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Corroded bolts stuck

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Discovered whilst removing the front wheels to replace my corroded wheel bolts that 2 of them have kind of welded themselves to the wheel. Or rather the 'cap' part that sits under the head of the bolt has - it seems to have broken off from the main shaft of the bolt. I'd not noticed this before. Tried to prise the them out of the hole but stopped before I caused any further damage and decided it was better left to the professionals. Anyone ever experienced anything similar? 

986-alloy-wheel-nut_2.jpg

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Maybe try a hot air gun very carefully and then use a mini pry bar to lever the stuck part out. 

Good luck 🤞 

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12 minutes ago, Tozerman said:

Maybe try a hot air gun very carefully and then use a mini pry bar to lever the stuck part out. 

Good luck 🤞 

 

Good idea! Cheers 

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Quite a common issue I believe... Due to galvanic corrosion of dissimilar metals & road salt acting as an electrolyte? :35_thinking:

 

Mine are also starting to corrode :34_rolling_eyes: so I've coated the bolts in Lithium grease...

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You should be able to knock them out from behind the wheel.  Sounds like they’ve not been lubricated, use some grease when you put them back 👍🏻

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Thanks all. I knew they needed replacing but didn't realise how bad the corrosion had got.  Presume the previous owner had not greased the bolts anytime recently either.  Lesson learnt!  

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On greasing the bolts - the owners manual specifies aluminium grease, and only on the threads - not the actual ‘sheath’ (cap) surface that contacts the wheel. 

 

I dont know what effects lithium / other greases might have on achieving the correct (130NM on a 987) torque on the bolts. And possibly grease between the sheath part of the bolt and the wheel surface might prevent the wheel from being ‘firmly gripped’ once torqued? 🤔

 

maybe a proper engineer like @Bushman can offer some insight?

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From page 254 of my owner's manual (emphasis added):

 

"Apply a thin coat of Optimoly TA (aluminum paste) on the thread and between the bolt head and movable spherical cap ring.  The bearing surface of the spherical cap facing the wheel must not be greased."

 

There's a picture on that page of my manual showing the two places where the anti-seize is to be applied to each bolt, but I can't figure out how to attach it here.

 

jD

Edited by jdavis8361
forgot to use quotation marks

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I followed the manual’s instructions.

 

I couldn’t find a small amount of aluminium grease online, so went down the opc and they just laughed and gave me a big dollop of their own in a freezer bag hahah! 

 

I read “online” you do have to use the right grease. Wrong grease like copper past etc is a bit on the dodgy side due POSs of wheel nuts backing out? I don’t know. Whether this is just theory I don’t know but didn’t fancy finding out. 

Edited by Buggyjam

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8 hours ago, Buggyjam said:

I followed the manual’s instructions.

 

I couldn’t find a small amount of aluminium grease online......

 

 

Me neither. So i 'borrowed' this from work.........🤣

 

sAsrtKy.jpg

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987 different to the 981 then ... as my 981 manual states that grease is not to be placed anywhere on the wheel bolts or on the mating wheel / hub faces. Pretty sure that my previous CR was the same and that both cars share the same torque value of 160Nm. 

 

The only place to add the Optimoly TA grease is on the three hub lugs that support the wheel. 

 

Other industry practice for torquing bolts that have been lubricated has the affect of changing the tensioning / torque levels due to the different coefficient of friction. 

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@Bushman - I knew you’d know the engineering behind it 😉. Cheers Steve. 👍🏻

 

Re ‘bolt-stretch’ - Whats your thoughts on whether bolts should be replaced periodically? i.e., do they ‘over stretch’ after multiple removals and re-torques and therefore new bolts might be advisable after ‘x’ number of torque applications? 🤔

 

Cheers, Jason

 

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Hi Jason. all bolts stretch, between the point where the thread stops and the underside of the head. there is a little bit of stretch on the last threads nearest the head too but this decreases to constant over about 1d. ( thread depth equals thread diameter..This elastic property is controlled by the stated torque figures that have been worked out over many years and on many different materials and alloys. correctly torqued bolts stay well inside this elastic boundary and it can be repeated many times. Age and vibration however can change the material properties, making them less elastic and prone to stress corrosion cracking. Stainless fasteners are especially prone to this. high tensile bolts (12/9) for example, normally found in Unbreko socket cap head bolts or similar will take much higher torque loadings whereas studding stretches like knicker elastic as it is really soft.

stretch bolts, often found in engine manufacturing, should only be torqued up once and discarded after stripdown.

hope this helps mate.

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Thanks again Steve - so much knowledge on this stuff 👍🏻

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Yes, thanks Steve for the comprehensive info!   👍

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