Trigger wheel failure

Non-engine, eg: aerodynamics, gearboxes, brakes, suspension
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pastaroni34
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Location: Texas, USA
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Trigger wheel failure

Post by pastaroni34 » Fri Nov 18, 2011 10:11 am

My fellow enthusiasts,

it is with a great deal of grief I present to you an issue with one of our products. A client has reported a failure of his crank pulley, citing that the screws used to fasten his trigger wheel have loosened and subsequently backed out. Thus the trigger wheel was free to flail about and do some damage to surrounding components.

It should be noted that we have made dozens of these crank pulleys, with this being an isolated incident. Even an isolated incident though, is unacceptable and thus we are replacing the damaged components free of charge.

The client purchased the part in 2009. I believe, however, we have already remedied this problem. In early 2010, I spent a good deal of time researching and testing fasteners. This research was immediately put to use to improve our products. Since then we have used Loctite 246 when affixing trigger wheels, taking care of any loosening due to vibration. We are also very careful about torquing the fasteners during assembly. For further reassurance, fasteners are marked after they are torqued, that way we know we don’t miss one during assembly.

I take any issue with our products very seriously. They have my name on them and they darn well better be perfect. That being said, mistakes happen and we do what we can to make things perfect again. I want to report this problem and hope that you will help notify anyone who has one of our crank pulleys with trigger wheels. I urge you to check the fasteners, and implement the procedures I have outlined above.

For the full write-up, see my blog.

I would like everyone to be aware of this issue, as it could happen with any setup configured in a similar way. This may also serve as a reminder of the importance of timing belt covers, which if they were implemented in this case, the damage would have been somewhat mitigated.
Attachments
Damage 2 small.JPG
Loose trigger wheel
Damage 2 small.JPG (218.74 KiB) Viewed 1710 times
-Jason Miller
Miller's Mule Machine and Design Inc.
Houston, Texas - USA

Guy Croft
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Re: Trigger wheel failure

Post by Guy Croft » Fri Nov 18, 2011 11:13 am

Can you upload a photo of a new one showing the fasteners that came undone?

G

pastaroni34
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Re: Trigger wheel failure

Post by pastaroni34 » Fri Nov 18, 2011 6:15 pm

Guy, here is an example of a new one:
Attachments
crank-pulley-with-trigger-wheel.jpg
Trigger wheel affixed to aluminum pulley via 5x M5 screws.
crank-pulley-with-trigger-wheel.jpg (30.86 KiB) Viewed 1698 times
-Jason Miller
Miller's Mule Machine and Design Inc.
Houston, Texas - USA

Guy Croft
Site Admin
Posts: 5003
Joined: Sun Jun 18, 2006 9:31 am
Location: Lincoln, UK
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Re: Trigger wheel failure

Post by Guy Croft » Sat Nov 19, 2011 11:23 am

Firstly Jason I think it's very professional & ethical of you to make this post.


I can't see anything fundamentally wrong with the bolting array and countersunk screws are known to be self-locking. There is always the worry that a client has not secured the screws properly and to be honest at M5 size they are rather critical.

G

TomLouwrier
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Re: Trigger wheel failure

Post by TomLouwrier » Sat Nov 19, 2011 11:47 am

Not many will come forward and 'blow a whistle' on one of their own like this. Respect to you, Jason.

I know these Allen (or Inbus) drive countersunk screws well and I'm not too happy with them. In theory they should be OK, but in practice the holes are often too small for the torque they need. Especially the smaller sizes have a nasty tendency for the hole to go round, damaging the key in the process.
Of course less than perfect tools (tips already rounded off, sloppy tolerances) do not help the situation at all.

As you already stated, using the right locking fluid is a must. There are locking rings available as well that can be used under these heads (the Schnorr type, dished form). For this relatively small size (M5) you may switch to Phillips or rather PoziDriv fasteners. The shape of the screw head allows more room for those pointed cross type holes, giving better tool location and torque.

regards
Tom
GC_29

Urbancamo
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Re: Trigger wheel failure

Post by Urbancamo » Sat Nov 19, 2011 2:29 pm

Firstly, it's great see that manufacturer carries responsibility years after. I really appreciate that!

Secondly i have found too that this type of countersunk swrews get loose casually no matter how tight they are.

I recommend using Loctite 242/270 if screws are secured permanently and there is no need to open them. These liquids never fail on any circumstance.
GC_25

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