Top Dead Center!

12vanthony

12vanthony

No idea what Im doing
Joined
Apr 20, 2009
Messages
414
I am getting ready to start installing my new valve springs and I was wondering exactly how I know it is at top dead center and how close it had to be to TDC, especially for putting everything back together for clearances and stuff. Thanks
 
There's a plug in the back side of the gear case above the vacuum/steering pump. Pull the plug out. Use a barring tool to roll the engine over while watching in the hole where the plug was until you see a hole in the cam gear line up with the hole. At this point, you're close. Take #1 valve cover off. Remove a rocker. Compress the valve spring and release the retaining hardware for the spring. Pull the spring up. Get a dial indicator with stand and set it up to measure the height of the valve stem (it's sitting on the piston at this point). Use the barring tool again and roll the engine one direction until you find the point the valve begins to move down. Mark that spot on your harmonic balancer at a point that lines up with something easily visible on the gear case. Roll the engine over in the other direction until the valve begins to move down. Mark that spot on the balancer at the same alignment point on the gear case. Measure the distance between your 2 marks over the outer diameter of the balancer. At half the distance between the 2 marks, make another mark. This is true top dead center.
 
To do valve springs just bar the motor over till you hit cross over on a cylinder. IE: one valve moving up and the other starting to move down. That will get you close enough to remove the spring. Then do them in companions 1,6: 2,5: 3,4
 
PRattenbury said:
There's a plug in the back side of the gear case above the vacuum/steering pump. Pull the plug out. Use a barring tool to roll the engine over while watching in the hole where the plug was until you see a hole in the cam gear line up with the hole. At this point, you're close. Take #1 valve cover off. Remove a rocker. Compress the valve spring and release the retaining hardware for the spring. Pull the spring up. Get a dial indicator with stand and set it up to measure the height of the valve stem (it's sitting on the piston at this point). Use the barring tool again and roll the engine one direction until you find the point the valve begins to move down. Mark that spot on your harmonic balancer at a point that lines up with something easily visible on the gear case. Roll the engine over in the other direction until the valve begins to move down. Mark that spot on the balancer at the same alignment point on the gear case. Measure the distance between your 2 marks over the outer diameter of the balancer. At half the distance between the 2 marks, make another mark. This is true top dead center.
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u can also just hold that plug in and bar the motor over untill it falls in the hole. when i had my head off we check to see just how close it was and its all most dead on. just make sure not to break it off:badidea:
 
jeffreystewart said:
u can also just hold that plug in and bar the motor over untill it falls in the hole. when i had my head off we check to see just how close it was and its all most dead on. just make sure not to break it off:badidea:
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They won't always be bang on though, thats why you need to double check.

You can also measure TDC by dropping the valves down with the rockers instead of a spring compressor. Still need a dial indicator, but you don't have to take the rocker off to do it. Not like that is much of an issue if you are changing springs, though.
 
cant i bar the engine over with the alternator nut? that is how i did it for my gov springs.

Garrett
 
jeffreystewart said:
yea but u can only spin the motor one way. Thats wat i did to get it close then barred it the rest of the way from the flywheel.
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You can do the whole thing with the alternator nut. Done it on 2 trucks and it worked flawlessly.
 
to find true tdc you need to pull a injector #1 and fab up a piston stop [old injector nut with a 5/16'' bolt 3.5 long or so welded in it].fab up a marker on the dampner somewhere.Run the piston up to the stop somewhere before tdc and mark the balance at the marker.then rotate the crankshaft the other direction to the stop and mark the dampner again and measure the gap between the two marks and split the difference.I found that my pin in the cam was 4.25 degrees off.A degree wheel is perfered, but very diffacult in the truck.
 
bansley said:
to find true tdc you need to pull a injector #1 and fab up a piston stop [old injector nut with a 5/16'' bolt 3.5 long or so welded in it].fab up a marker on the dampner somewhere.Run the piston up to the stop somewhere before tdc and mark the balance at the marker.then rotate the crankshaft the other direction to the stop and mark the dampner again and measure the gap between the two marks and split the difference.I found that my pin in the cam was 4.25 degrees off.A degree wheel is perfered, but very diffacult in the truck.
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Drop valve way is just as accurate, and less disassembly.
 
so, you are saying that using the pin isnt always accurate? should i do your guys' way of TDC before timing my pump?
 
Find true TDC, then set your lock pin to it, so it will be right from here on out.
 
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