Toque settings for MM head

for those with Series MM sidevalve cars produced between September 1948 and February 1953

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Ams07
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Toque settings for MM head

Postby Ams07 » Mon Jun 05, 2017 6:12 pm

Hi I can't find the toque setting for the head in the manual is 45 lbs per cubic ft right ?
Thanks
Andrew

firedrake1942
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Re: Toque settings for MM head

Postby firedrake1942 » Mon Jun 05, 2017 6:39 pm

viewtopic.php?f=4&t=51709 Says 44 on here I think. Can't find my glasses.

philthehill
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Re: Toque settings for MM head

Postby philthehill » Mon Jun 05, 2017 7:11 pm

There is no torque setting for the cylinder head nuts on the USHM2 engine specified in the BMC wksp manual.
Special tool/spanner 18G330 is used which is designed to apply the correct tightness/torque when reasonable effort is applied to the special tool/spanner. See wksp manual section A18 for details.
The torque of the cylinder head nuts as fitted to a MM (803cc) as specified in the BMC wksp manual is 40 lb ft which can be applied to the USHM2 engine.
I personally would not torque above 42 lb ft.


BLOWNMM
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Re: Toque settings for MM head

Postby BLOWNMM » Tue Jun 06, 2017 5:45 am

I have chosen to torque my head and main bearing studs (both ISO Metric 10 mm. x 1.5 pitch) to 45 lbs/ft. I have based this on two things - I am using studs made from Vew V155 material (now Bolher V155) with a tensile strength of 1180-1380 N/mm squared which is equivalent to 'Unbrako' grade 10 with a tensile strength of approx. 1300 MPa, and the fact that Richards table of Thread Sizes gives the tightening torque for a 3/8" UNF A series head stud at 44 lbs/ft. I doubt the A series head stud is made from 1300 MPa material and in view of the fact that the diameter of the MM stud is 10 mm. I had no hesitation in using a torque of 45 lbs/ft. The area where a problem may occur is with the four studs on the left side of the motor - no's. 6, 8, 10 and 13 (in the head tightening sequence) because they penetrate through to the water jacket and the female threads are subject to damage from corrosion and when corroded studs are removed. I have fitted stainless steel thread inserts in these four stud holes.
Bob
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RobThomas
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Re: Toque settings for MM head

Postby RobThomas » Tue Jun 06, 2017 6:35 am

Main bearing studs from the Aston Martin DBR9 will fit the longest 6 holes in the Alta head. And before you laugh, they cost £2 each!!!
dbr9caps.jpg
dbr9caps.jpg (229.44 KiB) Viewed 940 times

BLOWNMM
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Re: Toque settings for MM head

Postby BLOWNMM » Tue Jun 06, 2017 7:12 am

Nice bit of detective work Sherlock!
Bob
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philthehill
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Re: Toque settings for MM head

Postby philthehill » Tue Jun 06, 2017 8:03 am

The correct torque setting for a Minor OHV 'A' series head nut is 40 lbf ft and is specified as such in the Minor wksp manual.
Only when the later higher tensile strength studs were fitted to non Minor engines was the head nut torque increased to 50 lbf ft.
Whilst most Minor OHV 'A' Series head studs/nuts will be forgiving at 44 lbf ft it should not be assumed that the stud/nuts/block will accept the increased torque setting.
Only if new studs/nuts (preferably the later higher tensile type) are fitted and the threads in the block are perfect would I consider increasing the torque of the head nuts.


BLOWNMM
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Re: Toque settings for MM head

Postby BLOWNMM » Tue Jun 06, 2017 8:22 am

Phil
My figures were for a MM head stud being 10 mm. dia. and newly made for the MM motor and using new grade 10 nuts. Any suspect threads in the block were fitted with 'Re Coil' thread inserts. These figures are not necessarily related to an A series motor. Not having info on the A series motor I assumed Richards torque figure of 44 lbs/ft was correct and I used it as a guide as explained to arrive at my 45 lbs/ft figure. If Richards torque figure is not correct perhaps it should be amended.
Bob
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RobThomas
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Re: Toque settings for MM head

Postby RobThomas » Tue Jun 06, 2017 8:23 am

The HT ones either had a pointy tip or the letter Y stamped into the tip. Is that right?

WRT those Aston studs, the Alta has 2 studs that protrude into the exhaust ports so they need to be decent material to prevent corrosion holding the head in place, hence all the screwdriver marks on the underside of Ian's head and consequent welding. Still looking for good nuts for the MM. BMW flanged nuts might be an option, as are some Honda ones. Bob??? :D

BLOWNMM
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Re: Toque settings for MM head

Postby BLOWNMM » Tue Jun 06, 2017 8:39 am

Rob
I use grade 10 (class 12.9) nuts with 5.0 mm. thick washers made from Vew V155 steel. I did this originally on the aftermarket Kleinig alloy head to spread the load and prevent the nuts damaging the alloy boss. I still use the same washers on the iron head. I think this would be OK for your Alta head if suitable flanged nuts are difficult to source.
Bob
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philthehill
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Re: Toque settings for MM head

Postby philthehill » Tue Jun 06, 2017 9:51 am

Bob
I quite agree with you on all points.
The 10mm studs used on the SV engine being approx. 1/64" larger in diameter than the 3/8" UNF studs can safely accommodate the 42lbf ft torque max as recommended in my post above provided the block threads/fixings are good.
Your spec studs can easily cope with 45lbf ft torque.

Richard
Can you please review the specification for 'A' Series head nuts in light of the conversation above and include the torque setting for the later high tensile head studs used on 1275cc Marina/Ital/Sprite & Midget engines as quite a few Minors are now fitted with those engine mentioned.

Rob
Correct
Plus a centre dot/dimple in the top of the stud and the nuts are flanged.
Phil


RobThomas
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Re: Toque settings for MM head

Postby RobThomas » Tue Jun 06, 2017 10:24 am

FWIW, UK BOLT Co sell 20 x 12.9 black HT Metric 10mm std nuts for under £4, inc postage, roughly the price of one BMW head nut.


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