Hidden Cyl Nut 850/1000

What is Allen key size for the so-called ‘hidden’ / ‘socket’ nut in cylinder head (top centre), I think it’s 10mm but just want to be sure. Tonti 850 / 1000 models Ta in advance…

Mike go get a set of the allen keys that are straight and go into a socket so you can use a tourque wrench to put it back mate ALWAYS follow the correct undo-tighten sequence OR you can

The usual Allen key is really hard to get the damn thing out

warp the head resulting in blown gaskets and oil leaks and

have one very tight nut to undo

3 5 2

1 6 4

Is the TIGHTEN sequence undo therefore 6 first 29-30 ft lbs tourque settings

NB when doing this remember:

The wee small rubber seals top and bottom of studs
The small washers on the rocker spindles these washers and bolts are very important as they allow the lubrication of the spindles and HAVE to be correct
Make note of the spring and washer on the rocker spindles , take a pic so they go back in the same position

Apologies if this is the egg sucking thing but hey hope it helps

OK more exact info - sorry my fault - reason I’m asking is I want to buy a 1 off long hex allen key socket 1/2" drive to use with a 1/2" drive torque wrench - the mail order web page is open now waiting for me to finish, just want to double-check I have the correct size http://www.toolbuddy.co.uk/franklin-100mm-hex-allen-key-socket-12-drive-choose-sizes-6mm---12mm-1371-p.asp

I cut one up with a grinder to suit a drive socket. The dimension evades me ‘a ce moment’. Am sure someone has that stuff in their noddle and will revert.

as far as I know its 10mm I have just removed some on a spada engine I am rebuilding to be honest I bought a set (and you can all bugger off I had a set last engine I built and lent out ) as they are good for spinning them in all over the engine (you can just put ratchet on and spin them to avoid obstructions)
before you remove it give it a day to soak in plus gas penetrating oil and they seem very tight -mine went with a massive crack thought I snapped them, some times a bit of tighning first also helps Ex smokingbiker2013-09-02 22:09:35

Agree with the 10mm size and the idea of buying a set to use as spinners.
As GB says “at the risk of…” etc The top thread needs a really good clean before reassembly as the corrosion can cause the torque wrench to click early.
Worked on a couple of bikes with repeated head gasket failure caused by this.
All the best

Totally agree I also think the heat/cool cycle also makes it rather tight.

The first time I took mine off I had to use one heck of a long Tommy bar, By the way well worth investing in the Hex head sockets as opposed to the ones that grip the edges.

The head nuts are in oil the only ones exposed are the one behind the plug and it’s opposite number.

I always clean and use a good quality hi temp copper grease. I have been known to buy new Nuts and if there is ANY sort of wear on the Allen heads REPLACE them.

I have also found that the heads all need re tourquing at 500 miles and 1200 miles only rarely are they needing a touch at the 5000 service BUT it is not unusual .

The tiny oil seals top and bottom also have to be put on carefully so they are seated

Thanks all, just to be clear not taking anything off, just want to make sure the torque is correct. Can’t remember if done after last time heads were off. Now I’ve got me own kosher torque wrench to play with (instead of borrowing the bike shop’s) can do it. While at it might as well have proper means of using it in socket nut instead of ‘guessing’ with a bit of steel tube over an Allen key. Anyway purchased it now so better be 10mm (or else) EDIT: PS - had already bought another one of these earlier in the year for the fork caps (14mm) also from toolbuddy, seem to be well made tools.
Mike H2013-09-03 13:41:46