There are lots of firsts in a parent’s life. Baby’s first steps, first words and first teeth are so commonplace that mementos are commercially available. As the father of boy-girl twins, I’ve written several times in the past about many of my kids’ firsts in our motorcycling world. From first rides to first races and first road rides together on separate bikes, they’re all memorable days in our family. A chain of random occurrences recently led to another motorcycling father-and-son first in our family that encompassed three generations.

A few years ago my dad came across a trio of Honda CT90’s, a.k.a. Trail 90’s. We bought them as a package deal. He kept his for a while and sold it; mine was too good to sell, with only 1,300 miles on the clock, and it would be generous to describe the third as a rolling basket. Its engine was apart when we got it and the reason for the teardown was unknown. Our seller got it that way and that is the worst kind of rolling basket.

The bike languished in storage a few years with the head, cylinder and carb off and the timing chain and connecting rod hanging out of the case for all to see. This is the same bike I wrote about that surprised me with a snake when I rolled it out of storage to try and sell it. It turns out nobody really wanted a tore-up Trail 90, not even for 75 bucks, so now it was on my mind and in my way.

My son was scheduled to be home a few weeks between college graduation and his forever job, so after looking over the bucket of parts and the ones still bolted on we hatched a plan to make this his first rebuild of the engine and make it run again. A quick inventory showed we would need a piston, rings, wrist pin, circlips and new gaskets for sure. A few quick measurements revealed the piston was the original size and for our purposes, we would do a light hone and replace it with another original-sized piston and rings as opposed to boring the cylinder and putting in an oversized piston. With a click of the Buy it Now option on eBay, Baby’s First Rebuild was about to begin.

Naturally, we couldn’t find a single source vendor who had all the hard parts we needed in the right size, so the parts arrived a few days apart. That gave us time to remove the engine for convenience sake, clean it up, stuff rags in the openings and brush up on the rebuild process with the book and on YouTube. There are multiple videos covering the rebuilding of a CT90 and they all make it look just a bit easier than it really was.

When the parts arrived we scurried to the garage and were confronted with the first conundrum: a three-piece oil ring. I’d never encountered one of these in person before, having used mostly vintage one-piece rings in the past, but we worked through it. After checking the gaps on the other rings we were ready to connect the piston, con rod and wrist pin and it went pretty well except we forgot to install the circlips that hold the wrist pin in place—one of several mistakes we made. We took it apart, popped the clips in—no small task—and re-assembled.

There are several fiddly parts on these small overhead cam engines, mostly relating to the timing chain and camshaft. We inadvertently assembled the engine 180 degrees out of time, so we took it partially apart again. This time the engine was in the bike, but we got everything lined up and checked the points timing with a homemade light. After setting the valves we were ready for oil and gasoline, the latter of which immediately coated everything in sight due to a rodent having made the fuel line a midnight snack at some point in the past. Once that was replaced, we stole the battery out of my 90 and began the bump-start boogie—pushing the bike to the top of the slight grade outside our garage and taking turns being pushed. After a few trips, it fired and ran well enough for my son to pull away from me on the bike! A list of additional needs for the bike is accumulating, but we’ve reached the point where the whole is worth more than the sum of its parts and we each have a “remember the time we rebuilt that engine” story to last a lifetime as well as having a pair of running CT90’s we can use.

Understanding how a motorcycle engine works gives you a better understanding of how a bike works and should make you a better rider. Recognizing that there is a lot going on when you twist the grip or squeeze a lever raises your awareness. Spending time with your kids on projects like these allows each generation to teach and to learn while helping preserve a piece of motorcycling history.


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