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davies
United Kingdom
699 Posts |
 Posted - 25/06/2008 : 17:31:15
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| is there a special spanner required to torque down the cylinder head nuts ? thanks for info. plus tips .Regards Rich |
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LewPalmer
USA
3248 Posts |
Posted - 25/06/2008 : 23:25:07
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Required? No. Available? Yes. There is frequently found a single-ended 3/8" BSP ring spanner bearing the MG octagon logo for exactly that purpose.
Lew Palmer
Registrar, NAMMMR |
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kimber
United Kingdom
1529 Posts |
Posted - 26/06/2008 : 06:42:53
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Lew, the MG cyl. head spanner you refer to will fit every Triple-M except an M-type which has 5/16" BSF nuts.
I have a slim 5/16" BSF spanner which has been ground to make access easier but I'm not sure if there ever was an 'official' special spanner for this purpose.
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David Allison
United Kingdom
665 Posts |
Posted - 26/06/2008 : 10:31:31
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Andrew
You are right - the special tool is for the larger head nuts only.
Britool used to offer a "crows foot" socket for 5/16 - 3/8 - which does the job very well.
I have used Dads many times but I am not sure if they are still available.
Regards David |
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talbot
United Kingdom
718 Posts |
Posted - 26/06/2008 : 10:47:11
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My torque wrench only takes sockets so I am unable to "torque" down the M Type's cylinder head. I've also ground down the jaws of a couple of old spanners so they fit on the head nuts but what's the best way of ensuring I have tightened them sufficiently
Jan T |
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bahnisch
Australia
674 Posts |
Posted - 26/06/2008 : 11:58:47
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| I do not have a set of "crows foot" spanners (are they too bulky?) but instead have bent an old ring spanner into a U-shape and welded a square onto the "upper" end so that I can use a torque wrench directly above each stud. |
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David Allison
United Kingdom
665 Posts |
Posted - 26/06/2008 : 12:19:51
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Barry
That is a good way of getting around the problem
Regards David |
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Cymber
United Kingdom
966 Posts |
Posted - 26/06/2008 : 19:42:13
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Before I could afford a torque wrench I used a piece of pipe over the tommy bar of my socket set with a loop of string positioned a known distance from the centre of the socket and a spring balance and the same can be done with a ring spanner. It's relatively easy to work out the torque. Sounds crude but does the job.
Maurice Blakey. |
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sven
Sweden
436 Posts |
Posted - 26/06/2008 : 19:58:17
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Now
among my collection of various BSF spanners there is a cylinder head spanner marked MG which is 5/16 inch.
Regards to everyone
Sven |
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LewPalmer
USA
3248 Posts |
Posted - 27/06/2008 : 00:21:39
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Yes, of course. I knew the M has 5/16 studs, but simply forgot.
Lew Palmer
Registrar, NAMMMR |
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Blue M
United Kingdom
1474 Posts |
Posted - 08/07/2008 : 05:48:08
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Can anyone tell me the correct torque setting for the head nuts on an M? I had to replace the head gasket yesterday which had blown between 2 and 3, but since both the block and head have been ground recently ( around 4000 miles) I wonder if it went because the head wasn't tight. I have been using 29 lbs (although the markings on my wrench are a bit vague).How high can I go with 5/16?
Ian |
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bahnisch
Australia
674 Posts |
Posted - 08/07/2008 : 11:10:40
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| It is almost certainly due to the head not being down tight enough! For the first time in my life I am religiously retightening my heads having recently blown gaskets in both my F and M (the latter having been on the road for many years!). At the same time you are fairly game putting 29 ft-lbs on your nuts, I only go just over 20 ft-lbs. I have not seen any specs on these heads, but 20 or so is (to my understanding, anyway) as much as you can safely go with 5/16ths. However I retension them every so often (hence the "modified" spanner referred to above) when the engine is at running temp. It is amazing how much you get (ie half a turn, etc with copper/asbestos gaskets anyway) especially the first time or two! |
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Blue M
United Kingdom
1474 Posts |
Posted - 08/07/2008 : 23:13:35
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And I though 29lbs might not be enough! It sounds like it's tight enough, but that I should be going round checking the evenness more often. I have a gadget on the lines of your bent spanner so it's easy enough to do but I have never liked doing it in case something 'went'. I hope it's just that because it has happened before in the same spot. It happened this time just when I was experimenting with different needles, so do you think a too weak mixture at high revs could have anything to do with it or would that just be coincidence?
Cheers
Ian |
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bahnisch
Australia
674 Posts |
Posted - 09/07/2008 : 11:00:48
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| Ian, Probably a coincidence but I am pretty naive, other readers are no doubt more knowledgable. |
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Gordon
United Kingdom
693 Posts |
Posted - 09/07/2008 : 19:22:35
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To get the correct clamping force you must make sure that the nuts spin down the threads freely so the toque loading is applied in stretching the stud and not wasted in overcoming thread nut friction. This was taught to me by an ex director at RR Motors Crewe when I was helping him fix a 20/25 with a blown head gasket. Before assembly he ran the appropriate die down the threads and tap through the nut and lubricated them before assembly - the engine had been recently rebuilt by a "well remowned" firm specialising in RR cars!
Sorry if I am repeating what is well known but thought it might be helpful.
Gordon
Gordon |
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ags
United Kingdom
275 Posts |
Posted - 10/07/2008 : 12:04:31
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Hi Ian,
To answer your second question first, I would suspect something more than coincidence if you had managed to get the mixture too far out at the top end. I do not know the detail of M-type heads, but from memory cylinders two and three are quite close together, and being at the centre of the block are possibly not cooled too well even though the 57mm bores do allow water all the way round. If this has happened before in this position I suggest that you check the flatness of the mating surfaces with engineers blue after withdrawing all the head studs. Even though you have had the surfaces ground you might find some discrepancy which can provide you with some evidence to go back to your "precision" engineers.
I did not use copper asbestos gaskets for years, as I found that they only had a limited running time life (apart from the need to discard them after one use). I made myself a solid copper gasket and lapped the block and head surfaces together and, provided that it is properly annealed each time and everything is absolutely clean it will go back time after time. So a few man hours are now paying back about ú55 a throw. This sounds like a lot of work but I can remember that I was surprised how quickly the surfaces conformed to each other when lapping - only two evenings as I recall.
This vaguely brings me back to your first question about the torque setting. On the PB 3/8" studs I have used 39 lb/ft for as long as I can remember. I originally looked this up in a data source that is no longer available to me, but it seems about right as I have never had trouble with the studs but nuts do have a limited life of only four or five changes. My handy back of the envelope Casio says that 39x(5/6)x(5/6) is almost exactly 27 lb. ft. I would guess therefore that your 29 is just a bit OTT. If you have been using this for some time then you may have pulled the top face of the block into raised rims around the stud positions. The blue check will indicate this because you would have blue rings around the stud holes and little or no marking anywhere else. If you do find these rings then I am afraid you will have no grounds for complaint against your grinders. As a general precaution it is always best to lightly countersink all the stud holes in the block the first time you are fitting any type of head gasket to our blocks.
So my advice is an annealed solid copper gasket on lapped and countersunk faces with HMP grease as a sealant and 27 lb. ft. torque. To add to what Gordon has said it is essential that you arrive at the final torque in a gradual progression. For no very good reason apart from aesthetics I have always used a 0.5 series of torques so in your case I would start at 15 and do a run around the nuts in the proper sequence, then a round at 21, then 24, then 26 before arriving at your final 27. In other words always halve the gap that is left to the nearest one above.
This advice is probably a bad case of grandparents and eggs, but my excuse is that it works for me, since going to the solid copper gasket and this routine I have never had gasket problems though the head has been off multiple times for other reasons.
More technical ramblings from
Andrew Smith MMM571 |
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