RexSeven
RexSeven UltraDork
9/1/13 6:59 p.m.

One thing I plan on doing with my Alfa 164 while I have the valve covers off for powder coating is retorquing the cylinder heads. Alfa used head studs instead of bolts from the factory. Consider it preventive maintenance as the torque can loosen over time and possibly cause oil to leak into the coolant passages. Retorquing the cylinder heads to spec can prevent this from happening. I don't have any oil in my coolant (or vice-versa) but with over 206,000 miles on the car it seems like a prudent thing to do.

I have a copy of the FSM on CD and the torque specifications are as follows:

18.4 ft.lb. (+240° ±1°)
25nm (+240° ±1°)

What's with the angles, and how do I determine them?

DrBoost
DrBoost PowerDork
9/1/13 7:28 p.m.

They are just a more precise way to achieve the correct bolt stretch, though I'm used to seeing something closer to 90 degrees.
I'm almost 100% I have one of these, brand-spanking new. If you're interested I'll take a look when I'm in the garage tomorrow.
$7.50+shipping?

tpwalsh
tpwalsh Reader
9/1/13 8:06 p.m.

aren't the +x degree bolts usually stretch bolts? But these are stud. Then again 18ft-lbs isnt much, but 240 degrees is. Silly Italians.

RexSeven
RexSeven UltraDork
9/1/13 8:10 p.m.

I don't quite get what you are saying. So, for example, I torque the head nuts down to 25nm, then turn it another 240°? Sorry for the n00b question, never done this before.

Also, will I need to loosen the head nuts first, or can I just torque them down? I know each one has to be torqued in a certain order, but I don't need to remove the heads, so I'm not sure why I would need to loosen them first.

logdog
logdog Dork
9/1/13 8:13 p.m.
RexSeven wrote: I don't quite get what you are saying. So, for example, I torque the head nuts down to 25nm, then turn it another 240°? Sorry for the n00b question, never done this before.

Thats exactly it. Easy with a torque angle gauge. Easier with a fancy torque wrench that has it built in.

RexSeven
RexSeven UltraDork
9/1/13 8:19 p.m.

Cool, thanks!

DrBoost, I'll let you know via PM if I need it.

DrBoost
DrBoost PowerDork
9/1/13 10:21 p.m.
RexSeven wrote: Cool, thanks! DrBoost, I'll let you know via PM if I need it.

Cool. If your loosening the fasteners, check the book. There's usually a certain order for that as well. If you're just loosening them to re-torque it's not a big deal but I've heard stories about warped heads from not following the order.

motomoron
motomoron Dork
9/1/13 10:35 p.m.

TTY (torque to yield) fasteners are generally single-use. Maybe always single use. - I'd do some research and verify they can be re-torqued or that they even/ever need to be re-torqued. BMW mandates replacement if disturbed for all the ones I've encountered in reciprocating assemblies.

In any case the first number is the installation value. The fastener is installed w/ a conventional torque wrench to this minimal value to assure the assembly is held together and in alignment.

Then, in the sequence defined by the factory manual, the fasteners are twisted the specified amount. The fastener is designed to achieve a certain clamping pressure, and once tightened it functions effectively like a wicked strong spring holding your head/rod caps/main bearing caps on.

Here's the tool - a "torque angle meter" - in use.

driver109x
driver109x HalfDork
9/2/13 1:12 a.m.

I was wondering about that too. I'm planning on replacing the half shaft on my Volvo with a good used one and the Haynes spec'd it at 89 ft.lbs. + 60 deg. on the axle nut.

edit: I also noticed that the nut is not the staked or cotter pin style

Streetwiseguy
Streetwiseguy UltraDork
9/2/13 8:30 a.m.

If they give you a torque to yeild number, don't touch them. If its gone 206,000 miles without leaking, anything you do is likely to cause trouble, rather than fixing anything.

Kenny_McCormic
Kenny_McCormic SuperDork
9/2/13 11:04 a.m.

This is an Italian engine from the 70s we're dealing with, those studs aren't TTY, they just spec an above average accurate way to torque them. All fasteners stretch, that's how they work. Really old Rolls Royce shop books told you to put a dial indicator on the end of the stud and actually stretch the stud as specified.

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