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 - Shindy Intake/Exhaust Valve Set #07-002 for use on a Honda CT90

I am in the middle of adding a DrATV Big Bore Kit to my 1971 Honda CT90 and when I pulled and disassembled the head both the exhaust and intake valve had a pretty significant groove around the area where the valve seats.  The bike was running fine before I pulled it apart, so I could have just cleaned everything back up and used the old valves, but since I had it apart I figured I would replace the valves if I could find a set that wasn't too expensive.

I spent some time on eBay and kept seeing sets of valves made by Shindy with a part number of #07-002.  The funny thing was when the ad on eBay was for a CT90 the price was around $19.00, but I noticed the same set of valves being sold for Honda ATC's with no mention of CT90 and the price was only $13.55 with free shipping from within the USA which I thought was a great deal.

I ended up ordering the valves from eBay seller parts_giant and in a few days the parts showed up in my mailbox.  You can also get this set of valves at Amazon here at this link.





The valves are actually individually packaged within the main package which added an extra level of protection.


Given that there is no reference to CT90 on the packaging, I removed the valves from their packaging and compared them using a set of calipers to the valves I was removing from my CT90 and couldn't find any difference (except for the groove around the valve seat on the old valves).


The smudge on the seat of the new exhaust valve is just crud from when I dropped the valves into my head for a trial fit.

One nice feature of these valves is that they are made in Japan, which I assume means they should be of good quality.


When I did drop them into my head for a quick fit check the valves looked great.


After I get done cleaning the head to my CT90, I'll spend some time lapping the new valves into their respective seats and they should be good to go.

I am really happy with the purchase of these valves, especially given the price and free shipping from parts_giant on eBay, and would recommend them for your next CT90 project. If your someone who tends to always shop on Amazon, the valves are available here at his link.

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

Link to page with listing of CT90 parts available on Amazon



Comments

  1. UnknownJuly 13, 2020 at 7:02 PM

    I bought a set of these valves -- they seem high quality. Can you describe your lapping process? SInce the tops of these are textured, I had trouble getting the lapping suction cup to stick. Tried the tubing trick from below, but not sure if I was getting a really good job done. Have you ever taken a head to a machine shop to have new seats cut?

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