Tree Hugger
Full member
- Location
- Scotland
Have searched the forum but must be too thick to find the relevant posts. I am trying to decide how essential these repairs are, perhaps on a scale of 1 to 10 
.
Thanks
David
. Thanks
David
Valve seat to plug cracks
- Thread starter Tree Hugger
- Start date
The Sock
Hero member
- Location
- London, England
Unless the cracks run all the way through, they aren't a major problem.
I believe they were the reason behind the cast iron skull heads.
I believe they were the reason behind the cast iron skull heads.
Tree Hugger
Full member
- Location
- Scotland
Is there a risk the valve seats become loose?
pf1
Hero member
- Location
- Portsmouth UK
I don't like the look of that first pic but I will await our expert's verdicts because I would like to know myself.
Eventually, yes. But they won't fall out, the alloy edges are swaged over the seats.
Those heads make a nice conversation piece as a doorstop.
piet
Tree Hugger
Full member
- Location
- Scotland
…… or a brolly stand 
It’ll be going back on the lovely engine Keith rebuilt back in May. Just need some work done on the head I suspect.
It’ll be going back on the lovely engine Keith rebuilt back in May. Just need some work done on the head I suspect.
chrisk
Hero member
- Location
- Brisbane, Australia
The Honda engineering spies asked exactly the same question. Notably the first smiling Japs since WW2.
Probably they found one location at Laverda that reminded them from their own casting quality.
I consider Laverda had chosen this porous alloy, one of the reasons being its casting properties that allow the very fine fins to be sand cast.
Their manufacturing was dependent of this alloy. I would have thought because the porosities are just gas voids, that strain hardening would have helped with the cracking issue, at least to some extent. I mean something like machine sanding the combustion chambers, then shot peening them using certain steel balls with certain pressure, also just before the final cut on the seat recesses, and finally polishing the combustion chambers. A forming tap to be used for the spark plug hole instead of cutting tap. Not sure how these would have performed in practice.
I consider the reason for the skulls was them to be heat barriers on the older Laverda four stroke designs. Give nicely more torque especially on the middle range, and they were one way to increase combustion temperature while allowing better combustion with less developed combustion chamber shapes. However, with thermal barriers usually the extra torque fades away when engine speed goes up enough, this depending of several parameters including dimensions, secondly the barrier increases its own surface temperature this finally leading to detonation when the engine output is increased enough and especially on long runs. Without the skulls the compression ratio needs to be higher to get the combustion temperature back up, but now the shape of the combustion chamber is more critical. This is why I consider the all alloy versions of the heads belong to the most highly revving and highly tuned engines. Probably worked better if revved 10 000 rpm all the time on the 24 hour race, was not a big problem even to scrap the head after the race.
On the production runs, were the all alloy heads paired with the hotter cams and higher compression ratios than the skulled heads?
Hotter cams themselves require higher compression ratios, secondly the all-alloy head.
Did they also had delivery problems with skulls leading to these used on engines with lower tune? To my understanding the skulls came from another foundry than the cast alloy parts.
-Jouni
Their manufacturing was dependent of this alloy. I would have thought because the porosities are just gas voids, that strain hardening would have helped with the cracking issue, at least to some extent. I mean something like machine sanding the combustion chambers, then shot peening them using certain steel balls with certain pressure, also just before the final cut on the seat recesses, and finally polishing the combustion chambers. A forming tap to be used for the spark plug hole instead of cutting tap. Not sure how these would have performed in practice.
I consider the reason for the skulls was them to be heat barriers on the older Laverda four stroke designs. Give nicely more torque especially on the middle range, and they were one way to increase combustion temperature while allowing better combustion with less developed combustion chamber shapes. However, with thermal barriers usually the extra torque fades away when engine speed goes up enough, this depending of several parameters including dimensions, secondly the barrier increases its own surface temperature this finally leading to detonation when the engine output is increased enough and especially on long runs. Without the skulls the compression ratio needs to be higher to get the combustion temperature back up, but now the shape of the combustion chamber is more critical. This is why I consider the all alloy versions of the heads belong to the most highly revving and highly tuned engines. Probably worked better if revved 10 000 rpm all the time on the 24 hour race, was not a big problem even to scrap the head after the race.
On the production runs, were the all alloy heads paired with the hotter cams and higher compression ratios than the skulled heads?
Hotter cams themselves require higher compression ratios, secondly the all-alloy head.
Did they also had delivery problems with skulls leading to these used on engines with lower tune? To my understanding the skulls came from another foundry than the cast alloy parts.
-Jouni