Blown cylinder head gasket and duff wrench

[KiwiGF]

Just thought I'd share my experience......after 600 glorious miles following a 2 year rebuild the head gasket started blowing, not too badly but a bit of chuffing and down on power.

I found the 9 head bolts had slackened off a bit but rather than just tighten them I thought I'd take a look and take the head off and check the bores etc, all was well but the gasket seemed to have been leaking pretty much everywhere.

I had used an annealed solid copper gasket at 34lbft torque setting with  blue permatex and thought at first it must have been the permatex that was a mistake as it turned into black goo almost impossible to remove HOWEVER it occured to me to check my torque wrench, a tool i rarely use and which i bought from repco, Motoguard brand, the type that clicks when the torque setting is reached.

Using some scales and with the 1/2 inch drive clamped in a vice  i found i had to set the wrench to 60lbft to get an actual 34lbft!

So the head gasket leaked because i had originally only torqued the head bolts to less than 20lbft, if theres a moral to  this story it would be to buy decent quality tools i guess.

Ive fitted the new solid gasket without any gasket sealant this time so ill see how that goes.

[muskrat]

 Good job you found that KiwiGF. It would have happened again and again. All measuring tools need calibrating now and then. I check my micrometers nearly every use, but haven't done the TW for a long while. Thanks for the reminder.
Cheers

[bsa-bill]

Thanks for that KiwiGF a good point made there - also for others it may be an idea to compare your torque wrench with a friends if you have one within striking distance (thinking of you folks down under), also they are not that expensive that a spare is going to be within  reach of the more affluent amongst us.
Another thing perhaps not obvious to those of us not used to working in a mechanics world is to reset the wrench to zero when not in use.
Sure I read someplace that factories and such that use them daily have them calibrated on a regular basisi, might be different these days maybe they just replace them

[Triton Thrasher]

Did you not re-torque the head after some use?

[metalflake11]

Don't trust 'em........... God gave us the senses of touch and feel for this purpose. Ok if you are using them all the time for torque critical stuff, but only using them once  every blue moon which means a re-calibration is needed, seems pointless to me!...................Now pass me the socket wrench and a 2 foot steel tube!

[bsa-bill]

..Now pass me the socket wrench and a 2 foot steel tube!

and now pass me the helicoil kit

[wilko]

Oh no! You mean my new bigend shells in my XF Falcon are going to fly apart?

[metalflake11]

Bill. that genuinley made me laugh out loud!...........I have stripped the odd one now and then.

[KiwiGF]

Hi thrasher, no i did not retorque the bolts, i was going to after a week but then i got carried away and did 600 miles in that week, it only took 1/8 turn to return then bolts to the original (too low) setting.

Wilko, you have reminded me the only other time i used the torque wrench was on the con rods bolts

I shall be writing to mr repco in due course, ill post a pic of the offending wrench so others will recognise the piece of junk, a pic before i jumped and down on it.....and set fire to it...

[Stephen Foster]

That is certainly a timely warning !
I didnt realise a torque wrench needed calibrating ?
Mine is the torsion bar type ..I am wondering if this design also need periodical attention ?
I am not a mechanic & have litttle knowledge in these areas .

Steve...

[muskrat]

the torsion bar type are in my opinion the best and the better ones have an adjustable indicator so easy to re-calibrate if doped from a great height.
Cheers

[bikerbob]

Hi there. Something that I was taught many years ago with torque wrenches was that when you are finished using it you should always zero the setting that way the wrench is not kept stored at any tension.

[BSA_54A10]

A torsion bar is simply a spring rolled ot straight. ( or visa versa if you like )
Like all springs it looses springiness over time and faster stil with useage.
Thus over time your tension wench will need recalibrating ( replacing will be cheaper for most tools ).
The actual torque numbers are no where near as important as most people think, + / - 20% will make little difference in reality.
the important thing is that all bolts are the same.
Like all precision instruments it will be closest to accurate in it's mid range so it is a good idea to have more than one.
I have an 8" & 10" ( marked in inch/lbs ) for doing alloy and 3 larger ones for for things like roller big end journals.

So one needs to be a bit careful and not expect a wrench marked 10 - 200 f/lbs to be any where near accurate @ 30ft/lbs.

And if you want some real fun, cut a 1" length off a 1/2" Allen key. tane it and 2 x 1/2 socket heads to you local tool store sip the heads on two tension wrenchs and run then against each other.
You will be very lucky if you find any two that indicate the same tension.

[bsa-bill]

And if you want some real fun, cut a 1" length off a 1/2" Allen key. tane it and 2 x 1/2 socket heads to you local tool store sip the heads on two tension wrenchs and run then against each other.
You will be very lucky if you find any two that indicate the same tension.

#

Might give that a miss Trevor, my local Halfords has a large fierce looking lady manager

Lbs/Ft - now that I am happy with but it's increasingly difficult to get torque wrenches marked in Lbs/Ft so conversion charts and factors get involved, more chance for error with Newton/meters or whatever.
Reminds me of a science meeting I had at our local U3A where our lecturer talked about "turning movements", I sussed out after some time she meant "levers".

[Butch (cb)]

I too do pretty much everything by feel; it mostly works out. I had been told that with an iron head you pretty much pull it down as hard as you can anyway.