Timing for Cam Swap
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Joined: Jul 2006
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Car: 1987 Pontiac Trans Am
Engine: 350 Vortec
Transmission: 700R4
Axle/Gears: 3.42
Timing for Cam Swap
My motor is finally finished and I've been working on timing it. The problem Im having is that I cannot get the timing mark to line up. The motor is a 96 Vortec 350 with a XR270HR cam. The timing cover and damper is from the 305 if that makes a difference. Would the larger cam cause the timing to be off and need adjusting?
Thread Starter
Member
Joined: Jul 2006
Posts: 304
Likes: 0
Car: 1987 Pontiac Trans Am
Engine: 350 Vortec
Transmission: 700R4
Axle/Gears: 3.42
Re: Timing for Cam Swap
Joined: Sep 2005
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Re: Timing for Cam Swap
No the "larger" cam doesn't have anything to do with "it".
Yes it is entirely possible that it can run right with the marks in the ozone. In fact, it can even run perfectly fine with no marks at all. The engine does not look at the marks and decide accordingly how to run. All it cares, is when the spark occurs, in relation to piston and valve motion.
I'm going to guess at this point that you have a stock damper and an aftermarket timing cover with the tab in the pre-1980ish location. Your stock timing mark will be about 35° off with that mismatched combination.
Put the crank so that #1 is EXACTLY at TDC, measured with a dial indicator or piston stop.
Assemble the engine: put the gears & chain on the cam, with the crank dot at 12:00 and the cam dot at 6:00. This position is #6 firing, and at the same time, THE OTHER instance of #1 TDC, when its exh valve is just closing and its int is just opening. If it's already assembled, just turn it to get it to this spot.
Without turning anything, put the timing cover on dry with just a couple of bolts to keep it from falling off, and slip the crank damper on.
If the marks aren't lined up, make a new one: cut a little groove in the damper with a die grinder or hacksaw EXACTLY in line with the 0 mark on whatever tab you have, and fill it with white paint.
To get the dist in right, rotate the crank exactly one full turn from this point to put the engine at THE OTHER instance of #1 & #6 TDC, which is #1 firing. At that point, the crank dot will again be at 12:00, #1 will be at TDC, the timing mark you just made will again line up, but this time the cam dot will be at 12:00 instead of 6:00, and the cam will be at #1 firing & #6 valves changing over. Drop the dist in with the rotor pointing about 15° to the front of straight toward the driver's side. It will rotate CW as it drops in. After it engages the oil pump drive rod and seats, it will be pointing about 15° to the driver's side of straight ahead; and you'll put the #1 plug wire on the cap tower just to the DS of the front, and your plug wires will then be in the factory position and routing and will look the least like a bird's nest.
Yes it is entirely possible that it can run right with the marks in the ozone. In fact, it can even run perfectly fine with no marks at all. The engine does not look at the marks and decide accordingly how to run. All it cares, is when the spark occurs, in relation to piston and valve motion.
I'm going to guess at this point that you have a stock damper and an aftermarket timing cover with the tab in the pre-1980ish location. Your stock timing mark will be about 35° off with that mismatched combination.
Put the crank so that #1 is EXACTLY at TDC, measured with a dial indicator or piston stop.
Assemble the engine: put the gears & chain on the cam, with the crank dot at 12:00 and the cam dot at 6:00. This position is #6 firing, and at the same time, THE OTHER instance of #1 TDC, when its exh valve is just closing and its int is just opening. If it's already assembled, just turn it to get it to this spot.
Without turning anything, put the timing cover on dry with just a couple of bolts to keep it from falling off, and slip the crank damper on.
If the marks aren't lined up, make a new one: cut a little groove in the damper with a die grinder or hacksaw EXACTLY in line with the 0 mark on whatever tab you have, and fill it with white paint.
To get the dist in right, rotate the crank exactly one full turn from this point to put the engine at THE OTHER instance of #1 & #6 TDC, which is #1 firing. At that point, the crank dot will again be at 12:00, #1 will be at TDC, the timing mark you just made will again line up, but this time the cam dot will be at 12:00 instead of 6:00, and the cam will be at #1 firing & #6 valves changing over. Drop the dist in with the rotor pointing about 15° to the front of straight toward the driver's side. It will rotate CW as it drops in. After it engages the oil pump drive rod and seats, it will be pointing about 15° to the driver's side of straight ahead; and you'll put the #1 plug wire on the cap tower just to the DS of the front, and your plug wires will then be in the factory position and routing and will look the least like a bird's nest.
Thread Starter
Member
Joined: Jul 2006
Posts: 304
Likes: 0
Car: 1987 Pontiac Trans Am
Engine: 350 Vortec
Transmission: 700R4
Axle/Gears: 3.42
Re: Timing for Cam Swap
No the "larger" cam doesn't have anything to do with "it".
Yes it is entirely possible that it can run right with the marks in the ozone. In fact, it can even run perfectly fine with no marks at all. The engine does not look at the marks and decide accordingly how to run. All it cares, is when the spark occurs, in relation to piston and valve motion.
I'm going to guess at this point that you have a stock damper and an aftermarket timing cover with the tab in the pre-1980ish location. Your stock timing mark will be about 35° off with that mismatched combination.
Put the crank so that #1 is EXACTLY at TDC, measured with a dial indicator or piston stop.
Assemble the engine: put the gears & chain on the cam, with the crank dot at 12:00 and the cam dot at 6:00. This position is #6 firing, and at the same time, THE OTHER instance of #1 TDC, when its exh valve is just closing and its int is just opening. If it's already assembled, just turn it to get it to this spot.
Without turning anything, put the timing cover on dry with just a couple of bolts to keep it from falling off, and slip the crank damper on.
If the marks aren't lined up, make a new one: cut a little groove in the damper with a die grinder or hacksaw EXACTLY in line with the 0 mark on whatever tab you have, and fill it with white paint.
To get the dist in right, rotate the crank exactly one full turn from this point to put the engine at THE OTHER instance of #1 & #6 TDC, which is #1 firing. At that point, the crank dot will again be at 12:00, #1 will be at TDC, the timing mark you just made will again line up, but this time the cam dot will be at 12:00 instead of 6:00, and the cam will be at #1 firing & #6 valves changing over. Drop the dist in with the rotor pointing about 15° to the front of straight toward the driver's side. It will rotate CW as it drops in. After it engages the oil pump drive rod and seats, it will be pointing about 15° to the driver's side of straight ahead; and you'll put the #1 plug wire on the cap tower just to the DS of the front, and your plug wires will then be in the factory position and routing and will look the least like a bird's nest.
Yes it is entirely possible that it can run right with the marks in the ozone. In fact, it can even run perfectly fine with no marks at all. The engine does not look at the marks and decide accordingly how to run. All it cares, is when the spark occurs, in relation to piston and valve motion.
I'm going to guess at this point that you have a stock damper and an aftermarket timing cover with the tab in the pre-1980ish location. Your stock timing mark will be about 35° off with that mismatched combination.
Put the crank so that #1 is EXACTLY at TDC, measured with a dial indicator or piston stop.
Assemble the engine: put the gears & chain on the cam, with the crank dot at 12:00 and the cam dot at 6:00. This position is #6 firing, and at the same time, THE OTHER instance of #1 TDC, when its exh valve is just closing and its int is just opening. If it's already assembled, just turn it to get it to this spot.
Without turning anything, put the timing cover on dry with just a couple of bolts to keep it from falling off, and slip the crank damper on.
If the marks aren't lined up, make a new one: cut a little groove in the damper with a die grinder or hacksaw EXACTLY in line with the 0 mark on whatever tab you have, and fill it with white paint.
To get the dist in right, rotate the crank exactly one full turn from this point to put the engine at THE OTHER instance of #1 & #6 TDC, which is #1 firing. At that point, the crank dot will again be at 12:00, #1 will be at TDC, the timing mark you just made will again line up, but this time the cam dot will be at 12:00 instead of 6:00, and the cam will be at #1 firing & #6 valves changing over. Drop the dist in with the rotor pointing about 15° to the front of straight toward the driver's side. It will rotate CW as it drops in. After it engages the oil pump drive rod and seats, it will be pointing about 15° to the driver's side of straight ahead; and you'll put the #1 plug wire on the cap tower just to the DS of the front, and your plug wires will then be in the factory position and routing and will look the least like a bird's nest.
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