There were two variations of the Honda CX500’s rear engine cover through the course of the CDI models. One of the Honda CX500 Custom variants was the first to receive the later rear engine cover – from looking at the parts fiches it appears to be the 1980 model (USA, Australia and elsewhere). Other models in 1980 (e.g. the Australian CX500 Shadow) still had the original 415 part. The original part number was 11310-415-000 and the later number is 11310-449-000 (see the product codes page for info on deciphering those). Note that the TI rear cover for CX500s and GL500s is different again and is not covered in this article.
Functionally they are identical in terms of fitment – the 449 item has more reinforcing webbing in a number of places. In all of the below photos the 415 unit is on the left and the 449 on the right. Around where the starter motor is inserted:
Inside, where the stator sits:
The rear engine bolt webbing is slightly different – this may just be variation between the individual castings or a subtle change, I wouldn’t know:
Different lettering inside:
Inside the base – apologies for not being able to clean the 415 prior to shooting:
The little vent beneath the pulser cover is more nicely formed on the 449, but that could just be copy to copy variation/wear(??):
That’s all the differences we could see. Given the year that the different cover was introduced it seems unlikely that this is related to the change in mechanical seal aperture size – we were sadly unable to measure both at the time in terms of that to conclusively say.
Why the change? Who knows… the engine is a stressed member – perhaps the answer lies there. Or that Honda had seen/foresaw rear engine covers cracking. Can’t say I have heard of the latter but perhaps someone else has…