need some detailed tech questions

03-02-2005, 05:57 AM

I keep seeing the same answer to check a bad head gasket is a compression check. I may not be ase certified but I do know that a compression check should only be used to decide if a engine is rebuildable. If you would like more detail about your engines condition and cover the major areas use a leak down test. Doing this is easier than it sounds. Buy a adapter from any auto parts store (+/- $20)that threds into your spark plug hole and connect it to a compressor. Rotate engine to move each cylinder your testing, to top dead center. "Intake and exhaust valves closed and pistion up, for lamens" Lock engine still or SLOWLY (OR ENGINE MAY ROTATE WHEN YOU DONT WANT IT TO) increase air pressure to about 90 psi. Not confusing "sea-shell" sounds from air leakage listen for air leakage. Disconnecting intake and opening throttle valve to listen or even feel air coming out could test for intake valve seating problems or bad valve timing, listining to tail pipe or feeling air rushing from tail pipe can tell you you have again bad valve timing or burnt /bent exhaust valve, remove the oil cap and you will hear a little of usuall blow-by, this one you have to realy listen and compare each cylinders air flow one may be a little louder or feel more air coming out could be bad compression rings, and the biggy for the 7mge is the head gasket test, before inserting the air into the chambers remove the radiator cap "only when cold of coarse", top the radiator off "I only suggest distiled water" anyway Slowly release the 90 psi into the cylinder and once there watch for spitting water from radiator "a bad leak" or look inside radiator for any signs of bubbles, bubbes there is a deffinate sign of a bad head gasket. If looking into buying a car and cant perform this test, a good way to tell is the coolant reserve tank. A good engine that has never had a blown head will have a clean white overflow tank, one that has blown, may be yellowed or dingy, looking inside maybe even a prominate line of dingy yellow from oil in the water or cooked fluids. This is commanly over looked by private sellers or dealers trying to armor-all a car just to sell it. Also i may not have spelled all this right, but try it, youll be suprised how much this is used by shops and how much it can tell you.

03-02-2005, 05:57 AM	#5
LES Guest Posts: n/a	I keep seeing the same answer to check a bad head gasket is a compression check. I may not be ase certified but I do know that a compression check should only be used to decide if a engine is rebuildable. If you would like more detail about your engines condition and cover the major areas use a leak down test. Doing this is easier than it sounds. Buy a adapter from any auto parts store (+/- $20)that threds into your spark plug hole and connect it to a compressor. Rotate engine to move each cylinder your testing, to top dead center. "Intake and exhaust valves closed and pistion up, for lamens" Lock engine still or SLOWLY (OR ENGINE MAY ROTATE WHEN YOU DONT WANT IT TO) increase air pressure to about 90 psi. Not confusing "sea-shell" sounds from air leakage listen for air leakage. Disconnecting intake and opening throttle valve to listen or even feel air coming out could test for intake valve seating problems or bad valve timing, listining to tail pipe or feeling air rushing from tail pipe can tell you you have again bad valve timing or burnt /bent exhaust valve, remove the oil cap and you will hear a little of usuall blow-by, this one you have to realy listen and compare each cylinders air flow one may be a little louder or feel more air coming out could be bad compression rings, and the biggy for the 7mge is the head gasket test, before inserting the air into the chambers remove the radiator cap "only when cold of coarse", top the radiator off "I only suggest distiled water" anyway Slowly release the 90 psi into the cylinder and once there watch for spitting water from radiator "a bad leak" or look inside radiator for any signs of bubbles, bubbes there is a deffinate sign of a bad head gasket. If looking into buying a car and cant perform this test, a good way to tell is the coolant reserve tank. A good engine that has never had a blown head will have a clean white overflow tank, one that has blown, may be yellowed or dingy, looking inside maybe even a prominate line of dingy yellow from oil in the water or cooked fluids. This is commanly over looked by private sellers or dealers trying to armor-all a car just to sell it. Also i may not have spelled all this right, but try it, youll be suprised how much this is used by shops and how much it can tell you.