Compression test. How's it done?

[simonjrwinter]

After my misfiring problem (mostly) solved by adjusting the tappets on my non-leadfree head, I thought I'd test the compression on the cylinders to see if the valve seats are damaged.

I've bought a Gunson tester, but when it arrives I'd like to able to use it and I don't know how.

Any advice gratefully recieved.

 

Simon

Edited May 14, 2006 by simonjrwinter

[Richard Crawley]

Simon

Read the instructions initially!

 

Seriously though; first remove all the plugs & disconnect the low tension lead from the dizzy - stops all those nasty sparks interfering with your pacemaker!

 

There are two types of compression tester; one type (usually the cheapos) has a large rubber bung on the end & all you do is push this down onto the spark plug hole while cranking the engine.

 

The best type screws into the plug hole & will register & hold each cylinder pressure after you’ve cranked it over. Always crank the engine for at least 5 seconds to get a full reading. The guage should also have a pressure release button on the side, allowing you to release the pressure & repeat the process; I always take & record at least 3 readings per cylinder.

 

When you’ve recorded all the pressure readings, they will typically be anything between 100 – 180 PSI. The actual pressure is not that critical as the gauges can vary but what you’re looking for is a difference in the pressures; anything up to 5 PSI is OK but if significantly more, there could be a problem. Squirt a little oil into the low ones, if they come up it’s rings if they don’t it’s the valves!

[jean]

And don't forget to fully open the throttle and may be cut the fuel pump off, what will prevent flooding the cylinders.

Jean

[Richard Crawley]

And don't forget to fully open the throttle and may be cut the fuel pump off, what will prevent flooding the cylinders.

Jean

Good thinking Jean.