One nasty thought I had:

These Kirby-Lauson engines were running in the 50s and 60s when fuel was leaded.

What happens/happened to them with unleaded fuel? Were the valve/valve seats hardened (I'm guessing unlikely if the machine was built in Oz), and/or could this be a cause of them failing?

Also Grumpy said in the past that:
Quote
It was not a nice engine to operate in my experience, but they were quite durable mechanically.

Does anyone have an idea about what grumpy meant by "not a nice engine to operate"?

Thanks,

Patrick