you're applying to the bolt. Some of that force will generate actual clamping force, while some will be eaten up overcoming friction between the surfaces of the bolt and what you're screw-ing (seriously, that word is censored 🤣) it into.

• If the engineering instruction is to simply tighten down the bolt to a specific torque value, and surface conditions are not the same as what the engineer designed/intended, then you may overtighten or undertighten it, i.e. achieve too much or too little clamping force to some degree, which may or may not be significant. E.g. if you cover the bolt in oil then this will significantly reduce its surface friction leading to overtightening. (And understand than overtightening could mean pushing a bolt beyond its yield point or even to snapping). You might not expect it but even a simple difference like whether a bolt has a shiny metallic surface or a black one can have a significant difference in surface friction. I've read about a real life situation whereby a manufacturing company received a batch of bolts which were black instead of metallic coloured, or vice versa, the production staff used them without question and suddenly their product failure rates were increasing; installation instructions (torque specs) had to be adjusted to compensate. Similarly whether or not things like threadlocker or grease were intended to be applied, and whether or not you do apply such things, can have a very significant impact. So you really want replacements to be as identical as possible, and if there are differences then the greater the torque spec, the greater the risk.
• If however the engineering instructions are to tighten it to some torque value and then turn it further by some specified angle (e.g. 90-degrees), then you don't need to worry so much about surface friction since the majority of the clamping force is produced from the angle portion of the instruction, and differences in surface friction will simply make it easier or harder to turn it through that angle.

A final note while we're on this topic in case you don't know this - it is very important that you hold your torque wrench in the correct place while tightening. Intuitively some people assume it wouldn't matter, but a torque wrench (click style at least) has two pivot points and it absolutely does!

Thank you for all the information and insight into the use and anatomy of 'stretch bolts'.

What I am taking from your reply is that I can use any stretch bolt so long as the dimensions and attributes match the original bolts.

My question remains though, where can I purchase these with the specifics needed? Is there a website where you can enter all the details needed or is this something I can get made somewhere?

58 minutes ago, FergieP said:

Is there a website where you can enter all the details needed or is this something I can get made somewhere?

Might seem like an obvious question, but have you tried to buy these bolts from a Ford dealer ?

If we knew the Ford finis number then it should be possible to track these bolts down to a supplier.

Is this your engine ???

https://partsouq.com/en/catalog/genuine/unit?c=FORD201911&ssd=%24*KwEGMiNLelFhfFNfXABVDF5Kam1zAg0AARM8D0dBcmZ6fnx_Oi0Ba0VBRXRie2osMTsGD2ZBVVtBWRlDK2AMEgEEBQQdX1NOAEtRWlB1AQBeU05KUwNzGQMCA1RVSA0ABE1SB3IBXlABXVhTVFF1VQBcVkkAAgoDBkteWQMIP0pHclZKR1tULVABQ1wAcwUHCwBUAAAAAAgjVOo%3D%24&vid=0&cid=8533&uid=15849&q=

Firstly thank you for your reply.

I have tried to contact Ford but can't seem to get a straight answer from anyone. 

The current engine is code H9FA.

 

Regards,

Peter

2 hours ago, FergieP said:

The current engine is code H9FA.

What is the VIN or the Registration number ?