Interesting stuff here. I will add a few OE air filter pics, from the parts that came with my recent purchase of #957, a 1/70 HLS30. It came with a pickup load of spare parts. Some of which are early OEM items. This air cleaner is the early part number 16546-E3210.

 

Not related to this topic but I have to share this pic of two packages of OE spark plugs, NGK in Nissan branded packaging, 10 plugs per package.

 

Time for the obvious question... Does the air cleaner clamshell fit together tightly when there is no filter inside?  

Yeah, I know. But someone has to do it. 

1 hour ago, Captain Obvious said:

Time for the obvious question... Does the air cleaner clamshell fit together tightly when there is no filter inside?  

Yeah, I know. But someone has to do it. 

Mine does, definitely sealed, and the filter is clamped. Lol. I reached in with a tool, and could not feel any play with the filter fit.

 

Here is with the filter removed, and yes it clamped. Lol

Edited October 11, 2024Oct 11 by CanTechZ

6 hours ago, inline6 said:

Wild.  I found this on the motorsport auto site - it looks to me that the genuine filters are too tall now.  

 

Interesting, I would think more people would have the same issue you are having and complain to the vendor. I got mine at a swap meet from an ex Nissan mechanic who had 3 screw carb set as well. All 72 stuff. Mine did not come in a box, just a clear plastic bag, No Nissan printing. 

Please disregard my filter, I had a 72 box and old A/C in my hoard and it has the large filter too. That seems to fit well in the box. 

The rubber seal is petrified so it does not compress, I see that it would though. So it looks right.

Also now that I compare my new and old filters the new one I mentioned is smaller in all aspects. L x W x H So maybe it is for another application. A Roaster Solex car perhaps Like I mentioned it was a swap meet purchase. 

That puts Inline6 back at post one, why won't his filter fit???

On 10/11/2024 at 3:05 PM, Captain Obvious said:

Time for the obvious question... Does the air cleaner clamshell fit together tightly when there is no filter inside?  

Yes!

I took a few more measurements today. Outer filter case is not quite 2 7/8" from front surface to curled lip.

 

With the filter sitting inside the outer cover, laying against the seal, there is only about 5/16" left of "depth" to the edge of the curled lip on the back.

 

Filter is against seal on the back plate.  So, again, when the cover goes on, seals are seating on both sides of the filter element, and leaving about an 1/8" inch gap between the seal and the curled lip of the cover.

 

Is this the correct back plate?

 

OK, so we have seemed to confirm that you have the correct filter. And your housing does clam shut if there is no filter installed.

Sp what about the possibility that it's simply a rubber compressability issue with the new seals inside the airbox that squish against the sides of the filter? In other words.... Do you think that the airbox would close tightly if those two rubber seals inside were not present?

1 hour ago, Captain Obvious said:

OK, so we have seemed to confirm that you have the correct filter. And your housing does clam shut if there is no filter installed.

Sp what about the possibility that it's simply a rubber compressability issue with the new seals inside the airbox that squish against the sides of the filter? In other words.... Do you think that the airbox would close tightly if those two rubber seals inside were not present?

The seals inside are original.  They are made of a type of rubber that I don't think ever compressed much. 

I am beginning to think that my problem is the back plate.  I suspect that somehow it the outer edge has been bent back... If you envision it mounted to the carburetors, then I think the outer portion of the plate has been bent towards the engine.  

I took my back plate off the engine last night and set it on a work bench.  I examined everything very carefully.  At the front of the filter housing, the gap (to the cover) is a bit larger than at the rear.  

Though it is hard to see, upon close examination, I see that this circled area of my filter back plate is pushed in a bit.  With this surface pushed in, the outer part of the housing moves away from the housing cover.

 

I found this picture of a back plate on eBay - note the "plane" of this surface:

 

And here is mine:

While I think this is part of the issue, I am not sure it is all of the issue.  At the back carburetor location on my filter housing back plate, I don't see evidence that it is bent like the front.  And the filter cover doesn't contact the seal there either.  I'd say the distance at the back is about 1/8".  While at the front, the gap is about 1/4".  

I am going to try getting creative with my hydraulic press to attempt to address this.  I have in mind putting the front air horn down face first, and then using some plates or boards to bridge across the backside of the plate, and then use the hydraulic pressure to push on the plate on the curled edges.  Effectively, the area where the horn is should move "up" (horn will be face down in the press) and the back plate will move "down".  I will try to protect the paint with soft rags placed in suitable locations.

If anyone can do some examination (to see if bent) and measuring of their back plate (if not bent), that would be helpful. 

Edited October 13, 2024Oct 13 by inline6

10 hours ago, inline6 said:

The seals inside are original.

Sorry. I somehow missed that detail earlier on.

I don't have a smoking gun, but I have a couple interesting observations...

First of which is the picture of your airbox clammed together with no filter. It kinda contradicts your thoughts that the ends are bent down. In fact, if you look at that pic, it actually appears that the ends are contacting before the long flat center section:

Next observation is that the backing plate pic from ebay is different than what you have. If you look carefully, it appears there is a difference in "offset" between the main face of the backing plate and the surface to which the sealing rubber gasket is attached.

Here's the one from ebay. Note that the rubber gasket looks pretty much even with the surface you pointed to with the arrow:

While on yours, the gasket is clearly stepped away from that same surface. By about the amount you are struggling with:

Is that really the case, or is a trick of the camera angle?

On 10/13/2024 at 9:46 PM, Captain Obvious said:

First of which is the picture of your airbox clammed together with no filter. It kinda contradicts your thoughts that the ends are bent down. In fact, if you look at that pic, it actually appears that the ends are contacting before the long flat center section:

Next observation is that the backing plate pic from ebay is different than what you have. If you look carefully, it appears there is a difference in "offset" between the main face of the backing plate and the surface to which the sealing rubber gasket is attached.

Here's the one from ebay. Note that the rubber gasket looks pretty much even with the surface you pointed to with the arrow:

While on yours, the gasket is clearly stepped away from that same surface. By about the amount you are struggling with:

Is that really the case, or is a trick of the camera angle?

On your first observation, know that the picture you are referencing was a picture supplied by @CanTechZ 

Something to point out is that I am unaware of differences in the back plates for the "earlier" cars.  The parts book shows the same part number until June of 1972.  



I think it is the camera angles... and possibly that these back plates are relatively easy to "damage" by bending.  The front of mine is (was) bent as can be seen if you look closely here (compare at two blue arrow locations:

 

That said, I worked on the filter back plate a bit yesterday in my hydraulic press.  I corrected what was obvious to me, but the filter doesn't really fit much better, maybe a little bit at the front.

So, I don't know. 

I do know that the car came to me with two air filter housings.  Out of the two back plates and covers, I selected the best ones and restored them.  I don't seem to have to other pieces.  I think I sold them with a batch of parts some time ago.

Edited October 16, 2024Oct 16 by inline6

Maybe you ended up with one half of each unit?

7 hours ago, inline6 said:

On your first observation, know that was a picture supplied by @CanTechZ 

I am unaware of differences in the back plates for the "earlier" cars.  The parts book shows the same part number until June of 1972

Sigh. You are correct. I accidentally referenced someone else's pic. That's two strikes for me on just this page alone.

I think maybe I'll just sit here quietly and watch for a while instead of unnecessarily muddying the waters.