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Thread: engine wont turn more than 180 degrees after rebuild

  1. #1
    1972 240z Rust Bucket's Avatar
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    Default engine wont turn more than 180 degrees after rebuild

    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??
    sometimes breaking something isn't always a bad thing, merely an opportunity to make it better.

  2. #2
    Registered User Jeff G 78's Avatar
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    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.
    Jeff
    Northville, Michigan
    IZCC #1285
    '78 280 10:1 CR, Arizona Z Car header, urethane bushings, Tokico springs, Illumina struts, Panasports w/Hankook R-S2 225/50R16 tires, Maxima 105 amp alternator
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  3. #3
    1972 240z Rust Bucket's Avatar
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    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?
    sometimes breaking something isn't always a bad thing, merely an opportunity to make it better.

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    Registered User grantf's Avatar
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    FSM = Factory Service Manual Download from http://www.xenons30.com/

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    Quote Originally Posted by Rust Bucket View Post
    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.

  6. #6
    1972 240z Rust Bucket's Avatar
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    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?
    sometimes breaking something isn't always a bad thing, merely an opportunity to make it better.

  7. #7
    Registered User LeonV's Avatar
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    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.

  8. #8
    1972 240z Rust Bucket's Avatar
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    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?
    sometimes breaking something isn't always a bad thing, merely an opportunity to make it better.

  9. #9
    Registered User Jeff G 78's Avatar
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    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.
    Jeff
    Northville, Michigan
    IZCC #1285
    '78 280 10:1 CR, Arizona Z Car header, urethane bushings, Tokico springs, Illumina struts, Panasports w/Hankook R-S2 225/50R16 tires, Maxima 105 amp alternator
    http://www.classiczcars.com/photopos...00&ppuser=7975
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    Registered User d240zx2's Avatar
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    Do you have the FSM yet?
    First & Third owner of HLS30-00721
    B. 01/70 D. 03/12

    New owner of HLS30-15653
    B. 12/70 D.

    Frank in Houston, Texas

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    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.

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    Registered User beermanpete's Avatar
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    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.

  13. #13
    NUTs according to wife ChrisZ's Avatar
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    Just pull the engine, put it on a stand and do it all over again, you do not re build a engine without measuring the end gaps of the piston rings, or measuring the bearing clerance, download the manual and follow it from point to point.

    Period
    -73 240Z HLS30-171039
    -66 Roadster SPL311-05204

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    Fired Up! JLPurcell's Avatar
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    If your one of those people who needs to have manual in hand, I have an extra set of factory service manuals one for engine and another for body. JLP
    Jerry Purcell
    1970 HLS30 00029 Owner since 1976 Now owned by Les Canaday (Classic Datsun Motorsports)
    1972 HLS30 93606 IZCC Registion #105 Original owner back home after full restoration by Classic Datsun Motorsports

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    Unless ur bottom end was over 100,000 miles, I wouldnt have even touched it. Make sure ur not mistaking the sub timing marks as TDC. I have not personally took apart this engine, but sometimes if u get the timing off you can make valves contact the pistons. As long as u were turning it by hand it should be okay, Im not sure if all the head/block combos are non-interference engines.

    Did u take the camshaft out? because its inline bored and some people have trouble making it work after they took it apart. It may be binding on the camshaft. Although, people say u dont need to remove the camshaft to take the head off...im not sure I have not looked at the valvetrain with the valve cover off yet.

    As of removal of the head, you want to start from the outside and work your way in in a criscross pattern. Like this

    X x x x x x x
    x x x x x x X

    Reassembly U start from the middle and work ur way out doing the top and bottom bolt, then working ur way out in a criscross pattern.


    You dont want to completely remove the bolts all at once, u want to make a few passes at each bolt to uniformly lift and tighten the head down.
    Last edited by 71Nissan240Z; 05-31-2011 at 10:17 AM.

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    1972 240z Rust Bucket's Avatar
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    hey sorry, its been a while since i've been on. i actually just bought an L28 to throw in there, but only because i want it running. i love puzzles and i feel like the l24 is gonna be a good one.
    to answer some questions,
    yes, i followed all of the torque specs and bolt tightening patterns as is in the chiltons manual.
    no...i still do not have the fsm because i still do not have a computer that i am able to download that onto.

    i was not the original owner of the car. the first time i ever touched the headbolts they were loose. i am not sure if that would be a contributing factor to the low compression, but that plus a disintegrated head gasket are what i think caused it.
    i just swapped the head over onto the L28 and i found nothing in the L24 that would have caused it not to turn over. in fact, even with the engine out of the car, and the head off, the engine is still impossible to turn.
    sometimes breaking something isn't always a bad thing, merely an opportunity to make it better.

  17. #17
    1972 240z Rust Bucket's Avatar
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    Quote Originally Posted by JLPurcell View Post
    If your one of those people who needs to have manual in hand, I have an extra set of factory service manuals one for engine and another for body. JLP
    is there any way i could get those FSMs from you?
    sometimes breaking something isn't always a bad thing, merely an opportunity to make it better.

  18. #18
    1972 240z Rust Bucket's Avatar
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    Quote Originally Posted by beermanpete View Post
    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.

    i only disassembled in down to the head and also replaced the timing chain. and im 99 percent that i got the valve timing right.
    i did the first compression test about a week before i started tearing into it. after about another week, everything was put back together is when i attempted the second one. so altogether about 2 weeks between the two tests.
    sometimes breaking something isn't always a bad thing, merely an opportunity to make it better.

  19. #19
    Registered User 71Nissan240Z's Avatar
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    maybe he reused the head bolts, when you take them out your supposed to replace them since they stretch a little bit when u have final torque.

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