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MG MGF Technical - Now it's our turn

to have an HGF:-(((

Ordered bits from Mike this morning, having the car sorted at Gwyndaf Evans' place.

BTW 48,000 miles and went on back right hand corner of the block. At least it came outwards, so no gunky mess in the sump.
Ddraig

I reckon someone at MGR has trained a monkey to put the engines together, but forgot to tell them about the extra turns on the stretch bolts, mine went in same place after 13k miles.
Mike
Mike

Which leads to the question: Has anyone with K-engine experience actually measured the torque needed on the head bolts when un-doing them after a HGF ?

Time to do some re-torquing at let say 20,000 miles ?

BR, Carl.
Carl Blom

Don't blame the monkeys at least they can fly spaceships;-)
Mike.
mike

Carl, I'm not sure how this would help you: the stretch bolts are first torqued up to 20 Nm, and then turned a further 360 degrees in two steps.

Who honestly knows what the torque setting should then be?

If you don't know what the final torque should be, it makes interpreting the release torque very difficult.

It also makes 're-torquing' the bolts 'impossible' (insofar as what should the re-torque torque setting be?)

Work I've done on engines in the past have used 50year old technology, so these stretch bolt things aren't really in my repetoir of experience.
Rob Bell


Hi Rob,
as usual a bit hard to explain correctly in english but my idea was to use one of these "no click" torque wrenches that has a pointer on a circular scale. If not to 100% one is at least close to find out the final torque when doing the last 180 deg. It would be very interesting to compare that number to the one needed to un-do the bolts after a HGF... Maybee then one finds that the bolts have slacken in use and to avoid a HGF they need an additional 90 deg.in order to be safe for another 30.000 miles or more. Compare this with what´s written in the manual if one over-torque a bolt : Undo that bolt and do it all over again !

BR, Carl.
Carl Blom

I can see what Carl is getting at - how much have the bolts stretched or slackened since the were torqued up on head fitting - and using an idicator wrench rather than 'break' wrench will certainly give an idea.

Ted
Ted Newman

Thanks Carl, I understand what you are saying. But I wonder why MGR choose not to give 'final' torque settings, and instead have indicated that torque should be '20 Nm, then turn the nuts though an additional 180 degrees on two occasions in the normal torquing sequence'?

Perhaps this is because of stretch and 'give' in the stretch bolts? The final torque will never be quite the same from bolt to bolt, from engine to engine?

I think you make a good point though - perhaps the engines where the leak occurs over the alternator have a common connection through inadequately torqued bolts - but perhaps other factors, such as the height of the cylinder liners for example, have more of an impact upon how the clamping forces are distributed over the head? No idea...

Perhaps an experienced K-series engine builder can comment?
Rob Bell

OOO OO OOO, Ah Ah Ah, OOO Ah OOO OO

:)
Chimpy Magoo

Oi you, what are you doing at MGR, you've got a war to run!

Will
Will Munns

Err, mate, sorry about it.

I wonder when it gets mine :(
(No I woun't get experiance)

Hope you get it sorted in right manner.
Don't forget to register as 294th to http://shame.4mg.com

Cheers
Dieter
Dieter K.

Registered.
Just waiting for the parts now.
Ddraig

The reason for using rotation instead of a torque figure is that the thread resistance when tightening can't be guaranteed. The use of a specified rotation ensures an accurate compression force. The amount of stretch will always be the same due to the thread pitch. On very large Diesel engines it is quite common to stretch bolts on con rod caps and main bearings using a hydraulic ram so that you set the torque with the amount of pressure you use then the nut is run up finger tight and the pressure released this is the most accurate method that can be used.
HTH Paul
Paul

This thread was discussed between 17/02/2003 and 24/02/2003

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