Lav triple cam block studs torque - best practice?

Paul LeClair

Paul LeClair

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Location
Calgary, Alberta, Canada
for the 82 1200 TS project, just finished timing the A11 cams with a degree wheel and dial indicator on a fresh cam chain from Andy chain. As near as I can measure, the cams are accurate within a degree or so on true crank TDC, using the stock timing gear timing marks on the center cam blocks. Rather than fool around slotting the cam gears, I am going to call this "good enough".

now to do the head and cam block toque sequence. I remember reading of misprints/false info on torque figure's for the head and cam blocks, but can't remember what "proper" torque should be.

Anyone?

Paul LeClair
 
Paul LeClair said:
Rather than fool around slotting the cam gears, I am going to call this "good enough".
Click to expand...

You have gear driven cams?  :o

Slotting the cam sprockets would have been a bad thing to do anyway. The holes in the sprockets are threaded.  You need to slot the holes in the camshaft flanges. ;)

Within a degree is near enough. That's about as good as you can measure with a degree wheel anyway. I reckon Andy's un-lubricated chains will give you a pretty accurate reading straight off. No need to wash the grease out of the links. Might be interesting to check it again in a few thousand km to see there's any elongation in the chain.

Cam
 
torgue.jpg
 
Don't agree with that tightening sequence, Cape!

Normal practise on multi-cylinder engines of any type is to start near the centre of the head ond go outwards from there, either in a spiral or criss-cross fashion.  You forgot the 2 M8 studs fore and aft of the cam chain tunnel...

First I button everything down with about 10N/m, a bit more than finger-tight, checking the cam bearings slot cleanly into their locating grooves.  I begin with final tightening on the centre cylinder M9 studs in a cross-wise pattern in 2 steps, radiating outwards from there, then the M8 cam bearing studs in no particular order, finishing off with the outer M7 and the chain tunnel M8 studs.

As the M8 cam bearing studs do not have any influence on the pressure on the head gasket, they can be neglected in that regard, just need a bit of checking that the cams don't start binding.  The cam bearings should have "found" their position when the M9 studs are tightened, further tightening of the M8s should not change anything.  I have found 22N/m for the M8 studs, and 32N/m for the M9 studs to be enough.  No leaking, no nothing... if the head and barrel surfaces are in good condition.

piet
 
Don't understand that tightening sequence either.
2-3-5-6 are wrong. You want to spread the head outwards whilst tightening, not create knots in that nice malleable alloy.
Paul
 
Interesting that Cape?s tightening sequence for the 9mm nuts, ie the ones in blue, is seen as being incorrect.    This is the sequence shown in two factory publications that I have, namely my 3C owners manual and the 1000-1200 workshop manual.   

Tom
 
tom3c75 said:
Interesting that Cape?s tightening sequence for the 9mm nuts, ie the ones in blue, is seen as being incorrect.    This is the sequence shown in two factory publications that I have, namely my 3C owners manual and the 1000-1200 workshop manual.   

Tom
Click to expand...

They were incorrect in other aspects as well. 

The factory attempted to spread the load as evenly as possible, if I were to use that sequence I would proceed in far smaller steps of increasing torque.  Practise has shown that the "normal" procedure, starting in the centre and working outwards, has no ill effects at all, either on the functionality of the head nor causing any distortion.  Might be a bit detrimental if you drop the spanners in the middle of the tightening sequence and go out on the piss for a week or 2, head is bound to be bent by the time you return to finish the job!  Might even straighten the head, most are bowed upwards at the centre anyway.  Far more attention needs to be directed to the location of the cam bearing blocks when tightening.  Most heads I come across are more or less butchered in this area.

Same sequence shown in the RGS/RGA manual as well.    Might have seemed be a good idea at the time... ::)

piet
 
Thanks Piet, we live and learn!   
When using the factory's sequence I have always started with low torque and then built up to the final figure, approx five or six passes to get there.  And always in the same session!
 
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