Bit of a wide ranging question this as it is relevant to every engine build......as per title really, when (if ever) do you use a thread lock solution (Loctite as an example) on nuts and bolts inside an engine? About to start doing final assembly and want to know whether or not to use the stuff on bolts like main caps and big ends (as an example). I know there wasn't any on them originally, but seeing as some fixings do like to shake loose over time (not that I've ever had a main cap bolt come loose) is it best to apply some blue gloop whilst assembling or can this affect the torqueing process? Cheers
No, bits inside don't loosen if correctly torqued with new bolts/nuts/studs or ones in serviceable condition. On a mk2 Gti, iirc all I ever loctite'd was the front crank pulley bolt and the ones holding on the pressure plate to crank on the other end. The only possible exceptions might be if you are fitting a different stroke crank for example that sets up harmonic imbalance. And at that it's the likes of oil pump retaining fasteners you'd loctite.
Yeh, my thoughts exactly. I've used it with other engines I've built in the past but just thought I'd ask if there was any reason NOT to use in inside my abf. Being a rally car I've had stuff shake loose before (although not anything torqued to 65Nm mind) so was thinking about a small dab here and there just to make sure and for peace of mind.
What about if you have arp bolts? You have to use the lube how would that affect the thread lock? Would seem pointless
Its not the coming undone that's the problem, its over/under tightening of the fixing...that's what causes the failure. Thread lock will distort the torque wrench settings as the fixings/components were not designed to take its presence in to account, hence more risk of failure not less. IMHO.
Torqueing is not an exact science, tolerances quoted were +/-20% when I looked into this a while ago Jon
Ahh see, we disagree on that...for a change LOL. I think torqueing should be an exact science. Of course depends on the quality of fixing, if the quality of the fixing is +/- 20% then it all goes out of the window....that's why you pay for the money for the best fixing, certainty of quality + correct torque = safety.
Seems I've started an interesting topic again......boring stuff can be interesting it seems. So seeing as we are talking about torque ( lol ) and that there is a +/- 20% tolerance, how often do we DIY mechanics (professionals don't count as you all get your checked don't you) get our torque wrenches checked for accuracy?? I've got three and have not had them checked....although i'm a good boy and wind them off after every use. Other things to consider when torqueing fasteners then.... if contaminants like Loctite could possibly cause failure, would unclean threads due to oil cause the same? Should threads be super cleaned when assembling? Could this cause issues in the future with corrosion (although perhaps not inside a nice oily engine)? Discuss......
Definitely all threads should be clean. I usually have a drop of light oil on the threads and under the head, unless specified otherwise, so no point in using loctite.
Why though? As Jon says, it's nice to assume torqueing is an exact science, but it isn't by the sounds of it.
I don't because: 1. Threadlock can change the torque value required by acting like a lubricant. 2. When a bolt is torqued to the correct value stretches the bolt and creates the tension to keep it in place. 3. If there is enough vibration to shake the bolts out then you have other bigger issues. Gurds
On the engines I have had to work on, you need to pull the the bolts to achieve the correct clamping force including stretch. The torque method i.e. using a torque wrench is one way of getting the stretch within manufacturer recommended suggestions for a given fastener. I have to work with prototype engines that are blue printed and there is no instruction to use 'loctite' for internal engine components. I certainly have never seen instructions from OEMs or the aftermarket to do so.
a team of trained engineers spent hours designing the engine and how its put together , but you know best and want to put a dab of threadlock on to be safe?
I wouldn't use Loctite in a engine as it often runs where you don't want it and can cause unforeseen problems later down the line
