Originally Posted by Spillertwo
The engines where a Novarossi 35 Plus 21 and a JP FX 21 R03.
Both engines were in excellent condition.
I never had this happen to me in three years time.
Uhm.... haven't seen this in many many years, last time I saw this, happened to a 11port .21 engine (was a Cipolla, if my memory serves me good).
Never knew what happens with those ultra-high port engines and the yours (AFAIK, your two engines are 7+2 ports).
I can only aventurate an answer for you, maybe is true, maybe not, but... logical, tells that's possible. Let's see:
On those engines with such high number of ports, the metal thickness between ports is very reduced and suffers a lot the high temperatures, crankcase robs heat from the sleeve, but with such low quantity of metal to transfer the heat, it weakens and after some time it fails by the weakest part, the metal between ports (this is exactly where your sleeves failed).
Many years ago, the port craze finished (8,9,11 and up to 13 ports were available) and until few months, haven't seen a 9 port another time, but seems that old metallurgy problems still predate them.
Could be quicker, could be powerful, but they still suffer the reliability problems like the high competition engines, who have a short but very intense life. I feel so bad for you.
My advice, change them for some 7 port sleeves, maybe will not be so quick, but... will live longer.