I need a cam timing lession

[mrmaintain]

So the crank pulley is set at TDC? or after TDC? The #1 exost valve is starting to open in #1, closes than the intake valve opens?

[UncleBob]

on a 4 stroke engine, it will be at TDC twice after completing all 4 strokes. One TDC is compression stroke (neither valve will be open), and the other TDC is the end of the exhaust stroke (often called "TDC at overlap") Both valves will be very slightly open

When you are trying to find TDC for installing a timing belt or chain set, you usually set it to TDC on the compression stroke.

Most timing sets and timing belt setups will have marks on the cam sprocket to give you a visual indication of where to set it so you don't have to reference the valve openings

[curtis73]

Yup; go another 360 degrees until its at TDC again. I think you'll find both valves closed then. That is the TDC on #1 that is usually used for setting timing. You didn't mention which engine, though. Some engines (like IHC) use the #2 or #5 cylinder as the TDC mark. Some V- engines number the cylinders with the odd numbers on the driver's side (chevy, olds, ford for example) while others use odd numbers on the passenger side (cadillac). Others number then from 1-4 down the driver's side.

Usually inline 4 engines are numbered 1-4 from the crank pulley back, but I do have an old tractor engine that is numbered 3-1-2-4 so that the firing order can be 1-2-3-4.

I only say that to let you know that you may be looking at the wrong cylinder. (and to point out that it would be a lot easier if you included all the information that might help us diagnose your issue )

[mrmaintain]

All thery sounds good Ok, Thank you for all the help. I bought an overheated 88 Mazda 626 with a 2.2 4 cyl. They drove it too hot with a leaky heater hose. It took the head in and they "baked it" back into shape, shaved it and valved it ( rebuilt what they could to make it work ) The Machinest told me to make sure the cam pin/key was at the 12 o'clock position and set the cam pulley at #3 ( he said the tolerances where not suitable for #1 anymore) , Iset set the crank pulley at TDC ( and distributor at #1). I tryed setting the cam pulley at 1,2 and 3 ( after several hours of attemts, OMG,whats the trick to this anyway, to line the marks up ) but it doesnt seem to run right in any of the 1,2 or 3 cam positions. Thanks so much for your help

[UncleBob]

you need to buy a manual from the sounds of it. Not sure what your machinist was telling you, but you always use the manufacturers marks unless he moved the pin locations, and I assume thats not what he did

The "1" mark should point straight up on the cam sprocket and line up with the notch on the inner cover/valve cover

The crank sprocket keyway should be pointing straight up, and there is a notch for that also

You might have the distributor in wrong, but I believe it only goes in 2 ways at most

[mrmaintain]

Bob Thank you for the advice. I have a Chilton's and even went to the dealer to look at there shop manual. They are all seemingly general. So the pine/key was never moved. The part I dont get is , The Machinest said that I would have to adjust the pulley (retard it ) because of new tollerences, If I take the pulley off the cam shaft and reset it to 1, 2, or ,3 pointers will it hit the valves? (by the way I tried very hard to get all the marks to line up but it's aways 1 or 2 teeth one way or another off). I have a nice Nissan manual that show an exact piicture of the position of the cam and lobes for #1 TDC lineup. Are all 4 cyl engens going to line the lobes up the same? ( can I use this picture as reference?) Thank you.

[UncleBob]

yes, most 4 cylinders will have very similar valve timing and should definitely be semetrical, but the position of the cam(s) and valve actuation style can make for very different visuals

If #1 is at TDC compression, then #4 will be at overlap. They will be mirror images of each other

I'm still trying to figure out what your machinist was talking about. I can only assume he decked the head which changes the distance between the sprockets and will effect the timing. If this is what he's referring to, its completely a non-issue. Most head resurfacing is .005" or maybe .010".....that would have so little effect on the timing its pointless to even mention it


I believe this engine isn't a interference motor so you should be OK on the valve/piston contact, but from the sounds of it, you've already tried settings that are way off from where it should be, and would have already found out the hard way if it was an interference motor.

Gotta be very careful when timing engines. Randomly throwing on the belt and trying to run it is a bad way to discover the correct position!