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Showing posts from March, 2017

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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Options for Honda CT90 Paint

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Given that most CT90's you come across are over forty years old they all tend to have a few battle scars and faded paint and show their age.  In some ways I like the look of an older bike and think it adds character, but sometimes the damage is such that you really need to remove the rust or fix the damaged plastic and apply a new coat of paint.  If you look hard enough you can find sources where you can purchase paint in the original colors or take color codes to your local automotive paint supply house and have them mix you up a pint, but if your like me and like to keep the cost of your project under control, you might look at the following paint options for your CT90 or CT110. I have also recently updated this post to include a listing on Honda Paint/Color codes at the end of the post.
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Simple CT90 Valve Spring Compressor

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If you do ever get into doing work on your CT90's engine one thing you will be faced with doing at some point if pulling the valves.  I cobbled together a simple valve spring compressor using a C clamp and a piece of thick walled aluminum tubing I had setting around my garage. I took a piece of the aluminum tubing about 1 1/2 inches long and cut an opening in the side of the tubing about half way through and about 70 percent of the length.  The tubing was a little over an inch in diameter and had about a 3/4 inch inside diameter.
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Simple CT90 Valve Seat Check/Inspection

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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.
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Repairing CT90 Plastic Covers and Air Filter Assemblies

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Most of the time when you pick up an old CT90 the plastic covers or air cleaner housings are either missing or in need of repair. If you have the money new plastic's are readily available, but if you're cheap like me and not to picky you can possibly repair these parts to a serviceable condition. I'll describe the process I followed and hopefully it will enable you to salvage some of your old plastic parts. With this approach I use I need a seperate plastic cover or air filter assembly that has an undamaged section that is the same as the section I am trying to repair on the damaged plastic.  This usually isn't a problem for me as I have several CT90's, but you may have to borrow a good part from a buddy. For this example I was trying to repair part of the air cleaner on one of my 1971 CT90's and the picture below shows the part to be repaired on the left and a good part on the right.
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Dealing with Old Hard Rubber CT90 Carb to Air Cleaner Boots

I have had a couple of CT90's where the rubber boot between the carb and air cleaner and also the rubber elbow in-between the end of the air cleaner and the rack on the back of the bike have been almost rock hard and very difficult to deal with when trying to disassemble or reassemble these installations.  I have found that if I take a hair dryer and heat up the rubber that it will become pliable and enable easier removal or installation.  The softening effect is not permanent and the rubber will go back to being rock hard when it cools, but it does make things workable until you have a chance to go out and buy new rubber boots. I have mad another post on a permanent way to soften up old rubber parts at this link that works very well and recommend you take a look. Helpful Links   (Shop Manuals, Wire Diagram, Model Information, etc.)
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