Pre war supercharged Comet..........Zoller supercharger.

greg brillus

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I don't have this bike here as of yet , so I don't have any clue as to what kind of head it has........Perhaps Brian can shed some light on what his one has....... STT 28.
 

Cyborg

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"Skull heads" were pretty common back then.......Norton for one used them........Large bronze center with the alloy fins cast over it all.........interesting concept.......must have been tricky.
This one could be a little tricky. Cracks radiating out from the bronze combustion chamber through the aluminum.

 

oexing

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That "skull" is huge, so no surprise that the head developed cracks, not a lot of aluminium around it, so it seems. The Laverda type is much smaller in cast iron, but then you can see the effect of deep sitting valves from reworking seats many times. Big question what to do in this case ?

Vic
Laverda head
 

timetraveller

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I don't know how big the skull is in the Laverda but I can tell you how a problem was solved in a cast iron cylinder from a marine diesel. I was going from mainland Spain towards Ibiza using both the sails and the twin cylinder inboard diesel when it went onto one cylinder. I got into the harbour and took the cylinder head off to investigate. One exhaust valve seat, machined directly into the cast iron head ,was severely eroded. I asked around an finally found a workshop which repaired lorry engines. No problem. We machine it out, cut some cast iron tube and machine it to fit, insert it and then grind the seat. I paid lorry prices rather than yacht prices and it was still there over twenty years later when I sold the boat. If there is enough metal around the seats on the Laverda then that could be a solution.
 

oexing

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Greg, when hunting for info about Zoller maybe have a look at Judson superchargers, same type of design. I don´t think graphite vanes are great to use with oil, at least for vaccum pumps in aircraft , same sort of machines, you do your best to protect the pump from any trace of oil as it will destroy the vanes in short time. When you look at the Judson in my link, what do you think about these vanes, hardened steel ?
Norman, I did new high chrome steel rings in our Ford Capri engine for running it on unleaded, easy to do with a solid cast iron head , just the exhaust seats. But in a Laverda head I don´t know, depends on the actual engine.

Vic
Judson supercharger

photo5 092.jpg
 

Cyborg

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That "skull" is huge, so no surprise that the head developed cracks, not a lot of aluminium around it, so it seems. The Laverda type is much smaller in cast iron, but then you can see the effect of deep sitting valves from reworking seats many times. Big question what to do in this case ?

Vic
Laverda head
Yes good question... I was surprised to see that cracking... haven’t seen it before, but haven’t seen that many bronze skull heads. This one needs the intake seat repaired, but machining for a seat insert isn’t a good idea because it would partially intersect the head/cylinder mating surface, so I think TIG is the only option.
Laverda head looked like it has spent most of its life as a boat anchor.

David... was it you that mentioned a Series A skull coming adrift?

C55AC63C-4413-4554-9B57-E17400D7AC6E.jpeg
 

TouringGodet

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I wonder how detrimental the long path from the output of the supercharger to the cylinder head was.

Note the worm drive clamps used, in the pictures posted by David. Someone on a car forum was commenting on how a car from the 60's would never have had that type of clamp, as they weren't available in the 60's???
 

Simon Dinsdale

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Note the worm drive clamps used, in the pictures posted by David. Someone on a car forum was commenting on how a car from the 60's would never have had that type of clamp, as they weren't available in the 60's???
The worm drive clip is called a Jubilee clip in the U.K. and was invented in 1921.

So yes it would be possible for the Vincent factory to use such clips in the 1930's.

Simon
 
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