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 Cl...
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CT90 Video Links

Sometimes a video can be very helpful in understanding how to work on something on your CT90, so I have tried to capture the most useful videos I have come across on the internet in the list below.  I have also included video's that I have found interesting or entertaining related to what people do with their CT90's.  I plan on updating this list on a regular basis as I come across useful and interesting videos.

The video at the link below shows how all of the internal components of a CT90 work while the engine is operating and includes detail views of the piston and clutch.
Video of cut-away CT90 engine that shows all of the internal gearing and components

Engine Rebuild - This series of videos is from a CT90/CT110 Tech Day back in 2011 that was sponsored by DrATV and has a lot of great detail information on doing a complete engine rebuild.
First Phase
Second Phase
Third Phase
Forth Phase
Fifth Phase
Sixth Phase

Nice series of video's from SoCal Bruce on his 1967 project bike with detail video's on engine disassembly and reassembly along with other topics.  The link to the video below is on engine disassembly, but it will get you to his channel so you can view his other video's.

Nice video here at this link  of the complete assembly of a CT90 engine

Here is another video at this link on how to assemble a CT90 engine

Video of nice simple valve spring compressor tool built by Hardy Tool and Mfg.

Adjusting the gap on the points
First Link 

Checking a CT90 Condenser

Setting Engine Timing
First link
Second link
Third Link showing static timing light with correctly adjusted timing
Forth Link showing an example of using a dynamic timing light and what happens with an increase in RPM's and the timing advances

Clutch Assembly
This is a video I made on adjusting your clutch
A simple video on checking to see if you reassembled your clutch pack correctly

Another video that explains how a Honda clutch actually works.


Adjusting the Carb Idle and Air Screws
First Link
Second Link

This is a good video on rebuilding a basic Honda CT90 Carb

Adjusting Valves
First Link This video is on adjusting valves on Honda 50/70's, but is still applicable to CT90's as the explanation is clear and well done.

This link is a nice video on adjusting the valves and points on a Handa CT110.

Top End Rebuild - This is a nice series by SoCal Bruce on rebuilding the top end of his ATC 110. I have included the first three parts of the series as much of what is done during this part of the rebuild is very similar to what would be done on a CT90 and Bruce provides a lot a great detail that helps ensure a good top end rebuild.
Part 1 - Piston and Rings
Part 2 - Cylinder and Head
Part 3 - Valve Timing and Clearance

Replacing Engine Cylinder Head Studs

A complete basic CT90 build - This is a series of video's from Jennies Garage on Jake's Honda Trail 90 Project.  This is actually a good series as it takes you from cradle to grave in bringing a barn find non-running CT90 back to life and is also very entertaining.
Part 1 - Yard Sale Rescue
Part 2 - Engine Teardown Discoveries!
Part 3 - Seized Piston vs. Hammer!
Part 4 - Theres Parts Under That Rust!!
Part 5 - Engine Assembly & Apparition
Part 6 - Valve Adjustment & Ignition
Part 7 - The Quest for Combustion
Part 8 - Homebrew Exhaust & Camera Drama!
Part 9 - Scooter Interrupted
Part 10 - Custom Parts & Finishing Up!
Part 11 - The First Ride!! (Finale)

Complete build of a C90 - While these are not CT90 video's the C90 Is a very close cousin and a lot of the information is very applicable to rebuilding a CT90.
Part 1 - Teardown
Part 2 - Painting
Part 3 - Wheels
Part 4 - Detail painting and Assembly
Part 5 - More Assembly
Part 6 - The Finale! - This is a very well done video



Wheel Related Video's
CT90 Rear Wheel Damper Check


These two videos are very good sources for how to lace up and true a wheel: Video 1, Video 2

Here is a video on how to coat your CT90 wheels with Plastic Dip

Charging System - This is a nice video link that discusses the part of the CT90 charging system that is active when you turn on the headlight and can be useful during trouble shooting.

Headlight Mod - This video link shows how to modify a stock CT90 headlight to accept a socket
that will allow you to use replaceable bulbs.

A nice simple video on checking your headlight on charging circuit.

Simple Turn Signal Wiring Diagram Video

This is a nice well done video on your horn and how to adjust and get an old horn working again

This video is an old Honda CT90 commercial that is great!

Basic description on how an automotive ignition system works

Spark Plug Related Video's
NGK Video on plug heat range
NGK Video on reading your plug to tell if your are running to rich or lean
Good video on how to read your plugs to tell if you are running to lean or rich

This is a good general video (not CT90 specific) or lacing/re-spoking a motorcycle wheel.

This is a good video explaining various methods to remove rust.

Misc. Video's
A home made CT90 Work Table that's can be very helpful
This is an old Honda CT90 commercial from the 1960's
This isn't a CT90, but it is a cool video on a very unique small Honda bike

Video of the manufacturing line at Honda for the new Super Cub

If you like fly fishing and CT90's (or 110's) this is the video for you

Postie Related and the Adventure Video's

Postie Road Trip - Melbourne to Uluru
Sydney to London on a Postie
Apex Outback Postie Bike Ride
Bright Blue Postie Bike Rides
Honda CT 110 Trail Ride - Rubicon and Blackwood Trails
Postie Bike Setup for Adventure
Postie Bike Chronicles

From Adventures Unknown
For The Adventure - The Trail 90 Mission!
I Hate Trail 90's


 Entertaining Video's
Ed March YouTube Video Index
Ed March Hitler video #2

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