I am replacing the head that someone else pulled off. do i verify that the engine is on tdc when i replace the head or just align the cam gear with the notch?

First pull the timing belt tensioner then slip the belt off the cam gears. You then need to find TDC (Top dead center). 3 ways to find TDC 1) There are marks on the crank pulley align them for TDC. 2) Remove timing cover and use crank gear mark seen in link below 3) Put the dip stick in cylinder 1 and turn engine until dip stick stops going up. After finding TDC align cam gear marks seen in link below. Now make sure both cam and crank stay in position and slip timing belt back on (you can move the cam gear to get the belt on but make sure the marks are aligned after the belt is on). Last tighten the belt tensioner, I usually use my finger or an extension to get some more tension on the belt. You might have to remove engine mount bracket makes life much easier as the front cover section is TIGHT !!!. Turn engine a few times to make sure you have compression and engine turns without getting stuck. See link below good luck.

http://bladeagenos21.soup.io/post/374487151/timing-marks-on-mazda-626-1994-diagram

remove ignition cover , put piston next to cam chain at tdc and move cams round with chain over cogs till aligning marks on cogs line up with head face edge and replace cam retainers , some engines have small dots on cams that line up on the retainers which have a mark on so you can see them aligne too , if ok then fit chain tensioner and guide and rotate engine in direction of rotation with bike in gear and rotate rear wheel by hand to check if valves miss pistons etc ! all ok then refit all parts and run up P...

place crank at TDC. turn cam until all the valves over number one are closed. your valve train will now be in time. however there should be timing marks on the cam gear and crank gear, with the motor at TDC align the marks and your valve train will be in time. you dont have to have your valve adjusted, you can either watch you pushrods move or watch the valves move in an overhead cam application

With the belt off and the tensioner pulley pushed back, you will need to set cylinder 1 (far passenger side) to top dead center. There is a mark on the block you can see just behind the crankshaft gear that needs to be aligned to the mark on the crankshaft gear. CAUTION NOT TO TURN THE CAM PULLEY TOO FAR IF ANY PISTONS ARE AT TDC, they will contact the piston on this motor. turn the crankshaft gear forward or backward 1/4 turn off of TDC when you move the cam pully. Once this is done, you will need to set the camshaft pulley to a poorly designed mark on the cylinder head. (it is the corner point of the casting for the cylinder head, it forms a triangle at about the 10:00 position when looking at the cam pulley). Install your belt, it will be tight even with the tensioner pulled back so making sure it doesn't cause either of the gears to move off their marks. Once it on recheck the timing marks upper (cam) and lower (crank), release the tensioner, put your other belt on and you're done. http://www.mivec.co.nz/tech/4G9x_Engine_Manual.pdf

take the head off bent valves thats for sure

turn engine to TDC No1 cylinder at this point the cam cog has a hole drilling which should be at 12 o/clock position and alignes with a V notch on the cyl head as you look thro the cam drill/hole and when crank pully is at TDC the cog has a marked tooth which should align with mark on engine approx 12-30 pm position these marks are all clear to see and belt change takes around TWO AND HALF HOURS to do

Put the engine at TDC compression stroke , Thats when the valves are both closed on No 1 cyl and the piston is on its compression stroke .then align all cam and crank marks. set dizzy on No 1 cylinder (rotor pointing at #1 plug wire) . rotate engine 2 revolutions and recheck all marks. Fire away

It's more to it than aligning the marks since the cam pulleys turn about three times or more to one turn of the camshaft on this engine. You need to find someone that is experienced on this vehicle.

You obviously need to replace your TPS, and you may need a new belt tensioner as well. On these cars the timing belt setup is not about no 1 cylinder being top dead center. Here are the proper steps to do a timing belt on this vehicle:

To change the timing belt first place the right side of the vehicle on a jack stand and remove the right front tire. Remove the plastic cover inside the wheel well to expose the harmonic balancer. Remove the serpentine belt (standard 3/8" rachet will set in the belt tensioner to relieve tension). Remove the harmonic balancer (19mm). Place a jack under the engine on the right side of the vehicle, then remove the engine mount from the top of the fender well, (17mm deep well socket and 17mm wrench required) it is not necessary to remove the mount from the side of the engine. Remove the timing cover, (10mm) it has 2 nuts. Loosen the timing belt tensioner, (10mm) then pry it away to relieve the tension. Slide the timing belt off of the cam gear.

To position the new belt, the cam gear has a arrow on it, and the cylinder head has a small dot. Align the arrow with dot, and make sure it is aligned (the arrow must point up). The crank gear has a notch and the engine has a groove to align the notch. Again, make sure the notch and groove are aligned (they again will be up). Place the new timing belt in position around the crank gear, the water pump and belt tensioner and leave the slack at the top. Again relieve any tension from the belt tensioner, and slide the belt on to the cam gear. Place a slight bit of tension on the belt and tighten the belt tensioner. Use the 19mm bolt from the harmonic balancer and turn the engine 2 complete turns and verify that the cam gear and crank gear are in their proper positions and aligned with the dots and notches. After 2 complete turns of the engine, and verifying everything is still aligned, re-assemble in reverse. No further adjustment is necessary.

Note:There is no timing adjustment for this vehicle, and if you are not properly aligned on the cam gear and crank gear it will not run properly.

yes you should always have the cam sprockets aligned with tdc and the engine should be on tdc whenever removing or installing the heads.