Honda CT90 Engine Reassembly

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I have one 1971 CT90 where I was going to rebuild the clutch because the kickstarter just wasn't turning over the engine like it used too,  and I also had a Big Bore kit from DrATV that I wanted to install. My intent was to just do the top end and rebuild the clutch with new disks, but when I opened up the cases to rebuild the clutch pack I found a slick black slime in the bottom of the case.  I didn't like the idea that there could be black slime in the rest of the engine, so I decided to disassemble the entire engine to make sure I cleaned everything out.  Since I was tearing everything apart I thought I would document step by step how everything goes back together in this post in case others were interested in knowing what the inner workings of a CT90 engine look like. Links to Related Posts: My Honda CT90 Clutch and Headset Nut Tool Cut Away of a CT90 Engine - CT90 Engine Exposed! Repairing Damaged CT90 Spark Plug Threads Using a Time-Sert Thread Insert CT90 Clutch P
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A 3D Printed Functional Rear Air Filter Housing for use on a Honda CT90 K2 and Later

I have on and off been looking at trying to model or scan some of the different CT90 air filter housings so I could make 3D printed versions, but have had limited success. 

Related Posts: CT90 K2 and Later Air Filter Housing 3D Printed Seal 

After some effort I was able to create a functional design of the rear portion of the air filter housings used on K2 and later CT90's.  The picture below is of the next to the last configuration that I designed and then printed during a trial fit on one of my bikes.

The final design has just a few minor changes to the one I shared in the picture above, and while it isn't an exact copy of a stock Honda CT90 air filter housing, the interfaces are all the same as the stock Honda filter housing, so it should be a good functional part.

If someone would like to print this housing, you can download the .stl file at Pursaprinters here at this link.

This part takes about 17 hours to print at the settings I was using and I printed it in the configuration shown in the picture below to try and minimize the amount of supports required.  I think by increasing the layer height and making a few other changes to the settings the print time can be reduced, but it's still going to be a print that takes a considerable amount of time.  This orientation also ends up having some minor surface issues where the supports are attached, so the next time I print it I'll do it with the larger opening down on the table, but that will require more supports.


The following pictures are of the 3D printed filter housing next to a stock Honda housing so you can get a feel for the differences between the two designs.


My ultimate goal is to create exact copies of the all the CT90 air filter housings and other plastic parts so they can be 3D printed, but I'm finding that that won't be an easy task.

I've started to play around with scanning and photogrammetry to create an accurate model of the air filter housings, but I have a long way to go before I get up to speed and am knowledgable enough to create good models.

The picture below is a basic scan that I was abled to do using the face recognition system on my iPhone and while it really isn't usable, it's a start.


I hope you found this interesting and I'll be making future posts as I hopefully make more progress in modeling and 3D printing CT90 air filter housings.


Helpful Links (Shop Manuals, Wire Diagram, Model Information, etc.)




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