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head bolt torque - 5/16 Whit?
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jp928



Joined: 07 Jun 2016
Posts: 247
Location: Australia

PostPosted: Sun Feb 19, 2017 6:31 am    Post subject: head bolt torque - 5/16 Whit? Reply with quote

This is on my 26 Rover 9/20. Engine was completely rebuilt in the early 90s. The receipt notes that the head should be retightened twice after running up to temp. I have run it for a few minutes several times months ago without doing anything, but now I have the fuel tank back in place I have been able to run it up to 65C . There are 6 nuts of 5/16 Whit, and 4 longer bolts acting as valve cover fixings, which have 1/4 whit hex on most of their length. I suspect (hope) the working thread is 5/16. Any idea where I can find a 1/4 whit crows foot to get on a tension wrench?
thanks
jp


Last edited by jp928 on Sun Feb 19, 2017 12:44 pm; edited 1 time in total
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peter scott



Joined: 18 Dec 2007
Posts: 6211
Location: Edinburgh

PostPosted: Sun Feb 19, 2017 9:46 am    Post subject: Reply with quote

There are tables on the web of torque for bolts of certain diameters and materials but in days of old the instructions usually said " tight but not with Herculean force. "

HTH

Peter
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jp928



Joined: 07 Jun 2016
Posts: 247
Location: Australia

PostPosted: Sun Feb 19, 2017 12:47 pm    Post subject: Reply with quote

I have seen some of those tables and they worry me. One listed 5/16-24, grade 8 at 20lb/ft, which seems very low to me for a head. Modern cast iron block & head engines are up in the 70+ area IIRC.

thanks
jp
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Kleftiwallah



Joined: 27 Oct 2016
Posts: 222
Location: North Wiltshire

PostPosted: Mon Feb 20, 2017 12:59 pm    Post subject: Reply with quote

As my instructor into construction plant used to say,
"Tighten it 'till it sheares then back it off a flat"!

Cheers, Tony. Very Happy
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PAUL BEAUMONT



Joined: 27 Nov 2007
Posts: 1280
Location: Barnsley S. Yorks

PostPosted: Mon Feb 20, 2017 1:13 pm    Post subject: Reply with quote

Firstly, are you sure that the thread form is Whitworth as I would have thought, for the application BSF would be more likely. The tightening torque needs to be considered alongside the tensile strength of the fastener. Do you know if the fasteners are original or have they been reproduced in a modern steel.
You should not really consider modern engine specifications when trying to answer this question as, I suspect, you have a quite modest compression ratio. What you are trying to do is resist the compression and prevent the blowing the head gasket.
Assuming your fasteners are typical "R" quality then a torque of 20lbft will induce a tensile load of about 3500lbs in the fastener assuming Whitworth and a little more they are BSF. I would have thought that that would be more than adequate. I suspect that the tightening regime recommended takes account of modern gasket materials.
Hope this helps
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Kenham



Joined: 12 Mar 2012
Posts: 182
Location: Kent

PostPosted: Mon Feb 20, 2017 5:33 pm    Post subject: Reply with quote

I probably would not even use a torque wrench if it were mine , not too long a spanner and tighten evenly. Father never had a torque wrench and mended many vehicles with no troubles, just use common sense and have a feel for the job in hand. A bit different on modern (post sixties ) machines with more compression etc.
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jp928



Joined: 07 Jun 2016
Posts: 247
Location: Australia

PostPosted: Mon Feb 20, 2017 9:59 pm    Post subject: Reply with quote

OK, all good info.
First, all I know is the hex is a Whit size, but of the actual thread I know not. The 4 'studs' that extend up as rocker cover fixings are 1/4 whit hex and thread are all black and look original. The rest are nuts , 3 on the left side on the head face, those on the right on top of the rocker shaft pedestals. These latter nuts are bright, and may be modern replacements.
After the first run up to temperature I applied ~ 30lbs/ft as best I could on the nuts, and by hand on the studs, and got a few degrees of rotation, so I will leave it at that, hoping nothing is overdone.
Next funny. The gear lever was not fitted when I got the car, with the hole covered with a plastic bag. As I went to fit the lever, retained by a round plate with 3 bolts, shaped for the ball pivot, I found 3 more bolt heads under the plate. mmmmm Plate aint going to hold the lever properly with them there, out they come. Que? 2" long 1/4-20 bolts? Their holes are also countersunk. Quick look underneath - looks like the turret for the lever has an extension on the main casting , retained by these bolts, so now on the hunt for more bolts that dont seem that common....Might have to machine the heads to countersunk, and driver slot them if they are made of Unobtainium.

jp
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