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Hoyle

Tensioner roller bolt?

I've read a few horror stories of these snapping - I believe the Audi part is 10.9 grade - just wondering what people have used instead of the standard snapping bolt?

Not overly clued up on bolt grades, but would I be right to assume a 12.9 grade bolt would be less likely to shear?

Cheers  
Alex Rhys

My new tensioner came with the new bolt. I didn't check the head for the grade tho :/
Hoyle

Alex Rhys wrote:
My new tensioner came with the new bolt. I didn't check the head for the grade tho :/


Yeah the tensioners do   and mines did, just after reading about these snapping, I thought I'd best upgrade it.
dhali

Are they snapping because of over torque on fitting ??
Hoyle

dhali wrote:
Are they snapping because of over torque on fitting ??


I've no idea! I believe the torque setting to be 20Nm.
suf3r

Hoyle wrote:
dhali wrote:
Are they snapping because of over torque on fitting ??


I've no idea! I believe the torque setting to be 20Nm.


If i correct it's 15. Lats time i did it, setted mine to about 17...
Aragorn

IIRC, and its a while ago, when we bought the kit for my brothers S4, it already came with a 12.9 bolt.
suf3r

Aragorn wrote:
IIRC, and its a while ago, when we bought the kit for my brothers S4, it already came with a 12.9 bolt.


Maybe it depends on which brand?
aidank1981

need to be a little cautious here as increasing tensile strength also increases how brittle it is! a higher tensile bolt isn't 'better' in every application
okkim

suf3r wrote:
Hoyle wrote:
dhali wrote:
Are they snapping because of over torque on fitting ??


I've no idea! I believe the torque setting to be 20Nm.


If i correct it's 15. Lats time i did it, setted mine to about 17...


It is 20 Nm.
suf3r

okkim wrote:
suf3r wrote:
Hoyle wrote:
dhali wrote:
Are they snapping because of over torque on fitting ??


I've no idea! I believe the torque setting to be 20Nm.


If i correct it's 15. Lats time i did it, setted mine to about 17...


It is 20 Nm.


Thanks for correction.
Hoyle

aidank1981 wrote:
need to be a little cautious here as increasing tensile strength also increases how brittle it is! a higher tensile bolt isn't 'better' in every application


This is what I needed to know - I thought maybe an 8.8 would be better as it'll bend rather than shear!
Burnzybubbles

Is was reading into bolt tensile strength last night, it's not as easy as just fitting a different strength bolt, the issue with this bolts application is cyclic stress iirc, no bolt is designed for high cyclic stresses, the idea of a higher tensile bolt is to use a higher torque rating to hold whatever it is tighter together to stop it moving.

You then have the issue of what material your screwing into, if it goes into an alloy casing then you could tighten it to a point it'll strip the threads out the casing, if it's the block and cast iron then the extra torque is probably ok if you use as much of the thread inside the block as possible.

You also have another issue with 12.9 tensile bolts and that is hydrogen embrittlement, and this is caused by electroplating mainly but not solely, so the best bet would to buy non electroplated 12.9 bolts in any important application.
Hoyle

Burnzybubbles wrote:

You also have another issue with 12.9 tensile bolts and that is hydrogen embrittlement, and this is caused by electroplating mainly but not solely, so the best bet would to buy non electroplated 12.9 bolts in any important application.


Yeah, that's why I bought the standard finish ones. It's going into a stainless helicoil too    as the alloy threads stripped on removing the old bolt!
Burnzybubbles

So really the limiting factor is the alloy head the tensioner is bolted too.
confusionhunter

Happened to me back in 2006 ( wow, Ive been messing around with B5's for that long?)

See here:
http://forum.rs246.com/viewtopic....28550&hilit=tensioner#p128550

I immediately went out and spent a small fortune on a snap on torque wrench!
mikey-s

I personally think that roller needs a bigger bolt.   Although I've never seen this issue myself,  I know Grizz@Unit20 has seen it once or twice and they are anal with torque settings and they torque absolutely everything!    If the thread is already stripped I'd consider retreading to the next size up & drilling out the roller to suit.
Burnzybubbles

That's probably the best solution to the problem tbh mikey,
bboy82

Doesn't that roller bolt screw into the flange for the front crank seal? Would it not be a good opportunity to renew the crank seal and flange, as opposed to risking a repair?
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