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Cylinder Heads


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Is there a source that talks about the different Guzzi cylinder heads?  Looking at a 1000cc (square head) bike with broken fins, just wondering what options are for a replacement head if I move forward.

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IIRC, the 1000 cc square fins had different versions: "large valve", "Medium valve", . . . was there a "small valve?"

Pretty sure your Quota heads (valves) are different from the Sport (?)

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Thanks doc!  To further the inquest, is the casting the same between the heads so just different valve sizes?  Or, can I turn a medium valve head into a large valve head by swapping valves and a little machine work?

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Pretty sure I only just asked more questions.  :huh:

On the verge of buying 1000S, I did learn that there were valve size (head) changes. Apparently, the earlier 'large valve' head was "fussy?" And the "medium valve" was considered an improvement?

I know, just more questions.  There is also the matter of heads used on Sports vs LeMans vs Quota vs "California/EV"  . . .

Seems there might be quite a variety of 1000 cc Guzzi heads . . .

(Waiting for an aficionado to chime in. Like @pete roper . . . . :oldgit:

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Prior to the 1100 Sport series there were basically three different cylinder head designs and valve sizes. With the 700 and 750cc loops there were other tiny differences but by the time the motors got taken out to 850cc right the way through to the last of the 950's there were basically three types of of combustion chamber design, small valve, mid valve and big valve. These were matched with a variety of pistons to give different compression ratios and from the 850T right the way through to the 1000S they all used a 78mm throw crank. That 'Golden Age' of the Tonti framed bikes was really one where Guzzis were like Meccano sets for grown ups! You could mix & match pretty much end thing.

Of all of them the 'Big Valve' heads, which only came in squarefin form, have always been a bit of a 'Holy Grail' for people wanting to build rorty-snorty motors but IMHO the 'Big Valve' motor used in the MkIV-V LeMans and some 1000S's is a horrible thing! To get the compression up due to the combustion chamber being huge to accommodate the big valves the incredibly heavy, cast, pistons have an enormous alp of alloy on the top of them. This in turn makes the flame path long and convoluted and leaves all sorts of nooks and crannies for end gas to lurk to pollute the next incoming charge lowering combustion pressure and risking detonation issues. Bleargh! Horrible! Also big valve heads are absolute murder on valve guides! No idea why really as the 1100 motors, even the 'Sport' ones with similar sized valves and guide length don't seem to flog out so quickly as the smaller bore 'Big Valve' heads.

If I was in the market for a 1000S I'd actually prefer one of the mid valvers with 36mm carbs. While no doubt it would get me sneered at by people who 'Know better' the fact is that the mid valve LeMans III/1000S motor and it's even sweeter close cousin used in the SPIII are to my mind the apogee of the 78mm stroke engine's development. The Mk III was an 850 and to my mind every bit as sweet as the 950's.

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Thanks Pete!  This is what I was looking for.  I rode a Mk III a little while ago, about the only thing original about it was the owner, but that bike only seemed happy with half throttle and above, but I am not sure of what all was done to it besides the obvious things I could see.  And that has me looking for a mid/late 80's Guzzi again.

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The commonest thing that happens to MkIII's is that some prick gets a hold of one and sees that the jetting on the carbs is different from the earlier mid valve, roundfin, LeMans. This causes them to phoam at the mouth, chew the carpet and accuse the evil gubmint of trying to stifle the fun of the poor motorcyclist in the name of emissions. This is absolute bollocks as the carbs are completely different. Apart from the PHF, (From memory. I haven't touched a carb in years, thank @#!#$#!) designation they are a different instrument.

 

The *Experts*  will install earlier jetting and turn the bike into an overfuelling pig that will wear itself out in 20,000km. and won't pull the skin off a rice pudding.

 

Next step is to install K&N pod filters to 'Free Up' the breathing. The only advantage being of this being they'll @#!#$# the carb bodies and slides so they need to buy new ones at the same point 20,000km down the track when they are replacing the barrels and pistons and rebuilding the heads!

Back about the turn of the millennium I had a bloke bring me a completely stock, low km Mk III. It was fifteen or so years old and very low Kms. I went through it front to rear replacing anything that was rotted or leaking, serviced it and rode it.

 

I took it around Test Track 'C'. Bungendore, Tarago, Goulburn and back down the Federal Highway, a three lane motorway/freeway. It was butter smooth, sprightly and I saw an indicated 195kph on new tyres. It was lovely.

 

Then they dumped that for the 'Big Valve' LM IV! An ugly, physically larger and heavier, vibratory turd that went no faster and had only minimally better acceleration. That was the beginning of a decade in the wilderness. Some would say twenty years.......

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