Timing marks? Installing timing chain need to know timing from cam to crank?

The marks on the chain are for your convenience i.e. no need to count links between crank and cam(s).

The chain markings shift depending on the number of links in the chain and number of teeth on the crank and cam gears, but the number of links (rotational distance) between crank and cams remains the same.

Once you turn the crank it it may take dozens of revolutions to sync back to the marks on the chain, unless you reverse the same number of revolutions.

So if you want to recheck timing after multiple crank revolutions, you need to count links from crank to cam and cam to cam or redo the timing procedure.

Think of it this way... you could stretch a chain around the moon and timing will be good but it will take hundreds of thousands of revolutions before the marks return to earth and likely still not in sync with gear marks.

In the old small block days no one counted links because crank and cam gears were adjacent, in the same planes and timing intuitive.

As long as the timing marks on the cams and the crank are correct and the chain is the correct length. And the chain tensioner is set correctly, the chain doesn't need to be marked.

With Cam Caps loosened, FIRST loosen timing chain tensioner, press it in to loosen tension, Crank using ratchet to TDC (Top Dead Center on crank pully, (to keep from damage to pistons), align Exhaust Cam Timing Mark to mark on #1 Exhaust cam cover, then take up slack between Exhaust & Intake Cams (on top between the cams), Then align the Intake Cam to mark on #1 Cam Cap, "Now" loosen the 17mm bolt to tighten timing chain, rotate engine using rachet two times, reset TDC at the crank, and look at "Cam Timing Marks on both the Exhaust, and Intake Cams. If you did all this correctly the "Timing Marks" should be lined up so TDC,Exhaust, and Intake marks are all the same.

It's on TDC so align marks on cam shaft and crank shaft with center of cam & crank shafts and the ECM will go from there. so you will have to change the timing chain if its loose or worn out.

Timing the Cam to the Crank

There are several ways to time the cam to the crank. Be sure to check the manual before you install the timing chain or belt.

• Some timing sprockets are properly timed when the marks face each other.
• On others, there must be a certain number of chain links between the marks.
• Sometimes chains have colored links that must be aligned with the marks on the sprockets.
• Some overhead cams have a mark on the cam gear that lines up with a mark on the cylinder head when the timing mark on the damper is at the TDC mark.

Align the timing marks for the camshaft and crankshaft sprockets before removing the timing belt or chain.

If the old parts are available, carefully compare the new gears or sprockets with the old ones. Check the keyway and timing marks just in case there might have been an error made in manufacturing. Sprockets are sometimes stamped backward. Its much better to find the problem during assembly, rather than waiting until problems show up after reassembly and reinstallation.

Maintaining Valve Timing

During a valve job, it is essential to keep the timing chain or belt in place to maintain correct valve timing. Position the number one cylinder at TDC. Some overhead cam engines use a single long chain for a cam drive. The chain can be wedged against its guides with a tapered block of wood.
the chain tensioner on some ohc engines must be wedged to keep the chain in position during cylinder head removal. courtesy of nissan motors.

Some engines have a lower and upper chain. These engines do not require special attention to wedging the chain. Be sure to look for hidden head bolts and check the repair manual before removing the OHC head.

By :"specs" I assume you need install position? To index the gears, whne you take it apart, turn the crank pulley 'till the timing mark aligns with the "0" on the timing scale. Don't turn the crankshaft again. When you are ready to install the chain, locate the mark on the crank gear and align the mark on the cam gear so they point to each other. The mark on the crank gear should be at 12 o'clock and the cam gear mark at 6 o'clock. Make sure when you put the cam gear on the cam that the location pin fits into the gear to position it correctly. Jeep recommends that after putting the chain and gears on, you rotate the engine by hand and place the crank mark at 6 o'clock and the cam gear at 3 o'clock, then count the number of pins in the chain (pins, not links) between those two points. There should be 15 pins. If you are rebuilding the engine and have the cylinder removed, it's a good time to check the front crank pulley (some have the outer ring move on the rubber). Put a piece of flat steel across #1 cylinder with a bolt through the steel extending into the bore center. Turn the engine by hand 'till the piston contacts the bolt. Make a mark on the pulley and turn the engine in the opposite direction till contact is again made. Your timing mark on the pulley should be exactly between the two marks you made. If not, make a new mark at that point and use that as your actual TDC reference. If it is radically off, replace the pulley.
When setting up cam position I always use a degree wheel. If you are installing an aftermarket cam
its important to do that. If you're just replacing a stock chain, You will be fine with the method I've outlined.

During most engine rebuilds, a completely new timing assembly should be installed. If wear exists on any component, replacement of the entire assembly is necessary. Wear in the chain, gears, or sprockets means a timing lag, which results in poor engine performance.
The timing chain or belt is generally installed with the gears in their correct positions. Before installing a new chain, soak it in oil.
OHC (Overhead Cam) Engines
Some OHC engines use a chain drive; others use a belt drive. Removing the cover on some OHC engines that have timing chains is more difficult, because the cover often fits between the oil pan and the cylinder head. There are special procedures for replacing cam timing components in these engines.
Before a chain repair job, perform a leakage test on non-freewheeling engines to check for bent valves, so that an accurate repair estimate can be made.
OHV (Overhead Valve) Pushrod Engines
On many OHV pushrod engines, the crankshaft sprocket is installed on the crankshaft nose and the crankshaft is rotated to position piston #1 at TDC. At this point, a mark stamped onto the crankshaft sprocket is pointing directly upward (toward the camshaft).
The camshaft sprocket is then temporarily bolted to the cam and used to rotate the cam until a mark stamped on the cam sprocket is pointing directly downward (toward the crankshaft). The sprocket is then removed from the cam (without allowing the cam to rotate).
The timing chain is looped over the cam gear, the mark on the cam gear is positioned directly downward, and the chain is looped around the crankshaft sprocket. When the cam sprocket is attached to the cam, the timing marks on the crank and cam sprockets should be pointing toward one another. NOTE THIS IS FOR 2WD 4.0

complex job chains have coloured links to line up with gears and a set number of links between timing marks, best get a manual or a professional to do job

I don't have a diagram but here are written instructions.

I don't know how much you know about the subject so I will start at the beginning. First you have to get to it, you can pull the motor or leave it in the vehicle. Its a little harder with it in depending on the space you have in engine compartment. If your leaving the motor in, which I imagine you are, your going to have to take the front end of the vehicle apart. Remove the grill, bumper if need be, radiator, fan, water pump, harmonic balancer, you will need to buy a puller and a installer for the harmonic balancer. You can get a puller kit from harbor frieght tools for $10. You can buy the installer from Summit racing (web site) for around $30 or you can buy one that will do both the install and removal from summit for $70. Once you have removed your harmonic balancer you can remove your timing cover to expose your timing chain. Turn the motor using a socket wrench until the timing marks on the crank gear and cam gear line up. The marks are usually just white dots, you want the crank mark to be up towards the cam and the cam mark towards the crank, the marks will be up and down from each other. Once you have the marks lined up remove the bolts holding the timing chain to the cam and crank. Remove the timing chain as a whole unit with the cam and crank gear still on it. If the crank gear doesn't want to come loose use your puller on it. when you get it off just put your new gear on and line up the timing marks then put it back on as one unit. If you cant get the crank gear on all the way by hand buy a crank install tool (summit) they run about $24. While you have the thing apart it would be a good Idea to put a new timing chain on. Depending on your vehicle this would also be a good time to change your cam if need be. Its not that hard to do it just takes a while, take your time and don't force anything. If you need anymore help my email is [email protected]

if you mean the timing chain then on your crank gear and your cam gear there will be a mark on each sometimes they look like a dot the dots need to look like this for perfect timing ( . . ) this will be there closest position. Your crank turns once all the way around (360 degree) and your cam gear will do two complete revolutions to the one of the crank gear. so when you set your marks as above when you turn the crank one half turn the mark on the crank gear will be at the bottom and at the same time your cam gear will have made one complete revolution, so when you turn the crank another half turn your cam would have turned again a complete revolution and the two marks should be at their closet point again.