Outdoor Power Equipment (Lawn Mowers, Snow Blowers, Chain Saws and more) Discussions

Folks--I was reading on another forum and the topic of "compressioin reading for the engine to be healthy) was discussed.  They had an engine that would not start and made a statement it had a compression reading of 60 to 65 pounds.   All the other 2 items---spark and gas were present but it would not start.  That sounds too low to me.  What do you that are regularly working on engines have to say about this?--Will

Will,
So many of these small engines use decompression valve....that its impossible too get an accurate and sensable reading.
Very few manufactures will even publish compression pressures.
I work exclusivly on single cylinder engines.....I imagine twin cylinders might have some use for testing...just too compare between 2 cylinders.
Leak testing cylinders is much more relevent too me.....you can spot a bad valve in an instant.
Visually inspecting pistons and cylinders is what I do as often as I can.
I will still use my compression tester on 2-cycle engines, ones that I have specs for (Homelite) and some others that I know about what they shoud read. (Like poulon.)
I used too test all motorcycle engines....They didnt have decompression valves, the manufactures all published exceptable readings, and most were multi-cylinder.
If guys are using compression testers...and they find that they work....more power too them. I just find that my tester gets used less and less every year..

Will - I actually use one any time I have a problem engine to repair, as I want to know exactly what I'm getting into before I start replacing ANY other parts. You can replace a coil or rebuild a carb, but it still won't run for darned if there is low or no compression. Most engines do have a compression release & I have found that ANY of them having less than 30 psi compression have "internal" problems to correct before the engine will run. Just my own experience. Buttlint does this for a living & knows his stuff. I do this part time as a hobby & have MUCH less experience, so I have come to rely on my compression gauge as a vital diagnostic tool...

Marty

I have an old Tecumseh H50 and was told the normal range was 60-90 psi. If  you're used to automotive readings that sounds low, but these are low compression  engines by contrast.  Mine is old and reads around 65. It's really only useful compared to another of the same type, or over time.

The HMSK80 I have has compression release so as mentioned above it's not meaningful.

Thanks to all of you for your posts.   I was not taking into consideration the compression release system.  Will talk to you all by posting later--your friend--Will

I'm told if you really want to get compression an engine with mechanical compression release, rotate it backwards. I've not tried this myself.

Garandman wrote:
G.
Only one problem with that.....How do you rotate an engine backwards?
Pull and electric starters only turn the engine one way.
I am sure that there are ways it can done.....but I also think setting that up would take more time than it's worth.