Cam shaft timing causing engine to jam when rotating by hand

Not knowing how far your cam timing is off, your valves may be hitting the top one of a pistons. That may be why cam wont turn anymore.
May be best to back up the cam a bit, remove the spark plugs & with screw driver or wooden dowel probe the cylinders to see which piston is near the top.
Then rotate crank a bit to lower piston down the cylinders DO NOT USE STARTER to rotate engine while timing belt is off or valve damage may occur.

bent push rods come from improper movement of the rocker and valve
This can be from an incorrect length push rod-- some v8 engines run different lengths for inlet and exhaust
from rocker arm jamming on the shaft or rocker ball
hydraulic cam follower pumping up and jamming the valve spring to a solid block
bent valve stem above the valve guide
valve spring Colette moved or misplaced incorrect rocker for that valve-- some engines run different length rockers for inlet and exhaust
what to do-- if this engine was running all right for some time then the rocker can be omitted. if the problem has been occurring since the cold weather the the oil may be too thick and not allowing the follower to leak down properly
check the follower or replace it , change to a lighter viscosity oil for the duration of the cold weather
unless you have had a recent head change or other mechanical work done the problem will be in those areas.

On. An Indica petroll or diesel there aren't aany timing marks as to say, firstly remove cylinder head, then attach a power bar or ratchet with socket to to bolt on crank shaft pulley. Rotate the engine anti-clockwise until piston one is at TDC (highest point it can go). Then at Te front of engine halfway down the block where engine meets bell housing there is a hole to. Insert a 8mm long bolt, this will lock the crankshaft. On the head on the cam shaft end cap is a hole, insert a screwdriver to fit and rotate cam with. A ratchet until the screwdriver slots in place and the cam cannot move. Replace the head, torque the bolts, fit the timing belt and tension it. Once this is done remove the locking bolt and screwdriver, Replace the cam-tappet. Cover and start the engine

Remove the rocker cover to ascertain the damage done . It may not be bearings but seized valve in the head. To fix cam bearings properly it may necessitate the head removal and machining both the head surface and then the bearings should be line bored to realign the cam shaft correctly. Some Nissan products have the cam bearing housings adjustable with shims to align the holes correctly and if not done will break the cam shaft. IT may be the cam shaft is broken and jammed . What ever it will not be just a case of putting in new bearings until you have the head and bearing alignment checked out by an engineering shop.

Hi Robert, It would help to know what engine is in your vehicle? A rule of thumb way to set up the valve timing is as follows. Rotate the crank shaft until the crank shaft mark is about 90 degrees from TDC. This will protect the valves from damage when rotating the cams to align them. With the tappet cover removed rotate the cam shaft or shafts so that the number one cylinder is on compression (both inlet and exhaust valves fully closed) and the last cylinder in line on overlap, Look for adjacent timing marks on the cam gears and somewhere close to those look for the alignment marks (maybe notch marks, holes or indented match marks). (Some manufactures use the machined gasket surface where the tappet cover closes onto the cylinder head). Look closely for the static mark on the cylinder head and align the cam(s) to it or them. Once completed, set the crank at Top Dead Center and look carefully for a timing mark which aligns with the gear and set them. Fit the belt so the marks align when the tensioner bearing is released and presses the belt under load. (follow the manufactures recommended tightening instructions.) . (Remember never to crimp a timing belt, if it has been, throw it away and get another, even if it is new!) If the belt snapped and that is the reason for replacement, internal damage may have resulted inside the engine. A snapped belt may cause damage to the valves, the camshafts, the cam shaft caps and to the pistons. If the engine turns much faster than expected and sounds as if there is no compression, you have problems! (Those I've just mentioned. I hope not for your sake. best of luck Regards John

Required tools:
13mm open end wrench 10mm shallow and deep socket 8mm socket long flat-head screwdriver 17mm deep socket T50 torx socket 1/4", 3/8ths and 1/2" ratchets and extensions E10 inverted torx sockets 6mm allen wrench 15mm open end wrench 7mm socket 12mm open end wrench 14mm socket 12mm socket 8mm, 9mm and 10mm allen head sockets 19mm socket pry-bar needle nose pliers
If you are doing this because your timing belt broke you will also need to buy a complete cylinder head, head gasket set, and both idler pulleys. ALL DAEWOO MODELS WILL BREAK THE INTAKE AND EXHAUST VALVES WHEN THE TIMING BELT BREAKS.
Start by removing the air cleaner assembly from the throttle body, remove the air filter and housing jack up the vehicle and remove the wheel, remove the plastic shielding in front of the accessory drive belt assembly, remove the accessory drive belt, place a jack with a block of wood on top underneath the engine oil pan remove the front engine mount, remove the crank shaft pulley ( the 4 allen head bolts only not the 17mm bolt in the center.) remove the metal plate behind the engine mount bracket on the engine, remove the plastic timing belt cover 3 clips on top 2 10mm bolts on bottom. Rotate the engine until the #1 cyl. is at Top Dead Center on the compression stroke or line up the crankshaft timing mark with the mark on the inner timing belt cover ( notch in cover with notch in pulley) on the camshaft pulleys -- ( intake cam line up the line on the pulley with the line on the inner cover)( exhaust cam line up the arrow on the pulley with the arrow on the inner cover) loosen the 13mm bolt in the belt tensioner and using the allen wrench rotate the tab until there is slack in the belt. Remove the belt. At this time I would recommend you replace the water pump, both plastic idler pulleys as they tend to overheat and lockup, and the belt tensioner. Make sure all your marks are lined up, you may need a helper to hold the Exhaust Cam in place as it tends to move during belt installation. Put the timing belt underneath the crankshaft pulley, install the belt leaving the intake cam for last and NO BELT SLACK on the right side between the crank and the exhaust cam. Once the belt is installed rotate the crankshaft over 2 revolutions and make sure is rotates freely, and your timing marks are aligned perfectly if not the engine will not run properly, tension the belt as needed. Installation is the same as removal.

Daewoo has interference engines in them, so if the timing belt broke while the engine was running, you will need to replace half of the valves which were bent when the pistons crashed into them when the cams stopped turning and the crank shaft continued to turn. Minimum of $700-1000.00 (usually more). If you do it all yourself and the valve guides are not damaged, still at least $400.00 worth of parts to fix. Pull plastic air dams around bottom of engine on front and right side . Support engine with jack. Drain antifreeze from engine and radiator. remove air filter housing and serpentine belt. remove front engine mount. remove cam belt cover. remove broken cam belt and check cam tensioner bearings and idler bearing as well. They are usually bad. Then remove spark plug cover. Remove valve cover. Remove intake from head. remove coil from head. remove heat shield from exhaust manifold then remove manifold from exhaust and from head. remove water hoses and connecting assemblies from side of head and rear of head. remove Cam shaft bearing caps loosening them all evenly so as not to bend cams. remove cams. remove head bolts. remove head. remove valve hydraulic lifters, compress valve springs and remove valve retainers and dissassemble valves. Clean everything very well. Make sure head is not damaged. Remove valve guide seals. install new valve guide seals, new valves. Seat valves with valve grinding compound. clean well. instal valves in reverse order of dissasembly. Before putting head on, make sure number 1 cylinder is at top dead center position. install head using proper torque of 18 ft # in a spiral application rotation from the center outward in a clockwise direction. Then do spiral rotation again tightening bolts each one-quarter turn. Repeat the tightening process two more times only turning the bolts one-quarter turn each time. Use new head bolts. They are designed to stretch in the process of installation and are not to be re-used. Align cams to proper orientation then bolt into place. do not overtorque cam bearing cap bolts. Less than 5 ft # of torque can stretch these bolts. Snug them then tighten them 90 degrees. Then tighten them another 90 degrees (quarter turn). Snug them all then go back and tighten all of them a quater turn, then go back and tighten all of them another quarter turn. Install the cam idler and tensioner and install the cam belt. then install the intake, exhaust and all other items in reverse order of assembly. Do not turn engine over unless you are sure you have the cam belt on with the crank shaft pulley aligned at top dead center and the intake and exhauste pulley marks aligned to their proper marks with the cam belt properly tensioned. You can't be even one tooth off. This must be right before you turn the engine over! Remove spark plugs and turn engine over by hand two rotation clockwise using a wrench on the center bolt of the crank shaft pulley. Check that the timing of cams is still perfect. If not, correct, retension cam belt, double check timing positions again then rotate engine two revolutions. Check cam timing positions again. The timing should not change! The engine should turn over relatively easily. If it feels like it doesn't want to turn, don't force it. You may have the timing off and be pressing a piston against a valve. If you are at this point, then you need to remove cam belt and unbolt cam shafts to release all tension on any of the valves. return the number one cylinder to top dead center position and then reinstall the cams and cam belt. Once it is assembled and in time, then reattatch the rest of the components that were removed in dissassembly. Do this in reverse order of dissassembly. then connect battery and fill radiator fluid. Start car.

The crankshaft pulley and bottom half of the plastic cambelt cover needs to be fitted. Of course the cambelt is also already fitted on the crank.
Get the crank on TDC. No 1(furthest from the gearbox) cylinder's piston must be at the top. To determine this look on the bellhousing, there is a large plastic plug which needs to be removed. Inside the bottom of this hole you will see a piece of metal(looks like an arrow) pointing downwards
Remove the sparkplug on cylinder 1. Use a long wooden dowel, about 10 inches to be safe, insert it into the plug hole and try to keep it as upright as possible. (You can also use a screwdriver but you have to be careful not to get it jammed since it will scratch the cylinder walls and/or piston crown) Rotate the engine till the dowel is at its highest point. Now look in the bellhousing where you removed the plastic plug. You should see a line with a 0 stamped next to it on the edge of the flywheel. Line this up with the pointy piece of metal visible inside the bellhousing.
Next on the cam pulley(on the inner/engine side) is a little dot stamped into the metal on the side of one of the teeth. Line this up with the front top edge of the head. Looking at no 1 cylinder's cam lobes they will now both be pointing upward away from the valves lifters, so that both valves are closed.
Last you have to line up the intermediate shaft(that drives the distributor). It also has a little dot stamped on a tooth, but on the outside of the pulley. Turn it until it lines up with the notch in the crankshaft pulley. If you dont you may not be able to get the distributor lined up to set the ignition timing. Fit the cambelt over the intermediate shaft first and then starting at the front of the camshaft pulley(ie keeping the tension over the intermediate shaft) fit the belt over it and you're done.

Remove number one spark plug.Rotate engine hand and cam separately until piston is at top for number one cylinder and ignition rotor is aligned at number on hole. Now you can install timing belt. Rotate engine by TWO crankshaft resolutions. Recheck timing marks. Now perform compression testve to with all spark plugs out on all cylinders. If one is low then you have an interference problem and will have to remove cylinder head to have bent valves repaired.

i use a wedge shaped piece of plexiglass/plastic to jam the timing chain up and against its guide rails after timing is set TDC....slide it through opening below cam gear before removing gear and head