[Aitch]

What are people's experiences of stretch bolts on ups? It was always my intention to self-spanner and there are lots of things I'd like to fit/fiddle-with eventually but the prospect of having to buy endless single-use nuts and bolts is new to me.

 

[freemansteve]

Depending application, I think stretch bolts exist somewhere on most cars these days; what is the concern?

 

[Aitch]

Thanks. I guess interested in general advice/experience. Are they generally in stock at dealers when you call, are they expensive? Presumably there is a much greater chance of them snapping in situ unless your torque wrench is accurate? Does the same go for nuts as bolts?
My last car was a VW but I practically ignored it mechanically and didn't really get involved beyond servicing. Previous to that was a now-20yo Renault, so haven't used stretch bolts before. I'm imagining they discourage tinkering? Hoping to learn a bit more

 

[freemansteve]

If your torque wrench is significantly out of calibration it could break, or under-tighten any bolt, stretch or not. All bolts are strength rated and so should be fine, but don't by cheap monkey metal stuff on eBay! Provenance is king.

Which stretch bolts are you changing?

 

[Aitch]

Well I was assuming all bolts would have to come from VW anyway - I'm imagining having to read up on whichever job beforehand (using VW manual), making a note of all TTY bolts involved, then going to dealer to order parts. No particular jobs on the horizon although as an example I was considered trying a poly dogbone mount and partly didn't bother as I'd have to buy two sets of stretch bolts (second set to swap it back out to standard after I inevitably found the modification introduced too much NVH). I would almost certainly have to buy myself a new torque wrench too and was interested in recommendations there also. You can buy TTY-specific wrenches with a dial? Having never dealt with TTY bolts, I'm just imagining what could (won't? will?) go wrong

 

[freemansteve]

Yes, OEM stretch bolts would be my first choice, but I have no idea of costs. So long as you have a reasonably good torque wrench, preferably calibrated, I don't think fancy dials are needed for items like mount brackets. For cylinder heads and the like, using an angle dial might be a good idea - it's been a long time since I stripped engines, so I've run out of anything helpful to say here... Time for other forum members who have done real fettling on their Up!s to step forward!

 

[Percy247]

In my experience there are very few single use bolts used in regular maintenance and replacement of consumable items on modern VW's.

Unless you are considering a DIY engine or transmission rebuild then you might be overthinking things a little.

 

[Overdrive]

I think a lot of manufacturers recommend using new bolts for fear of litigation if something goes wrong.
BMW insisted that most of the suspension on my last one was held together by single use nuts and bolts (none were the stretch/angle type) I used the old ones - as long as the nyloc part is in good condition and there’s no corrosion there shouldn’t be any issues.
Stretch bolts are definitely single use only, particularly on the power train which has large temperature fluctuations, but I’d be surprised if there’s any on an UP, bar the power train.

 

[freemansteve]

I’d be surprised if there’s any on an UP, bar the power train.

Our mutual friend Aitch found that stretch bolts are used on the dogbone mount - which did surprise me!

 

[Aitch]

Thanks Gents.
I re-checked the manual I have and they do appear to be TTY for the dogbone. Annoyingly I can't just copy/paste PDFs but the main bolt is apparently 50Nm + 180deg whilst the two smaller bolts at the other end are 50Nm + 90deg. I'm comfortable reusing nyloc nuts with additional threadlock if needs be but don't fancy taking the risk with bolts that are rated in the manual like this, and especially not with ones that might be a 'mare to extract if they snap on reuse or that prevent use of the car.
My trusty Norbar wrench has served well but must be 25-30yo now and can't possibly be accurate, if it ever was. Presumably these bolts are close to shearing as they're 'torqued to yield', whereas a regular bolt you'd hope would be miles from its shear point at whatever torque rating its application calls for? May be I am overthinking (!).

 

[freemansteve]

25+ yo torque wrench? Unless you are using one all the time, and maybe worried about it, just buy a basic one with a cal certificate, which will do you fine for DIY - something like:

Sealey AK624 Calibrated Micrometer Torque Wrench, 1/2" Square Drive, 465mm : Amazon.co.uk: Automotive

Buy Sealey AK624 Calibrated Micrometer Torque Wrench, 1/2" Square Drive, 465mm at Amazon UK. Free delivery on eligible orders.

www.amazon.co.uk

Stretch bolts have a lot of tolerance by design* - it's really all about not coming loose rather than some esoteric thing and the 180/90 deg stuff is easy to visualize, unlike where they spec say, 35 degs.

*It's very hard bolts you need to get right, as they are, err, designed to not stretch! They will have a tolerance, but if you are not accurate, they snap, according to my very talented Mech Design buddy....

 

[Aitch]

Yeah, perhaps not so trusty after all, although it has never broken. I guess a tired wrench will under-deliver on the torque reading? Anyway, thanks all for the thoughts and, Steve, for the link, will save that to my Amazon wish list for the moment. Think I'll spend a little time doing some research on fasteners, torque/wrenches and the various methodologies. Cheers

 

[TEST DRIVER]

My old British Leyland mechanic always told me there is no need to bother with a Torque Wrench.

He said you just tighten the nut until it snaps and then back it off one notch.

 

[freemansteve]

BL used bolts?

 

[911ts3]

I don't use a torque wrench, as I have a regularly calibrated forearm..... 😂