Compression for GS550

['79 550]

Can anyone tell me what the compression should be on a 1979 GS550E? I can not find the information in the manual.

Thanks.

[DaveDanger]

This may not apply exactly, but just for giggles I looked up this topic in my 81 GS850 GLX manual, and under chapter 3 (Periodic Maintenance, Lubrication, and Tuneup)... I found a paragraph that refers me to "Table 10" at the end of the chapter. "Table 10" is "Compression Specifications". It says "Standard: 128 - 171 psi, Service limit: 100 psi, Maximum difference between cylinders: 28 psi"

I tend to think that unless an engine has fairly recently been overhauled, they'll most often be around 100 to 120 psi. That is under the following conditions:

1. Disconnect the primary wire to the coils, (disable the spark ignition)
2. All plugs removed
3. Battery charged up
4. Engine cranked over the exact same number of times per cylinder check.
5. Throttle held wide open while performing the checks.

I personally feel that the difference between cylinders is much more important than the absolute pressure itself. As an engine ages, the compression is simply going to begin to fall off. It will at some point reach a pressure low enough that you'll begin to notice a drastic lack of power. If however you have one particular cylinder lose compression more so than the remainder, you'll begin to feel a vibration or roughness, almost as if a plug were fouled dead or a plug wire loose. That roughness will affect the well-being of your engine and its longevity much more than evenly low pressures. This is true of basically any type of multi-cylinder engine.

['79 550]

Thanks for the response. I am reading between 110-120, so the numbers are okay.

At the very least it shows that the engine is worth working on.

Thanks.

[Donut]

I've read bottom ranges from 100 to 125 psi were the lowest you'd like to see. My mechanic wont work on bikes unless psi is 125 or better. He adjusted the valves on my bike and psi jumped from 125 to 140-145.

This page learned me a bit

http://www.dansmc.com/compression_test.htm

I can double check my manual( I've got a 79550L) I'm pretty sure I've read close to the same in there.