Question about TDC, camshaft and crankshaft
09-10-2016, 03:05 PM
#1
Safety Car
Thread Starter
Question about TDC, camshaft and crankshaft
Hi,
I've have a small question about TDC.
I'm helping installing a new camshaft in a BBC engine.
When I have piston 1 in TDC, and the "dot" on the top gear @6 and the "dot" @12 in the low gear, then I'm good to go right??
The reason I ask is because, I have the piston in TDC (and the needle is at 0 degrees in the damper), and I have the "dot" for the camshaft @6, but the "dot" on the low gear is not @12
I assume that the low gear, is installed wrong, and I just have to move the dot to @12??
Also is it normal that the "dot" on the low gear is a O, not a dot?
Thx.
I've have a small question about TDC.
I'm helping installing a new camshaft in a BBC engine.
When I have piston 1 in TDC, and the "dot" on the top gear @6 and the "dot" @12 in the low gear, then I'm good to go right??
The reason I ask is because, I have the piston in TDC (and the needle is at 0 degrees in the damper), and I have the "dot" for the camshaft @6, but the "dot" on the low gear is not @12
I assume that the low gear, is installed wrong, and I just have to move the dot to @12??
Also is it normal that the "dot" on the low gear is a O, not a dot?
Thx.
09-10-2016, 03:36 PM
#2
Le Mans Master
Hi,
I've have a small question about TDC.
I'm helping installing a new camshaft in a BBC engine.
When I have piston 1 in TDC, and the "dot" on the top gear @6 and the "dot" @12 in the low gear, then I'm good to go right??
Yes that is the simple way to install a new timing chain and gears
The reason I ask is because, I have the piston in TDC (and the needle is at 0 degrees in the damper), and I have the "dot" for the camshaft @6, but the "dot" on the low gear is not @12
I assume that the low gear, is installed wrong, and I just have to move the dot to @12??The timing mark on the damper/balancer and the pointer on the engine is for ignition timing- Cyl #1 firing. The timing gears/chain, the dots are closest together in Cyl #6 firing position. Cam gear at 6 and crank gear at 12
Also is it normal that the "dot" on the low gear is a O, not a dot?It could be, depending on who made the gears
Thx.
I've have a small question about TDC.
I'm helping installing a new camshaft in a BBC engine.
When I have piston 1 in TDC, and the "dot" on the top gear @6 and the "dot" @12 in the low gear, then I'm good to go right??
Yes that is the simple way to install a new timing chain and gears
The reason I ask is because, I have the piston in TDC (and the needle is at 0 degrees in the damper), and I have the "dot" for the camshaft @6, but the "dot" on the low gear is not @12
I assume that the low gear, is installed wrong, and I just have to move the dot to @12??The timing mark on the damper/balancer and the pointer on the engine is for ignition timing- Cyl #1 firing. The timing gears/chain, the dots are closest together in Cyl #6 firing position. Cam gear at 6 and crank gear at 12
Also is it normal that the "dot" on the low gear is a O, not a dot?It could be, depending on who made the gears
Thx.
Last edited by TimAT; 09-10-2016 at 03:39 PM.
09-10-2016, 03:58 PM
#3
Safety Car
Thread Starter
The reason I ask is because, I have the piston in TDC (and the needle is at 0 degrees in the damper), and I have the "dot" for the camshaft @6, but the "dot" on the low gear is not @12
I assume that the low gear, is installed wrong, and I just have to move the dot to @12??The timing mark on the damper/balancer and the pointer on the engine is for ignition timing- Cyl #1 firing. The timing gears/chain, the dots are closest together in Cyl #6 firing position. Cam gear at 6 and crank gear at 12
Hope this helps a bit
I assume that the low gear, is installed wrong, and I just have to move the dot to @12??The timing mark on the damper/balancer and the pointer on the engine is for ignition timing- Cyl #1 firing. The timing gears/chain, the dots are closest together in Cyl #6 firing position. Cam gear at 6 and crank gear at 12
Hope this helps a bit
09-10-2016, 04:22 PM
#4
Race Director
I am not sure I follow.
Post #2 answers your questions, as I understand them.
A dot, or 0 on the gear would be the same thing. The crank gear dot at exactly 12 o'clock should have the damper timing mark at zero.
When the two timing gear marks are closest to each other (12 and 6), you are at #6 firing position, even though #1 is at TDC, also.
You need both dots at 12 o'clock to be #1 TDC firing position.
Doug
Post #2 answers your questions, as I understand them.
A dot, or 0 on the gear would be the same thing. The crank gear dot at exactly 12 o'clock should have the damper timing mark at zero.
When the two timing gear marks are closest to each other (12 and 6), you are at #6 firing position, even though #1 is at TDC, also.
You need both dots at 12 o'clock to be #1 TDC firing position.
Doug
09-10-2016, 06:45 PM
#5
Safety Car
Thread Starter
I am not sure I follow.
Post #2 answers your questions, as I understand them.
A dot, or 0 on the gear would be the same thing. The crank gear dot at exactly 12 o'clock should have the damper timing mark at zero.
When the two timing gear marks are closest to each other (12 and 6), you are at #6 firing position, even though #1 is at TDC, also.
You need both dots at 12 o'clock to be #1 TDC firing position.
Doug
Post #2 answers your questions, as I understand them.
A dot, or 0 on the gear would be the same thing. The crank gear dot at exactly 12 o'clock should have the damper timing mark at zero.
When the two timing gear marks are closest to each other (12 and 6), you are at #6 firing position, even though #1 is at TDC, also.
You need both dots at 12 o'clock to be #1 TDC firing position.
Doug
09-10-2016, 09:31 PM
#6
Tech Contributor
Member Since: Aug 1999
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That's correct. Since many shop manuals (such as "Chilton's") state to assemble the gears with the two dots pointing together (crank at 12 and cam at 6), it is often assumed that this is TDC #1 firing position. This is not correct - it's just an easy way to assure gear alignment and clocking. Since the gears rotate at a 2:1 ratio, the gears can be installed at 6 & 12 or at 12 & 12. But to get the engine/cam/timing with cylinder 1 at TDC on the compression stroke (firing position), the gears must be at 12 & 12. Gears at 6 & 12 is firing position for cylinder #6. If you install your distributor with the gears at 6 & 12, the engine will never start.
09-11-2016, 01:02 AM
#7
Safety Car
Thread Starter
That's correct. Since many shop manuals (such as "Chilton's") state to assemble the gears with the two dots pointing together (crank at 12 and cam at 6), it is often assumed that this is TDC #1 firing position. This is not correct - it's just an easy way to assure gear alignment and clocking. Since the gears rotate at a 2:1 ratio, the gears can be installed at 6 & 12 or at 12 & 12. But to get the engine/cam/timing with cylinder 1 at TDC on the compression stroke (firing position), the gears must be at 12 & 12. Gears at 6 & 12 is firing position for cylinder #6. If you install your distributor with the gears at 6 & 12, the engine will never start.
09-11-2016, 08:13 PM
#8
Dementer sole survivor
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When I was a kid rebuilding engines I was lead to believe by a certain chevy car manual that 6 and 12 #1 tdc was #1 tdc firing and everytime I put in the distributor it would run like it was gonna explode or not at all. Then I would pull the distributor and rotate it 180*. I never could figure out how I was screwing it up.
Live and learn.
Live and learn.
09-12-2016, 10:06 AM
#10
Safety Car
Thread Starter
I've just seen your picture, we did it like yours Sunday morning, the problems was, the small gear was not installed correct from Ohio Crank, so we took it of, and installed it correct.