Finding TDC on LQ4
09-02-2012, 11:09 AM
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Finding TDC on LQ4
I know I'm going to catch hell for this but I really need help finding tdc on my motor so I can throw it together today/tomorrow. Shouldnt I just be able to put the crank dot up with #1 all the way up in the bore and then put my heads on and line my cam gear up dot to dot? I'm being thick headed today and can't figure it out.. Thanks for any help and sorry, I read through all of the search results and I still don't quite get it. 
09-02-2012, 11:26 AM
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Yes if you have the heads off you can see. If they are on it is going to take 4 revs of the motor to be on the correct stroke, in turn the dot should be up on the crank gear.
09-03-2012, 02:29 PM
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Shopkey/gm shows the camshaft dot facing up for #1 at tdc.... this conflicts every piece of info saying dot to dot on the timing set. what gives?
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10-09-2012, 10:42 PM
#10
Actually I don't think it really matters. The cam and crank sensors read the signal from the wheels on the cam and crank to determine their location.
It's not like a distributor.
As long as it's straight up or straight down. Remember As the crank turns 1 revolution or 360* the cam only turns half of that or 180* So at some point the dot on the cam will either be straight up or straight down relative to TDC or the dot straight up on the crank gear.
HTH
EDIT:
I would like to elaborate since both drawings are technically correct.
On a generation 3 LS motor the cam sensor reads off the back of the camshaft. This is something that can not be changed. It is manufactured into the camshaft.
On the crank they had 24x toothed wheel's on the Gen 3 and 58X toothed wheel's on the Gen 4 motors.
The crank spins 2 full revolutions to every 1 full rotation of the camshaft. If you lined the cam sprocket up at dot to dot. Or in other words Cam dot at 6 o'clock and crank at 12 o'clock, At 1 full revolution of the crank, the cam and crank would both be facing up at the 12 o'clock position.
Unless you spin the crank trigger wheel on the crank, It is physically impossible to have the timing out 180* on one of these motors. This is not a Distributor engine.
A good practice is to use the dot to dot method to ensure you're not 1 tooth off.
Hope that helps clear things up.
It's not like a distributor.
As long as it's straight up or straight down. Remember As the crank turns 1 revolution or 360* the cam only turns half of that or 180* So at some point the dot on the cam will either be straight up or straight down relative to TDC or the dot straight up on the crank gear.
HTH
EDIT:
I would like to elaborate since both drawings are technically correct.
On a generation 3 LS motor the cam sensor reads off the back of the camshaft. This is something that can not be changed. It is manufactured into the camshaft.
On the crank they had 24x toothed wheel's on the Gen 3 and 58X toothed wheel's on the Gen 4 motors.
The crank spins 2 full revolutions to every 1 full rotation of the camshaft. If you lined the cam sprocket up at dot to dot. Or in other words Cam dot at 6 o'clock and crank at 12 o'clock, At 1 full revolution of the crank, the cam and crank would both be facing up at the 12 o'clock position.
Unless you spin the crank trigger wheel on the crank, It is physically impossible to have the timing out 180* on one of these motors. This is not a Distributor engine.
A good practice is to use the dot to dot method to ensure you're not 1 tooth off.
Hope that helps clear things up.
Last edited by 1FastBrick; 10-16-2012 at 09:55 PM. Reason: Elaboration for clarification