Looking for a "How to compression test"

Hello everyone,

I'm trying to figure out exactly how i can do a compression test step by step. Been having a large amount of white smoke due to oil burning i think. So i want to make sure everything is fine with the motor. I am also new to this site and i am slightly new to the terminology of the motors and such. Bought a XJ 650 about a month back and have been have small problems with it since. Who doesn't with a new purchase of an old bike? I've been reading up on the conditions of the smoke why/how it happens. So i've basically pinned it down to the cyclinders. Yet to take the bike for a long ride to see if the smoke would wear off. Would love some feedback.

Thanks

 

Well - this one's pretty easy - this is directly from the service manual:

Compression Pressure Measurement
Insufficient compression pressure will result in performance loss and may indicate leaking valves or worn or damaged piston rings.
Procedure:
1. Make sure the valve clearance is correct.
2. Remove the headlight fuse from the fuse box.
3. Warm up the engine 2~3 minutes.
Stop the engine.
4. Remove all the spark plugs.
5. Install a compression check gauge.
6. Turn over the engine with the electric starter (make sure the battery is fully charged) with the throttle wide open until the pressure indicated on the gauge does not increase further.

Compression pressure (at sea level):
Standard ....... 11 kg/cm² (156 psi)
Minimum ....... 9 kg/cm² (128 psi)
Maximum ....... 12 kg/cm² (171 psi)

WARNING:
When cranking the engine, ground the removal spark plug wires to prevent sparking.

7. If the pressure is too low, squirt a few drops of oil into the cylinder being measures. Measure compression again. If there is a higher reading than before (without oil), the piston rings may be worn or damaged. If the pressure remains the same after measuring with the oil, either or both the rings and valves may be the cause.
8. Check each cylinder. Compression pressure should not vary more than specified value from one cylinder to any other cylinder.

Difference in gauge reading:
Less than 1 kg/cm² (14 psi)

 

How should i be manually starting the engine without the spark plugs installed? Do i manually start the engine from the left hand side panel?

 

You are not trying to start the engine. You are turning the engine over with the start button to get your readings. You want the engine to turn as easy aas possible when you do this test. Thats why the plugs are out and the throttle wide open to get as much air in the engine as possible.

MN

 

Pay special attention to the ground the plug wires - You can experience TCI damage if you don't. Alternately (and easier) you can unplug the TCI.

 

Heed this warning!!! You most likely will fry your TCI if you don't! An alternative is to disconnect the TCI.

 

The TCI Would be? New to the lingo sorry.

 

You strive to get the most accurate results doing a Compression Test.

Fully charged battery.
Remove Spark Plugs
Disconnect the Igniter Box

Twist the Throttle Grip to Wide Open Throttles and tape the Throttles to remain Wide Open during the Testing.
WIDE OPEN THROTTLES!

Connect the Guage
Turn On the Ignition
Bike in Neutral
Run Starter Motor until the Guage shows Maximum Pressure.
Record Pressure shown.

In the case that you find a Cylinder(s) with Low Pressure.
Retest after adding 1 Tablespoon of Motor Oil to the Cylinder.
Compare results.

Post results for remarks and further advice.

 

The TCI is your ignition module. It's about 3 inches square with two plug-in connectors on one side, and a label that says something like "TDI 14-something something;" mine has "4U8-whatever" on it, yours would have your bike's prefix. On the 550s it's under the seat right behind the gas tank; I don't know where they put it on your bike.

You need to unplug it because with the spark plugs ungrounded, it has no place to fire the spark and it will cook itself.

 

Thanks everyone for all the information. I have the numbers right here to show you.

Left front cylinder - 140
left mid cylinder - 150
right mid cylinder - 145
right front cylinder - 140

These are the numbers without oil. Did 2 test to make sure everything was right.

 

Great info as I am also working on this.

 

JCT88 those are decent numbers. All within spec, and more importantly well within 10% (14lbs) of each other.