Out of curiosity - a Griso8v head gasket question

[ohiorider]

I'm most likely going to purchase a Griso 8v this spring. So I've been going over available documentation on the bike, including some pages relating to the engine from the Parts Manual on Teo Lamer's website. Came across this ..... 3 different thicknesses of head gaskets.

0.65mm (.025")
0.85mm (.033")
1.05mm (.041")

My guess .... since the 8v runs a higher compression ratio than my 1200 Sport 2v, are these thicker gaskets available in the event the bike pings (that presumes the 8v comes with the thinnest of the three gaskets).

Bob

[draidt]

BOB

Your over thinking !

I don't know why they show 3 gaskets. The one used could be determined by measurements taken in the assembly process ?

Really haven't heard of a particular issue with the newer 8V's pinging, The newest factory maps seemed to have cured the issue. I expect Pete will be a long shortly to set me right.

[ghezzi]

Haven't done the math for a long time, 0.016" will not make a huge difference to the compression ratio or the actual compression pressure.

However setting the squish to more exacting tolerances can have benefits in quicker and complete burning of the intake charge. Which in turn should prove beneficial for emissions etc. This is my guess as to why Guzzi would bother, seeing as our bikes aren't at the leading edge of performance.

Ideal squish tolerances (gap between piston top and cylinder head - in a band around the circumference of the bore)are set to allow for things like expansion, rod stretch, carbon build up etc.

My RS485 has squish set approx 0.9mm (about 0.036")

[ghezzi]

Well I just did the math.
If the bike had a theoretical compression ratio of 11:1 using the thickest head gasket at 1.05mm.
Dropping to the thinnest gasket at 0.65mm would yield a theoretical compression ratio of 11.5:1

That would be felt by the seat of the pants!

On further reflection I wonder if the fuel quality and octane ratings in different markets may have neccessitated alternatives?

[pete roper]

You're both over thinking it!

The fact is the factory will build to a theoretical ideal not for performance purposes. Getting the squish close to 'Perfect' will reduce oxides of nitrogen caused by end-gas contamination of the incoming charge. I've been advised that the best thing to do in a rebuild is just use the /Middle' gasket. Personally I've always measured the one that comes off and used the same again. It shoud be remembered though that I'm really stupid.

You can, if needs be, buy the factory tool to dial guage it and do it perfectly and if I was swapping a barrel I would but unless you're doing that I'd just measure the one that's coming off. It's a metal gasket and incompressible. The coating on it will compress but you can work out what is what given the thickness differences. And yes. I have all thicknesses in stock as well as all other 'Consumables' for an 8V rebuild

Pete