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the book shows chev 4.3 L is a v6 chain driven and the valve timing is correct when the two dots line up with each other
if it is the ignition timing that you are talking about you are probably 180 degrees out in the distributor setting
no 1 piston firing lines the rotor button up at no one HT lead and not no 6
all engines regardless are timed of no piston tdc and chev engines are around the 12 degrees btdc for operation
the cam shaft may be identifiable but I doubt it as the lobes will be all the same .It may take a trial fitting of the cam shaft to determine which is which. Place the no 1 piston on TDC and install the cam in the exhaust side of the head. position a the no 1 piston cam lobe in the just closing position. Check where the timing mark will be in this position ( the engine make and sized would have been an enormous help here as the key position or timing mark on the gear would have revealed what cam it was). Place the other cam in the position where the no1 cam lobe is just opening.. This is called valve overlap and from the positioning of the timing marks will show if the cams should be interchanged . The marks will either both face down, face each other or face upwards. If they face out wards away from each other then interchange the the cams and if that makes the marks face each other then it may be right. Another way ( probably simpler will be to put a cam in place and the cam lobes will be directly in line with the rockers over the valves or directly over the valves. Workshop manuals are a big help when doing this work.
Are you needing the twin independent variable cam timing info or is this a cam replacement initial cam timing setting? the variable valve timing itself is dependent upon the part design, and is usually controlled by oil flow (causing the timing to change hydraulically and seems transparent to the driver). However, when replacing the cam, the timing is more of a position issue using the marks on the engine and camshafts to make sure the shafts are in the proper position.
If this is for a replacement, use the marks on the block ensuring the current valve position is the proper in relation to piston position (otherwise your pistons will punch the valves and blow the head)
You can set the timing 180 degrees out if you only go by the cam position I think. Basically the fuel and exhaust phase look the same by cam position. I believe you need to ensure the piston position at the time you install the timing chain by removing the plug and confirming the piston is at the top and the power stroke is just completed.
you are in a bit of a bind. Turning the engine over will result in bent valves so do not touch the crank shaft. you have to loose off all the rockers/ cam followers even to the point of removing the cam shaft. having done that remove no1 cylinder spark plug and by the use of a thin piece of wire turn the crank until the piston reaches top dead center. find this by rocking the crank back and forward until the piston dose'n move up or down check for the crank timing mark next replace the cam shaft and position the cam lobes for no1 piston in such a position that the inlet and exhaust valves move slightly up or down when the cam is moved slightly left or right. this is called valve over lap and with the piston on top dead center means that you now have valve timing for the engine. Cam timing marks can be dot on gear to shiny link on chain or if using a belt a dot on tooth lineing up with mould mark or join on head before starting up do a compression check to prove that there are no bent valves. if you are not mechanically minded enough to attempt the valve timing method it may be cheaper in the long term to let a qualified person do the job
Loss of compression can be due to a bent head, bent valve not closing all the way, bad head gasket, hole in the piston, dropped piston, bad or broken piston rings, compression checked on cylinder with valve in the open position.
Engine Timing Belt/Chain Illustration
Figure 1 Before installing tool. If the belt broke turn the engine so the #1 piston is half way up. This way you will not bend the valves while turning cams. If you feel that the cams are very hard to turn or stops turning then turn crank by hand to lower piston away from valve. Then turn the cams clockwise or counter clockwise slow one at a time too the proper slot position for the tool to fit. Once the cam marks are lined up bring the #1 piston to its TDC.
Its because your pistons on 1&4 are up top that is why your bent valves got bent you are doing exactly the same thing so turn the crank back 15degrees position your cam and reset your crank,it seems to me you may be out of your depth lets hope not or it may be expensive
Turn crank so that timing mark on front pulley is at 0 degrees.
Remove the timing cover and you should see a mark for the cam to line up with.
You want the cam lobes on No.1 cylinder to be pointing away from the followers wether they be rockers above cam or buckets below. This will be the compression stroke.
Once the cam timing is set you can recheck the distributor. It should point to No.1.