The BSA A7-A10 Forum
Technical (Descriptive Topic Titles - Stay on Topic) => A7 & A10 Engine => Topic started by: KiwiGF on 11.01. 2013 11:17
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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.
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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
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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
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Did you not re-torque the head after some use?
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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*
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..Now pass me the socket wrench and a 2 foot steel tube!
and now pass me the helicoil kit *smiley4*
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Oh no! You mean my new bigend shells in my XF Falcon are going to fly apart?
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Bill. that genuinley made me laugh out loud!...........I have stripped the odd one now and then. *doh*
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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...
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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...
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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
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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.
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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.
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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.
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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".
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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.
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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 ...
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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.
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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...
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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.
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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
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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.
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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.
Thats brilliant, sorry for dragging up the past but really needed to show appreciation for this.
Jase
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I recently used a cheap click-type torque wrench to set the big-end bolts a little less than the aim. I also checked with an old type with a flexible shaft and a pointer fixed from the handle to the scale. Hard to describe I know, so I'll post a photo soon. When the needle pointer reached beyond the lower setting, it started to move the nut. Repeated with the Click-wrench for final setting. Better than nothing, but who can you get to check the click-type?
Col
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I've always thought that with most jobs, evenness of tension is more important than the actual figure.
Until I had to replace the headbolts on my 2000 9-3 Saab. These are the bolts designed to stretch, and to get to the stretch torque you need to get to the recommended torque (42ftlbs)
and then tighten an additional 90 degrees. I think it results in a figure somewhere over 100ftlbs.
I had borrowed my pal's 'quality' torquewrench to do this job, but interestingly my cheapo one was very similar.
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Warren & Brown 4 me as well.. *good3*
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I recently used a cheap click-type torque wrench to set the big-end bolts a little less than the aim. I also checked with an old type with a flexible shaft and a pointer fixed from the handle to the scale. Hard to describe I know, so I'll post a photo soon. When the needle pointer reached beyond the lower setting, it started to move the nut. Repeated with the Click-wrench for final setting. Better than nothing, but who can you get to check the click-type?
Col
You can check a torque wrench yourself, I described how I did it in an earlier post in this thread, using a vice and weights made from bottles of water. My wrench was almost 50% out, and under tightened bolts.
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I use the correct length spanner and judge torque applied by feel, just like they did in the Triumph factory if you have ever seen the film. I'll get my coat. *whistle*
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I use the correct length spanner and judge torque applied by feel, just like they did in the Triumph factory if you have ever seen the film. I'll get my coat. *whistle*
I do use a torque wrench for some jobs, but always 'calibrate' the setting first by feel using it against a bolt clamped in the bench vice.
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I agree, eveness is the most important thing with head bolts and its the only job I use a torque wrench for. I only have the cheaper type with the springy handle and pointer. I have compared this with and expensive wrench and they both read the same.
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One of the reasons why deflecting beam wrenches tend to stay in calibration much better than the micrometer adjustment type is defecting beam wrenches are never left with a load on the torsion bar.
I can not count the number of times have gone into some one's shed to see the tension wrench sitting there on the pegbaord, still set to the XY ft lbs that was last used .
Now we all know what happens to the valve spring that has sat fully depressed for 2 years yet they are happy to leave the compression spring in their wrench loaded between uses.
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One of the reasons why deflecting beam wrenches tend to stay in calibration much better than the micrometer adjustment type is defecting beam wrenches are never left with a load on the torsion bar.
fully agree
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Yes, I now turn mine down again - after each use. I was given my torque wrench by my brother. I took it to our local classic-bike-enthusiast engineer, when he was doing something else for me. He's a brilliant guy that makes our hobby all the more enjoyable. He said mine is an standard-quality click-type. He had a top-of-the-line one, with perfect calibration. He put a socket on his - to match mine, facing it (must have been a 3/16). He set them both to the same foot-lbs, then turned them against each other. The clicks weren't simultaneous, but very close. He did it again, at another setting - and the same closeness resulted. That was enough to judge mine "close enough"...
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Old school for me I am afraid, I do it by feel. IMO the only thing my TW does is check that the bolts are done up evenly.
If my TW clicks too soon and I dont think its tight enough I wind it up a bit more until I personally am happy that its tight enough.
Just to be particularly annoying to some, I have never retorqued a head in my life on an A10 and have owned them for at least 49 years, I will add that I have never blown a head gasket either.
All of mine have alloy heads and I do them up then leave them overnight. I check them again the next day and then whack the rocker box on, job done IMO.
Just make sure the head surface is flat, always use a properly annealed solid copper gasket and make sure the threads are perfectly clean before trying to fit the head. I will admit most of my bikes only do 2 to 3 thousand miles a year but thats only because I have 6 of them and normally try to use them alternatively.