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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Making a Transparent Timing Cover for your CT90

I was working on a post about dynamically timing CT90's recently and decided to make a clear plastic cover like the one in the picture below so that I could view the timing marks while the engine was running and not have to worry about the small amount of oil that splashes out.


To simplify the overall effort I went on Amazon to see if I could find a clear plastic disc that was the same or very close to the diameter of the generator access cover and found the disc here at this link on Amazon.

The disc is made from Acrylic and was 5.0 inches in diameter and a 1/4 inch thick. At the time I purchased the disc it was only $8.75 with free Prime shipping, but when I checked recently the price was now $11.85 for the Prime option.


The 5.0 inch disc is slightly smaller then the side cover it is meant to replace, but is still large enough to have plenty of room to drill the holes needed to mount the disc to the CT90 engine.  The disc I received was delivered with a nice protective paper cover on each of the two faces which will protect the disc while drilling the holes in it.

To drill the holes in the disc I simply used the side cover as a a guide and centered the disc on the back of the cover and then placed them both in a vice to hold them together while I drilled the holes.


I used a 1/4 inch diameter drill bit that is just the right size for the 6 mm screws I used to mount the cover to the engine.


With the holes drilled, I just peeled off the protective paper and had my finished transparent cover.





To mount the transparent cover I just used some short 6 mm pan head screws like are used elsewhere on the CT90 and a standard gasket.


While not a necessity, the transparent cover is nice to have and it makes it easy to use a timing light without having too much of a oily mess to clean up afterwards.  If you are thinking about making this cover here is the link to purchase the disc on Amazon.

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

Link to page with listing of CT90 parts available on Amazon


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