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V8 cylinder head bolt vs. stud torque

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Sonus
Posts: 208
Joined: Wed Apr 13, 2016 2:19 pm

V8 cylinder head bolt vs. stud torque

Post by Sonus »

Is there any difference between the torque used to tighten the bolts for the saloon engine versus the studs and nuts for the SP250 engine?

Ozzsp250
Posts: 284
Joined: Tue Feb 16, 2016 12:35 am
Location: Arizona, USA

Re: V8 cylinder head bolt vs. stud torque

Post by Ozzsp250 »

Yes there is a difference from memory the bolts as used in the saloon are ~ 5 f/lbs higher than the studs/nuts on the SP250. I don't have access to my manuals but when I built my spare SP250 engine recently using bolts instead of studs/nuts I uncovered the difference prior to running the engine and increased torque. As I won't access to my manuals for a couple of weeks, I hope someone else will jump in with both values.

fireboss
Posts: 45
Joined: Wed Feb 24, 2016 10:20 pm
Location: Whitby, Ontario

Re: V8 cylinder head bolt vs. stud torque

Post by fireboss »

These are the ones I got from Barry for the SP, a place to start from?

All the listed torque settings for the SP 250 are as follows:-
Cylinder head where studs fitted with nuts - 40/45 lbs. ft.
or where Bolts are fitted – 50/55 lbs. ft.
Connecting rod nuts – 28/30 lbs. ft.
Main bearing nuts – 25/30 lbs. ft.
Oil Sump screws – 10/13 lbs. ft.
Flywheel bolts – 43/48 lbs. ft.
Clutch to flywheel bolts – 14/16 lbs. ft.
Pinion bearing nut – 95/105 lbs. ft.
Differential bearing nuts on caps – 35/40 lbs. ft.
Crown wheel bolts – 50/60 lbs. ft.
Road wheel nuts – 60/65 lbs. ft.

fredeuce
Posts: 76
Joined: Mon Feb 29, 2016 10:56 am
Location: South Australia

Re: V8 cylinder head bolt vs. stud torque

Post by fredeuce »

My factory manual for the 2.5 saloon paints a rather confusing picture. For those that have this manual can check this independently.

On page B.27 it states figures of 55-60ft.lb. The description mentions bolts.The accompanying illustration clearly shows bolts.

Turning to page B.38 it states figures of 40-45 ft.lb. The description mentions bolts also but the accompanying illustration show studs and nuts. Just a tad confusing.

As a matter of general understanding the coarse threaded (UNC) bolt will require greater torque to produce a similar clamping force compared to the fine threaded stud/nut (UNF) arrangement.

Sonus
Posts: 208
Joined: Wed Apr 13, 2016 2:19 pm

Re: V8 cylinder head bolt vs. stud torque

Post by Sonus »

Thanks all, needed the numbers to torque down a head to check a repair. Used the stud and nut figure for bolts. I am considering upgrading to ARP studs and nuts when I do the final assambly.

tjt77
Wise Man
Wise Man
Posts: 525
Joined: Wed Mar 23, 2016 7:01 pm

Re: V8 cylinder head bolt vs. stud torque

Post by tjt77 »

One thorny issue is that coarse thread bolts are rather tricky to torque acurately.. and there are a number of factors that can give false torque reading :- slightly gummed up threads.. friction between washer and bolt head ( these often have 'tight spots' as the bolt often has 2 raised areas right where head joins bolt shaft.. the washers are chamfered to compensate..but are often installed upside down) and whether they are installed lubed or dry.. frankly I'd much rather use studs with a fine thread for the nuts at the top end ( as per original SP 250 set up) because its far easier to obtain accurate torque settings with them.. but so far i have not found source for them in chrome moly steel.

Warsash 2
Posts: 332
Joined: Sun Feb 28, 2016 1:53 pm
Location: Southampton

Re: V8 cylinder head bolt vs. stud torque

Post by Warsash 2 »

Hi
Perhaps I am being a bit thick here or miss read the thread. If as I think is being said that all but the late SP's have UNF threads and the late SP's and the Saloons have UNC threads then to use bolts in the early engine means block has to be rethreaded. If the holes are the same size then some sort of rethreading device such as a bush has to be used making an extra point of weakness. Whilst we are on my incomprehension if you use a saloon block in a SP how do you change the dip stick position. Do you have to drill the revised position and plug up the usual saloon position.

Regards

Colin

fredeuce
Posts: 76
Joined: Mon Feb 29, 2016 10:56 am
Location: South Australia

Re: V8 cylinder head bolt vs. stud torque

Post by fredeuce »

Colin, the usual engineering practice when it comes to cast iron cylinder blocks is to use a coarse , UNC style thread.
I expect the early SPs with the studs to have coarse threads on the end inserted into the block. The fine thread UNF is on the other end. So, once the stud is installed and the cylinder head fitted then the nut onto the stud will need to be torqued according to the specification for the nut and stud arrangement. If they were to be removed and replaced with the bolts as fitted to the later engines then of course the torque spec for the bolt applies.

tjt77
Wise Man
Wise Man
Posts: 525
Joined: Wed Mar 23, 2016 7:01 pm

Re: V8 cylinder head bolt vs. stud torque

Post by tjt77 »

Colin:- just to be clear... all the the daimler 2 1/2 v8 cylinder blocks have coarse threads.. the SP 250 utilized studs for cylinder head.. coarse one end.. and fine at the other for the actual Head nuts.. much easier to get an accurate torque reading with fine thread hardware.. this is likely the reason why there is lower torque setting on the SP250 v the Saloon ( which has bolts replacing the studs.. and coarse thread)

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