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 new Batch of 3D Printed Parts that can be used on a Honda CT90 and CT200

 I'm continuing to find and endless number of opportunities to utilize my 3D printer to make useful parts for my also endless number of CT90 project bikes that I am working on, so I thought I would share a few of the latest CT90 parts that I have designed and printed.

All of the designs I share below, I first modeled using my ViaCad 2D/3D modeling program.

Related Posts:

More 3D Printed Honda CT90 Part Designs

3D Printed CT90 K1 Rear Airbox Snorkel

CT90 K1 3D Printed Carb to Air Filter Boot

A 3D Printed Valve Spring Compression Tool


Speedo Light Bulb Socket Caps

On almost every older CT90 I work on (I guess they are all old...) the little rubber caps on that cover and help hold in the bulbs on the base of the speedo are cracked, disintegrating before my eyes or are just missing.

I modeled up both a short cap that has a hole for one wire and a taller cap that has a slot in its base that allows two wires to pass through as shown in the pictures below.



I have used these caps on speedo's from a K1 and a K3 and they should work on several other models.  I haven't checked them out yet on a speedo from a K0 or a CT200 but will do so soon.  Some later model CT90's and I assume CT110's have a bayonet mount that takes a larger diameter cap that I plan on modeling in the future.

I printed these caps using SainSmart TPU which is a nice flexible material, but significantly stiffer than the original rubber used for these parts. 

Here is the link to the .stl files at Prusaprints for both the short and tall caps.


CT90 Rear Fender Plugs

Another part that seems to be missing or in really poor shape on most bikes I pick up are the rubber plugs that go in the holes in the rear fender that support the addition of turn signals.

I modeled up both smaller round plug and the longer plug designed to three holes. I made the design of the features that fit into the holes slightly different than the original Honda plug designs as I printed these parts using SainSmart TPU which is significantly stiffer.

I have included links to .stl files below, but if you don't have a 3d printer I also sell a set of these plugs on eBay here at this link.



Here is the link to the .stl file at Prusaprints for both the long and round plugs.


CT90 K1 Down Tube Support Bracket

It seems like a lot of the basket case CT90's I find are K1's which are kind of an odd duck in that many of the parts on this model CT90 are not common to any other models.

One part that can be hard to find if it is missing is the metal bracket that holds down the front end of the air filter housing and also provides the mount for the lower left side of the down tube cover.

I modeled up a working part and while its not as elegant as I would like the design, it is completely functional.



The bracket is designed with a small cavity at the end that you insert a standard 6mm nut into and that provides the threads for screw that is used to hold the lower end of the down tube cover.

I printed this part in PTEG which seems more than adequate for the application.  You'll also find an alternate design of this bracket that provides more clearance for the upper engine mount bolt.

Here is the link to the .stl file at Prusaprinters


CT90 K1 Speedo Housing Gasket

The other part I modeled for the CT90 K1 was the gasket that goes between the speedo and the headlight housing. You can find this gasket readily available on-line at the normal sources, but I had an itch and decided to model and print it up for one of the K1's I am currently rebuilding.


I also printed this part in SainSmart TPU.

Here is the link to the .stl file at Prusaprinters


CT200 Air Filter Housing Gasket

The last part I will share is a gasket that is used on a CT200 between the air filter housing and the frame.



This is one of the simplest parts I have modeled and I also printed this using SainSmart TPU.

Here is the link to the .stl file at Prusaprinters


I hope you found this information useful.


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











Comments

  1. Jolly Roger CT90April 18, 2021 at 3:00 AM

    You are the man. Always love going through your blogs when I am curious or stumped about something. Bought your clutch tool a while back and it was very essential while I did my rebuild. Thank you for all you do and share.

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  2. Keith in AZJuly 2, 2021 at 10:51 PM

    I always look forward to your next project. I learned a lot in life growing up and older around guys like you. I have plenty of abilities as a result. 3D printing is a new frontier and I know nothing about the process in getting things made, just interested and impressed with your talents and unselfish sharing of your accomplishments with the group and me. I have all of your posts saved. Keep it up. You are appreciated. I own a 1974, 1976 CT90 and a 1984 CT110. Also have a 1974 BMW R90/6. I was raised around those machines, and the BMW was my father's from when he bought it in 1974 with a few hundred miles on it. He hung up his helmet for the last time 2 years ago and at 91, is healthy and quite active. At 65 I caretake it for a while. The 90s are special as I never had one back in the day buy friends did. I also own a 1969 Z50A minitrial project. Just need a gas tank or fix the original. Again, thanks for all you do.

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  3. Butch MillerNovember 25, 2021 at 9:49 PM

    Dude ..... Nice Job !! Just found a beautiful 1970 CT 90 K2 , all original it has all those parts, but considering buying any of yours that are on Ebay just so I can pull the original parts and keep in good shape and put away safely so as to put them back on as original if I do ever sell this. Only 1600 miles on mine and everything is in great shape. Even thinking of making both seats so as to save the originals .... both seats perfect shape mostly. Just some sun faded white pipping ... I'm planning on riding it back to some lakes up in the high country that I won't take my 4Runner up and into .

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