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Compression questions

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Hello all ,

this question came up while discussing another and I thought it more Appropriate here

I tested my compression on my V 12 1946 Lincolns engine. 

I did not have the choke opened at all,or  the throttle opened , while doing this test and it was cold .

I was told by Ray to put a little bit of oil in each socket and crank it over 6-8 times then wait 30 Minutes prior to testing 

The results 

clean plugs       Black plugs 

12 90.               11.  60. “ Wet” 65 

10 105               9.   90

8   100.              7.    80

6.  110.               5.    95

4.   95.               3    80

2.   100.              1.   85

the car has only run for an hour total in the last unknow amount of years . 

I was told that the valves may be gunked up on cylinders 1-11  especially on 11  seeing how the carbon build up was on the plugs ( new plugs , hour of use Idling ) 

I was told of an old method that may help to un gunk the valves if that’s the problem. 

  I was also told that it could be running rich on that side causing the black plugs . As the carburetor could be feeding  each cylinder row independently. It is a stock model 06h 

Is this true ?
Also Could I have a distributor issue causing the excess carbon build up? And  Is it normal to have bad compression on one side of the engine if it’s  just the rings ect.  

I hope this is clear  if not I can try to explain better


thanks all in advance  . 


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Is this a new rebuild or an engine with many miles on it?


I would not make a decision on an action plan until I could do the compression test on a warm engine with the choke and throttle wide open.



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Hey Tom ,

your right,  I am taking it slow and  gathering info prior to Jumping the gun. 
The engine has lots of miles, I can only assume bases on lack of info condition,   I will now try the “old” trick   On that one cylinder, And retest all on a warm engine , and wide open.  
Thank you for your expertise.



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  • 2 weeks later...

Hey ! I redid the Compression test with the same results on cylinder 11, 65 psi 

and this time I got oil coming out of the exhaust system.  And I found out I have no spark on the passenger side plugs .   
 She is fighting me !! 

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Sounds like you have piston ring issues and maybe valve issues too.  If you did a compression test on a cylinder and you got oil out of the tail pipe, might be a piston ring issue or a valve issue.  If you didn't fill the upper cylinder with oil to do a pressure test not sure how the oil could be coming out of the exhaust system!  Usually you just squirt a little oil in each spark plug hole, let it set for a short time and then with the pressure gauge you crank the engine to see what pressure is pumping  up by the piston in each one.  It should be reading and holding over 100 psi for a good cylinder!   If not then either the piston rings are bad or the valving has issues, perhaps both!   Also you could have a bad head gasket leaking.  Doesn't account for the oil in the exhaust system.  The firing camber has to be properly sealed including the valves to get an accurate reading of compression on your pressure gauge!

Edited by Ray500 (see edit history)
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It sounds like you have a problem with the valves or a head gasket leak on cylinder 11 . You can do a cylinder leak down test on Cylinder 11 and listen for bubbles in the radiator or air rushing sounds in the carburetor or exhaust pipe.


If the radiator has bubbles, the head gasket is gone or your block is cracked. You should also see water or foam in the oil.


If the air rushing sound is coming from the carburetor, the intake valve is stuck or burned, if it is coming from the tail pipe, the exhaust valve is burned or stuck.


You can also pull the head and intake to check out the problem.


The missing spark on one bank can be incorrect voltage at the input of the coil, bad condenser or bad coil.

Check the voltage at the input to the coils. One coil should have battery voltage and the other should have about 3V. If you have this, leave the meter connected to the side with battery voltage and tap the starter or hand crank the engine until the voltage drops. If it drops to the same level that the other coil input did, your resisters or OK. The other side should now be at battery voltage. If it is not, either the coil or the condenser is bad. Try replacing the condenser and see if conditions change. If not, send your coil to Skip Haney in FL.

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