2 stroke compression

#1
How much compression should a good 2 stroke chain saw or weed eater engine show on compression gauge? What is the low acceptable reading for a good engine? How many pulls on starter to get reading? Thanks for info. Kettle
 

billr

wrench
Staff member
#2
Hmm, good question. My impression is that it would be about 10:1; that would give about 90 on first pull. Keep in mind, though, that the volume in the hose and such of a typical compression gage will be more significant with a small engine, like most two-strokes. It effectively increases the combustion chamber size and lowers the compression ratio, thus lowering the pressure you will read
 

alexandjojo

MAKE IT HAPPEN!
#3
I am told anything over 100psi. The unit has to pulled until highest reading. Usually about 4-5 pulls will make this accomplished. Also, do not use a compression tester for a car to check this. They are different.
 

nickb2

Wrench. I help when I can
#7
thx pat73. just put more oil in your weed eater, pull and ask ur wife to massage u. I sugest a good snap on guage, the rest is to you. 100 or 90 psi should do the trick if plug is pristine condition. Maybe need to check magneto if this applies to your model, a double folded matchbook carton gives about the same gap.
 
#8
Wondering why I never did a compression test on these oil burners, normally can tell by the force on the pull cord. When it gets easy, time to clean the piston rings and the reed valves. Seems like the spark plug has to be cleaned every two minutes.

Since I dropped from six to a third acre lot, just got a hundred foot extension cord and electric chain saw and weed eater. They work all the time I pull on the trigger. And as opposed to a two cycle, the more load you put on them the more torque you get. Son got a hundred foot retractable cord, I didn't get one of these yet. Must like hand winding it. Oh, and they are much quieter in operation.
 

nickb2

Wrench. I help when I can
#10
Sorry for bad espangol spelling, but I greatly disagree with Alejandro. A compression tester will always give a reading. 2 stroke or 4 stroke, even a 5 cyl in a cessna, PSI is PSI. Mazda had 5 stroke for a while, no diff . Just different specs. Just need proper adapter if spark plug is different thread. Most kits will have these, As not to be arrogant on this perticuler post, please disregarde that comment about compression testers for 2 strokes. If I am wrong, I will have learned something new. Hoping to get proved wrong on this. :thx
 

billr

wrench
Staff member
#11
I agree, a compression gauge should work in any kind of engine, 2-stroke or 4-stroke. The only important difference would be in range, the typical 0-300 psi gauge for spark-ignition engines isn't going read high enough or last long testing a diesel...