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 your own seat foam for a CT90

I have a number of CT90's I am working on right now and they all need new seat foam and covers so I thought I would take a crack at making the foam and sewing all the covers myself. While this post is on making the foam for a CT90 seat, I also have done a post here on how to sew a vinyl seat cover for a CT90.

Here is how I am going about making the foam support for each seat.

For the seats I have the covers were in really bad shape and the foam on each seat wasn't much better, but the shot below shows one of the foam supports I removed and a seat pan where I have already removed all the rust and repainted it so it's prep'd and ready to be rebuilt.






On interesting thing I learned is that the seat foam from one of my old CT90 seats is stamped that it was made by Bridgestone for Honda.



What I will be using for foam is multiple layers of carpet padding that I picked up at Home Depot and I decided on using one of the mid weight under laments that is relatively cheap and should give me a nice firm seat.



For the first layer I cut out a section to clear the raised feature on the front of the seat pan where the hinge attaches so that as I add layers I don't get a significantly raised area at the front of the seat.



To attach the foam to the seat pan I used 3M Super 77 contact cement that is great stuff. You only half to wait around 30 seconds to a  minute after you have applied it before you can join the pieces you are trying to bond, so building up the seat is fairly quick.


for the first layer of foam was about 13 x 14 1/2 inches and was sized so that it would wrap all the around to the edges of the seat pan. when bonded on.



I next trimmed up the foam and got ready to add additional layers.


I followed the same process of using the 3M spray adhesive to bond each layer of the foam to the next and added six more layers to get the final thickness I was looking for. The nice thing about this approach is you can add as many layers as you would like to get the desired thickness which is great if you're trying to dial in a seat for a short or tall person.



I waited a few hours to make sure the adhesive had dried before I started to shape the foam.  I next cut off some of the excess foam on my bandsaw to get a significant amount of the excess foam removed before I started carving with a variety of sanders.



From this point on I started carving using a variety of sanders and found that the courser the grit the better it was at removing the foam. This steps can make a mess so you might do this in an area easy to clean afterwards.  Here is how the final CT90 seat pan with bonded foam turned out and I am pretty happy and now have three more to do and then I'll starting working on how to sew the seat covers.



Related Posts:
Making your own vinyl seat cover for a CT90


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

Link to page with listing of CT90 parts available on Amazon


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