Have heard of lock nuts being over tightened and stretching threads on tappet adjusters, which then lets them unscrew in use, although the lock nut appears to be tight.
It is possible that the case hardening on the cam/follower has gone, when this happens they wear quite rapidly. As regards anti-scuff compounds in oil, just use diesel oil, that has the additives already in it.
He means, of course, multigrade lube oil for diesel engines, not diesel fuel oil …
Barrel has to come off as well, at least assuming it’s like the older big blocks.
is it something simple like a stripped or faulty thread on the rocker arm allowing it to come loose ?, you say it was serviced by a garage ? why not take it back to them?
are you checking them hot or cold ?
have the cylinder heads been torqued down on the first service???
it may never have had any service work done
how old is the bike, is it still under warranty?
have you tried contacting the previous owner in case the low mileage was down to accident damage or speedo replacement ??it does not seem to have done many miles, thats not good for a big engine they need to be used, might be better contacting a small indepent specialist rather than causing any damage through lack of experience
I had a major gearbox problem, lots of people local to me told me to strip it and fix it myself, I took it to a chap reccomended by the club, he sorted it promptly and found a few other faults that i would have missed, its called experience 4 european trips later no problems
ps one of the worst problems with motorcycles is large motorcycle owned by middle aged posuers who ride short distances to the pub or cafe, never get the engine hot or up to temperature and fail to change the oil because they dont do enough miles
!!! I had a nice K100RS like that fat middle aged posuer, low mileage but massive engine problems with emulsion in the oil, engine removal and lots of new bits after that 120K on the clock with not a problem
As he wrote above, 2010, so most likely not ~ plus got it 2nd hand with 1,500 miles ‘on the clock’. So didn’t get it new.
Wow, lots of questions… Food for thoughts
Checked threads and they seem OK, anyway all bolts were tight, so problem should not be there.Â
Did not think to take the bike back to the garage because did not think they would fix it for free. Now I can’t anyway, unless it’s in a van.Â
Bike is not in warranty anymore… Things happen only when it expires! 
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From the little history I have of the bike, she had first service in April 2013 with 900 miles on the clock.Â
Last MOT before mine was in Sept 2013 at 1630 miles (bike bought in November with 1640 mikes)Â
I don’t know if head was torqued down during first service, what I can say is that bolts were pretty tight…Â
Have you taken the sump off yet and searched it minutely for little bits of metal … most likely collected around the wire gauze pick-up filter…
No, I’ve not done that yet.
I’m working slowly, too slowly actually, I should speed up. …I’m missing riding, as crazy!
Now I’m stuck with the head and barrel.
I cannot take the inner spark plug off. The is not enough room around it to fit a socket in.Â
I’ve bought a 10mm socket which looked pretty minimal too me, but even that one is too thick.Â
Has anyone removed it?
…I’ve seen there is a dedicated tool from Guzzi; is buying that the only way to remove the plug?
I’m not familiar with twin plug architecture, but does that have to come out for what you are doing?
Daft question time ~ do Cali Vintages normally have twin plugs per head?
I agree head should come off with the plug(s) still in
I don’t know if all Vintage models have dual spark plug, but mine does.
I’ve looked at the repair manual and from the engine there are 6 studs, 4 of them are longer and locked by the nuts on the rockers-holder, the other 2 studs are shorter and end up just below the spark plugs.
I’m afraid head and barrel do not come off without removing those 2 nuts.
Oh yes 'course not, spark plug is in the way.
Is the inner plug 14 or 10mm? The solution on the Breva 1100, (10mm) was a thinwall box spanner about 6" (150mm) long, should be available from Draper or Sealey.
it’s 10mm.
thank you for you suggestion, it’s what I was thinking, but I did not know the name of the tool!
Any more news on this?
no news unfortunately.
I’ve been a bi busy this week and could not spend too much time on the bike.
anyway below is a little summary.
inner spark plugs are ore PMR8B.
the spark plug socket I bought said “10mm” and it seems id does not fir the hole.
10mm plug socket actually seems to correspond to 16mm normal socket.
I’ve tired to get thin wall boxed sockets, but so far no luck - tried in local shops, no one seems to have the size I need.Â
on the internet I’ve only found this reference to dedicated tools - is this http://www.harpermoto.com/spark-plug-socket.html
they say “you NEED this”. picture on site is not he clearest one, but it does seem to me that this socket is thinner than the one I bought from Halfords.
On the user guide of the vintage it’s written “This vehicle is also fitted with two inner spark plugs (2); contact a Moto Guzzi Authorised Dealer to have them replaced. Use the following types of spark plug: Inner (long life) NGK PMR8B”. Tomorrow I’ll give a call to Moto Corsa to see what they say about this.
In the mean time I’ve drained to oil out and I’ve filtered it and I could not find metal shavings in it (but I still need to look in the sump)
I’ve noticed thou some deposit on the oil drain plug.
Also looking the oil flow down in a beam of light it look a bit “metallic” as if it is full of metal particles.
I’m thinking there should be a magnet on the sump plug, and the kind of debris we’re expecting will be ferrous so would collect on that. If you or a pal have an offhand grinder you should be able to thin the plug wrench down to fit - as long as it retains enough integrity to manage the torque. But as you say a chat with a dealer wouldn’t go amiss on that front.
As for the 10 mm thin wall socket - I found one of the local hardware shops had an ordered but unloved long thin narrow chap which apparently was required for a Skoobeedo  - might be worth a visit to your local Subaru dealer? Might be entirely wrong but may be worth a punt.
When mine went it was all collected around the gauze pick-up strainer, nothing on the magnetic drain plug (apart from the usual bit of swarf) or in the drained oil, as far as I can remember. So sump off jobbie to be absolutely certain, one way or the other.