750 SF cylinder head torque ?

markQLD

markQLD

Hero member
Location
QLD Australia
ok, from what i understand it should be 5 kg-m (36 ft-lb), correct?  & the green book also adds "and no more".
SF750cyldheadtorque.jpg


but,,  if 4 kg-m (29 ft-lb) is considered too much for a 9 mm stud (generally accepted?), why is 5 kg-m ok for a 10 mm stud ??  confused.  :-\

me story;
i 'av always used 3.5 kg-m (25 ft-lb) for the 9 mm studs on all me triples.  no problems to date.
today was major anxiety attack as i was tightening me SeFFie's head to 5 kg-m (36 ft-lb) and the 4th stud 'felt' like it started to let go.  phaaark !!
so, after i got me heart rate back under control with much loud profane language,  i backed it off a tad and got it back to a surprisingly good 25 ft-lb.
so i held me breath and went for 4.5 kg-m (33 ft-lb).  success.  :D
& no,, i ain't gunna give 5 kg-m another bloody go ay!  well, not this year anyhow!

cheers & season's greetings,  Mark
 
Hi Mark
I think that the issue is not what the stud will take, more what it is clamping.  On the triples, you're at risk of crushing the cam blocks.  No such concern on the twin.  And 5kgm is correct. 
Managed rather more than that on mine until I realised the (single sided) torque handle was upside down!  Fortunately no harm done.  Not sure about the twins but factory workshop manual recommends lubing the fasteners before torquing.
 
thanks Rob,
probably was a bit of kero on the nuts and studs but didn't have the guts to be putting any real slippery stuff on 'em at 5 kg-m.

maybe it was just the freshly annealed CU washer that let go?
& i thought some blokes 'av pulled 9 mm studs at 4 kg-m.  not just crush cam blocks.  but dunno ay?

maybe i should 'av asked.  "has anyone pulled a 10 mm stud at 5 kg-m?"
cheers
 
Mark,
Bear in mind that the later (read: properly engineered :D ) 120 triples used 32ft.lb on the cam bearing cap bolts and 28ft.lb on the shorter head bolts.  The longer studs should have more tension to allow a similar clamping pressure to the shorter studs (you need more ft.lb to create the same % stretch - ie clamping pressure - in longer studs).  I used to use those figures on the RGA and never stripped a case stud.  Eventually the cam bearing caps started to show signs of compression failure and I now use the "pipe and slippers 180" figure of 25ft.lb on all studs.  It's not really correct but works fine.

Getting back to the topic, shear area of the thread in the case is proortional to diameter, so an M10 will have 1.111 times more shear area than an M9 (for a given pitch).  So 32ft.lb used on later triples * 1.11 = 35.55ft.lb, or about the same as they're recommending for the 750.

All that being said, when tightening the head on the ICR SLC, I set the torque wrench in increasing increments toward the 36ft.lb target and tend to get to around 32ft.lb and say to myself "that's faarken tight-e-faarken-nough for faarken me, fark".

cheers
SteveB
 
but,,  if 4 kg-m (29 ft-lb) is considered too much for a 9 mm stud (generally accepted?), why is 5 kg-m ok for a 10 mm stud ??  confused.  :-\
 
Click to expand...

Don't be confused anymore Mark - simple mathematics - 29ftlb plus 23% = 36ft lbs and the area of a 10mm stud compared to a 9mm one is 23% more (all approx.) The 750 stud has a very long length into the crankcases and is not too close to the liner cutaway. - merry Christmas - Phil
 
yea Lee,  got meself a SF2 #16190.  looks a good one?  only 4,800 miles and so far everything inside is very clean and pristine.
the SF3 i had back in the 80's was an honest motor-bicycle.  & the only cycle i've ever regretted parting with.

back then, i'm guessing i used 36 ft-lb on me SF3 when i took the barrels off to stop the porosity leak.
unless you or Ted told me something else at the time?
reckon, i'm hearing 36 ft-lb is good for the 10 mm studs.  & they are an integral part of the frame ay.
cheers
 
Always 36 ft/lbs and never had a prob (and on a head that's been off many times over several hundred thousands of k's). Sometimes the 'soft' feedback that can scare is the copper washer flattening out. My main concern is usually the corners of the top cover deforming and crushing the top cover gasket). Always good to check that your torque wrench is clicking off correctly - cheap ones are hard to trust. Bringing it up in two or three stages helps.
I work with a lot of carbon fibre in bicycles and it must be torqued correctly - cheap wrenches?  ??? NO!
 
yea, thanks Q.  is good to know what you SF elders are doing ay.
fairly confident all is well.  reckon it was probably the cu washer crushing down and spreading, that spooked me.
'av dicked around a bit more and oiled me nuts and torqued 'em all down a couple of times to a good 33 ft-lbs.  no worries.
so reckon they'll go to 36 without a prob.

i'm guessing me old 3/8" drive Warren & Brown wrench is still a goodie.  has served me well over the decades.
cheers,  Mark
 
Dellortoman said:
Q ?  Isn't he the bloke with all the gadgets in James Bond movies?
Click to expand...

No, Dellortoman! Don't touch that! It's a Lucas indicator from a 1973 model Laverda motorcycle - but if you so much as turn it on, you'll blow the whole blessed lot of us to kingdom come.

:-*
The 'real' Q
 
markQLD said:
i'm guessing me old 3/8" drive Warren & Brown wrench is still a goodie.  has served me well over the decades.
Click to expand...
Ah the trusty W & B. You're on a good'un there - got one for the bicycle shop and the uninitiated never looked back! You can get 'em recalibrated too - someone used the shop's item to undo a very tight nut - unidirectional ONLY!  :-X
 
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