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SP250 Head Cylinder Torque

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Culbu
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SP250 Head Cylinder Torque

Post by Culbu »

Hello,

I need for your help...

According to the Daimler SP250 Workshop Manual, the head cylinder torque is from 54 N.m to 68 N.m !! That represents a gap of 25% !! What is the procedure that I have to follow please ?

Kind regards,

Julian

Vortex O'Plinth
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Re: SP250 Head Cylinder Torque

Post by Vortex O'Plinth »

Culbu wrote: Fri Aug 24, 2018 9:03 pm According to the Daimler SP250 Workshop Manual, the head cylinder torque is from 54 N.m to 68 N.m !! That represents a gap of 25% !! What is the procedure that I have to follow please ?
My SP250 Service Manual gives the cylinder head nut torque as 40 - 45 lbf.ft ; equivalent to 54.2 - 61.0 N.m. The higher figure represents an increase of 12.5% over the lower. I would suggest you set your torque wrench to 58 N.m for the initial tightening down.
Nick

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tjt77
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Re: SP250 Head Cylinder Torque

Post by tjt77 »

the factory manual gives different torque figures for SP250 (studs with fine threads at top for the nuts) and V8 2 1/2 litre (bolts only)..
the comparative difference listed in the later, revised official factory manual for saloon (publication E.1002/2) is 10ft lbs:-
45-50 ft lbs for SP 250..(studs and nuts) 55-60 lbs for the saloon with head bolts..
logical reasons for this :- with fine thread and smaller area of thread, the nuts will pull up more accurately as regards 'reading' on a torque wrench.. with the bolts there is more thread which travels a greater distance per turn, due to it being 'coarse' thread.( less thread per inch= more movement per turn) .
There are 'other' issues to take into account as well..the SP250 stud and nut set up is more forgiving to the assembler.. the bolts require more attention to detail to do the job right..
The bolts have chamfered washers, designed to fit with chamfer up.. to avoid the slight ridge (2 per bolt on opposite sides under the head of bolt) often present on the bolts (which are produced by 'rolling' when hot)..but they can still bind.. they can also bind in the threads in block if not fully clean...any binding adds resistance, which will then give false (higher at actual pinch up) reading on the torque wrench.
One needs to exercise extreme care when replacing cylinder heads :-cleanliness is critical.. run a 'thread chaser' (7/16"NC) down into every stud hole and blow out any loose residue with compressed air.. clean the thread on each and every bolt.( a bench mounted rotary wire brush will do this well) . check the washer chamfer is upwards.. and check each washer with each bolt to see that it turns without any binding, and also witty thread into full depth in cylinder block after cleaning.. IF it DOES bind on washer .. then take a fine file and remove the part its binding up on. and test again.. use some anti sieze compound on the threads of each bolt and some light oil under washers...
if this course is followed.. you should get accurate torque readings.. one very common thing that WILL cause damage is over tightening.. NEVER go above 65ft lbs or you will stretch the bolts and render them weak as well as possibly distorting the head and valve train posts.
but by far the biggest problem with these engines is unsufficient torque of cylinder heads due to careless assembly..anything binding will give a false (high) reading.. its essential that everything is clean and free of any binding 'as it is supposed to be'..

Culbu
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Re: SP250 Head Cylinder Torque

Post by Culbu »

Hello guys,

Thank you for your fast and very complete replies.

I join the document where I've taken my informations. It says 40-50 ft.lbs (which makes an max increase of 25%).

I will follow your advices and come back to you if I have any problem.

Kind regards,

Julian
Screen Shot 2018-08-25 at 13.29.12.jpg

daimlersteve
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Re: SP250 Head Cylinder Torque

Post by daimlersteve »

is that from another source ? the printed page that is .
steve

Culbu
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Re: SP250 Head Cylinder Torque

Post by Culbu »

Document found on the web. No idea about the source...

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