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 Cl...
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A 3D Printed Piston Holding Tool for a Honda CT90

Maybe I'm just getting old, but when I am rebuilding a CT90 engine one of the things that can be a little bit of a pain is holding and compressing the rings on the piston when you're sliding on the cylinder.  Sometimes its not to bad, but other times I fuddle around before I can get it to all come together.

Related Posts:

CT90 Engine Reassembly

I decided to design a removable tool that I can 3D print, that helps support the piston, so I can focus more on compressing the rings while installing the cylinder.  The tool is also nice as a way of closing off the opening to your crankcase to keep dirt and crud out if your engine is going to have the cylinder off for an extended amount of time.

Here is what the tool looks like installed.



The tool is made up of two pieces composed of an upper half and a lower half.  The lower half has a post feature that supports the piston rod and helps keep the piston centered on the opening.



I've also made a short YouTube video showing how to use the tool here at the link below.


If you think you can use this tool, I've uploaded .stl files at the links below, so you can print your own.

Here is the link at Prusaprinters


I hope you found this information useful.


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




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