The fixing of objects and systems can be therapeutic, but only if the repair perform is the one that was needed. Spend a day “fixing” something just to have to take it apart again and you will understand the importance of good diagnostic skills. Some diagnostic skills come from experience, but with the proper approach just about anyone can be success in finding the problem they are having the first time. Here are my four tips to diagnosis your broken stuff.
Start with the obvious
Before you go straight to the toolbox to begin ripping parts off, slow down and look around. The crankshaft on my Honda XR250R was not able to make a full rotation, so I started with looking for anything obvious. Think a bulge in the case, oil level being low or speckled with metal particles. This first check should involve no tools at all other than your eyes.
Do what’s easy
Now the tools come out, but don’t get carried away right off the bat. Inspection covers are named the way they are for a reason, so use them. On automotive engines, easy items to pull like the valve covers and throttle body or carburetor can give you a good glimpse into the innards with minimal hardware removed. This is handy in two ways: You don’t have as much work to do just to look around, and there is less likelihood of breaking a bolt or otherwise going from bad to worse.
Look where you can, to see what you can’t
This sounds little funny, but the concept is simple. By understanding the systems you are inspecting you are able to look at the function of one parts and gain insight into the condition of another. In the case of this XR250, I suspected the cam chain had broken and was wedging against the crank as it rotated, however by looking at the rocker arms while rotating the crank I could see they were moving and thus the cam chain was intact.
Take a methodical approach
Think of how each system you are looking at works and how various breaks or failures in the system would affect function. One quick test or look can then tell you a lot of information if you approach the system with a strong understanding of how each part functions and interacts with the others.
Unfortunately, the diagnosis of this Honda was not good. One of the intake valves broke and wedged itself into the crown of the piston. No simple fix here. Saving the cylinder head will likely require some serious repair, and if it gets that repair you’ll probably see how it’s done on a later episode of Kyle’s Garage.