I'm stumped, TDC Timing question.
08-19-2014, 10:29 AM
#1
I'm stumped, TDC Timing question. Alright, I'll try and explain this as best as possible.
I have my short block all put together, I was setting the #1 cylinder to TDC and the timing marks are perfectly aligned, dot to dot. Cam dot is at the 6 o'clock and crank at 12 o'clock
However, looking at the lobe's of the camshaft, it looks like the intake lobe is in the position to "open" in the #1 cylinder. Is this normal??
by rotating the crank I can see the intake lobe "opening", as I continue to rotate the crank, the intake lobe "closes" and now the piston is at TDC again at the compression stroke or firing position, but the timing marks are not the same, the cam dot is at 12 o'clock and the crank is also at 12 o'clock. Again, is this normal?
I understand that the computer controls the ignition timing. I also triple checked all my alignment marks, there is no other way the cam can go so I'm sort of loosing my mind if this is normal for LSx engines.
Any help to ease my mind would be greatly appreciated.
I have my short block all put together, I was setting the #1 cylinder to TDC and the timing marks are perfectly aligned, dot to dot. Cam dot is at the 6 o'clock and crank at 12 o'clock
However, looking at the lobe's of the camshaft, it looks like the intake lobe is in the position to "open" in the #1 cylinder. Is this normal??
by rotating the crank I can see the intake lobe "opening", as I continue to rotate the crank, the intake lobe "closes" and now the piston is at TDC again at the compression stroke or firing position, but the timing marks are not the same, the cam dot is at 12 o'clock and the crank is also at 12 o'clock. Again, is this normal?
I understand that the computer controls the ignition timing. I also triple checked all my alignment marks, there is no other way the cam can go so I'm sort of loosing my mind if this is normal for LSx engines.
Any help to ease my mind would be greatly appreciated.
08-19-2014, 11:02 AM
#2
that's exactly where it should be. You've got it set correctly.
If you have a cam card, a degree wheel and a dial gauge, you could degree the cam to confirm that the intake centerline lines up exactly where it should.
If you have a cam card, a degree wheel and a dial gauge, you could degree the cam to confirm that the intake centerline lines up exactly where it should.
08-19-2014, 11:07 AM
#3
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The cam turns twice as fast as the crank so every revolution of the cam the crank is alternating at 6 and 12 o'clock. Where they line up is next to each other is when the piston should be at the top of the stroke. If you turn it the firing is when the dot is at top dead center.
08-19-2014, 12:28 PM
#6
Alright, I'll try and explain this as best as possible.
I have my short block all put together, I was setting the #1 cylinder to TDC and the timing marks are perfectly aligned, dot to dot. Cam dot is at the 6 o'clock and crank at 12 o'clock
However, looking at the lobe's of the camshaft, it looks like the intake lobe is in the position to "open" in the #1 cylinder. Is this normal??
by rotating the crank I can see the intake lobe "opening", as I continue to rotate the crank, the intake lobe "closes" and now the piston is at TDC again at the compression stroke or firing position, but the timing marks are not the same, the cam dot is at 12 o'clock and the crank is also at 12 o'clock. Again, is this normal?
I understand that the computer controls the ignition timing. I also triple checked all my alignment marks, there is no other way the cam can go so I'm sort of loosing my mind if this is normal for LSx engines.
Any help to ease my mind would be greatly appreciated.
I have my short block all put together, I was setting the #1 cylinder to TDC and the timing marks are perfectly aligned, dot to dot. Cam dot is at the 6 o'clock and crank at 12 o'clock
However, looking at the lobe's of the camshaft, it looks like the intake lobe is in the position to "open" in the #1 cylinder. Is this normal??
by rotating the crank I can see the intake lobe "opening", as I continue to rotate the crank, the intake lobe "closes" and now the piston is at TDC again at the compression stroke or firing position, but the timing marks are not the same, the cam dot is at 12 o'clock and the crank is also at 12 o'clock. Again, is this normal?
I understand that the computer controls the ignition timing. I also triple checked all my alignment marks, there is no other way the cam can go so I'm sort of loosing my mind if this is normal for LSx engines.
Any help to ease my mind would be greatly appreciated.
08-19-2014, 01:09 PM
#7
Alright, that's a big sigh of relief. I was worried something was totally wrong, I did have the cam and crank degreed at the machine shop.
I've always heard that TDC is during the compression stroke aka when the piston is TDC to "fire".
I guess its slightly different with LS engines as the TDC of the Timing marks is at the beginning of the intake stroke (in other words when the cam and crank are alined and no.1 cylinder is tdc, its the beginning of the intake stroke, when all the exhaust gases have already exited)
I've always heard that TDC is during the compression stroke aka when the piston is TDC to "fire".
I guess its slightly different with LS engines as the TDC of the Timing marks is at the beginning of the intake stroke (in other words when the cam and crank are alined and no.1 cylinder is tdc, its the beginning of the intake stroke, when all the exhaust gases have already exited)
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08-19-2014, 01:39 PM
#8
You also need to take into consideration any advance/retard Grd into the cam. Dot to Dot is only to set the cam to the manufactures specs, not straight up with no advance/retard unless it was Grd that way. Furthermore the actual cams specs and the advertised specs are not always the same, as stated above already.
Last edited by 99Bluz28; 08-19-2014 at 01:45 PM.
08-19-2014, 02:51 PM
#10
Crank at 12 o'clock is TDC for the crankshaft.
Cylinder 1 valves are only closed with the cam timing mark at 12, not 6.
Dot to dot (6 to 12) is used for setting the cam timing, but as far as the valves are concerned the engine is 180 out. Therefore marks at 12 and 12 are TDC compression stroke.
Been like this for decades across most OHV engine platforms.
Cylinder 1 valves are only closed with the cam timing mark at 12, not 6.
Dot to dot (6 to 12) is used for setting the cam timing, but as far as the valves are concerned the engine is 180 out. Therefore marks at 12 and 12 are TDC compression stroke.
Been like this for decades across most OHV engine platforms.
Last edited by Marc 85Z28; 08-19-2014 at 07:40 PM.
08-19-2014, 06:21 PM
#12
With the dots aligned, cyl #6 is at TDC firing...not #1.
This means that your setup is exactly right.
This is the way it is with the LS motors.
All other engines that I'm aware of, use dot to dot #1 @ TDC.
I went through the same thing when assembling my LS1 engine.
In reality, the firing order is 6-5-4-3-1-8-7-2.
>>> From "Joseph" LS1 engine builder
Re:When torqueing the rockers
Glenn, I'm glad you found my info helpful, not many people know the valve events for all 8 cylinders and when they happen. You would naturally assume with the dots aligned it would be the firing position of cylinder #1, when its actually the start of the intake stroke as far as the piston/intake valve is concerned. With the dots aligned cylinder #6 is the one to set preload/lash/ or for installing rockers. Each 90* (720* / 8cyl = 90*) on the crankshaft gear is another cylinder firing, while each 45* (360* / 8cyl = 45*) on the camshaft gear is another cylinder firing. Having the timing cover off helps to watch the sequence. Here's a copy/paste of a manuscript I'm working on that may help also:
LSX Firing Order 1, 8, 7, 2, 6, 5, 4, 3
TDC Cyl. #1) Camshaft dot at 12:00 / Crankshaft dot at 12:00
TDC Cyl. #8) Camshaft dot at 1:30 / Crankshaft dot at 3:00
TDC Cyl. #7) Camshaft dot at 3:00 / Crankshaft dot at 6:00
TDC Cyl. #2) Camshaft dot at 4:30 / Crankshaft dot at 9:00
TDC Cyl. #6) Camshaft dot at 6:00 / Crankshaft dot at 12:00
TDC Cyl. #5) Camshaft dot at 7:30 / Crankshaft dot at 3:00
TDC Cyl. #4) Camshaft dot at 9:00 / Crankshaft dot at 6:00
TDC Cyl. #3) Camshaft dot at 10:30 / Crankshaft dot at 9:00
If you have that and the timing cover off you don't even half to measure how far you turned the engine over, just line up the dots to the correct orientation and install. Thanks, Joseph
This means that your setup is exactly right.
This is the way it is with the LS motors.
All other engines that I'm aware of, use dot to dot #1 @ TDC.
I went through the same thing when assembling my LS1 engine.
In reality, the firing order is 6-5-4-3-1-8-7-2.
>>> From "Joseph" LS1 engine builder
Re:When torqueing the rockers
Glenn, I'm glad you found my info helpful, not many people know the valve events for all 8 cylinders and when they happen. You would naturally assume with the dots aligned it would be the firing position of cylinder #1, when its actually the start of the intake stroke as far as the piston/intake valve is concerned. With the dots aligned cylinder #6 is the one to set preload/lash/ or for installing rockers. Each 90* (720* / 8cyl = 90*) on the crankshaft gear is another cylinder firing, while each 45* (360* / 8cyl = 45*) on the camshaft gear is another cylinder firing. Having the timing cover off helps to watch the sequence. Here's a copy/paste of a manuscript I'm working on that may help also:
LSX Firing Order 1, 8, 7, 2, 6, 5, 4, 3
TDC Cyl. #1) Camshaft dot at 12:00 / Crankshaft dot at 12:00
TDC Cyl. #8) Camshaft dot at 1:30 / Crankshaft dot at 3:00
TDC Cyl. #7) Camshaft dot at 3:00 / Crankshaft dot at 6:00
TDC Cyl. #2) Camshaft dot at 4:30 / Crankshaft dot at 9:00
TDC Cyl. #6) Camshaft dot at 6:00 / Crankshaft dot at 12:00
TDC Cyl. #5) Camshaft dot at 7:30 / Crankshaft dot at 3:00
TDC Cyl. #4) Camshaft dot at 9:00 / Crankshaft dot at 6:00
TDC Cyl. #3) Camshaft dot at 10:30 / Crankshaft dot at 9:00
If you have that and the timing cover off you don't even half to measure how far you turned the engine over, just line up the dots to the correct orientation and install. Thanks, Joseph
08-19-2014, 09:31 PM
#14
With the dots aligned, cyl #6 is at TDC firing...not #1.
This means that your setup is exactly right.
This is the way it is with the LS motors.
All other engines that I'm aware of, use dot to dot #1 @ TDC.
I went through the same thing when assembling my LS1 engine.
In reality, the firing order is 6-5-4-3-1-8-7-2.
>>> From "Joseph" LS1 engine builder
Re:When torqueing the rockers
Glenn, I'm glad you found my info helpful, not many people know the valve events for all 8 cylinders and when they happen. You would naturally assume with the dots aligned it would be the firing position of cylinder #1, when its actually the start of the intake stroke as far as the piston/intake valve is concerned. With the dots aligned cylinder #6 is the one to set preload/lash/ or for installing rockers. Each 90* (720* / 8cyl = 90*) on the crankshaft gear is another cylinder firing, while each 45* (360* / 8cyl = 45*) on the camshaft gear is another cylinder firing. Having the timing cover off helps to watch the sequence. Here's a copy/paste of a manuscript I'm working on that may help also:
LSX Firing Order 1, 8, 7, 2, 6, 5, 4, 3
TDC Cyl. #1) Camshaft dot at 12:00 / Crankshaft dot at 12:00
TDC Cyl. #8) Camshaft dot at 1:30 / Crankshaft dot at 3:00
TDC Cyl. #7) Camshaft dot at 3:00 / Crankshaft dot at 6:00
TDC Cyl. #2) Camshaft dot at 4:30 / Crankshaft dot at 9:00
TDC Cyl. #6) Camshaft dot at 6:00 / Crankshaft dot at 12:00
TDC Cyl. #5) Camshaft dot at 7:30 / Crankshaft dot at 3:00
TDC Cyl. #4) Camshaft dot at 9:00 / Crankshaft dot at 6:00
TDC Cyl. #3) Camshaft dot at 10:30 / Crankshaft dot at 9:00
If you have that and the timing cover off you don't even half to measure how far you turned the engine over, just line up the dots to the correct orientation and install. Thanks, Joseph
This means that your setup is exactly right.
This is the way it is with the LS motors.
All other engines that I'm aware of, use dot to dot #1 @ TDC.
I went through the same thing when assembling my LS1 engine.
In reality, the firing order is 6-5-4-3-1-8-7-2.
>>> From "Joseph" LS1 engine builder
Re:When torqueing the rockers
Glenn, I'm glad you found my info helpful, not many people know the valve events for all 8 cylinders and when they happen. You would naturally assume with the dots aligned it would be the firing position of cylinder #1, when its actually the start of the intake stroke as far as the piston/intake valve is concerned. With the dots aligned cylinder #6 is the one to set preload/lash/ or for installing rockers. Each 90* (720* / 8cyl = 90*) on the crankshaft gear is another cylinder firing, while each 45* (360* / 8cyl = 45*) on the camshaft gear is another cylinder firing. Having the timing cover off helps to watch the sequence. Here's a copy/paste of a manuscript I'm working on that may help also:
LSX Firing Order 1, 8, 7, 2, 6, 5, 4, 3
TDC Cyl. #1) Camshaft dot at 12:00 / Crankshaft dot at 12:00
TDC Cyl. #8) Camshaft dot at 1:30 / Crankshaft dot at 3:00
TDC Cyl. #7) Camshaft dot at 3:00 / Crankshaft dot at 6:00
TDC Cyl. #2) Camshaft dot at 4:30 / Crankshaft dot at 9:00
TDC Cyl. #6) Camshaft dot at 6:00 / Crankshaft dot at 12:00
TDC Cyl. #5) Camshaft dot at 7:30 / Crankshaft dot at 3:00
TDC Cyl. #4) Camshaft dot at 9:00 / Crankshaft dot at 6:00
TDC Cyl. #3) Camshaft dot at 10:30 / Crankshaft dot at 9:00
If you have that and the timing cover off you don't even half to measure how far you turned the engine over, just line up the dots to the correct orientation and install. Thanks, Joseph
See, the reason why I asked this question in the beginning of the topic was for a lot of "Old school" engines for gm, dodge, or ford, would have the "dot to dot" timing and the piston would be a TDC at the compression stroke, and then you'd set the distributor rotor on no.1. ignition. (engine may vary of course) this is what I've always assumed.
Well obviously the LS engines don't have a distributor, all ignition timing is done via computer, so this explains a lot of whats going on inside the engine and helps me know more about the engine as I put it together.
Thank you to everyone who helped answer my question. Really puts my mind at ease.
08-20-2014, 09:22 AM
#15
See, the reason why I asked this question in the beginning of the topic was for a lot of "Old school" engines for gm, dodge, or ford, would have the "dot to dot" timing and the piston would be a TDC at the compression stroke, and then you'd set the distributor rotor on no.1. ignition. (engine may vary of course) this is what I've always assumed.:
08-21-2014, 12:12 PM
#17
Good info here as I am ready to perform this step soon for pushrod length checking and PTV clearance.
Marc, I originally posted here that I thought you were wrong about the old school small block. It was bothering me so I did some more research and found out you were right. I have personally put together 3 old school small blocks and 1 big block and thought that dot to dot (crank at 12 Oclock and Cam at 6 Oclock) is Cylinder #1 TDC firing. Then I remembered that I always set the valves after that and found #1 TDC firing by watching the valves or listening for compression out of the #1 spark plug hole. Thanks for setting me straight.
Marc, I originally posted here that I thought you were wrong about the old school small block. It was bothering me so I did some more research and found out you were right. I have personally put together 3 old school small blocks and 1 big block and thought that dot to dot (crank at 12 Oclock and Cam at 6 Oclock) is Cylinder #1 TDC firing. Then I remembered that I always set the valves after that and found #1 TDC firing by watching the valves or listening for compression out of the #1 spark plug hole. Thanks for setting me straight.
Last edited by Aston Tibs; 08-21-2014 at 12:33 PM.
08-29-2014, 07:55 PM
#18
I have to admit, this is still not quite clear to me. Like the OP, I installed the cam and have dot to dot with #1 @ TDC. I compounded the problem by measuring for pushrod length on #1. I have to re-measure again for the pushrod length but if I am understanding this correctly, I need to redo the cam so the dot is at 12 o'clock with #1 @ TDC and then the measuring can be done on #1.
Can someone please confirm that I have it correct.
TIA,
Can someone please confirm that I have it correct.
TIA,
08-30-2014, 05:30 AM
#19
TECH Fanatic
I have to admit, this is still not quite clear to me. Like the OP, I installed the cam and have dot to dot with #1 @ TDC. I compounded the problem by measuring for pushrod length on #1. I have to re-measure again for the pushrod length but if I am understanding this correctly, I need to redo the cam so the dot is at 12 o'clock with #1 @ TDC and then the measuring can be done on #1.
Can someone please confirm that I have it correct.
TIA,
Can someone please confirm that I have it correct.
TIA,