Compression test query

**OzEo** · 18th May 2015, 07:38 PM

Hi All
another chainsaw question if I can;

I read that a normal compression tester gives a false reading on a small motor because the tube on the gauge adds a lot of volume relative to the volume of the pot, and so you need a specialised gauge with a tyre valve arrangement on the end of the tube. Then I went into my local saw/mower shop and was told there's no way to get an accurate measure of compression, and that they don't make compression testers for chainsaws.

Can anyone clear this up for me please?

Many thanks, Eo

**BobL** · 18th May 2015, 08:13 PM

That's bollocks

A decent compression testing kit will come with special small engine tube for chainsaws and lawn mover, or include and adapter that uses no tube at all.
Look here http://www.mityvac.com/user_manuals/05530.pdf

I have a tester that is called a "sten tester" and looks like this http://www.carid.com/actron/stem-com...pn-cp7821.html

Stem testers use narrow tubes (~5mm in diameter) which have a total volume of about 2cc so the error introduced when measuring a 50cc jug is 4% and only;y 2% on a 100cc saw. The compression meter itself is probably only good to 2% anyway.

**OzEo** · 18th May 2015, 08:29 PM

Thanks Bob- I though it sounded a bit strange. I got a low reading on my saw and was hoping it might be the gauge- and I suppose it could be because it's a cheap one. But the saw is old- '91, so most likely it's a bit worn out. Cuts OK though so no worries

Cheers, Eo

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