Lining up the timing marks, no belt on

[dpr64]

Say if I were to work on my 2000 V8 Tundra and the timing belt is OFF and the cam marks are mixed up and the crankshaft mark is unknown and not lined up. Could I possibly just align the crankshaft at '0' top dead center (compression or exhaust stroke unknown) and just adjust the cam timing marks so that they now align with the marks, would everything workout okay? Or would I still have to know if the crank was on a compression or exhaust stroke?

Will rotating the crank around a few times or the cams a few times without the belt on damage each other?

[kovawa]

The white mark on the crank dampener indicates "top dead center" for the number 1 cylinder only. The camshafts position, relative to crankshaft position, determines whether or not the pistons are on their intake, compression, power, or exhaust strokes.Since each piston reaches it's own TDC once per crankshaft revolution, 1 piston out of 8 is at TDC for every 45 degrees of crankshaft rotation. If you need to realign the camshafts to the crank..... be aware that the toyota V8 is an interference engine. Valve damage will occur if you rotate the crank without using caution. The following is the safest way to realign the timing belt without risking major damage to the engine.
1. remove the spark plugs, this step will allow you to turn the engine by hand and let you feel for any piston to valve contact.
2. Gently turn the crank to 22.5 degrees BTDC ( before top dead center ) or ATDC (after top dead center). This position will assure that none of the 8 pistons is at TDC, which reduces the chances of piston to valve contact.
3.Realign the camshaft pullies to the respective timing marks.
4. Rotate the crankshaft back to TDC.
5. Install the timing belt on the engine.
6. Rotate the engine by hand a few times and double check the belt alignment.
7. Reinstall the spark plugs.
Provided that you put everything else back together correctly during the reinstall phase, your engine should run fine.

good luck

[Hi Volt]

The white mark on the crank dampener indicates "top dead center" for the number 1 cylinder only. The camshafts position, relative to crankshaft position, determines whether or not the pistons are on their intake, compression, power, or exhaust strokes.Since each piston reaches it's own TDC once per crankshaft revolution, 1 piston out of 8 is at TDC for every 45 degrees of crankshaft rotation. If you need to realign the camshafts to the crank..... be aware that the toyota V8 is an interference engine. Valve damage will occur if you rotate the crank without using caution. The following is the safest way to realign the timing belt without risking major damage to the engine.
1. remove the spark plugs, this step will allow you to turn the engine by hand and let you feel for any piston to valve contact.
2. Gently turn the crank to 22.5 degrees BTDC ( before top dead center ) or ATDC (after top dead center). This position will assure that none of the 8 pistons is at TDC, which reduces the chances of piston to valve contact.
3.Realign the camshaft pullies to the respective timing marks.
4. Rotate the crankshaft back to TDC.
5. Install the timing belt on the engine.
6. Rotate the engine by hand a few times and double check the belt alignment.
7. Reinstall the spark plugs.
Provided that you put everything else back together correctly during the reinstall phase, your engine should run fine.

good luck

Very good writeup, but just one clarification. On #6, rotate the engine and check the crank and cam pully marks for correct alignment. The belt marks will take many revolutions to all line up exactly as you installed the belt. A couple of rotations is all that is required to know you have it right.

[george60]

TopDeadCenter "position" is reached on each turn of the crankshaft - however the TDC for engine timing purposes is only reached every other crankshaft rotation. (Four-cycle engine). TDC occurs at the end of the compression stroke of a piston when it has reached the top of the cylinder bore and is ready for the spark plug to fire.

For the purpose of setting the timing between the camshafts and crankshaft (SetEngineTiming) yes, you would need to know whether the crank was on exhaust or compression stroke.

[kovawa]

For the purpose of setting the timing between the camshafts and crankshaft (SetEngineTiming) yes, you would need to know whether the crank was on exhaust or compression stroke.

Determining whether or not the engine is on a compression or exhaust stroke is a moot point when it comes to realigning the belt to the camshaft and crankshaft marks. It's the relationship between the crankshaft's position relative to the camshafts that determines which stroke the piston is on. The OP was asking how to realign the timing belt, if it were off the engine and the crankshaft and/or cams had been rotated out of "time". "TDC" is "TDC" the #1 piston will be at the top of it's cylinder- that's all that matters. With the crank set to "TDC", the camshafts can be aligned to the factory timing marks or 180 out of phase and the engine will still run. The Toyota V8 uses an "DISTRIBUTORLESS" ignition system, so...... gone are the "old days" of needing to determine if the engine is on the intake or exhaust stroke prior to "droppin in the distributor". The ECM handles all the ignition timing chores.

[dpr64]

Awwww!!!!! I see said the blind man! Thanks for all the info, that really helps!

[dpr64]

One last question I would like to know about.....if the belt was off and the crank moved around a bit or the cams turned a bit, would any damage really result? Or does that only happen only if it is running and they gnash into each other? Once I get it up and running, will there be any tell-tale sign that the piston/valves/etc suffered any damage?

Thanks.....

[Hi Volt]

Only if the valves/pistons contacted each other with some force, such as if the belt broke while the engine was running, you may have bent a valve. If there was some contact only while turning the crank or cams by hand, chances are you would not have any significant damage. About the only way to tell is to get the belt on ( properly set up ) and roll it over by hand. A bent valve may bind in the guide and cause a tight spot. About the only real way to tell is to do a compression test, and compare the cylinder results. The actual pressure reading gives and indication of the overall condition of the engine ( wear etc ), while the difference between the individual cylinder values is most important as it can spot various problems like burnt or bent valves, bad rings, blown head gasket etc. A significantly lower reading on a single cylinder could mean a valve sealing issue ( there are a number of things that can cause a low cylinder, but we will assume the engine was in reasonable shape before the belt change ).

The factory spec. is done with a warm engine, but for your purposes a cold engine is what you will have to work with ( I recommed doing the compression test before firing the engine just to ensure there are no issues). Make sure you have a fully charged battery and hold the throttle fully open while the test is done. Normal cylinder pressure is 192 PSI or higher ( 142 PSI minimum ) with a cylinder variance of 14 PSI or less ( the lower the variance the better ). If you fall within these specs you are probably fine and can procede to run the engine.

[dpr64]

Thanks for that info, it really helps. On the compression test, should I do 1 plug at a time out or take them all out at once and start checking?

[Hi Volt]

Have all the plugs out at once so the engine rolls over easy and cranks at maximum speed. Also have the throttle wide open while cranking so that you get unrestricted air into the cylinders.

[pearldrums287]

excellent thread. very helpful. thanks.