Checking engine compression | Kyle's Garage - Ep. 23 - Hagerty Media
With all the projects going in the garage, the last thing I needed was another. However, my boss, Jack Baruth, called my bluff after I reckoned I could fix up a tired-looking 1982 Honda Goldwing lurking on Craigslist. Now there’s one more machine in my already-full, reasonably-cluttered 2.5-car garage. The bike is running, but it sounds a bit rough, so to determine just what I have gotten myself into, I dove straight into a compression test.
A compression test paints a clearer picture of the interior of the engine without actually looking inside. Essentially, a the procedure measures how effective the piston rings and valves are doing their sealing jobs. This Goldwing’s flat-four has 79,000 miles on the clock, and even with proper maintenance could be pretty tired with that kind of usage. Between the grungy nature of the engine and signs of long-term storage, it would give me good peace of mind to know that time spent getting the engine running properly would not be wasted on a tired-out or already-broken engine.
The process is fairly straightforward. Get your hands on a quality compression tester that has the appropriate adapters for your engine; that means an adapter with the correct thread diameter and pitch to tighten down to the cylinder head without cross threading or stripping out the delicate threads. Remove all the spark plugs from the engine, thread the adapter into one of the cylinders, attach the gauge and get ready to crank the engine.
Use the starter to spin the engine while holding the throttle wide open. I typically rotate the engine 5-6 revolutions or until the needle of the compression gauge levels off, whichever comes first. Write down the gauge reading and repeat the process for each cylinder.
In a perfect world, all the numbers would be the same, but the world is not perfect. A commonly accepted variance between cylinders is 10 percent, and I often look for 100-120 psi readings to consider the cylinder to be in good condition. That is just a general rule of thumb, though, so consult your service manual for a more accurate range for your specific application.
This Goldwing came in a little under what I would like to see, yielding 85-90 psi on all four cylinders. I think the piston rings are a little stuck from improper storage, so I’ll first try a few heat cycles and some oil down the spark plug holes—hopefully the compression numbers will bump up. If I wanted to be even more thorough with my evaluation, I could use a leak-down tester, but with only $500 tied up in this project I am going to just trust the evidence I’ve seen so far indicating that the engine is not completely trashed inside.
Yes, it’s yet another project, but one that’s likely to be tucked off to the side for the winter and then prepped for a road trip this spring. I need to focus in a bit on some of my other projects that have been on the back burner for awhile. If you want to see my progress on those, be sure to subscribe to the Hagerty YouTube channel to never miss a video.