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Compression loss

Learn about the causes of compression loss in engines, such as compression leaks and breathing problems. Discover symptoms of blown head gaskets, burned valves, worn piston rings, damaged pistons, broken valve springs, and more. Find out how to diagnose these issues through vacuum testing, compression testing, and leak down testing. Complete the homework assignment to further your understanding of engine compression.

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Compression loss

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  1. Compression loss • Another reason for engine overhaul is compression loss • This can be traced to two causes • compression leaks • Breathing problems

  2. Compression leaks Compression can leak due to several causes A blown head gasket Burned valves Worn or broken piston rings Damaged pistons Or broken valve springs

  3. Blown head gasket symptoms Loss of coolant Overheating particularly under load Rough run/ loss of power White smoke from exhaust

  4. Burned valves can cause Lower or no compression Which valve is this and Why is it the most likely To burn out of the two Examples of severely Burned valves

  5. Broken pistons or rings This piston and ring were damaged from detonation There are several Examples of this Type of damage In the class room

  6. Broken valve springs Almost always accompanied with water in the crankcase as acid is a byproduct of combustion that builds up in engine oil. When this acid combines With water, corrosion speeds Up and the resulting rust Raises the stress on the Surface of the spring, Causing it to brake

  7. Tight valves If valve clearance is lost due to improper adjustment or From valve face wear which causes the valve to move up In its seat, Or any other problems That don’t let the valve Fully close can result in Loss of compression And burnt valves

  8. Breathing problems Late valve timing caused by worn timing chains, or by Incorrectly installed timing belts cause the engine to suffocate Carbon buildup on the Valve stem can also suffocate The engine. So can a plugged exhaust Or a restricted air filter

  9. Testing for cause complaint Vacuum testing Compression testing Leak down testing

  10. Vacuum testing Engine manifold vacuum can tell A technician a good ideal of engine Condition. Find a manifold vacuum source to Connect the gauge to. This will have Vacuum at idle and at 2500 rpm. Some vehicles make this easy others Can be difficult to find a place to Connect the gauge.

  11. A : Idle vacuum is high B : cruise/2500 rpm vacuum is moderate C : wide open throttle vacuum is near zero/zero W.O.T. = wide open throttle

  12. Raise rpm to 2000 rpm Snap throttle closed and watch for a vacuum increase of 2-6 inches Above normal Worn rings will not increase vacuum enough Generally the higher the jump in vacuum the better the condition Of the rings

  13. To test for weak or broken valve springs Raise engine rpm gradually too 2000 rpm Look for rapid fluctuations of the needle as the speed increases

  14. To test for a restricted exhaust Raise rpm quickly to 2000rpm to cause the vac. Reading to Momentarily go low, then release throttle quickly Vac should return smoothly and quickly to higher than normal A slow, hesitating return can indicate a breathing restriction

  15. Other causes of low vacuum

  16. Cranking vacuum Looks for internal vac leaks to perform a cranking vac test 1: close throttle all the way 2: plug the breather hose to the air cleaner 3: disable the ignition system 4: crank engine, it should produce over 3 inches of vac. most engines will produce more than this The needle should be steady

  17. Homework assignment Finish reading chapter 3 Answer study questions 1-15 A.S.E. style questions are extra credit

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