Can a slipped timing belt directly result in low compression, and does belt valves always read 0 compression?

55

Asked by Jan 06, 2010 at 04:34 AM about the Mitsubishi Galant

Question type: Maintenance & Repair

4g63 N/A twin cam.

3 Answers

155

A slipped timing belt will usually result in the valves coming into contact with the pistons. The 4G63 is an interference engine, meaing that when the pistons are at top dead center a fully open valve will come in contact with the piston. Usually in an interference engine valves will bend a little but the big worry is a hole are crack in the top of the piston. A bent valve or cracked/damaged piston will give very little if not zero PSI readings in a compresion test since the valve will not close fully or there is Considerable blow by on a cracked piston.

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55

On a dry test, i received the following compression results (psi) 50,50,48,70. This is what is confusing, the compression test seems to high to be a bent valve? im assuming a healthy engine should be around 140-150psi?

55

the timing belt slipped like 10 teeth, but i must have been praying to the car gods cause i have 160psi+ comp and now she is running like a legend.. thanks for nothing. p.s im a really respect mechanic.

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