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

greg brillus

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Hi there folks........Does anyone have the foggiest idea where to look for the whereabouts or info, pictures anything at all about the small Licence built Zoller supercharger's used on the 2 factory built Singles.......I know they were unsuccessful only due to time limitations (mostly from over heating from what I understand)........Anyone with possible factory drawings, sketches anything that might help in the quest to put one back together (actually possibly both bikes........you never know).........Much appreciated.........Cheers......... Greg.
 

greg brillus

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I've read most of the available literature about it, and it appeared to have 2 issues........like all small run hand-built machines, they simply did not have time to develop it enough........So with tuning as in carburetion and ignition adjustments, plus the fine-tuning of the oil delivery........too much would smoke and foul the plug, not enough could potentially destroy the blower........And second, more critically was the bad overheating........piston rings turned blue, so lost tension, loss of compression. Became all too hard and they removed the lot, returning the bikes back to being naturally aspirated. The HP gains were marginal....... I think a figure of about 36 BHP comes to mind.........If they had run alcohol fuels this might have helped but who knows now..........The cylinder head is not a very strong casting, I am not sure what the head material on those 2 bikes was, but the alloy ones are very weak.
 
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davidd

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The original aluminum Series A aluminum head had a cast-in web that contained the two valve seats and the spark plug. That was the weak point and upon running the web would separate from the casting and leak air out at the spark plug hole. This would have been on the outside of the spark plug, not the inside, as the compressed charge was finding its way around the web insert on the backside of the insert as the compression rose. The cure was to cast up an aluminum head.

There was a CI head and a Bronze head, but for shedding heat, the aluminum head was the best.

David
 

greg brillus

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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.
 

Martyn Goodwin

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The original aluminum Series A aluminum head had a cast-in web that contained the two valve seats and the spark plug. That was the weak point and upon running the web would separate from the casting and leak air out at the spark plug hole. This would have been on the outside of the spark plug, not the inside, as the compressed charge was finding its way around the web insert on the backside of the insert as the compression rose. The cure was to cast up an aluminum head.

There was a CI head and a Bronze head, but for shedding heat, the aluminum head was the best.

David
I seem to remember that the Velo"porcupine" heads were cast in Silver
 

oexing

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The Laverda 750 ohc twins had cast iron sculls in alu head, with valve seats machined in. So no seat could ever drop. But today not so great with unleaded fuel so in the long run you´d have to do something about seat wear.

Vic
 

davidd

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I cannot specifically remember the material. It was likely bronze when I think back on it. Carleton had it fail in practice, I believe. We did not strip it down as he knew what was happening. I tried to repair it with some Loctite, which was the only apparent thing to do. I think it worked for a lap.

David
 

Chris Launders

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Even Honda used them in their small racing bikes, I saw a bag full of new ones at a patternmakers where they were making patterns for replica heads, probably there wasn't room for 4 shrink in valve seats in a 50cc head.
 

delboy

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Even Honda used them in their small racing bikes, I saw a bag full of new ones at a patternmakers where they were making patterns for replica heads, probably there wasn't room for 4 shrink in valve seats in a 50cc head.
Hi Folks,
PEI talks about Cast Iron "Spectacles" [valve seats and plug boss] cast into Ariel "Red Hunter" alloy heads on pages 174/5 of Motorcycle Engineering.
Page 214 of "Back to A" has a pic' of an "A" alloy head with Bronze cast-in spectacles.
I recall being told at a Series "A" meet some years back, about the "A" Twin there with Alloy heads; had Bronze cast-in "Spectacles". It was thought that they had come loose in the heads and were leaking gas.
No Idea if it was ever rectified in any way? Would seem nigh impossible to fix
Regards, Delboy..
 

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
 

TouringComet

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VOC Forum Administrator
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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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VOC Member
VOC Forum Moderator
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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