CAMSHAFT QUESTION
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CAMSHAFT QUESTION
I HAVE A 350 CHEVY ENGINE BORED 60 OVER, DOMED PISTONS, STEEL HEADS WITH 202 INTAKE VALVES. WITH THE ENGINE ON # 1 COMPRESSION STROKE THE CAM GEAR AND CRANK GEAR DOTS ARE 180 DEGREES OFF.THE ENGINE STUMBLES OUT OF THE HOLE BUT RUNS GREAT FROM 3000 RPM TO 7500 RPM. THE PUZZLING PART IS I HAVE TO RUN 50 DEGREE TIMING FOR THE ENGINE TO PERFORM GOOD. I CAN TURN THE TIMING AS LOW AS 30 DEGREES OR AS HIGH AS 90 DEGREES AND THE ENGINE CRANKS FAST AND WILL RUN. WITH 50 DEGREE TIMING THE SPARK PLUGS ARE THE CORRECT COLOR, NOT LEAN. HAVE YOU EVER HEARD OF A CAM BEING GROUND THAT WOULD CAUSE THIS OR POSSIBLE THE CAM WAS DRILLED WRONG TO MATCH UP WITH CAM GEAR. WHEN LINING UP THE DOT TO DOT ON CAM GEAR AND CRANK GEAR THE VALVES ARE IN THE WRONG LOCATION FOR FIRING #1 CYLINDER.
Joined: Sep 2005
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Re: CAMSHAFT QUESTION
That's REALLY HARD TO READ, IT'S LIKE YOU'RE SHOUTING AT ME!!!
I'll be polite to you though.
When the engine is on the #1 compression stroke, the dots on the sprockets are both at 12:00. When you assemble the engine, it's easier to see what you're doing and get it right if you put them dot-to-dot, which is why it's customary to build them that way; but that's the OTHER instance of #1 TDC, which is when the #1 exh is just closing and the 1 int is just opening, and also is #6 firing. If you put the engine together dot-to-dot, you have to turn the crank exactly one turn to get to #1 firing.
Most likely, the reason your timing marks don't line up and make any sense is because you have a stock damper, which is expecting the timing tab to be at 12:00 like it was when it was stock; but instead, you have an aftermarket timing cover and timing tab (chrome?) on it, which locates the timing tab at about 1:30. This mismatch causes the timing marks to be about 35° off, such that if you adjust the timing to where they line up, the ACTUAL ignition timing will be 35° retarded. To fix it, locate #1 TDC ACCURATELY with a piston stop, and put a new mark on the damper that lines up with wherever your replacement timing tab happens to be.
I've heard of cams and timing sprockets being made wrong but I've never seen one off more than a couple of degrees. See my signature for a helpful hint about logic.
I'll be polite to you though.
When the engine is on the #1 compression stroke, the dots on the sprockets are both at 12:00. When you assemble the engine, it's easier to see what you're doing and get it right if you put them dot-to-dot, which is why it's customary to build them that way; but that's the OTHER instance of #1 TDC, which is when the #1 exh is just closing and the 1 int is just opening, and also is #6 firing. If you put the engine together dot-to-dot, you have to turn the crank exactly one turn to get to #1 firing.
Most likely, the reason your timing marks don't line up and make any sense is because you have a stock damper, which is expecting the timing tab to be at 12:00 like it was when it was stock; but instead, you have an aftermarket timing cover and timing tab (chrome?) on it, which locates the timing tab at about 1:30. This mismatch causes the timing marks to be about 35° off, such that if you adjust the timing to where they line up, the ACTUAL ignition timing will be 35° retarded. To fix it, locate #1 TDC ACCURATELY with a piston stop, and put a new mark on the damper that lines up with wherever your replacement timing tab happens to be.
I've heard of cams and timing sprockets being made wrong but I've never seen one off more than a couple of degrees. See my signature for a helpful hint about logic.
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