Interesting! As stated earlier, I've been using these engines for almost half a century, as have a number of my mates. Between us, we have yet to encounter this issue. Sounds as if the experience of ChrisM (ffkiwi) is similar. Clearly it can happen, but I still don't believe that this is an endemic issue - if it was, more of us would be experiencing it!

I have also yet to encounter a shaft breakage with one of these units, either with my own engine or anyone else's. I think that Raglafart was a bit unlucky there - I'm satisfied in my own mind that this too is not an endemic flaw. That said, any model diesel can break a shaft - all it takes is a manufacturing flaw in the component or some heavy-handed treatment in service.

I had a look, and I can't readily see any design differences between the red -head and plain-head cases. Perhaps they switched to a stronger casting alloy??

I agree with Raglafart that the switch to sawn ports from drilled ports with the so-called "modified" engie was a step backwards in design terns. My own tuning efforts have clearly showed that the original Oliver-ported version had far more potential. They should have stuck with that and developed it further. A well-tuned one of these can give a Mk. IIIOliver a good run!

Finally, the "finger-biter" issue noted by John C is not unfounded - in fact, it's a common issue with ball-race diesels, in particular those with short strokes. Short stroke engines tend to snap over faster than long-stroke ones in any case, andthe addition of ball-races simply exacerbates this problem by reducing the snap-over resistance! This is why Olivers are so user-friendly - that slightly longer stroke.

Cheers!