Worth the effort

[GuzziNZ]

When I purchased my 850T it was pinging like mad.
Never looked for a fix as I pulled the motor down shortly after but now the motor is going back together I am trying to make sure everything is spot on.
Fitted new Giladoni cylinder sets and found the pistons are stopping 1mm short of flush.
Is this worth correcting? Would machine cylinder base if needed.
Also found timing marks were all 2 degs advanced which I have corrected.

[Kiwi_Roy]

I don't think 1mm would make a lot of difference, I can't say I took notice where mine ended up.
Does 1mm really matter?
I usually time my bikes with a probe in the plug hole and a lamp across the points rather than rely on a mark.

[Tony F]

If the pistons are 1mm short of the top of the barrel you will have 2mm squish (assuming a 1mm head gasket). That is more than ideal and less efficient, I'd fix it. You could probably machine the top or the bottom of the cylinder. Have you checked the piston to valve clearances?

[Scout63]

Top ends are fairly quick to pull apart.  How about assembling and running to see if the power is ok for you, then machining the cylinders later if need be?  Did the Gilardonis come with the pistons?  I would worry most about piston valve interference when altering things.  On the big blocks I’ve assembled the pistons come flush with the cylinder top.  This is where I would entrust things to my machinist but I’m a lightweight.

[GuzziNZ]

Yep, cylinders came with pistons.
Will do a bump test and check valve/piston clearance before I machine cylinders.
Dave in Guzziology says to am for 1mm squish and head gasket is 1.20mm so with piston flush with top of cylinder it should be good to go. 

[Tony F]

You could use thinner base gaskets to loose the 1mm.

[Turin]

THIS^^^^^^^

I used copper head and base gaskets to set my squish to .04 "

https://coppergaskets.us/

[jacksonracingcomau]

THIS^^^^^^^

I used copper head and base gaskets to set my squish to .04 "

https://coppergaskets.us/

THIS ^^^^

But one proviso
Measure compression ratio and valve clearances
Blueprint the thing, esp if a cam is going in too
Cam timing first, compression/squish measure, then valve clearance
Adjust gaskets  or machine with knowledge what will happen to all (everything is affected)

[GuzziNZ]

So have made some spacing tubes and pulled the barrel down firm on the base. Piston is now 0.60mm down which is the same thickness as the base gasket.
Easiest would be the ditch gasket and just use sealant ?
Can't see an issue as its only sealing for oil splash.

[John A]

So have made some spacing tubes and pulled the barrel down firm on the base. Piston is now 0.60mm down which is the same thickness as the base gasket.
Easiest would be the ditch gasket and just use sealant ?
Can't see an issue as its only sealing for oil splash.

I delete the base gasket and use Locktite 515 flange sealant successfully if I’m putting a tuneup on a Guzzi, setting the squish. Before assembly clean the mating surface as if you are painting it or it may leak. The flange sealant needs an oil free surface initially to seal. I suggest lacquer thinner because it is a better oil solvent than acetone. Last one I did hasn’t leaked in over ten years and 100K miles. https://datasheet.octopart.com/18637-Loctite-datasheet-8472317.pdf
Page 52
Edit I used their primer as well, the first time I did it, it developed a leak so when I redid it, that I took all precautions and had good results