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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Simple CT90 Valve Seat Check/Inspection

One of the best things you can do to your CT90 is to make sure your valves are seating and sealing to ensure that you have adequate compression. If you have your head pulled off the engine an easy way to check how well your valves are seating is with a small LED light.

In the picture below I am holding the light I use and it was a cheap LED light that has a flexible gooseneck that makes it easy to stick into tight places and is a pretty common light you can find usually on the counter at your local auto parts store.




What I'll do is turn on the light and then insert it in through the intake or exhaust port until it is up near the backside of the valve I am interested in.



At that point I turn off the lights in the room and carefully look around the edge of the valve and see if there is any light coming through.



If there is light coming through like in the picture above then I pull the valve and either lap the valve & seat or cut/grind the seat and then lap the valve and seat.  When I follow this approach and get the valves to where there is no light visible, then I always have good compression (assuming the piston and rings are good).


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

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