Over the last year talked to a number of dealers, perused the net and in general the low number for a healthy engine is all over the place, 50, 60, 70, and 90. This is the first time I’ve seen 100 as a motor to stay away from.
Friiy said last year the tests were not so reliable and later explained about compression release which at the time was new to me. I’ve since found there are 4-5 basic mechanisms for compression release and not all have the same spec for psi release. For example there are many late 90’s early 2000’s that release at 45. No matter the amount of pulling or time on the electric start button the needle will no go past 45. The engines were fine and perfectly robust. With one of them I came close to beating my nemesis, a feared Honda track.
Some motors get a low compression test reading but do fine on a leakdown. If an engine gets a high reading then it’s probably ok. But a low reading does not necessarily KO the engine. It could be the compression release on that engine won’t allow a higher reading.
I’ve had a few motors that tossed fine with low compression. Most of the older machines around in good condition like Ariens and Toro machines have worn motors but still good for many years of use. Some still run, don’t smoke but can barely toss. One older Toro I had with a compression test of 90 belched oil when slightly loaded, 3-4 inches of snow.
For a while I was taking compression readings on every engine I got in and keeping track of them. It was just about impossible to count on any reading except high readings. During the winter with snow around you can take a reading then go toss with the machine to see how it does. During the rest of the year it’s impossible to put a load on an engine.
