If memory serves, they were "chrome liners" on these engines (and later 35/35X) - this is how my friend came a cropper with his earlier 35 (Partco offered him cast ones)!
As it's an AD3, it's direct injection (the injectors go in on an angle to squirt into the centre of the combustion chamber) - these were introduced on the 135s - 35/35X were indirect injection.
IIRC, my friend had to borrow the special tool from a local agricultural mechanic to get the liners out of both his 35 and 135. I didn't see him to either machine, just heard the long and boring stories (almost bolt-by-bolt!)
I have to admit, I much prefer the David Brown 3-pot engine - it's block-bored and seems to last longer before major repairs than Perkys do!
Although:
New pistons fitted because of:
If I had had the money when the piston failed, I would have rebored the engine as there's a thumbnail-sized scuff near the top of No1 bore. It's still pottering along, about eight years after the rebuild, so I'm not going to do anything about it at the moment! I reckon the problem was caused by two factors: someone took the thermostat out (before I bought it) and the piston was damaged just behind the thermostat housing/ water pump. The second factor being that it was an easy-start addict! Something that I hate to use - and haven't needed on any machine since the engine was rebuilt! Mind you, the Landy might need something in the winter - it's not a good starter in the warm weather and has a Perkins engine!