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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Product Review - Cylinder Flex-Hone


I had a couple of cylinders that I pulled off of some bikes that I picked up that weren't running and was surprised that they only had light rust, so I decided to order a hone to clean the cylinders up myself without having to send them out to get a new bore.

I ended up ordering a Flex-Hone cylinder hone manufactured by Brush Research from Amazon.  The Flex-Hone was 2" (51 mm) in diameter that was 240 grit, and was from the BC Series Flex Hones.  The price of the cylinder hone was $18.00 and it is made in the USA. 




The diameter of the stem on the Flex-Hone is about 1/4" so it will fit into just about any hand drill someone might have in there shop.  The Flex-Hone had a good fit in the CT90 50 mm cylinder bores I was working to clean up and overall I am very satisfied with both the performance and how long it is lasting given that I have used it on several CT90 cylinders now.

If you're looking for information on how you would actually use a cylinder hone like the one above, I found this link to have good basic info to help someone get started honing their own cylinder.

Here is another video on how to hone a cylinder that provides good basic instructions.

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

Link to page with listing of CT90 parts available on Amazon


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