449/511 Important Urgent Flywheel Inspection

So is the consensus that the factory got the torque spec wrong and made them too tight, which, combined with the weakened hollow fastener made them break or back out? Seems odd that some would back out if over tightened.

well, if you get just beyond the yield point of any fastener (and before it fails), it kinda loses it's "stretchy-ness" which supplies the clamping force.

Also the crank rotates in the "wrong" direction IIRC, which may or may not be a factor. I'm thinking that when the fasteners start backing out, some get sheared (at the hollow-point) during acceleration. I raised this point a year or two ago, but nobody jumped on it, so who knows (well- I bet the beemer guys do. check their forum out).

I doubt that the total clamping force is the biggest factor... I'm thinking it's just keeping the fasteners in which is the important thing. if you could keep the fasteners in with only 3ft/lbs, I'm betting everything would be dandy

OTOH- I don't have a 511, my son does. And he moved away so I don't really work on 'em anymore. so take what I say with the proverbial grain of salt.

OK lets put consensus, opinion, make or model, aside here as it is entirely irrelevant.

Traditionally fasteners have been torqued to a value dependent on their cross sectional area and tensile strength, so as to achieve the maximum clamping load possible whilst remaining within their respective range of plasticity. As these fasteners are not stretched beyond their yield point they can be reused.

A universal system identifies the tensile strength of individual fasteners whether metric or imperial and a premium of 8% is applied to fine threads.

As has been pointed out above, recently it has become more common for manufacturers to use torque to yield/angle torque fasteners - predominantly for head bolts. These bolts are not marked and must be torqued to the manufactures specification, this specification invariably requires the fastener to be lubricated, subjected to an initial low torque value and subsequent final tightening through a specified degree of rotation, such that the fastener is stretched into the lower end of its yield zone. The purpose of this approach is to provide a more even clamping load than can be achieved by the traditional torque to value method, particularly in high torque loads - hence its predominant use for head bolts. This method provides a more uniform clamping load by limiting the influence of friction and stretching the bolt slightly, evening out the loading so each bolt provides almost exactly the same amount of clamping force on the head gasket. This type of bolt should not be reused.

In rare instances a manufacturer may specify a single torque value that brings the fastener into the lower yield zone. In other words you 'may' have a torque to yield situation without minimising the influence of friction. In these instances the manual will provide a maximum length measurement for the fastener/mandate its replacement.

In the case of the flywheel bolts, in question, they are marked 10.9, ie they are graded, and the correct torque for a fastener of this grade and cross section is 13nm/9.5ftlb/114inlb.The specified torque value in the manual of 25nm represents a 92% increase above the value required to remain within plasticity range, an increase of this magnitude puts the fastener into the upper range of the yield zone - and this is not taking the reduced cross section of the fastener design into account.

Locktite; The purpose of a thread locking compound (or any form of fastener retention) is to prevent the backing out of a fastener due to vibration or other external forces, it/they DO NOT provide clamping load, nor can they maintain the integrity of a fastener stretched beyond its yield zone. A fastener that has been stretched beyond its yield zone will have reduced/no clamping load and a high chance of failure. If the locktite applied has integrity any failure of the fastener will result in the head separating at the point of smallest cross section with the thread retained. This type of failure is well documented in this engine.

If the locktite applied has lost integrity the reduced/no clamping load resulting from being stretched beyond the yield zone, facilitates the backing out of the fastener. This is also well documented.

Their are also numerous cases where a combination of the above has occurred and I am yet to see an instance where a fastener has failed anywhere except the point of smallest cross section.

It is also not possible to 'shear' individual fasteners if most of the remaining fasteners are still maintaining clamping load.

Whilst any fastener subjected to high vibration or external forces may back out as a result of loss of locktite integrity, any assertion that the failures in this instance are simply as a result of this, ignores the physical properties and torque load of these fasteners.

Campbell

Well said and true. So, it could be assumed that the torque spec given by husky and presumably BMW was used during assembly and has compromised the fastener. So, without even getting a different style fastener as I have, we could all just buy the same replacement low clearance factory screws and correctly torque them to 114in/lbs?

As you point out it is a assumption, an incorrect torque value in the manual does not necessarily equate to incorrect torque in production. However the types of failure occurring would indicate the probability.

The OE fasteners are 151,000psi, while Unbreako etc cap screws are 160,000psi, ARP 8740 SERIES 180,000psi and ARP 2000 series 220,000psi. How compromised are the OE screws by their design even at 114in/lb?

Given that the above choices provide superior (and known tensile strength) at I assume a cheaper price, and head space is not an issue - should be checked though as DM recommended, I would give the OE fasteners a miss.

Link to info from ARP 'Bolts ain't just Bolts'
http://arp-bolts.com/p/technical.php

Any idea what the original engineers were thinking? Surely their choice was not cheaper than standard screws like I put in.

Not really, these screws are only attaching the one way starter clutch to the back of the flywheel - perhaps a email to Speedbrain might shed some light. I can't imagine they would risk a DNF over something so easily rectified.

Hi Fella's
Wish I saw this earlier. 7100km of dirt on my TE511 and one screw adrift from the fly wheel/ ring gear.
Stator is toast and the flywheel not much better.
Bike kept on going until it ran out battery. Stator was still making 8V.
Keep checking these screws
Thanks
Franko

WARNING ; You can check your lotto ticket all you want it does not improve your chances of a win
These screws need to be replaced, re locktighted and correctly torqued to FASTENER spec.

What do they need to be replaced with?...

NM I found it!

ehhh, for 10.9 that's the correct dry torque, but for grade 12.9 I'm thinking it's more (+10% maybe, 12-13lbs). No?

With all this drama still going on, I think I'll change the fasteners in my son's 511 next time it's here. I'm looking for M6-1.0x12mm grade 12.9 (I'm going with socket head cap screws, but I suppose hex head would be fine?) correct? Can anyone confirm this?

[similar to these on ebay: http://www.ebay.com/itm/M6-1-0-x-12...246699?hash=item19e0e4646b:g:Ro0AAMXQ6DBSEkT8 ]

I'm going to hit all the threads up with brake cleaner, apply a little of the loctite activator to the male threads, put some 242 (blue) on 'em and torque to, say, 12ft/lbs.

Again, I don't believe clamping force is the culprit here as much as the fasteners backing out. hell, maybe I'll go 10-11ft/lbs 'cause of the loctite acting as a lubricant. any comments on my plan? Campbell? BT?

btw, cured loctite is pretty oil resistant- that shouldn't be a huge concern.

I think the big take-away for all you 449/511 owners is: replace your rotor fasteners. And also, if you hear a minor "ticking" suddenly, stop the motor.

Anyone out there in the know, can you confirm if 6mm head height is acceptable? Here are two options:
http://www.mcmaster.com/#95735a212/=12kykd2
http://www.mcmaster.com/#91290a318/=12kyixy

Checked mine, they were tight, I left them alone. 1500 miles or there abouts, lost speedo magnet took me a while to replace.

Speedo magnet: glue it in. Also- didja look all over the rotor? 90% of the time that magnet is hiding there.

Recon the flange head bolts would be better given their wider head and its wider torquing/pressure load area versus the hex head bolt (recognising the superior tensile strength of the hex head bolt suggested)

Replaced mine after my initial post where I checked mine.
I had planned to do the replacement at 200 hrs with my top end rebuild.
Unfortunately several things all conspired (Christmas holidays, lack of funds directly after and life) whereby I had to push my engine rebuild back a little.
The bolts ate my own stator at 237hrs.

All but one had worked loose, the heads was sheared off the first bolt to contact the stator.

I purchased a brand new stator unit and carried out some mods prior to installation.
I removed and discarded the original cap screws.
I removed the one-way clutch assembly from the rear of the flywheel and bonded it using Loctite 510 back to the flywheel.
This will prevent any torsional movement between the one-way clutch plate and flywheel.
I purchased standard grade 10.9 cap screws (vs the low profile originals) and carefully checked for stator clearance once assembled.
I used high strength Loctite and torqued the screws up.

I shouldn't need to be inside there again

arggggh. this means I gotta do my son's again for sure. Thanks for the update. (8mm heads on the new bolts?)

I would, yes.
That was about 6500km or so all off road.
Can't recall the head size sorry.
I'm away at work, so can't get to my spares either....

Well I knew about this thread, read the whole thing, figured I'd eventually get to checking my bolts.. too late. The bike has about 4k miles offroad.

It happened about 500ft from the house on day 5 of a 5-day trip to Colorado so the timing could have been much worse. I was in Europe for a couple weeks so I was able to get the part somewhat cheaper than what the cost would be in the US ($380 for the alternator assembly, gasket and the nuts/keys that need to be replaced) but it will still end up being a $700-$800 repair :/

Where did you guys get the replacement ARP bolts, a local dealer?