so, after letting my 72 Z sit for 2 years without doing anything to it, i recently decided to take on the project again. i bought a gasket kit for the Z and disassembled the engine. i rebuilt the carbs, replaced the head, valve cover, intake, and exhaust gaskets, replaced the timing chain, and started putting everything back together again.

the last thing i did was attempt to give the Z a compression test, and thats when i found out that the crank will only turn around 90 degrees before and after TDC. Any idea of what i could've done to the engine to make it bind up like that when i try to turn the crank? also, i gave it a compression test before i took everything apart and the engine turned fine. compression numbers were awful. low 20s to mid 40. maybe i put the timing chain on incorrectly and it doesn't have the right number of links between timing marks or something....?

Anything??

Yes, your valve timing is off and you need to re-time it. Pull the front cover and start over with the crank and cam marks pointing straight up. Download the FSM if you haven't already done so.

so does that mean when i turn the crank that a piston is making contact with the valves then? is that what is stopping it? what is the FSM and where do i download it?

FSM = Factory Service Manual Download from http://www.xenons30.com/

so does that mean when i turn the crank that a piston is making contact with the valves then? is that what is stopping it? what is the FSM and where do i download it?

Most likely. FSM is 'factory service manual'. Go to carfiche.com and download the manual. Don't forget to donate a buck or two to the cause. It's a great 'free' site that I have no connections to except to downloading lots of good info.

ohh ok, that makes sense. i will go download that when i have a computer that i can do that on.

but just an update,

i just adjusted my valve timing and the same problem is still occurring. I lined up the cam at TDC and then i lined up the crankshaft and TDC and put the chain back on. Am i doing this wrong? this is the first timing job i've ever done really. but is there anything else i need to be aware of in order to time it correctly?

i looked back at the numbers too, and i can actually only turn the crank around 30 degrees above and below TDC, i don't know if that information will make a difference.

it feels as if the piston is binding against something. i had to remove the starter to wedge the flywheel so i could take the crankshaft pulley off, does it sound plausible that maybe something fell down in the hole and the flywheel is now jamming against it at a certain place in the bell housing?

With the cam and the crank at their TDC positions, install the timing chain, sprockets, guides and tension block. The chain should be positioned so that the bright links are facing the front. Align one bright link to the crankshaft-sprocket dot, which should be at about the 4 o'clock position. Align the second bright link to the selected cam sprocket, start with dot 1. The link position should be at approximately 2 o'clock with the corresponding dowel hole in the sprocket hub aligned with the cam dowel. Install the cam sprocket to the cam nose. Once everything is in place, there should be 42 link pins inbetween the two timing marks, and the dash mark should be slightly to the left of the cam sprocket notch.

From http://www.oocities.org/inlinestroker/index.htm

You can also find the procedure in the FSM.

ok. so the timing is definitely right. i've checked like 3 different times just to make sure.

another question though: when i took the head off, only 3 of the bolts were even tight at all, and all the other head bolts were loose. the 3 bolts that were tight were the 1st and 2nd bolt in the loosening sequence, and then the 7th bolt in the sequence. so two in the middle and one other. do you think that maybe the block warped when i took the head off and now one of the pistons can't go all the way up/down?

Could something have fallen down in the intake and got wedged either in the cylinder or in a valve? Pull all of the plugs and shine a small flashlight into each cylinder looking for debris.

As for the loose head bolts... YOU built the engine, right? YOU torqued them, right? The only way bolts are loose before an engine is ever started is if they were never properly tightened to begin with. It sounds like you need to return to square one and pull it all apart again.

Do you have the FSM yet?

Reading that you do not have the FSM. Did you follow the torque specs in a haynes/chilton manual? I don't mean to insult your intelligence but you can't just go ahead and tighten down the bolts in any which way my friend.

Take it all apart and follow the manual, you can get it for free in many places on the internet, a few people have linked websites that contain it.

Rust,

How far apart did you disassemble the engine?

Did you find any reason for the low compression?

How much time past between your "before" compression test and your "after" compression test?

Does the cam move with the crank when you try to rotate the engine?

The loose head bolts will not prevent the enigne from turning but will definielty cause other problems.

If all else fails, remove the head again and look for foriegn objects, rust, or other problems in the cylinders. Make sure the engine turns easily all the way through before installing the head.