2N Compression Test

[Randy K. Crump]

I got my 2N to turn over. Now I need to check the compression to see if it needs to be overhauled. What is acceptable compression? Should all of the plugs be removed as I check the compression in each cylinder? By checking the compression, will it tell me if the head or block is cracked? Will it tell me if the head gasket is ok?

 

[Bruce (VA)]

Minimum acceptable pressure is 90 lbs w/ the lowest pressure reading w/in 75% of the highest reading. Remove all 4 plugs, remove the breather hose & make sure the choke and throttle are both open. Crank it at least 5 compression strokes or until the gauge stops moving. Write down the first compression reading (that is the valves seating) then write down the reading after 5 strokes or when it stops increasing. You should have two numbers for each cylinder. Then, add a tablespoon of oil to each cylinder & repeat the process, but you only need the final reading for each cylinder. Write down the results & post back for help figuring out what it all means.

" By checking the compression, will it tell me if the head or block is cracked? Will it tell me if the head gasket is ok?"

Sometimes, but a leak down test will tell you for sure.
75 Tips

 

[old]

My question would be why do you want to check compression?? Does it run or have you not tried to get it to run etc.

 

[Randy K. Crump]

It has been in storage in a barn for over 20 years. I have not tried to start it yet. I need to drain the gas tank, probably install a carb kit. The water pump will not turn and the radiator is very green at the bottom.

 

[Randy K. Crump]

Do I need to do the second compression test with oil since I placed MM oil on top of the cylinders when I was working to get it to turn over?

 

[Bruce (VA)]

Yes. That oil is long gone by now. Besides, it's to light weight anyway.

 

[old]

Ok so then before a compression test you need to d oa ATF treatment so as to make sure the rings and cylinder walls are covered with oil and the rings have been freed up or you stand a good chance of having low compression and maybe even broken rings and scored cylinder walls