Not a tractor mechanic, and I don't even know the years an 881 was made. I asume late 50's to mid 60's?
Anyways, you have to take compression readings with a small grain of salt as well as what so and so manual may say.
Firstly the method the test was done under. Was it done with all the plugs out? Was the throttle wide open? Did the engine turn the same number of revolutions at each cyl.?
Secondly what kind of guage was used? Was it a quality threaded into the spark plug type, or a cheapie hold on with one hand and operate the starter with the other? Also keep in mind that any guage is going to show some if not a large difference in reading bias from another guage, perhaps even of the same brand.
So to that end generally what we (I) look for with a compression reading is the difference between the highest reading and the lowest. And not necessarily an absolute pressure reading, because there are too many variables.
Lastly when taking compression reading for just gp (general principle) I always either take two readings at each cyl. or after removing the plugs crank the engine over a good number of times before starting the test because oil splash can throw off the reading between #1 and #4 by the time you get back there, ie. #1 starts out dry but #4's rings are partially sealed with oil after the cranking for the three cyl. tests before it.
Off the top I'd say your tractors piston rings and valves are in very reasonable shape. 130# to 140# for a mid 60's (?) small bore long stroke engine is probably what they tested out in the barn when the tractor was close to new.
Ahmmmmm, just a guess mind you.
