My 956cc has 250,000kms on the clock, appears to be original, looking closer it looks like it was loved, Oil changes must of been regular, and I'm following on with loads of tlc...
Both the Ventoux and the Cleon engines are more of less bulletproof.
They can take a lot of abuse. Specially the smaller engines can last for a long time.
If your engine is not causing you any problems leave it be.
With my first R4 (GTL 1983) I drove 485.000 km with normal service intervals (90.000 km per year) without any problem.
Only the timing chain needs to be replaced after 500.000 km and maybe piston rings replacement but anyway after 500.000 km a small engine overhaul is to be expected.
Cleon engines are extremely bullet proof uhhh that is to say it won't stand .50 caliber rounds
Thank you for your comments.
I was looking at the scenario of buying a car with a fairly high mileage on it.
I think my question has been fully answered now.
845cc : one of mine covered 155000 miles (248000 Kms.) without problems. It ended up needing new piston rings but with hindsight that might have been due to my using a slightly too light grade of oil (15/40 rather than 20/50).
Timing chains last for ever so long as the oil is changed regularly, and with the 845s even if the timing chain breaks no damage is done to engine or camshaft as the engine is "long stroke".
The 1108 engines last a long time as well: 'The smaller five-bearing-crankshaft Renault motors are renowned for their fantastic toughness' (J. Dewar McLintock, in 'Renault - the cars and the charisma').
The F6 has just got to 250,000 miles (c. 402,000 km); it'd done only 31,000 miles when I bought it in 1997. I got some really good advice in the mid-80s from an MOT inspector who told me: 'Change the oil every 3,000 miles, and if you can keep the arse on 'em, they'll go on for ever.' (delivered in an inimitable Gloucestershire accent). Wise words!
In any R4-related conversation in France, the adjective 'increvable' is likely to come up - in this context, 'bulletproof' is a great translation.