Head bolts

[Carolyn]

I went to tighten my new head cylinder head bolts that came with my usual gasket kit.

Length - spot on.  Thread correct.  But my 10mm double hex key wouldn't fit.  The sockets in the bolts are some mad 12 point version of a torx size.

I've bought these kits with bolts a few times with no problems and they are very good value.

I'm just wondering if the head bolts for a 1ZZ are slightly different in the States, as the label says, Chevrolet, Geo, Toyota.

Anyone come across this before?

[Call the midlife!]

I had to get an M12 spline bit for mine.

[Gaz2405]

Latest engine I've torn down had m12 splines on too.

[Carolyn]

Yes, 12 mm 12 point splines. On an M10 bolt.  But my 12 point spline key (which does normally fit, but is not quite the correct one to use) does not fit into these. These are .25 mm smaller.

I have a six point bit marked CR-V T66 that fits them nicely, but a six pointer will tear them up!

I have a set of 12 point metric bits, but none of them fit.

The correct one to use is known as a 10mm double hex, which I have also....

Go figure.

[Call the midlife!]

I only found out I needed a spline key after I'd killed two with a Torx as the first one I hit with it gave on the first pull of the bar, so I was confident it was the right bit and carried on.
I actually thought I'd cracked the stretch on the bolts with the 2nd and 3rd so kept going.
It wasn't until the next one properly stripped that I realised the second two were also mullered.
I ended up having to drill 3 of them out...

[m1tch]

They might be a triple square?

[Carolyn]

They might be a triple square?

Possibly, whatever the case-they are not the correct bolts.  As the ones I had taken put were still in tolerance according to the service manual - I put them back in.