Cam/sprocket bolt torque

[moribundman]

The factory sanctioned manual calls for 33 Nm (22 ft-lbs) plus 180.° This leads me to believe that this a torque-to-yield bolt, which of course must be replaced with a new one. Another manual calls for 70 Nm (51 ft-lbs).

Is there a way to guess if 22 ft-lbs plus 180° matches 51 ft-lbs? This probably an M8 bolt.

Also, if I use Loctite 242 (blue), how will it affect the torque I need to apply?

 

[Merkava_4]

Originally Posted By: moribundman
Is there a way to guess if 22 ft-lbs plus 180° matches 51 ft-lbs?


Hi mori, how did you come up with the 51 ft-lbs ?

I'm thinking you're supposed to torque the fastener to 22 ft-lbs and then use one of those torque angle meter things.

 

[Shannow]

mori, what's the effective length of the bolt and the pitch ?

Effective length is th length between the bolt shoulder and the engagement point of the bolt.

180 degree is either a very fine thread, or a very long bolt to still be within the elastic range.

 

[Shannow]

If 1.25mm pitch, the bolt would need to be around 400mm long to be in the elastic range...It's torque to yield.

When you are in those ranges, torque doesn't mean much, and the angular rotation is the most reliable figure.

 

[moribundman]

Originally Posted By: Merkava_4
Hi mori, how did you come up with the 51 ft-lbs ?


I didn't come up with it. That figure, as I stated, was from another repair manual.

 

[moribundman]

Originally Posted By: Shannow
mori, what's the effective length of the bolt and the pitch ?

Effective length is th length between the bolt shoulder and the engagement point of the bolt.

180 degree is either a very fine thread, or a very long bolt to still be within the elastic range.


Well, until I pick up new bolts I don't know for sure. From a picture that I've seen, I'd say it's an M8, about 35 mm long. I presume pitch to be 1.25, but I will have to confirm once I have the bolts.

Audi says the bolts are one-time use, but I suppose they are too short to be torque-to-yield bolts? I do know they have a 10.9 strength rating.

 

[onion]

51 ft-lbs is an awful lot of torque for an M8 bolt- even a grade 10.9. I'd be surprised if it doesn't break the bolt or strip the threads.

OTOH, I think 22+180 could work fine. It'd probably stretch the bolt- but that's apparently intentional.

 

[Eddie]

Follow the book 22 + 180 degrees. The bolt does not go to yield but, is in the elastic range. Yield means permanently deformed I believe.

 

[moribundman]

Originally Posted By: Eddie
Follow the book 22 + 180 degrees. The bolt does not go to yield but, is in the elastic range. Yield means permanently deformed I believe.


But it does seem like a large elastic range for a short bolt, doesn't it? I figured the bolt was torque-to-yield, because the manual says not to reuse it. I suppose a bolt that has been stretched to the limits of its elastic range will "never be the same again" either?

 

[moribundman]

Originally Posted By: onion
51 ft-lbs is an awful lot of torque for an M8 bolt- even a grade 10.9. I'd be surprised if it doesn't break the bolt or strip the threads.

OTOH, I think 22+180 could work fine. It'd probably stretch the bolt- but that's apparently intentional.


People have occasionally broken those bolts. I don't know if they used new ones -- probably they did not!

I am absolutely going to go with the official figure and method (22 ft-lbs + 180°). I'm simply trying to figure out a bit more about how the different approaches to torquing those bolts stack up.

As for the use of threadlocker, is there any reason to not use it?

 

[oilboy123]

I would be following the factory manual. New bolt at 22 ft lbs plus the 180 degrees. Sounds like a safe bet.

Sounds like torque to yield to me.... I use locktite blue on a fair amount of stuff and use normal torque specs. I guess I should probably back off a few percent, but I don't.

 

[benjamming]

This talks a little bit about bolt torque factors when using lubricant.
Bolts & Torque Specs

 

[moribundman]

Yeah, but threadlocker isn't listed, unfortunately. I'd say it lubes less than oil, so torque should probably be reduced, but by less than 15%. Maybe 5% less. That probably means just fuggedaboudit.

Who's in favor of even using threadlocker in this application?

 

[mechtech2]

I would not use any sealer or thread locker, unless specifically recommended by the factory.
An I'd use the TTY specs when tightening it.

 

[moribundman]

Originally Posted By: mechtech2
I would not use any sealer or thread locker, unless specifically recommended by the factory.


Any particular reason?

 

[oilboy123]

Originally Posted By: moribundman
Yeah, but threadlocker isn't listed, unfortunately. I'd say it lubes less than oil, so torque should probably be reduced, but by less than 15%. Maybe 5% less. That probably means just fuggedaboudit.

Who's in favor of even using threadlocker in this application?


I normally just torque to spec. I figure the difference ain't a big deal. I put the blue thread lock on a fair amount of things. I use thread lock on flex plate bolts/nuts, cam sprocket bolts, brake caliper bolts etc.

 

[doitmyself]

Originally Posted By: moribundman
Originally Posted By: mechtech2
I would not use any sealer or thread locker, unless specifically recommended by the factory.


Any particular reason?


This seems to be a critical fastener somewhat like a head bolt, so you are wise to be investigating this.

Here is a link that suggests Loctite has the same lubricating effect as oil and that torque values are to be reduced 25% when using it:

http://www.tractorforum.com/htdocs/users/Steve_S2/fasteners.pdf

I have learned not to trust all internet advice given by people like me!

Please share what you end up doing so we can all learn. Thanks

 

[onion]

Originally Posted By: moribundman

Who's in favor of even using threadlocker in this application?


I don't think it matters a whole lot either way. When dealing with nice, flat machined parts with no squishy gasket in between- you usually don't have to worry about bolts coming loose. So I don't think it's necessary.

OTOH, I don't think it would hurt anything- the difference in bolt stretch when lubed with locktite vs. oil would probably be negligible- especially when you'll be turning it another 180 degrees after the initial torque. If locktite will help you sleep at night, then by all means use it.

 

[mechtech2]

Locktite may give the wrong torque readings, and make it hard to remove. No mfr uses Locktite on TTL bolts.
But mostly, that part had better NOT need Locktite, or something is way wrong.

 

[moribundman]

Originally Posted By: Shannow
mori, what's the effective length of the bolt and the pitch ?

Effective length is th length between the bolt shoulder and the engagement point of the bolt.

180 degree is either a very fine thread, or a very long bolt to still be within the elastic range.


I got new cam bolts. I measure 27 mm from the first thread to the (tiny) shoulder. The bolt's diameter is 9.84 mm. There appear to be a hair over 20 threads per inch. I measure a pitch of just about 1.25. I'd say it's an M10 bolt with fine thread. Grade 10.9.

So, how does 33 Nm (22 ft-lbs) plus 180° sound?