Low compression on piaggio nrg engine

Are you sure it's actually a plug?
Are you getting oil on the plug?
The plug may be firing but you may be losing compression which gives the symptoms of a misfire. As you've changed the plug, lead and coil this points to to a problem elsewhere.

Your first course of action should be to get a mobile mechanic carry out a diagnostic check for you.

To put your mind at rest, do a 2nd compression test using a light oil squirted into the bores:

Doing a Compression Test
Warm the engine. Remove all the spark plugs.
Get a pencil and piece of paper to note down the readings.
Put the compression tester into the No1 cylinder and crank the engine for 10 seconds.
Note down the compression reading.
Repeat process for all cylinders.

Here's an illustration of what you may expect on a 4 cylinder engine:
Cylinder 1 2 3 4
psi 125 122 120 124

125 is the uppermost figure for that engine. Here, this engine is fine. There's a slight variation in psi figures, but that's perfectly normal.

Here's the same engine:
Cylinder 1 2 3 4
psi 110 112 114 112

The psi reading is down. However, as all the figures are pretty much equal it doesn't indicate head /gasket problems. It may point towards worn pistons or burnt valves.

Now consider these psi readings:
Cylinder 1 2 3 4
psi 125 84 86 124

There's more than a 10% drop - a difference - between cylinder 1 and 2, and cylinders 3 and 4.
The compression readings for cylinders 2 and 3 is down; low. There's something clearly wrong.

It suggests that there is a defective head gasket between cylinders 2 and 3 or a crack in the cylinder head. The rising piston compresses the gases which escape into the adjoining cylinder via the defective gasket or cracked head.

However, it could also mean that there is a problem with the valves (burnt/not seating properly) or perhaps piston / ring problems.

A burnt valve - it's usually the exhaust valve as they bear the brunt of the combustion - can cause a reduction in engine power simply because the combustion process isn't occurring properly. Compressed air/fuel gets squeezed out of that cylinder because of the damaged valve . There even may be a misfire - a surge as the car runs.

Worn or broken piston rings allow compressed gases to leak past into the crankcase. A compressed crankcase can force oil out of the dipstick tube. The pressure in the crankcase will leak to atmosphere anywhere it can find an outlet.

The 2nd Compression Test
The second compression test is known as a 'wet test'. The first compression test was the dry test because no oil was added to the bores. The second 'wet' test can give an indication of whether it is the rings or valves at fault (though bear in mind rings and valves do not cause overheating or water in the coolant symptoms).

Spray a liberal amount of light penetrating oil into each cylinder - aim for the cylinder walls, not the centre of the piston. You want the oil to run down the cylinder wall and around the piston to form a seal.

Place a rag over each spark plug hole and spin the engine to eject the surplus oil.

Then carry out a full compression test noting down the results.

Here's the previous results with the 2nd compression readings added:
Cylinder 1 2 3 4
psi 125 84 86 124
Wet 128 112 110 126

The readings have increased. This because the oil sprayed into the bores has formed a temporary seal around the piston, thereby enabling the compression to be raised. It also indicates that the bores/rings are worn on cylinder 2 and 3 - the 'oil seal' has increased the readings but is still low in comparison with cylinders 1 and 2.

This could also indicate that in addition to worn rings there is also burnt valves. Oil cannot form a seal around a valve. A worn or split valve will cause a low compression reading and misfiring symptoms.
Compressions readings should be taken in conjunction with other symptoms. It will help you identify the problem:

Low compression readings between two adjoining cylinders point towards a head gasket/head fault if your vehicle has shown signs of coolant loss, coolant in the oil system - mayonnaise, overheating, rough running and lack of power.

If those symptoms are not present it points towards burnt valves/piston rings. A worn engine may be difficult to start and pressurise the crankcase, but it doesn't cause overheating problems.

The valves allow air and gasoline to enter the combustion chamber, to be ignited by the spark plug, and to allow the burned gases to be exhausted from the chamber.

When the valves do not work, a mechanic needs to remove parts of the engine, to see what's wrong, and to make repairs.
It could cost you $500 to $1000 US dollars.

Maybe, time to "junk" the TEN-YEAR-OLD vehicle, and buy another one ???

you have a bad head gasket or a crack in the block or a bad valve seal

Checking the compression amounts to using a pressure measuring device either held and sealed by rubber gasket against the cylinder spark plug orfice, or could be threaded the same as your specific plug is. It is a measure of the compression pressure within your cylinder when it is on the compression stroke....meaning all valves closed and the cylinder going up toward the cylinder head resulting in compression. Reasons for low compression are worn piston rings, burnt or mis-adjusted valves, or could be a cracked cylinder wall, blown head gasket or a hole in a piston. Gasoline engines run much lower compression than diesels. For your compression pressure norm, Google in your engine or buy a service manual and it will have the specs in pounds per Sq. in.or PSI. Good Luck

You may have something keeping the reed assembly from closing. This is a check valve that keeps the gas going in one direction... into the engine as the piston goes up and down. It's located just below the carburetor. Maybe a piece of gasket material worked its way in there. Make sure you have a good solid spark and your plug is clean and properly gapped. Recheck your gasket replacement job as you check the reed assembly. Compression, gas, good spark and reed working... the engine will at least sputter.

You did not indicate whether or not you have compression now that you have changed out the gaskets and piston rings. If not, it seems to me that the problem could be a) cracked head or block, b) bad valve(s) or even c) a warped head.

Sorry for the bad news (if I am right).

Low compression is cause by a number of things. First a blown head gasket or loose head studs second burnt or bent valves or loose valve seat inserts. thirdly a hole in the top of the pistons from detonation or incorrect timing. Next broken rings and a scored bore will lower compression. Lastly an over heated engine will soften the rings material and they will no longer contact the bore to seal off the pistons. Blocked air filter will be a cause and carrying out the compression test with out holding the throttle wide open will also cause low compression readings

There can be several causes for low compression.
Chck the obvious first. the spark plugs must be checked that they are all in good condition. not burnt, the gap must be good( for your engine).Check the wires and coil so that good spark is obtained. Blue spark , not weak yellow spark. After everything is good. Check the cylinders to see if they have compression. To test the cylinders do the procedures shown below.

If the cylinder shows little leakdown or holds good compression when a little oil is squirted into the cylinder (wet compression test), it would tell you that the engine needs new valve guide seals and/or guide work. Most late model import engines have positive valve guide seals. Often, the guides are fine, but the seals are worn or cracked. The seals can be replaced on some engines without too much effort and without having to remove the head.

compression test will help you determine if the oil is getting past the valve guides or the rings. If the cylinder shows little leakdown or holds good compression when a little oil is squirted into the cylinder (wet compression test), it would tell you that the engine needs new valve guide seals and/or guide work. Most late model import engines have positive valve guide seals. Often, the guides are fine, but the seals are worn or cracked. The seals can be replaced on some engines without too much effort and without having to remove the head.

finally if the rings on one or more of the pistons can caus compression leak. It must be located and fixed.

Whoa whoa ... You've said that the car takes 7 quarts of oil. That's 14 pints. Depending on which engine variant is fitted, engine oil capacity is either:

• 5.75 litres + 0.4 litre if the oil cooler is drained
• Turbo - 3.85 litres + 0.6 litre if the oil cooler is drained
• These figures are for a UK 3 litre version of the 960

If you've filled the car with 7 quarts of engine oil that's almost twice as much oil as should be in the engine. Did you mean pints when you wrote quarts?

If you've filled it with 7 quarts it's overfull. Way too full. Check your oil dipstick - remove it, wipe it clean and then dip the oil level. At the bottom of the dipstick there is a flattened wider part. The oil level should not be below the bottom of this marker, and nor should it be above it. If the oil level is way above the flattened marker bar - you're overfull and will have to drain some oil out of the engine. An overfilled engine will try and blow oil out from wherever it can as the oil system will over-pressurised.

Ok .. so there's no problem with the engine compression. The crankcase isn't overfilled with oil (the crankcase is known as the oil sump in the UK). There's no oil fouling of the plugs and the car isn't burning oil, just leaking it. There's no misfires or running

If the engine isn't overfilled with oil there may be a problem with a broken/sticking piston ring or piston/cylinder. That high oil loss you mention seems severe. A problem with a piston/ring/cylinder can allow the compression to leak past the rings/piston into the engine oil sump and pressurise it. Under pressure, the oil will try and leak to atmosphere from anywhere it can.

A blue smoky exhaust is also an indication of piston/ring problems. A quick check is to start the car. If there's a cloud of blue smoke at start up which clears quickly, it's like to be worn valve guides. If, when driving the car with a warm engine there's blue smoke on acceleration - it points to a problem with rings/piston.

A quick check is to remove the spark plugs. Is there engine oil on one or more of them? An oiled up plug indicates that the engine oil is finding its way up past the rings/piston - and if oil can find its way up to a spark plug, then exhaust gasses/compressed fuel/air can find its way into the engine oil sump and pressurise it.

Another quick check is to start the engine and remove the oil dipstick. If fumes are 'chugging' out of the tube or oil is spitting out, that's another sure-fire sign that the oil sump is becoming pressurised due to a piston ring/piston/cylinder problem.

If you possess or can borrow an engine compression tester there is a further test you can do yourself to confirm whether or not there are piston/ring problems. Basically, a compression tester is just a gauge that screws into the cylinder head in place of the spark plug.

Warm the engine for 5 minutes so that the pistons expand fully in the bores.
Remove the spark plugs
Fit the compression tester into No1 cylinder and crank the engine for 10 seconds. Make a note of the compression reading on the gauge.
Do the same for each cylinder.

Here's an example of what you might find (the figures are for example only)
Cylinder Reading
1 115
2 120
3 118
4 95
5 96
6 117

Figures vary, but there should not be more than a 10% difference between the readings.
In the example above you can see that cylinders 4 and 5 have readings that are well below those of the other cylinders. This is indicating problems within those two cylinders. The lower compression could be due to a head/gasket fault or piston ring/piston problem. A split or worn exhaust valve in the head may cause low compression, a misfire and uneven running but it won't cause the engine oil sump/crankcase to pressurise. Now, some fine tuning to locate the exact problem:

Put a liberal squirt of oil into each cylinder - something like Redex, WD40 or engine oil.Put a cloth over each spark plug hole and spin the engine to get rid of the excess oil. The idea is that the oil you have squirted into the piston bores will form a 'seal' around the outside of the piston/rings.

Do the compression tests again and note the readings. If the readings go up significantly it indicates that the rings/pistons/bore has a problem. Readings that go up significantly are due to the oil forming a seal around the piston which raises the compression whilst testing. Here's an example:Cylinder Reading on 1st test 2nd test
1 115 118
2 120 121
3 118 120
4 95 110 Significant rise - more than 10%
5 96 98
6 117 119

Ok .. all this means is that cylinder 4 has compression problems due to the rings/piston/bore. The 2nd compression reading (with the oil squirted in) is higher simply because the oil formed a seal. Cylinder number 5 still has a low reading which didn't increase significantly on the 2nd 'wet' (when oil is added) test. This suggests that the problem is an exhaust valve/head gasket/head problem.

If there had been no significant increase in the reading on number 4 cylinder, this would suggest valve/gasket head problem. Low readings on adjoining cylinders (and which don't increase with the 2nd compression 'wet' oil test) would indicate a faulty head gasket between those two cylinders.

I'll continue this article ... ran out of word space