Honda are currently recalling only the manual transmission 2017 and 2018 model cars, which covers cars built before some point in 2018.
If all 1 litre engines on these cars are identical, it would be hard to understand why only those with manual transmissions are to be recalled, unless the fitment of automatic transmission somehow reduces wear and tear on the timing belt system. For example, it might be reasoned that automatic transmission provides consistently smoother gear changing than the manual variant, which would reduce shock loadings on transmission and engine components. If this reasoning included the timing belt system, then timing belt failure caused by shock loading might be less likely with automatic transmission. If that were the case, a manufacturer may choose to reason that failure of the timing belt would be less likely than with a manual transmission, and would not therefore require a recall of the automatic variant.
However, the 6NK Product Update which I posted on here on 10th Jan makes it clear that the cambelt itself is not the direct cause of failure, and clearly defines the issue as follows:-
"The timing belt tensioner behaviour becomes erratic due to progressive wear of the timing belt caused by out of specification pulley roughness. This results in excessive tensioner movement leading to fatigue of the tensioner spring. This changes the load on the timing belt teeth, which can result in the teeth chipping, loss of valve timing and engine stall."
The Product Update describes a self-destruction process within the timing belt system, initiated by the normal operation of a single incorrectly manufactured item within that system, and that damage to the timing belt and tensioner is a consequence of operation with the out of specification pulley. It does not state or imply that either the timing belt or the tensioner are not within specification, or are responsible for initiating the issue. The Product Update unfortunately omits to mention another possible (and widely-reported) failure mode of the system caused by the out of specification pulley and the consequential breakup of timing belt teeth, whereby the particles from the deteriorating belt pass into the engine lubrication system and eventually clog the engine's oil filter. At that point, the bypass valve within the oil filter opens correctly, allowing oil and debris to flow into both the engine's crankshaft bearings and the turbocharger bearings, causing damage and failure of those bearings leading to catastrophic damage within the engine.
I do not understand how Honda's assertion that "the belt was of sufficient quality and fit for purpose" can be valid, when there seems to be an admission that engine failure was apparently due to debris from deterioration of the belt. It seems to me that close examination of the crankshaft timing belt pulley from this engine would be in order, and its compliance with the manufacturing specification should be established.
