The first start

The first start attempt after rebuilding an engine is always a bit anxiety-inducing. On the XR500 it came with an extra job: setting the cam chain with the engine running, on a head I'd rebuilt with a new cam gear and cam chain.

Every bolt checked, still a mystery

Even after meticulously checking over every bolt and part, putting in the proper fluids and checking tolerances, it's still a bit of a mystery what happens when the bike is kicked over — and even more so how it will behave once it fires up.

The four-stroke unknown: the cam chain

I've mostly worked on two-stroke engines. A four-stroke adds an unknown and challenging element that two-strokes lack: the cam and cam chain.

I point out the cam chain specifically because, unlike the valves, which are adjusted and set before the engine runs, some four-stroke engines call for the cam chain to be set while the engine is running. The XR500 is one of them — the adjustment takes place after it fires up.

So along with the usual first-start jitters, I had the cam chain procedure to deal with. I'd never done it on this motorcycle, and the head rebuild included a new cam gear and cam chain.

The process says to back out the adjustment screw — but not too far. Too far allows too much slack, and the chain can come loose or even come off, and do considerable damage to the engine internals.

Back out the adjuster too far, and the chain can come off and do considerable damage to the engine internals.

An afternoon of kicking

I had a very difficult time starting this motorcycle, and I tried unsuccessfully for the better part of an afternoon. There's a specific startup strategy for an engine like this one, and I wasn't yet versed in it.

A custom decompression cable

I had to make a custom decompression cable, since the originals are quite difficult to source now.

I bought a decompression cable for a different model Honda. It was way too long, so I cut the cable to length, looped it around a bolt, and locked the loop with a cable lock. To adjust it, I'd loosen the cable lock and pull the cable shorter.

The decompression lever opens a valve a little, letting some compression out so the engine is easier to kick through. I adjusted the cable a few times, and at one point thought I was too light to get the engine to turn over.

The technique

That evening I watched a number of YouTube videos and realized there was a way to prime the engine and get the piston to top dead center before giving it a healthy kick.

It sounds like a lot of extra, specific steps, but it's the way to go for starting up a big-bore four-stroke.

Too weak a kick won't generate spark. Compression, fuel and spark all have to line up at once for the engine to start.

Too weak a kick won't generate spark.

Signs of life

The next day, with the research done and the technique down, the engine started showing signs of life.

Thankfully, when it fired up, the carb was set well enough that the revs didn't run away, and I had all the wrenches ready for the cam chain adjustment.

Setting the cam chain

I backed out the adjustment screw, let the bike run a minute, then retightened it.

I didn't notice any change in sound — but the bike runs well and sounds healthy.

The engine was smooth, with no extra hard knocking. The balancer gear was perfectly set.