Snapping head bolts

[spock500]

Hi all,

The repair of my C250D continues to be an enigma to me

Today I went to fit the reconditioned head with a new gasket set, all was fine until I wen to torque down the bolts -

I progressively went in sequence tightening the bolts 4/5 times with the (new) torque wrench set at 5ft lbs the lowest it will go, (Haynes recommend 11ft lbs for stage one) I kept tightening but nothing, the wrench didnt 'click' instead one of the bolts snapped

Picture below is of the bolt and wrench (setting has moved at bit but it was on 1) The bolts are not new as they are within 1mm of the stretch tolerances.

 

[jibcl500]

You should have bought some new bolts, even if they are in tolerance I would never refit used head bolts.

jib

 

[spock500]

When I bought the other bits from MB dealer I asked them and they said it's not always necassary so I left it -

Will 5 ft lb of torque do this to a bolt or is the wrench faulty?

 

[Aussie Nick]

I would suggest that if the wrench was faulty you would have torn out the thread from the head rather than break the bolt. It sounds to me that the bolt has been stressed and said "enough" when you gave it the final tweak. I think the advice not to replace the bolts was not sound.

I saw this on a reworked Johnson marine two stroke once. Used the same bolts after a rebuild including rebore and new oversize pistons. One of the head bolts snapped and the top half of the bolt got sucked in throught the inlet port creating total disaster in that chamber and sending steel fragments through the rest.

 

[spock500]

I would suggest that if the wrench was faulty you would have torn out the thread from the head rather than break the bolt. It sounds to me that the bolt has been stressed and said "enough" when you gave it the final tweak. I think the advice not to replace the bolts was not sound.

I think you guys are right, new bolts needed - i am bit worried though as 5ft lbs is tough, 11 is the next stage but what is it going to be like on at stage 4 on 27 f lbs, I dont think I will have enough strength or the star socket will give out - nearly lost my arm when the bolt snapped

 

[Autofix]

- i am bit worried though as 5ft lbs is tough, 11 is the next stage but what is it going to be like on at stage 4 on 27 f lbs,

5 lbs is nothing. You should be able to pull a tool that length to 5 lbs with one finger. It sounds like the wrench is faulty.

 

[Richard Moakes]

5 lbs is nothing. You should be able to pull a tool that length to 5 lbs with one finger. It sounds like the wrench is faulty.

I second that, I think the wrench is faulty or out of it's operating range below 10 lb/ft

 

[spock500]

This is the culprit

http://cgi.ebay.co.uk/3-8-drive-tor...ryZ30906QQssPageNameZWDVWQQrdZ1QQcmdZViewItem

The instructions dont make any sense and are misleading, that said is it set correctly above ?

 

[bigasotonuk]

Hi,
I,m think you have faulty torque wrench.
I,m looking at the torque wrench settings in the pic and a torque of 5lbs ft. your quoting in your posts, 5lbs. ft of torque is nothing you can get more applied torque on a screwdriver.
If 27lbs ft. is what you are saying as final head torque seems really really low as I would have thought it would 70-80lbs ft.

 

[spock500]

Yup, stage 2 (according to haynes) is 26 lbf ft or 35 Nm

then stage 3, angle tighten through a further 90 degrees

stage 4 wait 10mins

stage 5, angle tighten through a further 90 degrees

I just feel something is not right here, not sure whether to undo all the bolts or leave it until I get another wrench

 

[bigasotonuk]

I would slacken them off, If you have sheared a bolt off that diameter, worn out or not you have a lot of torque there on them, and is not equally disapated due to bolts being missing. Slacken them off in stages as you would when removing the head starting from the middle and working your way out.

 

[television]

!0lb is equal to a 6" spanner,, it must be a faulty wrench

 

[spock500]

Thanks Andy, nipped out and loosened them all off in reverse sequence - hopefully no damage done

Anyone have any rec's for good torque wrenches, the ones on ebay all seem the same with the twisting handle - the halfords stuff looks ok

http://www.halfords.com/webapp/wcs/...1_productId_178843_langId_-1_categoryId_76866

Andy, you commented on 70-80 ft lb for head bolts, these only go up to 45

 

[bigasotonuk]

Hi,
Looks ok, check this link out.
http://www.machinemart.co.uk/shop/p...le-torque-wre/path/ratchets-torque-wrenches-2

 

[spock500]

Ok, problem solved with the wrench -

I put the socket into a fixed mount then set it to 10ft, nothing using max force - then twisted the grip all the way to the top (80 ft) and back half way tried again and 'click', went down to 10 ft and 'click' (very easy)

So I guess it was jammed or in transit mode

Thanks all for your help

 

[horgantrevor]

new bolts new wrench my best bit of advice

 

[pomm001]

Its clear from the pictures that the bolts have fatigued, the taper profile just before the break gives it away
As mentioned by the other replies, 5 Nm is about what you could get with a screwdriver, if you are using your wrench correctly, throw it away and buy a real one, if your lucky you will not have damaged the threads in the block.
Get new bolts make sure the threads in the block are clean and free from any liquids as not to ‘hydraulic’ them. Do not oil the threads of the new bolts, just fit, torque and the add angle in the sequence set out in the manual and all should be OK

 

[Mr Teddy Bear]

Hi plus find out the correct torque setting.
27 IMPERIAL Pounds per foot of applied leverage isnt right as suggested thats out by at least a factor of x3.
Possibly the author has taken a Nm figure and c**ked up the conversion?
TB

 

[spock500]

Hi plus find out the correct torque setting.
27 IMPERIAL Pounds per foot of applied leverage isnt right as suggested thats out by at least a factor of x3.
Possibly the author has taken a Nm figure and c**ked up the conversion?
TB

Nope, its correct, I checked the MB workshop manual - the extra ft lbs are added during the angle tightening sequence which adds another haklf turn (180degrees) to the bolt :wink: