Bad cam? Low compression?
Teching In
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From: tallapoosa,Ga
Originally Posted by WE TODD DID
Yes, a worn out cam will cause low cranking compression, among other things. Just like if you were to advance a cam, and then retard the cam. The compression is going to change.
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Teching In
Joined: Feb 2007
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From: tallapoosa,Ga
lets say the intake valve doesnt open at all....
and the engine was shut down with that particular piston at tdc.....
there would be no air to compress...
less air in=less air to compress....
no air out=egr effect=lower compression
and the engine was shut down with that particular piston at tdc.....
there would be no air to compress...
less air in=less air to compress....
no air out=egr effect=lower compression
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TECH Junkie
Joined: Dec 2005
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Now that would be one wore out cam if the valves did not open. But within the guidelines of the original question I would have to say the compression will not be affected. Now if you want to throw in other scenerios like worn valves, guides etc than yes if the valves are not seating correctly.
Teching In
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From: tallapoosa,Ga
DYNAMIC EFFECTIVE COMPRESSION RATIO* is the correct name
it is affected by crankshaft stroke. which affects piston speed
and it is affected by intake valve closing point @.050 abdc
in other words yes! static compression is the same (mathmatical compression)
dynamic compression(which is while the engine is running) does change due to cam design.
if the valve closes late the dcr will be low
if the valve closes early the dcr will be higher
i dont know how much it would take for a cam lobe to effect the measured pressure? but if it is worn it will not allow as much air in the engine i do know that
FYI- U.T.I drivibality classes teach a worn cam lobe will cause low compression along with worn rings, bent pushrod,broken rocker arms, valve guides, seats, gaskets, bla bla bla......
it is affected by crankshaft stroke. which affects piston speed
and it is affected by intake valve closing point @.050 abdc
in other words yes! static compression is the same (mathmatical compression)
dynamic compression(which is while the engine is running) does change due to cam design.
if the valve closes late the dcr will be low
if the valve closes early the dcr will be higher
i dont know how much it would take for a cam lobe to effect the measured pressure? but if it is worn it will not allow as much air in the engine i do know that
FYI- U.T.I drivibality classes teach a worn cam lobe will cause low compression along with worn rings, bent pushrod,broken rocker arms, valve guides, seats, gaskets, bla bla bla......
Originally Posted by mountainmagic
DYNAMIC EFFECTIVE COMPRESSION RATIO* is the correct name
it is affected by crankshaft stroke. which affects piston speed
and it is affected by intake valve closing point @.050 abdc
in other words yes! static compression is the same (mathmatical compression)
dynamic compression(which is while the engine is running) does change due to cam design.
if the valve closes late the dcr will be low
if the valve closes early the dcr will be higher
i dont know how much it would take for a cam lobe to effect the measured pressure? but if it is worn it will not allow as much air in the engine i do know that
FYI- U.T.I drivibality classes teach a worn cam lobe will cause low compression along with worn rings, bent pushrod,broken rocker arms, valve guides, seats, gaskets, bla bla bla......
it is affected by crankshaft stroke. which affects piston speed
and it is affected by intake valve closing point @.050 abdc
in other words yes! static compression is the same (mathmatical compression)
dynamic compression(which is while the engine is running) does change due to cam design.
if the valve closes late the dcr will be low
if the valve closes early the dcr will be higher
i dont know how much it would take for a cam lobe to effect the measured pressure? but if it is worn it will not allow as much air in the engine i do know that
FYI- U.T.I drivibality classes teach a worn cam lobe will cause low compression along with worn rings, bent pushrod,broken rocker arms, valve guides, seats, gaskets, bla bla bla......
yes a bad cam will effect compression. when you do a compression test you have to hold the throttle blade open so the motor can get the air it needs if your valve is not opening all the way it will affect how much air gets into the cylinder and will affect the compression reading. you would then use a CLT tester on the low cylinder to find out if it was a leak or a worn cam
TECH Junkie
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I have to see if I understand the argument correctly. A cam of 260 degrees duration and .450" lift will have less compression than a cam of 280 degrees duration and .600" lift in the same motor. Consider the 260 degree cam to be a worn out 280 degree cam.
