The BSA A7-A10 Forum

Technical => A7 & A10 Engine => Topic started by: KiwiGF on 11.01. 2013 11:17

Title: Blown cylinder head gasket and duff wrench
Post by: KiwiGF on 11.01. 2013 11:17
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.
Title: Re: Blown cylinder head gasket and duff wrench
Post by: muskrat on 11.01. 2013 12:09
 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
Title: Re: Blown cylinder head gasket and duff wrench
Post by: bsa-bill on 11.01. 2013 14:01
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
Title: Re: Blown cylinder head gasket and duff wrench
Post by: Triton Thrasher on 11.01. 2013 15:50
Did you not re-torque the head after some use?
Title: Re: Blown cylinder head gasket and duff wrench
Post by: metalflake11 on 11.01. 2013 20:19
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! *beer*
Title: Re: Blown cylinder head gasket and duff wrench
Post by: bsa-bill on 11.01. 2013 20:40
Quote
..Now pass me the socket wrench and a 2 foot steel tube!

and now pass me the helicoil kit *smiley4*
Title: Re: Blown cylinder head gasket and duff wrench
Post by: wilko on 11.01. 2013 22:18
Oh no! You mean my new bigend shells in my XF Falcon are going to fly apart?
Title: Re: Blown cylinder head gasket and duff wrench
Post by: metalflake11 on 12.01. 2013 00:59
Bill. that genuinley made me laugh out loud!...........I have stripped the odd one now and then. *doh*

Title: Re: Blown cylinder head gasket and duff wrench
Post by: KiwiGF on 12.01. 2013 05:52
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 *problem*

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...
Title: Re: Blown cylinder head gasket and duff wrench
Post by: Stephen Foster on 12.01. 2013 06:30
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...
Title: Re: Blown cylinder head gasket and duff wrench
Post by: muskrat on 12.01. 2013 13:48
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. *eek*
Cheers
Title: Re: Blown cylinder head gasket and duff wrench
Post by: bikerbob on 12.01. 2013 13:52
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.
Title: Re: Blown cylinder head gasket and duff wrench
Post by: BSA_54A10 on 14.01. 2013 07:31
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.
Title: Re: Blown cylinder head gasket and duff wrench
Post by: bsa-bill on 14.01. 2013 10:44
Quote
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".
Title: Re: Blown cylinder head gasket and duff wrench
Post by: cyclobutch on 14.01. 2013 15:17
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.
Title: Re: Blown cylinder head gasket and duff wrench
Post by: Stephen Foster on 14.01. 2013 19:06
I know this is a dumb question but can Someone please enlighten Me how to calibrate a torsion bar torque wrench ?
I admit to not being mechanically gifted
I have no idea ..this is a serious question .

Thanks in advance ,

Steve ...
Title: Re: Blown cylinder head gasket and duff wrench
Post by: KiwiGF on 14.01. 2013 23:53
Hi Stephen, I can tell you how I checked/callibrated my wrench, but I'm sure others will have alternative methods, my "callibration" was simply to work out what the wrench needed to be set too to get the REAL torque setting I wanted, these figures are shown below.  

I guess some wrenches will have an internal adjustment of some sort that means you can adjust it so the wrenches reads correctly. I'm pretty sure my wrench can be taken apart to get at the callibration adjustments, but as I'm intending to return it to the shop I'm not going to do that.

I checked my wrench by clamping the 1/2 inch drive in a vice so the bar was horizantal and the weight of the bar was resting on the ratchet, with the ratchet set in the "tighten" position.

I decided to use "check point" 1.378 (420mm) from the middle of the 1/2 inch drive as a point to add test weights. This was very close to very end of the wrench.

With no test weights on the wrench the (upward) force needed to lift the "check point" just off the ratchet was 1.54 lbs. I've called this the "zero" weight in the results below.

I then made up a selection of test weights and weighed them. I used bottles of water, but anything will do as long as you can hang it from the "checkpoint". I have some scales which are accurate to 5kg so I made up a few test weights at less than that (I've converted the weights I used from kg to lb in the results below).

I then hung the the weights on the "check point" using a piece of string and adjusted the wrench torque setting so it was nearly, but not quite "clicking" to indicate the torque setting had been reached. With my wrench the extra little "push" down to get it to click was much less than 1 lb so having the wrench "nearly' clicking was accurate enough. My wrench was quite good at "repeatedly" giving the same reading for a given weight. Shame it consistently gave a wrong reading!

For the "torsion bar" type wrenches which do not "click" but just give a reading I think the same method can be used to check those.

I then used a calculator to work out the "real" torque on the wrench, for each test weight and wrench reading.

The results were as follows:

Zero Weight  Test Weight (lbs)   Total Test  Calcuated Torque ft lb    Observed/actual Wrench
 (lbs)                                      Weight      (Total weight x1.378)     Setting ft lb
1.54               16.54                 18.08         24.91                         50
1.54               23.15                 24.69         34.02                         60
1.54               30.87                 32.41         44.66                         70  


So I know to get my head bolts at 34 lb ft I set the wrench to 60 ft lb, and for the (billet) con rods to get 45 ft lbs I set the wrench to just over 70 ft lb.

Once I'm done using the wrench (I parted the crankcases last night to re-do the con rods) I intend to return it to Repco as it has a lifetime warranty, and in my opinion the inaccuracy is way outside of what it should be, even though I've owned it a couple of years I've hardly used it. I'm not expecting them to replace it but it's worth a go.  

A quicker/easier method to test the wrench is to set it the other way up in the vice, set it to various settings starting (say) at 25 ft lb and use bathroom scales to push the end of the wrench "up" and then use the same calculation as above, I also used this method and obtained pretty much the sames results, but note bathroom scales may be quite inaccurate around the 20 to 40 lb mark (especially if the wife has adjusted them).  


For those with metric wrenches, which usually measure in kg meters, the conversion for that is:

1 kg meter =  7.233 ft lb  (so 70 ft lb = 9.67 kg m)


If it helps understanding ... if one has a 1 ft long spanner on a bolt, and exert a force on it of 30 lbs, you have done the bolt up to 30 ft lbs, if the spanner is 2 feet long the same force of 30lbs will do the bolt up to 60 ft lbs eg double the tightness, the same principle applies to torque measured in kg meters.
Title: Re: Blown cylinder head gasket and duff wrench
Post by: Stephen Foster on 15.01. 2013 02:37
Well I thank You for that !
Wont pretend Ive understood it but I will print it out & read it slowly !
The "Blonde Bombshell" may be able to take it onboard also !

Regards,
Steve...
Title: Re: Blown cylinder head gasket and duff wrench
Post by: Desburnett on 15.01. 2013 06:03
Like a lot of tools you get what you pay for, typically a professional tool from Norbar (www.norbar.com) is not cheap but it's the tool for the job. Their website has a section for calibration but this is more of a service than a DIY job.  As mentioned earlier the quality of the fixings is important and equally so is most torque values are quoted as "dry' figures, ie with no grease or coppaslip type compound. Applying grease or any other medium to the threads will introduce error.
Title: Re: Blown cylinder head gasket and duff wrench
Post by: muskrat on 15.01. 2013 09:28
 I use two of these, one inch/pounds the other Ft/Lb  http://www.youtube.com/watch?v=bfj8vJJkc5g
http://www.toolworks.com.au/warren-and-brown-322500-10-120ft.lb-1-2-drive-torque-wrench.html
Great job kiwi, I do similar with scales like in the fruit market. In 35 years of use they are both within 3% of original settings.
Cheers
Title: Re: Blown cylinder head gasket and duff wrench
Post by: BSA_54A10 on 15.01. 2013 09:46
A foot pound is 1 pound of weight applied with a lever that is 1 foot long.
Which is the same as a 2lb weight with a lever that is 6 inches long.

So you can check your calibration by suspending a known weight at a known distance an see if the wrench "signals" ( or reads for non signaling )
I have a 20 lb weight ( from an old set of balances ).
Same as the others, clamp the square drive in the vice, move the weight along the wrench till it signals then measure the length from the center of the square drive and the string holding the weight
This is a little rough as it does not take the weight of the wrench itself into account, but as I mentioned earlier the actual numbers are not all that impotant just so long as you are in the ball park.