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Author Topic: Crankshaft bolts  (Read 285 times)

Offline slow-n-steady

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  • Posts: 19
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  • Model: Alhambra Mk1
  • Spec: 01 TDI 115 AUY+EHH
  • First Name: Steve
  • Region: South West
Crankshaft bolts
« on: November 20, 2020, 04:24:49 PM »
Crankshaft pulley socket head bolts rounded on AUY engine. 

Damaged bolt heads

Hi everyone,
Timing belt time again for my diesel Alhambra.  My first problem is that all 4 socket head cap screws (Allan screws) holding the aux belt pulley to the toothed belt sprocket have ‘rounded off’ internally. 
Despite what appears to everybody to be an excessive tightening specification (by the book, 10Nm + 90 degrees) there is no suggestion in the literature that they are single use fasteners.  My experience suggests they should be. 
When I last changed the belts etc. the 4 x set-screws were removed without mishap. 
They were re-used, but tightened to 10Nm + 45 degrees only. 
The bit used to tighten them was Cr-V and undamaged.  It still shows no sign of wear or other damage. 
The 4 socket head cap screws are stamped 12.9 so are the correct material at least. 
Now to the problem.  The caps are recessed within the ‘cup’ of the crankshaft pulley.  It is not possible to grip them around their outside. 
I appear to have a number of options, but not one of them is straightforward. 
1   First I have ruled out heat, by any means, because of the likelihood of damaging adjacent components. 
2   Have a toolmaker grind down 8mm hex Cr-V steel, to slightly over 6mm and hammer the new ‘hex bit’ into the hole, and try again.  The heads will not take a quarter inch Cr-V hex (being 6.35mm).  Maybe it could be hammered into position.  I haven’t tried yet, it is raining and my garage is the front drive! 
3   Drill them out, and once the pulley is off the sprocket, hope that the remaining shank can be drilled further without damaging the threads in the sprocket.  (I understand that 12.9 steel machines relatively easily.) 
4   Remove the sprocket from the crankshaft with the pulley still attached.  I suspect this is impossible without damaging the guard for the toothed belt.  Then have a machine shop machine them out.  This would probably work out more expensive than purchasing new sprocket, pulley and fasteners.  The cost for parts would be about £65 as far as I can establish. 
5   I don’t have welding equipment, but I suppose there is he possibility of welding the bit in place, and try again. 

Anybody have thoughts on any of these options please? 
Thanks, Slow-n-steady

Online johnnyroper

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Re: Crankshaft bolts
« Reply #1 on: November 20, 2020, 10:16:07 PM »
I had same issue with mine,I hammered a 12 point socket on to remove them. From memory it was a 12mm 12 point half inch socket I used. You could also try hammering a torx or ribe bit in them. T45 size would do it. Hear what you are saying about heat but a bit of local heat with a blow lamp shouldn’t cause any problems. I wouldn’t use oxy/acetaline mind nor would I try and go cherry red.

Online johnnyroper

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Re: Crankshaft bolts
« Reply #2 on: November 20, 2020, 10:18:43 PM »
As for drilling if that is how you end up going once heads are off and pulley removed the remaining bits will most likely come out fairly easy as the tension is off.

Offline champagnecharly

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Re: Crankshaft bolts
« Reply #3 on: November 25, 2020, 10:17:37 PM »
Wouldn't the +90 deg suggest that they are TTY?

Offline slow-n-steady

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  • Model: Alhambra Mk1
  • Spec: 01 TDI 115 AUY+EHH
  • First Name: Steve
  • Region: South West
Re: Crankshaft bolts
« Reply #4 on: December 04, 2020, 06:01:14 PM »
Hi guys,
Sorry for the delay.  A tumble down stairs left me crock for some time. 

Johnnyroper,
Thanks for your responses. 
I tried a 12 point star bit, but only succeeded on one, didn’t try Torx but an old 12mm, 12 point socket did the trick.  Thanks. 
Heat of any kind would not be good because I have a damper pulley and the polymer between the inner and outer could be damaged. 
Having removed the 4 screws, I could not persuade the pulley to come loose. 
I tried scraping around the edge of the centre screw, with no luck.  I left PlusGas to soak around the centre screw, but no help.  Tried a three-leg-puller, gently I thought, but broke the flange of the non ferrous casting. 
Seat franchise pulley £500.  Thank goodness for after-market equivalent by INA £40! 
I abandoned the pulley in favour of removing sprocket and pulley together. 
An electric rattle gun claimed to deliver 550Nm anticlockwise failed miserably on the centre screw. 

As the centre screw head is so shallow, I was concerned it could fall off during use.  I formed a strap to retain the socket loosely in place, but clear the half inch square drive extension bar.  At the same time it acts as a counterhold against the aluminium bracket that supports the transfer pipe, bolted to the right hand end of the sump.  I cut a hardwood disc to fit tight inside the pulley, but clear the socket and to fill the space between the back of the pulley and the strap.  This gave support to the two lengths of stud-bar I used to fasten the strap through the pulley to the sprocket, hopefully putting the stud bars in shear, and preventing them leaning over when the sprocket rotated but the counterhold stayed still.  Ideally this would have been a lump of steel, but needs-must, when the devil drives. 
I didn’t like the idea of torquing across the bolted joint between block and sump, so looked for additional anchorage.  Screwdriver through vented disc and engage 6th gear provided a second line of defence. 

The outer end (female) of the half inch square drive extension bar was supported clear of the wheel arch, on an axle stand. 
Finally, wiggling everything into its tightest position, reposition the breaker bar for greatest effect, (downward pressure against the axle stand) and out it came. 
I removed all of the temporary gubbins and the pulley and sprocket came away together. 
I left the pulley/sprocket interface soaking in PlusGas again overnight, supported the pulley in an upturned pipe coupling and drifted the sprocket out with a purpose made drift. 
Once separated, initial measurements suggested that the pulley would not fit over the centre bolt skirt.  Careful cleaning, without removing metal shows there was space when new.  About 0.03mm! 

The problem seems to be electrolytic corrosion between dissimilar metals. 
From new, the pulley has a cover fitted in the ‘bowl’, to exclude detritus from the heads of the fasteners.  It was missing from my engine when I first changed the belts, and I didn’t bother to replace it, so plenty of opportunity for moisture to gather.   
The sprocket is a machined ferrous forging. 
First there is a thin (1mm) ferrous plate, bonded to the back of the pulley. 
The inner part of the damper pulley is a non-ferrous casting. 
The centre bolt is stamped and rolled from a ferrous billet of 10.9. 
I have tried to attach a sketch, but it is hard to believe the problems caused by corrosion in such a small (2.3 x 0.3mm) space, all the way round the 30mm diameter hole in the pulley.  There is no sign of corrosion or erosion anywhere else on the crankshaft, sprocket, pulley or centre screw. 

I have manufactured a counterhold for replacement of the sprocket centre screw.  Much more sturdy than the other, and it rests against the bottom wishbone mount, which is fairly robust.  It has the facility to hold the socket in place while tightening. 

Champagnecharlie,
I cleaned up the cap screws.  They are actually 8.8.  The replacements purchased from my local Seat agent look identical, and are again stamped 8.8.  You are right of course, plus 90 degrees should make it obvious, but Haynes etc. tell you to replace the centre bolt, which has a final tightening of plus 90 degrees, so why not make the same remark about the four pulley screws?   

If we learn by our mistakes, I have learned a lot over the years. 

Regards, Slow-n-steady. 

 

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