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Cam position

3814 Views 16 Replies 7 Participants Last post by  steves280
My son replaced the head gasket on 75 with a stock engine. Car wouldn't start and after taking off the valve cover can see the cam is not lined up to TDC. What is the best way without taking off the head to line up the cam? The number one piston is at the top, the crank pully mark is at 0 and the rotor is around the 9 o'clock positon. Should I just slide cam out and rotate or take off the cam towers? and what do I need to do with the rockers?

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Here are the ponts to line up with cylinder 1 at TDC

Watch the timing chain in the front. it can do this:

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Get piston to TDC then remove Cam sprocket and try to get the orientation of the numbers on teh sprocket and the V aligned.

Each tooth you are off is ~9° of advance or retard.
If your son torqued the head down without having both it and the pistons at TDC when he did it, then you almost certainly bent a valve stem somewhere. This is just a slow-motion repeat of what happens to valves when a timing belt slips-a valve and a piston come together and as you continue to torque the stem bends and the head goes on. I'm not just guessing at this; I have actually made the exact same mistake in the past and I bent two valves.I also marred the top of a piston. You have to pull the head off. Sorry. I keep the brand new bent valve on my workbench as a reminder to follow directions, take my time, and think before I turn a wrench!
By the way....it is possible to install the head without putting it at TDC first....just don't install the rockers until you have everything at TDC. This is the way I prefer to install a head; without the rockers in, none of the valves are protruding so if you drop it or something the stems don't get bent. The camshaft also turns freely so getting the timing chain and sprockets and timing marks all lined up is a little easier. Put the rockers in after you have the cam and block properly timed, and you can't damage the valves. Just don't mix the rockers up; they must go back in the same order they came out. Try it this way when you re-do your job.
thanks guys, my problem is i think it is 180 off and i need to rotate the cam it wont rotate without hitting the pistons so do i just take it out and rotate it or take off the towers? I guessing just take pull the cam out a little until I can turn it to get it right. Do I need to do anything with the springs and lash pads?

Thanks again,
I wouldn't actually pull the cam out to rotate it. and you should avoid removing the cam towers if at all possible.

First put the engine at TDC (also check your distributor timing to verify).

to take off the rockers: using a large screwdriver to push down on a valve spring, using the non-machined surface of the cam as a fulcrum point.
you had to rotate the engine to remove all the rockers, so put it back to TDC after this.

once all the rockers are removed, block the timing chain tensioner, and take off the cam sprocket. the cam should rotate freely. put the sprocket back on making the timing marks line up like in the above pictures.

then look at your distributor and make sure it's sparking at #1.

are you sure the cam is out 180 deg? what about if you rotate the crank 360 deg, then how does it look? if you think you're out 180 deg exactly, you probably have a spark timing issue instead.
If you turn the crankshaft 360 degrees, the cam should be in line if it is 180 off as you say. The crankshaft turns 2 times for every 1 turn of the cam. Double check your ignition timing and maybe do a compression test. If you have already cranked the engine then it will either be toast or not.
Stonehenge69's pic advises setting the cam timing slightly advanced which kills any chance of having some top end power. I always set them with the cam slightly RETARDED which makes the car perform much better. I've tried various settings and with it set as Stonehenge69 sugests, the cars I've tried this on run like a dog.
I'm telling you...no doubt about this! If you torqued the head down with the timing off, and then tried to start the car, you bent valves. If you just take the rockers off and rotate the cam to tdc and then put them back in and try to start the car, you are gonna have a whole lot more damage in a second or two...holes in the tops of your pistons, broken valves, ruined head. I bent two valves just torquing a head down...I didn't even try to crank it; I realized my mistake as soon as I went to put the sprocket and chain on. But if I hadn't fixed the valves, it would have led to a complete engine failure, ALMOST INSTANTLY. You MUST pull your head back off and make sure you haven't bent any valve stems before you try to start that motor.
That's strange, I own 44 Z cars and none of them "run like a dog."
Have you actually ever tried the cam in another position? I've never seen an L28 that ran better with the camshaft advanced and most other people who have tested this agree. Norm the 12 sec SU guy posted this same thing and even with aftermarket cams they ussually like being retared rather than advanced as far as making power. Maybe you think one should set a new chain this way so it can "stretch" later on or something? Or was it because you used "hole #1" and that's where it ended up?

And dude, I don't care how many Z's you own, I've worked on thousands of these! Why would anyone want to own 44 of these cars anyway? :)

Seriously advancing a camshaft on these cars kills any chance of them making much power over 4000 and really doesn't give back enough on the bottom end for what it gives up on the top end. Anyone who doubts this, try it yourself and see. After I tried advanced/straight up and retarded on about a dozen different combos, I decided that it's a pretty universal when using a stock cam to install it slightly retarded.
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steves280, the positions shown in my pic are there to help the average shadetree mechanic correctly install a "new" timing set using "stock" settings. Have I ever tried another position? yeah, I've tried every position there is and I run different settings for different setups (and yes I agree, slightly retarded is preferred for top end power), however, every engine I build is initially setup to the stock position and all tweaking is done after the break in period.
If this is "to help the average shadetree mechanic correctly install a "new" timing set using "stock" settings" why are you posting it using an adavnced "non-stock setting? Like I said, I've never seen any -setup- on a zcar that made more power with the cam set advanced.
You might want to read your FSM a little closer (EM 19 and EM 20 in the 77 FSM) to enlighten yourself as to what the "factory settings" actually are. It was written by top Nissan engineers, but what do they know.
You might want to try checking the actual cam timing and you'll see the cam is straight up when the marks are aligned.

"What they know" is they have to make sure the engine passes the strict initial EPA EMI inspection and it probably needs the camshaft to be advanced to do this. Someone who is building engines in the field doesn't have to do this so should be assembling the engine so it performs it's best, which sometimes means doing some experimentation and learning from it rather than strictly following the FSM. Wonder how many good running small block chevys are built using 77 vintage FSM specs?
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