Wednesday, April 15, 2009


In this world of increasing electronic gadjets and gizmos, some down to basic mechanical principles are to be observed. No amount of manipulation with the ECU mapping of ignition or fuel injection can compensate for weak compression, leading to power loss, high fuel consumption.

Of course, a sharp minded may ask - what is the cause for low compression ? Let me list what I can think of in a flash, in lesser degrees of severity first;

a. Incorrect valve clearance - need to re-adjust valve clearance for non-hydraulic valve actuating mechanisms. Most cars nowadays uses shims, and great skills is required, including the ability to read the micrometer.

b. Incorrect timing belt alignment - came across this problem in a Subaru XT-Turbo as it is a flat four with unconventional alignment points for both cylinder banks.

c. Particles lodged at valve seats - can be due to broken air filter allowing dust to stream thru, or excessive carbon in the cylinders causing valves not to seat properly.

d. Cylinder head distorted - due to overheating, the cyl. head may distort and throw all valve clearances haywire. Some valves may not even seat, causing blow-by. Came across this on a 73oi BMW, whose owner continued to drive with temperature at red. After coooled down, engine would not start, and I had the car towed back to my workshop, where I re-adjusted all the valve clearances.
A good indicator in-place of a compression tool may be the vacum gauge. The techniques on reading and interpreting the vacumm gauge will not be covered here, but I am sure most readers will be intrepid in searching the internet on this topic.

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