General head bolt query

[Boriskov]

I'm doing a cylinder head on a Suzuki Jimny 2011 at the moment... Naturally, I turn to suzuki for their head torque specs when I see this:

a) Tighten cylinder head bolts (“1” – “10”) to 20 N·m (2.0 kg-m,
14.5 lb-ft) according to numerical order as shown by using
a 12 corner socket wrenches.
b) In the same manner as in Step a), tighten them to 40 N·m
(4.0 kg-m, 29.0 lb-ft).
c) Retighten all bolts 60° according to numerical order in figure.
d) Repeat Step c).
e) Tighten bolt “A” to specified torque.
Tightening torque
Cylinder head bolt for M8 (a) : 22 N·m (2.2 kg-m, 16.0 lb-ft)
Cylinder head bolts for M10
(b) : 40 N

My understanding is you go around 4 times, the last two being 60 degrees each? (120 degs total).

I've used plenty of TTY bolts before, but never seen this particular wording in my many years of doing this, and it seems unusual to put two angles post torque.

Is this a common thing on ally heads? 99% of my career has been real engines that are at least 4x the capacity of this toy

Just after some clarification. Cheers

 

[Old.Tony]

It sounds to me like they're being very careful about keeping the head quite straight and level as it is clamped into place. The wording is a little unusual - they're usually not that specific.

My reading of the instructions gives the same meaning as you describe: 4 times around, the last two being 60 degrees.

However, insterestingly enough it would seem that doing so might overtighten the bolts. If I read it correctly, the M10 cylinder head bolts should be done up to 40Nm. You reach that in the second step - if you add a further 120 degrees of turn to each bolt, they'll be a lot tighter than 40Nm!

 

[Boriskov]

Yeah, I'm thinking 40Nm + 120 degrees is extremely tight too. 40Nm would be the theoretical torque for an 8.8 grade bolt. I'll just have to assume that the resulting torque will be approximately 90-100Nm, based on a yielded 10.9 grade, which doesn't seem THAT far off expectations.