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DIY fix for screwed up crank noses
by
lord_verminaard
on 17 Apr, 2008 09:19
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Figured I would post this here, as apparently this is a common problem with 16v engines that get a serpentine conversion. This guy has made a jig so you can drill into the crank nose and press in hardened dowel pins to prevent the keyway from shearing off. Before, this fix required pulling the engine and crank and having a machine shop do the work.
http://forums.vwvortex.com/zeropost?cmd=tshow&id=3793002Enjoy! Rob, (the guy who posted the thread) has done a lot of various fabricating for the Scirocco crowd and he really knows his stuff.
Brendan
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#1
by
GoKraut
on 17 Apr, 2008 11:42
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#2
by
zukgod1
on 17 Apr, 2008 13:13
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Man what I wouldnt give to have a serp system on my car..
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#3
by
GoKraut
on 17 Apr, 2008 16:13
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#4
by
GoKraut
on 17 Apr, 2008 17:24
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#5
by
jtanguay
on 17 Apr, 2008 17:32
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and those 4 holes won't weaken the crank nose too much??? looks really interesting... that thing isn't going anywhere!! :lol:
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#6
by
GoKraut
on 17 Apr, 2008 18:38
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and those 4 holes won't weaken the crank nose too much??? looks really interesting... that thing isn't going anywhere!! :lol:
The holes are 5mm deep and the material for the crank is one hell of a lot harder than the cog. Thats less than 1/4" deep. Now I can't say this for sure because obviously I haven't driven it around yet but my educated guess is it will be just fine. The thread for the crank nose starts at about 7mm into the crank. So as far as that goes it shouldn't weaken the mounting.
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#7
by
commuter boy
on 18 Apr, 2008 01:21
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I did a similar repair, but with just two holes. As long as the key can't start moving due to the pins it should be fine. Four holes looks like overkill to me.
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#8
by
GoKraut
on 18 Apr, 2008 15:36
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I did a similar repair, but with just two holes. As long as the key can't start moving due to the pins it should be fine. Four holes looks like overkill to me.
I thought that originally too...but then I read other people's stories. First they tried one, then two. Finally by the third it seemed to be OK. There is a LOT of force that causes them shear in the first place - because on the one hand you have the crank bolt which is supposed to be around 77ft/lbs + 1/4 turn and THEN you have the 7mm key. It takes a lot of force to shift the cog and shear off the key.
And I do agree with you partly. The cog must not be permitted to move even a little. I don't know if you've ever tried it but on a clean nose and new cog, there is very very little movement maybe one quarter of one degree. Unfortunately that is why we're here. Even that little amount of movement could not overcome those forces I mentioned earlier. The idea behind using 4 pins is pretty simple really. Take equal loads across the geometric span of the cog - not in one or two places.
Though we'll see. Believe me I don't want to be proven wrong here, not because of my ego - but because I just rebuilt everything and another failure would mean 3 cylinder heads. :roll:
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#9
by
jtanguay
on 18 Apr, 2008 16:24
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I did a similar repair, but with just two holes. As long as the key can't start moving due to the pins it should be fine. Four holes looks like overkill to me.
I thought that originally too...but then I read other people's stories. First they tried one, then two. Finally by the third it seemed to be OK. There is a LOT of force that causes them shear in the first place - because on the one hand you have the crank bolt which is supposed to be around 77ft/lbs + 1/4 turn and THEN you have the 7mm key. It takes a lot of force to shift the cog and shear off the key.
And I do agree with you partly. The cog must not be permitted to move even a little. I don't know if you've ever tried it but on a clean nose and new cog, there is very very little movement maybe one quarter of one degree. Unfortunately that is why we're here. Even that little amount of movement could not overcome those forces I mentioned earlier. The idea behind using 4 pins is pretty simple really. Take equal loads across the geometric span of the cog - not in one or two places.
Though we'll see. Believe me I don't want to be proven wrong here, not because of my ego - but because I just rebuilt everything and another failure would mean 3 cylinder heads. :roll:
well vw over engineers their engines for a reason. i think there is no way you're going to bust this off, unless the crank bolt somehow loosens itself completely, and then falls out, and even then i have a hard time seeing this setup fail due to the belt tensioning, unless the pins are loose enough.
good work! keep the diy coming
its what owning a vw is all about
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#10
by
commuter boy
on 19 Apr, 2008 00:21
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The other thing to look at is making sure the end of the crank is perfectly flat to mate with the gear when it's bolted down tight. My dad's been noticing some of them aren't exactly flat, which might cause more wobble, especially if a less than perfect torquing procedure is used on a new bolt.
If you're going to this much trouble, and you're that risk adverse I would have thought you'd pull the crank and machine a TDI shaped D on the end of the crank nose matched to a gear to a light press fit.
Do keep up posted as to how the fix works though, I'm curious.
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#11
by
GoKraut
on 19 Apr, 2008 00:52
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#12
by
jimfoo
on 19 Apr, 2008 12:40
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That is just a pulley, not a harmonic balancer as there is no rubber or mass to dampen out the harmonics.
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#13
by
GoKraut
on 19 Apr, 2008 13:54
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That is just a pulley, not a harmonic balancer as there is no rubber or mass to dampen out the harmonics.
That would be why it's in quotations. :wink:
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#14
by
jimfoo
on 20 Apr, 2008 13:56
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Guess I missed them. :oops:
