Compression check

Hi, does it matter if I take out one spark plug at a time to check compression or all at once. Thanks

 

Take them all out, disconnect your TCI and hold your throttle wide open. thats the only way to get an accurate reading for each hole.

 

And a fully charged battery!

Kenneth

 

All solid advice; done properly it will only take 5~6 "cranks" before the gauge stops rising.

I think you'll be surprised at how quickly the motor spins with no plugs in it.

 

Thanky, Thanky, Thanky.

 

Aww man, wish I would've known that! I took one plug out at a time and cranked for ~ 8 sec without disconnecting anything. Got 140psi, 110psi, 125psi, 130psi on cyl 1-4 2 days ago before I took the valve cover off... I really don't wanna put it back on to do it this way before going to work on the shims. Do you think my numbers were greately affected by taking the readings?

 

Don't know. What number on the totem pole is a "GEAR GRINDER" ?

 

& remove the air filter.

 

Removing the air filter doesn't make much difference with the stock airbox being as big as it is; I've done them both ways (with the carbs on or off even) on the same XJ550 with virtually the same results.

 

Just quoting the book.

 

Do the Test over again, ... without the Plugs.

Your readings may not vary a great deal.

AFTER you record the Test Results for 1 thru 4 -->> Dry.
Conduct a WET Test.
Place a Tablespoon of Motor Oil in the Hole and do the Test all-over again.
See if he Number change.

::: FYI :::
When you have Low readings on Cylinders that are Side-by-side, ... that means you should follow-up the Compression Test with a LEAK-DOWN Test.
Pump AIR into the Hole with the VALVES Closed and LISTEN for a Leak.
Search: Leak Down Test.
Fabricate Tool:
>> Gut a Spark Plug
>> Epoxy an Air Valve salvaged from a Inner Tube into the Plug Base

:::::: Homemade Leak-Down Tool ::::::

 

Hmmm. Honestly never heard that one.

My factory 550 book just says:

"Procedure:

1. Make sure the valve clearance is correct.
2. Warm up the engine 2 ~ 3 minutes.
3. Remove all the spark plugs.
4. Install a compression check gauge.
5. 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."

Plus there's a "warning" about grounding all the disconnected spark plug wires. Disconnecting the TCI is easier and quicker.

And that's it. My experience has been that's all it takes.

 

Run engine for 10 minutes[*] Stop engine, remove all spark plugs, screw in compression tester[*] Remove air filter and open throttle body fully with a wire or string[*]Disconnect electronic ignition module or remove the primary battery terminal from ignition coil[*]Crank 4 times.
There, I knew I never dreamt it.

I recon the thinking is that perchance the air filter was impregnated with oil.

 

Get your shims sorted out first, that will hopefully even out your compression readings.

Ps: woooo, redliner!!!