Author Topic: Bristol Cranked spanner wanted  (Read 2562 times)

Exowner

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Bristol Cranked spanner wanted
« on: December 18, 2018, 07:38:23 »
Hi All. I'm after one of the Bristol cranked cylinder head spanners or info regarding what else can be used, as I'm sure there must be other ways of releasing/tightening them?
Any pointers gratefully received.
Glenn Burnage
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B.P.Bird

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Re: Bristol Cranked spanner wanted
« Reply #1 on: December 18, 2018, 13:11:20 »
Glenn,
There is a simple method:
1) Buy a good quality combination spanner 5/16" BSF
2) Buy a similar 1/2" drive socket. The nut size is unimportant, but don't go too big.
3) Cut the open ended spanner from the stem, leaving a ring and several inches of stem.
4) Weld the socket to the end of the stem so that the 1/2" drive faces upward. That is the weld is at the nut end of the socket.

This will not of course fit the Aceca tool tray, but is vastly superior to the Bristol spanner in engine assembly in that you can use a torque wrench. Bristol did not publish a torque figure, but many years ago their Service Department told me to use 30 lbs/ft and this has worked for me. Use the old aircraft engineers trick to keep the torque figure correct, even though you have added a little extra leverage with your adapted spanner, by keeping the stem of the spanner at 90° to the length of the torque wrench. Of course the exhaust side of the head poses no such problem and you can apply a torque wrench in the normal manner.
Here's one I did earlier





Exowner

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Re: Bristol Cranked spanner wanted
« Reply #2 on: December 19, 2018, 06:28:46 »
Barrie, Spot on! Exactly what I hoped my post might come up with. I've got both parts in the shed and enjoy making specialist tools (I've even got a dedicated drawer for them amongst the tool chests!)
Topic closed.

I thought some chancer might offer me a genuine Bristol  example which would then force me to re-mortgage my house!!!

Thanks again for taking the time to snap said tool and reply.
Glenn.

TTM

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Re: Bristol Cranked spanner wanted
« Reply #3 on: December 19, 2018, 11:23:25 »
Well, I have had passive worries on how to proceed if I ever need to remove/refit/retighten the cylinder head and this comes handy. Thank you Barrie for this excellent piece of information, especially the torque figure.

AC Ace Bristol

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Re: Bristol Cranked spanner wanted
« Reply #4 on: December 19, 2018, 14:55:47 »
..
As a follow up to Barrie Birds post ,  for further details and illustrations :
Reference August 2000 ACtion  VOl 26 No 4  pages  14 , 15 & 16.


 Bristol Engine Cylinder Head Torquing Adaptor
by Jake Snyder.

Was origonally published in 1975. ( illustrations courtesy of Bristol Owners Club)   And was revisited in Hints & Tips  .
Have emailed  Terry requesting he  reproduce the above  in  a future issue of ACtion. 
A big thank you Barrie for  posting  a very useful Tip. 
 
Keith



« Last Edit: December 19, 2018, 15:12:02 by AC Ace Bristol »

B.P.Bird

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Re: Bristol Cranked spanner wanted
« Reply #5 on: December 19, 2018, 18:39:21 »
Keith,
Yes that was a good article and I would not argue with the 35 ft/Lbs torque figure. I should have said that the Bristol figure was for a steel shim head gasket and a lapped in head. I have no idea what the torque figure should be for an unlapped head and the modern substitute composite gasket. Probably the same figure assuming that the limit to the clamping force is determined by the ability of the head studs to resist stretching ?
However the arithmetic in the article is incomplete and the correction calculation depends on the actual angle between the line of the torque wrench and the line of the adaptor spanner. As I said if you stick to 90° the correction is nil. Perhaps Rob Hendricks could confirm this for us ?
Barrie

TTM

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Re: Bristol Cranked spanner wanted
« Reply #6 on: December 20, 2018, 08:27:43 »
Shouldn't non-elastic studs be retightened after the first full heat cycle?

As for the Maths involved with the Physics, here is a simple sketch.

« Last Edit: December 20, 2018, 12:55:48 by TTM »

B.P.Bird

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Re: Bristol Cranked spanner wanted
« Reply #7 on: December 20, 2018, 14:59:24 »
Thomas,
Thank you - simple when you explain it. On the matter of re-torquing after a heat cycle I don't know the answer, except that I have always assumed that it is to account for the 'softer' forms of head gasket material relaxing and losing the initial clamping force. In the case of the steel shim, providing the studs are not over torqued and stretched, then a heat cycle should not alter the clamping ?  I have never re-torqued my Bristol heads with the steel shim gasket and have never suffered a head gasket failure.
Barrie

Exowner

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Re: Bristol Cranked spanner wanted
« Reply #8 on: December 22, 2018, 09:38:11 »
With regards to the question of re-torquing a head after a heat cycle, I have a BMW 328 engine with a Bristol head.
The specialist who built the engine recommended that it be re-torqued as soon as the engine had had a few gentle running-in miles on it. It has, what looks like, a solid copper gasket and it did, indeed need a bit of 'nipping down' after said period.
I seem to remember that the figure he quoted was 35ft/lbs.
Glenn.

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Re: Bristol Cranked spanner wanted
« Reply #9 on: December 23, 2018, 07:26:44 »
 With regards the sketch by TTM, am I correct in thinking that if the lengths (at centres) of the converted ring spanner and the torque wrench are the same, and right angles are maintained, the torque figure is the same as using a torque wrench straight on a bolt/nut, and the only thing that alters the torque imparted is the flex in the extension and anything else that flexes.
If this supposition holds up, (if it doesn't, please enlighten me) how does one make allowances for any lost toque due to flex?

Also, what if (as in my case) the torque wrench is, say, for instance 153% the length of the converted spanner? A really simple formula would be appreciated (I didn't do maths at school, I did rolling fags in the bike shed)
Glenn
« Last Edit: December 23, 2018, 10:17:53 by AE512 »

AC Ace Bristol

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Re: Bristol Cranked spanner wanted
« Reply #10 on: December 23, 2018, 10:16:55 »
.
Glenn

Many Ace Bristol and early BMW  owners  upgrade and fit  special High Tensile Head Studs and torque down to 45 lbs ..……  ..  ..As long as each stud is torqued down equally
and in sequence to the same final  setting thereby compressing the gasket  to form a proper uniform  seal  , Then  considering flex and wear and tear in your torque wrench,  Does the odd  1% or 2 % variance in your final setting of 35lbs or 45lbs really matter. ?? 
 
Keith
   
« Last Edit: December 24, 2018, 07:50:37 by AC Ace Bristol »

Exowner

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Re: Bristol Cranked spanner wanted
« Reply #11 on: December 23, 2018, 10:26:05 »
Keith, firstly thanks for the copy of ACtion.
With a solid copper gasket there is minimal, if any compressability and I haven't a clue if the studs are HT, I'd assume they would be (why wouldn't you?), but as he mentioned the torque figure of 35ft/lbs, maybe not - I'll ask him and see what he says.
I suppose I'll now have to carry a spare head gasket, now I'm all worried, and hopefully it'll come under the heading of 'Whatever spares one carries will not get used, and whatever one omits will be the first thing to pack-up or break'!!!
Glenn

B.P.Bird

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Re: Bristol Cranked spanner wanted
« Reply #12 on: December 31, 2018, 15:17:37 »
Glenn,
Just to get things crystal clear the calculation, demonstrated by Thomas above, correctly shews that the length of the levers involved (the length of the torque wrench and the length of the extension spanner) are irrelevant. The only time you need any specific calculation or recourse to tabulated torque corrections is when the angle between the torque wrench and the adaptor spanner are other than 90° so just stick to the right angle trick and forget any calculations.
With regard to any flex in the adaptor spanner it is likewise irrelevant: To achieve the measured torque the torque wrench will have to have flexed everything to whatever point is required. If you increase the desired torque then you simply increase the flexing and vice versa. The nut on the cylinder head knows nothing of this and simply resists the applied torque which is what generates your torque wrench reading. Thus it is the nut which has the final say and the torque figure will be read after any flexing has occurred.

bbrown

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Re: Bristol Cranked spanner wanted
« Reply #13 on: December 31, 2018, 18:15:05 »
A page of an old Snap On Tools manual illustrates the use of a right angle adapter.
See Figure 5.

Exowner

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Re: Bristol Cranked spanner wanted
« Reply #14 on: December 31, 2018, 21:39:04 »
Barrie, when you put it like that - it all makes sense. Thanks for taking the time to clarify

bbrown - many thanks for the diagram
Thank you and a happy new year to you all
Glenn