Compression on 8N ford

leroy9804@aol.com · May 9, 2016

I have a 1951 Ford 8N and I would like to know if the compressions are OK.
checked Dry: 120, 83, 105, 105.
Wet: 125, 105, 120, 100

These reading start with number 1 Cylinder back to 4.

Bruce (VA) · May 9, 2016

Looks like you have sticky rings on #2. Put
some ATF or MMO in there and let it sit
overnight. run it to operating temperature
and repeat the process. Might take 2 or 3
tries.
75 Tips

Dell (WA) · May 10, 2016

Leroy..........Ford spec; 90-psi min. (DRY) Most good runnin' N-engines about 110-psi. Brand new rebuilt N-engine about 125-psi. A 1-oz squirt of oil down the sparkie hole to evaluate the engine rings sealing will add about 20-psi to engine compression iff'n good. Iff'n BAD, compression will NOT INCREASE; usually a sign of BURNED exhaust valve. Sometimes could be stuck intake valve but that is really rare. Even in 1939, Ford recommended detergent oil. Modern multi-weight oil is even better. Me? I use Valvoline 20-50wt oil. I changed oil every 4000-mi in my 1969 BMW 2002 that I got at the factory in Munich. It now has 387K miles and is in semi-retirement. ........HTH, oily Dell

souNdguy · May 10, 2016

Isure would not rebuild it with those numbers. #2 has ring issues, but under dynamic pressure with a little oil sloshing.. it should run just up under the others.

Bruce (VA) · May 10, 2016

Minimum acceptable pressure is 90 lbs w/ the lowest pressure reading w/in 75% of the highest reading. Run the engine to operating temp, turn it off, 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.

That first reading on #2 will tell you if you have sticky rings or a bad valve.
75 Tips

leroy9804@aol.com · May 10, 2016

(quoted from post at 02:35:13 05/10/16) Looks like you have sticky rings on #2. Put
some ATF or MMO in there and let it sit
overnight. run it to operating temperature
and repeat the process. Might take 2 or 3
tries.
75 Tips

I thank all of you for the feed back it is very helpful.

leroy1142

leroy9804@aol.com · May 10, 2016

I thank all of you for the feed back it is very helpful.

leroy1142

leroy9804@aol.com · May 10, 2016

I thank all of you for the feed back it is very helpful.

leroy1142

leroy9804@aol.com · May 10, 2016

I thank all of you for the feed back it is very helpful.

leroy1142

Hobo,NC · May 10, 2016

You need to find the leakage,,, Google "cylinder leak down test"

http://www.hotrod.com/how-to/engine/116-0406-cylinder-leakdown-tester/

Compression on 8N ford

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