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Heh, that was a long time ago (96). They did two heads for me as I bought a spare in hopes that original was warped and it might cure the cooling system pressurisation. I stuck to standard valve sizes because of the blow up John had on the first Norturno engine (not yours!).

They had a big Kwacker single they were tuning and had similar problems getting the head joint to seal round the coolant passages.

Did John have any idea what caused the blowup, I've always look my bits after any disaster in case there is anything to be learned??
Hahne Power sell big valves and head conversion, presumably without problems.
I've used Rimflow valves made by Paul Ivey with good results in the past.
John

He did the gas-flowing himself and basically lopped the inlet valve guides off too much as I remember it. Too much waggle on the valve stems - bent valve. So no not a big valve problem as such, but I was alo wary after my experience with the Husky 510 which popped a head off a valve on being over-revved once too often. To my layman's simple mind a bigger head with the same stem size might introduce weakness. But perhpas the Hahne kit addresses that.

I have never shortened valve guides, just reduced the the diameter and extended the taper where it is inside the port, bigger valves have to be better quality than standard that's why I've always bought from race engine component specialists and only once had a big failure of an expensive con rod almost cutting a Kawasaki block in half I've change to Carrillo since and touch wood they are still going around
John

Maybe the craking cases are due to the early Saturno cases.
Remember the starting point was the Dakota 350.
Later Saturno cases are somehow reinforced.
I think i have sent you the pics some time ago.

Nordie cases are the better choice. If you have a saturno head you may switch to Nordie valves, cams and rockers (due to the extended lift of the Nordie cams the original rockers will touch the covers)
Then put this head to a Nordie engine and put it into the Saturno frame. Just plug it in
You will get a better case, a better crank shaft, the bigger water pump....
Another thought would be a Carrillo rod and a 100mm big bore kit.
There is still something availabel from Volker Heim whic his expensive, but well testet (Nordie cylinder rebored and recoated, JE piston)
Gottfire still has the 604 kit. Piston looks like it's from Pistal (which also is a very good choice).
The cylinder has a new liner from cast iron. Not a modern Nikasil coated design. But putting such a big hole in the original cylinder did cause a lot of problems. At least i have heared about this.

ciao Joachim

I copied this from a thread on gilera.de
From the photo's posted he had a piston of 105.5 to increase the engine to 650cc. The barrel was welded on the head face to give a support for the liner flange to sit on and the liner was proud of the barrel 0.4mm to increase the pressure on the gasket sealing face:-

Today the spec is:
Bore 105mm - 640cc
Stroke 74mm
Cams from Megacycle
Intake valve 39mm (36mm std)
Exhaust valve 33mm (32mm std)
Carburetor 2x36mm
New exhaust system

The spare engine is the same except the bore who is 103mm. - 616cc
I'm using piston from ‘Wahl Spezial Kolben’ in Germany. For the 105mm cylinder we made a new liners. The 103mm is bored from standard.
On the top of the liners we have made a small edge who is 0,4mm higher. That edge press harder to the aluminium gasket and all problem is gone
Cylinder head is of course modified for a better flow.
The carbs is two Keihin cr36
Flywheel is made of aluminium.
I have 2 exhaust systems. 1 on each side. It's easier to decrease the sound.

I don't think Megacycle cams are available. Mine is over 10 years old.

The last dyno drive showed 75hp (on the wheel) at 8500rpm.