Before Top Dead Center

[dvelker]

Just looking for some simple clarification from someone.

2014 LR4 SCV6 137k miles

Both heads and timing chains were taken off. Crank was NOT locked into any position. So now I'm faced with getting everything re-timed/lined up.

I have the reworked heads/gaskets on and torqued.

Crank is at top dead center (with the #1 cylinder being front driver side cylinder).

Cams are on and lined up with the locking devices installed.

So what is the exact location of "Before" Top Dead Center?

Do I measure it in degrees or in teeth or ??????

Any help would be welcome.

Cheers!

 

[greiswig]

I'm not sure I understand the question, but..."before" would be any number of degrees of rotation before that #1 cylinder hits TDC. Things like injection and ignition have to happen a set, different number of degrees before TDC for the engine to run right. And it even depends on the RPM of the engine.

For reassembly, you shouldn't need to worry about anything except TDC.

 

[djkaosone]

It's listed in the workshop manual that timing is set at btdc, before top dead center.

The chuck on the crankshaft should point at the 6 o'clock position and you need to lock it with the special crankshaft sensor tool. Lock up the camshafts with the special tools. There are 2 marks per intake and exhaust cam sprocket. Intake and exhaust markings are different either raised or dimpled in. There are 3 marks on the timing chain, 2 of the same color goes to the sprockets and the other color goes to the marking on the stationary timing chain guide.

With everything locked, there's still enough movement on each camshaft for you to rotate a degree clockwise and/or counter-clockwise to line up the chains. There should be very very little play in the chain.

Up for debate is the tensioner, the workshop manual recommends removing the pin to fully extend the push rod, compress it, and relock it before installation. Suggesting these are reusable. I'm old school and I think they're single use.

 

[dvelker]

dj that’s good to hear. I’ll do it the way you suggested. Thanks so much!

 

[dvelker]

Hey DJ, when you said “chuck” you meant the “keyway groove” correct?

 

[dvelker]

It's listed in the workshop manual that timing is set at btdc, before top dead center.

The chuck on the crankshaft should point at the 6 o'clock position and you need to lock it with the special crankshaft sensor tool. Lock up the camshafts with the special tools. There are 2 marks per intake and exhaust cam sprocket. Intake and exhaust markings are different either raised or dimpled in. There are 3 marks on the timing chain, 2 of the same color goes to the sprockets and the other color goes to the marking on the stationary timing chain guide.

With everything locked, there's still enough movement on each camshaft for you to rotate a degree clockwise and/or counter-clockwise to line up the chains. There should be very very little play in the chain.

Up for debate is the tensioner, the workshop manual recommends removing the pin to fully extend the push rod, compress it, and relock it before installation. Suggesting these are reusable. I'm old school and I think they're single use.

Hey DJ, is “chuck” the same as “keyway”?

 

[djkaosone]

Hey DJ, is “chuck” the same as “keyway”?

Yes, at the crankshaft there is a keyway or chuck where the crank bolt goes in.

 

[djkaosone]

Oh, I would also like to add that you should mark the position of the chuck on the crank pulley. It'll save you down the road from trying to find the position later.

 

[Red Top Engine]

TDC is attained using two special tools that temporary lock the crank in place. One is locks into the flywheel flex plate, the other into the oil vacuum pump. Both locks can go in only one way. If they don't slide right in, you're not at TDC.

 

[djkaosone]

TDC is attained using two special tools that temporary lock the crank in place. One is locks into the flywheel flex plate, the other into the oil vacuum pump. Both locks can go in only one way. If they don't slide right in, you're not at TDC.

The key is finding it.

Choke the wheels, put it in Neutral. If your battery is off the truck, pull the center cup holder and push the white plastic shift lock in to put it in Neutral. The way I found it is to stick a long kebab stick down cylinder 1 through the spark plug, rotate the crank clockwise until the the kebab is at its highest peak, and that's TDC, BUT timing is set BTDC. Disassemble the crank pulley to find the chuck or keyway sitting at the 6 o'clock position. If it's off, put the crank bolt back in and rotate the crank until its at 6 o'clock, but it should be very close. That means that you'll have to rotate the crank counter-clockwise just a smidge less than 1/16th of a rotation to find it in the correct position and then you can pull the crank sensor out to lock it with the crank timing tool. You'll need to pull out the starter and lock it with the starter locking plate. Then you can proceed with the rest.