8n rings seating

I have a 1951 8n that has a rebuilt engine. New pistons, rings,
sleeves, valves ( valves were lapped) , bearings, etc. the problem is
I have low compression (~85 per each cylinder). And the engine runs
a little rough. Will hesitate on take off. I have checked all the
electrical (at least to my knowledge) and can find no reason for the
rough running except the low compression maybe. I have spark to all
plugs. Timing is correct. Can mark is lined up with crank mark.
Wires, coil etc are good. It does not burn oil and I see no smoke
from tailpipe and no exhaust gases from oil breather. I'm at my wits
end. Could it be that the rings are not seating ?? What could I do to
get them to seat if this is possibly the problem. Thanks
 
(quoted from post at 15:45:27 10/20/18) I have a 1951 8n that has a rebuilt engine. New pistons, rings,
sleeves, valves ( valves were lapped) , bearings, etc. the problem is
I have low compression (~85 per each cylinder). And the engine runs
a little rough. Will hesitate on take off. I have checked all the
electrical (at least to my knowledge) and can find no reason for the
rough running except the low compression maybe. I have spark to all
plugs. Timing is correct. Can mark is lined up with crank mark.
Wires, coil etc are good. It does not burn oil and I see no smoke
from tailpipe and no exhaust gases from oil breather. I'm at my wits
end. Could it be that the rings are not seating ?? What could I do to
get them to seat if this is possibly the problem. Thanks

Can't say on the poor running issue but 85# compression on a rebuilt engine is horrible. Something is wrong there and I doubt it is ring seating.....

TOH
 
We need more dots. As we're unsure of how you obtained compression readings, please re-do the test following the steps below.

How confident are you on the accuracy of your compression gauge?

[b:64878c6007]Compression Test:[/b:64878c6007] Minimum acceptable pressure is 90 lbs. (dry) with the lowest reading within 75% of the highest.
1. Bring the engine to operating temp and remove all 4 plugs.
2. Disconnect the air cleaner and fully open choke and throttle.
3. Crank it at least 5 compression strokes or until the gauge stops climbing and record the final reading.
4. Complete the test on remaining cylinders.
5. Now add a tablespoon of oil to the cylinder just prior to sampling and repeat the process.

Interpreting results of adding oil: +10psi increase good engine; +20psi increase normal engine; +30psi increase worn engine. Stated another way; an increase in wet readings rules out valves and suggests ring sealing problems - Either the rings are stuck or the engine is worn out and needs an overhaul. No increase means a burned or stuck exhaust valve or a failing head gasket. If numbers don't improve, perform a cylinder leakage test to find out where you are losing compression. Remember, no improvement after adding oil, put the gauge away, move on to a cylinder leakage test.
 

O MY GOD the dreaded leak down test... Why anyone would want to pin point ZACKLY were the leakage is at before tearing it down is beyond me. My thoughts with no more info billy-bob fudged on the valves billy-bob is suffering from his lack of understanding how important valve sealing izz...

Leak down test waist 20 min of your time it wont lie to ya...



https://www.hotrod.com/articles/cylinder-leakdown-tester/

Anything below 20% things are going down hill fast...
 
(quoted from post at 10:43:29 10/21/18)
O MY GOD the dreaded leak down test... Why anyone would want to pin point ZACKLY were the leakage is at before tearing it down is beyond me. My thoughts with no more info billy-bob fudged on the valves billy-bob is suffering from his lack of understanding how important valve sealing izz...

Leak down test waist 20 min of your time it wont lie to ya...



https://www.hotrod.com/articles/cylinder-leakdown-tester/

Anything below 20% things are going down hill fast...

I'm with you on Billy Bob and the valves. A major engine overhaul should always include a full valve job with freshly machined seats and new or machine reground valves. Lapping old valves does not take the place of a real valve job. It won't fix out of round, non-concentric, or eroded seat angle conditions - it just makes them worse.

A leak down test is clearly in order. That said here is a thought from your article that jumped out at me. We are talking about low compression on a newly overhauled engine and it's why I mentioned improper (e.g. upside down) ring installation.

[i:18ed47bb00]Keep in mind that [b:18ed47bb00]cylinder pressure is used to help seal the rings to the cylinder bore[/b:18ed47bb00],...[/i:18ed47bb00]

Upside down compression rings can't use cylinder pressure to help them seal. The result is loss of compression from blow by. If the leak down test points to rings that is something to check.

TOH
 

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