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MG MGF Technical - H.G.F
|Talk to a guy on the MG club stand at this weekend classic car show at the NEC he says that he may have prevented the fault with the head gasket on the Fs by taking the rocker cover off and tighening the head bolts a 1/4 turn.He said the clubs F had been chipped and they have had no problems hope this helps all F owners|
|No, this is not a good idea.|
I am sure that there is a good amount more to the story than perhaps was relayed to you Paul, but over-tightening a stretch bolt certainly will not protect against HGF.
Given the various different aetiologies of HGF, one can't expect a 'one-fix fix-all' solution. If there is one, then it will be to replace the thermostat with the PRT - attempting to mess around with torque loadings on the cylinder head is not the way forward.
What a wonderfull word Rob - only from a Man of Medicine!
I had to google for it; so many hits but none for HGF so far ;-)
|That's a very bold statement Rob.|
Just raises all the same old questions.
Is the clamping force "correct" in the first place? Whatever correct maybe.
What constitutes overtightening?
Other manufacturers of aluminium engines have some very exotic procedures for tightening head bolts. It's clearly a problem for all.
MAYBE another tweak at the head bolts after a few thermal cycles is all that's required to stop some HGFs. Used to be common practice.
|>but over-tightening a stretch bolt certainly will not protect against HGF.|
You might want to worry about the oil rail, which is where the head bolts end up - its made of ally
|After all these years with HGF-discussions I never seen any figures on what torque the headbolts undo when the head is taken off after a HGF.. All still at the "stretch" or might it be that one or several are a bit loose? / Carl.|
|Good question. The thermal cycle will continually load and unload the bolt. Perfect fatigue cycle.|
|Retightening the head bolts may indeed help HGF ,who knows? It may also help the crank bearings to run oval as well 8-((|
|No problem, oval bearings won't cause an HGF. Will they? :-))))|
|Methinks it's about time for the Great HGF Prevention Survey - the Hall of Shame doesn't really provide useable data any more, so who's volunteering to start an up-to-date one? Noting which preventative measures were applied and when would eventually separate what is actually working from the false promises, which has to be in everyone's interests?|
If there's an Excel or Access wizard out there with some free time, it could even develop into an online summary page listing the options and the success factor of each - now wouldn't that be useful!
|mgtfGreat HGF Prevention Survey |
oh no!! not again !! ;)
However, if only contributors who had _NO_ HGF will be allowed to enter experiance !!?
Here's my instructions to get happy 65k miles in 5 years without HGF:
- warm up the engine oil to 70..80
|I've seen the PRT thermostat mentioned a couple of times but where can you get one and how much effort is it to get fitted? Presumably it's more than a DIY job :)|
|To me "re-tightening" can be done several ways.|
IMO the correct way to do it is to slacken one bolt at a time in the right pattern and just do a new re-torque as stated in the repair-manual.
I would be very reluctant to just "add a quarter of a turn" to each bolt. The "re-torquing" is much more used today to ensure right torque along the servicelife of the engine. I know for sure that several makers do it,SAAB is one. / Carl.
|The purpose of the stretch bolts is to *ensure* an even and consistent clamping force rather than relying on often inconsistent torque settings. It is far easier to build and calibrate a machine that gives one turn to a bolt than to use one which stops at a given torque. Overtightening will eventually cause the bolt to yield and may damage the oil rail threads, ultimately the pillars in the head will collapse a little and you will shed clamping force, maybe too muc of it. In short, the standard tightening procedure is fine and requires no re-visiting. The causes of HGF are pretty well known and the percentage of failures attributable to bolt problems is pretty small.|
|requires no re-visiting>|
Do you mean the head doesn't need tightening(in some manner)ever or no further discussion on the procedure is needed or both?
It would be good to hear your percentage breakdown of the causes of HGFs.
This thread was discussed between 06/11/2005 and 08/11/2005
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