750 SF "Skulls"

Interesting...if Massimo did a carbon copy, including the skulls, then the question should be...why did Honda/Laverda use skulls?

Not all the Honda models had this. In that Honda was big into the racing scene at the time, did this evolve from the racing department or a legacy from the old school engineers in the design department?

I think the CB77 had a displacement of 305cc. Couldn't be a horsepower issue. They didn't make a big load of power. Not a factor for servicing when working on the heads?
 
Julian,

Pity you are not doing a triple, as I have got an all alloy head here with no skulls....

Pete
 
Maybe problems with casting light alloy....although widespread, many companies had porousity issues, Laverda had them to the end!

Mass-production head designs were becoming more and more intricate in the 60s, casting technologie was perhaps not keeping step.  The skulls may have been a solution for a problem of sorts, but probably create a problem themselves!

piet
 
I personally think you are right Piet,

I think Laverda saw the Honda engine and thought  "hey, good idea, solves our porosity issues"  and tried it before waiting to see if there was a real reason or need.  On a road engine I think they would prove mostly fine and they seem to have done.  But for racing with high CRs and lots of heat etc you have to be quite careful although the 750SF&SFC record seems pretty good for endurance racing.  No idea if the race bikes in period had issues but would have thought "yes" otherwise there would have been no reason to change for the last version!

I know from my own testing on various engines that you can up the CR significantly when changing from one running cast iron heads to ally heads on the same engines. We have engines running 9:1 and on the pinking threshold with iron heads and can run the same engine at 9.8:1 with an ally head, all other things unchanged.

I was going to stay sensibly low on CR but now decided I want to run my "new" engine at 10.5:1 so we will see.  Squish etc will be very modified however so will just have to see what happens.  fingers crossed  ;)
Crank and rods etc already in the "slow" design stages, keep you informed!

Julian


Pete,
Can you just saw a combustion chamber off of the end  ;o)
 
Piet, Not sure if the factory added skulls to fix a problem, I think they just did it the same as the Hondas. Interestingly, they even put iron or steel inserts in the early triple head cam bucket holes.....not a good idea, as the buckets can seize in the holes... The early 3c heads were a bit of a muddle with aforementioned bucket holes and a very odd assembly to attach the carbs. Both ideas rapidly dropped (thankfully).

Julian - certainly can saw off a cylinder. Hammer and chisel engineering being my forte  :D :D

Pete
 
I have a 3CL head of around 1975 or 1976 vintage and it has no iron skulls in it, only soft alloy, so they must have changed their minds a few times, as later ones had iron skulls, and are we saying that earlier ones had iron skulls too?
 
My '74 1000 had iron skulls Grant.
I always preferred the iron skulls in the old Honda CB77 heads because the plugs threads didn't strip as easily as on other models. To a hamfisted teenager this was very important and I dont remember helicoils being around at that time either (1970), so you wrere up shit creek if you stripped a plug thread. Regards Pat.   
 
poffer said:
The early 3c heads were a bit of a muddle with aforementioned bucket holes and a very odd assembly to attach the carbs.
Click to expand...
My very early 3c (1477) actually had a steel tube acting as an oil gallery, emerging from the top of the barrels and fitting into a hole on the underside of the head, pumping oil to the top of the head. It meant that trying to skim the top of the head wasn't possible without removing the oil tube. And nobody I showed it to knew how to get it out. It was probably simply pressed in, but I tried gentle tapping at the bottom (locating flange at the top) and nothing moved, so I just left it and used Silvafros on both sides of the head gasket.
And yes it had the iron inserts in the cam follower holes and the rubber seals/spigots for the inlet ports. One of the rubber seals in the inlet ports had been installed wrongly at the factory, too.
I wish I hadn't sold that bike

Ken
 
the non skull triple heads were '77 and '78 then they went back to the skulls
they are known for cracking between seat and plug
all alloy is kinda nice if you want to weld up and reshape the chambers
fitting smaller plugs should reduce the cracking
shame the 750 heads don't have that ability without radical work
i have wondered about building up the steel in the chamber
but expect the shrinkage issue may cause more trouble than the effort is worth
 
3patC said:
My '74 1000 had iron skulls Grant.
I always preferred the iron skulls in the old Honda CB77 heads because the plugs threads didn't strip as easily as on other models. To a hamfisted teenager this was very important and   I dont remember helicoils being around at that time either (1970), so you wrere up shit creek if you stripped a plug thread.  Regards Pat.   
Click to expand...

Knackered the plug thread on my Bantam around 1969, got it helicoiled at the local Yamaha dealership in Glenroy, Melbourne.  It was located on my way to school, dropped the head off in the morning, picked it up on my way home in the afternoon.

Reckon the cam bucket sleeve and intake set-up of the earliest triples was simple over-engineering.... solving problems that hadn't yet shown themselves!  Shows though that they had donned the thinking caps in Breganze!

While the all-alloy heads are rather easy to repair when cracked, the iron skulls often crack also when seat inserts are fitted, but are a bitch to repair.  The Serdi doesn't really like cutting through welds....

piet
 
Piet, we were kids then and it was pure luck if anybody had any hands on knowledge. We had no money either, I still have 60's hondas from the USA with horrendous bodges in the plug area so it wasn't only me that didn't know helicoils existed. Can't remember when I first came across helicoils but it was probably not much later, a year was a huge amount of time when you were 16 though  :D
 
I think that the cast iron skulls were initially used because they expands less that the all alloy head, so less problems around. On the other hand, all alloy heads are easier to repair and all in all valve seats install is safer. Kind of a choice...
 
3patC said:
Piet, we were kids then and it was pure luck if anybody had any hands on knowledge. We had no money either, I still have 60's hondas from the USA with horrendous bodges in the plug area so it wasn't only me that didn't know helicoils existed. Can't remember when I first came across helicoils but it was probably not much later, a year was a huge amount of time when you were 16 though  :D  
Click to expand...

Know what you mean, Pat.

Summer vacation never seemed to end..... what are 6 weeks nowadays?

piet
 
It looks like Honda used iron skulls in the CB450 cylinder head too. Interesting as that engine was very remarkable for the time, DOHC, CV carburetors and torsion bar valve springs. I had an original factory shop manual years ago and it was more of an engineering document. Spoke of ring flutter, piston speed  and valve harmonics.
They were very proud of the technical expertise used in the CB450 design.
The shop manual did not refer to the skulls, as I recall.

Maybe an aircraft engine design too, from the web:

Air cooled aviation engines often are built with the cylinder fins turned as part of the steel cylinder, using ringed aluminum pistons. The aluminum cylinder head sometimes has an iron "Skull" cast into it, usually it's plain aluminum, and usually has internal threads to allow it to be screwed onto the top of the cylinder if it is a radial engine. Some, like the old Kinner radials, had a flange at the top of the cylinder and the head was fastened with short screws.

Checking back on Dr. Porsche and his air cooled engines. It looks like they did not use skulls.
 
poffer said:
Interestingly, they even put iron or steel inserts in the early triple head cam bucket holes.....not a good idea, as the buckets can seize in the holes...
Click to expand...

The CR93 125 DOHC 8v, and I think also the CR72/77 250/305 production racers, had replaceable bronze castings that were screwed to the heads and provided a bearing surface for the cam tappets.

Of course for the last 3 decades no one seems to have had problems with running the tappets against the aluminum head casting.

cheers,
Michael
 
True....I've got a couple of CB450 heads here with skulls - and several factory manuals too. They do read as though they were proud of what they achieved. Looked at in the context of the time they should be...
However they also read as though Phil Irving's books had been their design guide..An early Tuning for Speed edition and Motorcycle Engineering both treat Iron or Bronze cast in skulls as examples of superior practise at the time with inserted heads being rare.
However progress is inevitable and better foundry work became common along with better die casting alloys.
 
  Could be wrong here, but I think Velocette developed what they called the "Alfin" process that was a cast iron liner with the cylinder barrell cast round it to get full heat transferance from liner to fins - Regards - Phil
 
i'm familiar with the term "Alfin" being used with brake drums on sporting cars late 40's early 50's
likely the same process used for Velo liners.

my old formula junior cooper had  steel inserts for the brakes cast into the alloy wheels

cheers,
scott
 
Royal Enfield used cast iron skulls on some of their bikes,
interestingly, they are the marque which Roger Slater was very interested in (late 50's, early 60's) before he came accross Laverda, and pasion that he has now returned to.You might also like to note that it was Roger who first imported the Indian built Enfield single to the UK, before selling on that concession to others,who have since sold it ,to others, and even more others.
CLEM
 
Roger slater talked my partner at Morphy motors into foolishly taking the 1st two indian enfields that they imported - God - they were crap - wouldn't even pass the MOt - probably would have trouble passing water! - Regards - Phil
 
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