Air Cleaner Boxes

[kp]

Hi all. Now we've had wheels, spokes, exhausts etc but nothing on air cleaner boxes. I see that there are several different styles and would luv to know if anyone can get the discussion going around these. Andy told me a year or so back about the two distinct types of airbox, these being the 2 screw clamp and 3 screw clamp types. If there is anyone who can add to the discussion, especially when abouts the 3 screw type was introduced, would be great to hear. Are all Sandcast types the 2 screw type? Also, are there any specific differences within types? KP 

[Steve Swan]

Posted by Chris Rushton "Guest"

There are indeed two distinct types of airbox fitted to the sandcast bikes. Up to frame 1004006, the stays on the airbox top were of the two fixing variety. After that they were changed to a three fixing variety, with the stays them selves also being modified. The early stays also mount direct to the airbox top (no rubber packing), hence are even more prone to vibration cracking than the later three fixing type which incorporated rubber packings to attempt to reduce vibration effects. Parts list number 4 of September '77 gives details. There is also a difference in the airbox lower for French, German, and Dutch market machines which relates, I believe, to the inlet duct shapes. Machines for these markets were also fitted with different exhausts (more restrictive baffles) - possible lower output / quieter?

[736cc]

The pre-production candy gold CB750 at Brighton (April 1969) airbox inlet opening hood was black in color with rest of box candy gold.
On later airboxes, Honda added cotter pins to prevent the internal joining hardware from unscrewing and getting sucked into the motor ("I just hate when that happens"  )

[Steve Swan]

Posted by Chris Rushton "Guest"

The airbox on the gold pre-production "Brighton show" bike was actually of fibre glass construction, as were the sidepanels (you can see the fibre matting on the inside surfaces). The ducts were as correctly pointed out black - they were actually seperate moulded rubber "inserts".

[kp]

Hey Chris. That's great feedback on the airboxes from yourself and Andy. I'm sure the rest of the members will find the information enlightning and interesting. Good to see some of this secret squirrell business being revealed at last. This is the sort of stuff you don't find in the current publications. Maybe you'd consider doing a piece for the "Technical" pages which would be a valuable contribution for reference to present and future members KP 

[Steve Swan]

Posted by Chris Rushton "Guest"

Concerning the problem of the jointing hardware getting sucked into the motor, Honda did acknowledge this problem some time before officially incorporating cotter pins to the revised lower half securing screws. In a American Honda service bulletin (number 7 of 6th November '69) , they suggested that the two "loose" 6mm nuts screwed onto the securing screws (which are not actually shown in the parts lists) should be crushed in a vice to ensure that even if the securing screw came undone, nothing would get into the motor.
Bit of a bodge really!, but I guess that's why they changed the screws to the type using cotter pins.