Z1 airbox differences

Arcane Z1 stuff.

Mama Kaw produced two subtly-different Z1 airboxes, the most obvious & easily identified difference being the angle & spacing of two stiffening ribs below & in front of the airbox mouth where it makes the transition from the filter cavity to the small plenum.

Recently while cleaning four loose OEM airboxes, we stumbled upon a noticeable difference in material pliability.  All four had been in direct sun for an hour or so drying after being washed.  Once cooled to room temp, the differences in pliability were still apparent.

Two airboxes with 45mm rib spacing are clearly softer & more pliable at the plenum & carb mouths than the two other airboxes we cleaned that have 70mm rib spacing. Model years for the different rib spacing & angles are as yet unclear according the John Brooke's sixth edition handbook.  When asked, he indicated he was unaware of differences in material pliability.

The gauge (thickness) of the rubber are the same, or very similar, at the carb mouths, within the accuracy of a digital caliper.

All four airboxes are complete OEM in VGC that we've had on the shelf for decades. The steel plenum stiffener plates are present in all four. No dry rot, splits, cuts, major deformations or other damage. Just good, old airboxes that were removed in the day in favor of pods, we suppose. slmjim likely got them long ago from a now-defunct local shop that specialized in Z-bikes he frequented starting mid-1980's.

Admittedly a sample size of only four loose, uninstalled airboxes but, poking at the OEM factory-installed airboxes on all of our Z1's supports this observation.

Best guess:
Perhaps Mama Kaw changed to stiffer material in later production to resist collapse at WFO?  If anyone has convenient examples of the two different airboxes, could you please compare subjective pliability by poking / prodding / squeezing?  Results may appear in John's next edition.

Good Ridin'
slmjim & Z1BEBE
 

I'm aware of the subtle differences in design between ribbing but "highly doubt" they would change-up the Durometer composition of the material itself. Different exposure to the elements would have a more pronounced effect on the material itself. Might sneak-in a caliper to check thickness of material thru one of the carb ducts??  

That's where we checked thickness with a caliper on all four loose airboxes.

In addition to differences in rib design, the identifier "KHI DGM 13236 S" was embossed in later airboxes on the right side of the upper plenum where it's hidden by the upper frame rail & can't be easily seen.  We don't know if rib differences & the appearance of the KHI # follow each other.

With the loose ones, squeezing & flexing at the carb mouths, poking / pushing & different areas, revealed the different 'feel', and the differences were directly related to the rib design differences noted.  About the only thing we can do on installed airboxesis poking / squeezing on the outer bends of #1 & #4 just upstream from the carb mouths

It's a fairly long shot that anyone would have multiples of the two different airboxes to check.  Just thought we'd ask.

Good Ridin'
slmjim & Z1BEBE

Couldn't count how many of the OEM Z1 airboxes i'd given away for Christmas presents or just because some buddy needed one. Never rendered a nickel. So now i have none to compare to?? 

I think there was a lengthy post on the Z-Classic site about the differences.  But maybe my memory is faulty?