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Minimum compression for a Stihl 2 cycle

#1

PTmowerMech

PTmowerMech

Stihl chainsaws and (hand held) leaf blowers, I was told that 100lb is the minimum. Just wanna get a 2nd opinion. I have a couple of blowers that are about 70 to 80lbs. But don't wanna put any money into them if there's not enough compression.


#2

primerbulb120

primerbulb120

Read Bert's post on this thread: https://www.lawnmowerforum.com/showthread.php/40120-ECHO-PB-265L-Compression-Check

Lots of good information there.


#3

B

bertsmobile1

the actual numbers will vary from one tool to another
Getting accurate numbers without special tools is quite difficult because of the small volumes.
The end of the tester must protrude exact the same volume into the cylinder as the spark plug or the reading will be wrong.

my compression tester only gets used as a data gathering tool so I can plot it's reduction over time thus tell customers that a tool is on it's way out.

If a two stroke will not fire with a shot of starting fluid down the plug hole or through the carb and the timing is correct then it gets tossed into the parts bin.
The minimum amount of compression required to ignite the charge is fairly well fixed and is basically a property of the fuel being used and the Oxygen content of the air it is mixed with.

It is a lot lower than most would think.

If you can get them to fire then you can get them to work . the only thing that will change is the effiency of the tool.
A leak down test and a crankcase pressure / vacuum test will be a lot more useful.

Having said that 70 is getting very low


#4

PTmowerMech

PTmowerMech

bertsmobile1 said:
the actual numbers will vary from one tool to another
Getting accurate numbers without special tools is quite difficult because of the small volumes.
The end of the tester must protrude exact the same volume into the cylinder as the spark plug or the reading will be wrong.

my compression tester only gets used as a data gathering tool so I can plot it's reduction over time thus tell customers that a tool is on it's way out.

If a two stroke will not fire with a shot of starting fluid down the plug hole or through the carb and the timing is correct then it gets tossed into the parts bin.
The minimum amount of compression required to ignite the charge is fairly well fixed and is basically a property of the fuel being used and the Oxygen content of the air it is mixed with.

It is a lot lower than most would think.

If you can get them to fire then you can get them to work . the only thing that will change is the effiency of the tool.
A leak down test and a crankcase pressure / vacuum test will be a lot more useful.

Having said that 70 is getting very low
Click to expand...

I know my compression tester isn't exact. My any stretch. Like you, if I get a low reading, say 80-ish, I usually don't go any farther.
I had a weed eater brand leaf blower that would get 100 easy. But run it for 10 minutes and it would lose enough that it would die and wouldn't run again until it cooled off.

Do you use your compression tester as a leak down test also?


#5

B

bertsmobile1

No
I use one I made following the instruction on You tube.
It worked so well I made a couple more with different threads to go directly into different plug holes.
You have the luxury of HF but down here they are only available from pro tool suppliers at pro tool prices.
For hand helds it is just the pressure / vacuum tester .
I inherited a bulb type tester and since I have learned the value of doing this properly have invested in a proper vacuum pump ( Brake Bleeder ) and pressure tester.
When the drought hit & all I was doing was chain saws & line trimmer I upgraded to a Mightyvac but made the mistake of going for the cheapie plastic one which gave me no end of trouble so a metal one is on the wish list.
Down here they are only available from a single distributor who charges 4 times the USA retail price , dollar prices adjusted and I can not justify $ 400 right now for fixing things that I effectivly make a loss on.


#6

R

Romore

I seldom use a compression guage on two strokes for the reasons Bert mentions, I pop the muffler off and look at the piston and cylinder wall. Unless the machine is very old like my 1952 McCulloch chain saw, a two stroke seldom wears out unless air filter maintenance has been neglected.


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