Low compression

Hello, i have an XK140 with what ive come to find out has a later saloon motor with a B head. Im over that but i did a compression check before summer and had to low cyliders number 1 and 3 at 120 psi each all others 140 or abouts. The out of balance ratio is over the recomended 15 %. It seems to run fine but what is my next step should i just plan on pulling the head this winter. Will a leak down test really tell me anything new i need to purchase the equipment.

Pour about a teaspoon of oil in each cylinder and retest. If the readings go up it’s more than likely low compression is the fault of the rings.

If oil helps drive it hard for a few hundred miles and test again?

Leakdown tests are nice but you can also hear where the air escapes if you blow compressed air into the spark plug hole, through a rag.

If you haven’t already, you may want to check the valve clearances. It’s a simple matter of pulling the covers, removing the spark plugs and measuring with feeler guage. If they are too tight they may be leaking. Regardless, you will know that your valves are OK.
Pat H.

Enjoy doing whatever tests you like and get as well-informed as seems right, but don’t overlook your statement “It seems to run fine …)”. Think about how you use the car, I don’t generally fix things that run fine unless there is an imminent problem diagnosed. Thoughtful maintenance is worthwhile and a healthcare check on the engine is good idea.

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And I’ve heard that you should have the throttle plates wide open when you do the compression test.

I did a valve clearence check right after i found the compression low on two cylinders and the valves were tight on the intake side on those two cylinders and two others by 001 to 002. I may also note the paint is blistered around one of the two low compression cyllinders.could be a coincedence. The exhaust was spot on at .006