3D printed prefilter element for CRF 300 L

With the riding on hiatus, I`ve turned my attention to nonsensical tinkering.

My first project was to make turn signal cover plates in case I end up changing the blinkers for something else. The plates turned out pretty good so I decided to try something a bit more challenging.

Honda CRF 300 turn signal cover plates
Turn signal hole on the rear fender
The STL file has 3 different versions

The >> STL file <<


My filter was surprisingly filthy considering the rather tame riding conditions when it comes to dust. After removing the snorkel I thought that it would be fun to try to make a prefilter element of my own design.

I really don’t know that much about the subject, but you learn by doing, right? What I came up with is of course version 1.0, but it doesn`t look all that bad.

The only thing I`m wondering is if the removal of the snorkel and addition of the prefilter will even each other out? In other words do I now have more, less or the same amount of air flow?

I`m tempted to cut additional holes to the airbox side cover, but I haven`t yet figured out a satisfactory way to add a filter on it too. No sense in having a prefilter, if there is an unfiltered hole right next to it.

The dimensions of the element came out so good, that it seems to sit snugly in place without any glue etc.

The 3D model
Parts and assembled version

Removing the snorkel and replacing it with the prefilter unit increases the inlet surface area about 50%. Whether this is enough to counter the effect of the filter… I don’t know.

The red area represent the inner size of the snorkel and the blue are is the inner size of the prefilter element.

If you want the STL file for printing or editing you can download it below.
>> STL file <<

UPDATE 23.12.2021

The 1.0 version was far too restrictive. The filter needs to be bigger to allow for better air flow. The actual filter element also needs be fully utilized and not rest partially against the bottom side of the housing. In other words, the 1.0 was only allowing air flow from the oval shaped area. Rest of the filtering area was wasted.

1.0 on the left 1.1. on the right.

Version 1.1

The area that allows air to pass through the filter is now 300% bigger. The “sponge” filter is now fully utilizing all it’s surface area. This is done by raising the filter / adding height to the casing so that air can flow freely under the filtering element.

The unscientific “suck & blow through the inlet”™ method is yelding much much better results.

The problem

I did not account for the seat attachment hooks enough, so the filter casing is rubbing against the seat mounting hook on the right. I need to reshape the casing and maybe squeeze a few more square centimeters of filtering surface.

Almost, but needs works still
The 3d model of 1.1


The story is continued here to keep this post from getting too long.

2 Comments Add yours

  1. Nacho Reyes says:

    Thank you for this, I will try to built them and use on my CRF.


    1. JN76 says:

      better version is coming


Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s