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I think I smoked my motor in my 308 ?

Discussion in 'Technical Q&A' started by joeyy, Nov 12, 2006.

  1. joeyy

    joeyy Karting

    Nov 11, 2003
    190
    long island
    Full Name:
    joe
    we had a nice warm day in november and i decided to take the car for a ride. on startup it sounded like a few seconds of loud hung-up tappet noise. now it idles very low with no tappet noise but way down on power and popping through the 5-8 bank carbs. i think it may have jumped a tooth but whatever the case it is not going to be a normal football sunday i will have to move the tv to the garage. i had the motor out for a major service and am not looking forward to doing it again. to do the 5-8 head in the car seems like a nightmare. (going for an early morning compression test)
     
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  3. mk e

    mk e F1 World Champ

    Oct 31, 2003
    11,835
    The twilight zone
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    The Butcher
    It could be a lot of things. You have have aproblem with the front bank ingnition. It could be the belt slipped a tooth, with a mirror and a good flash light you should be able to see the timing marks on the cover.
     
  4. blainewest

    blainewest Formula Junior

    Aug 26, 2005
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    Kelowna, BC
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    Blaine W
    Don't get to wound up at this point. M ke is right this could be a minor problem including fuel delivery/mixture and or ignition problems. Check those first before you start removing a/c pump, belt covers etc. Is there a reason why you think it may have skipped a tooth...ie was the correct belt tensioning procedure not followed...did it feel to loose? Is there any belt residue that you can see inside the belt cover?
     
  5. Artvonne

    Artvonne F1 Veteran

    Oct 29, 2004
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    Paul
    I concur, dont freak out yet, you have a lot of diagnoses ahead of you. Pull the plugs for starters, they may or may not tell a story. Then, if you have any telltale marks from setting valve timing, slowly rotate the motor by hand to see if its jumped time. I guess the fact its been run, cranking it for a compression test shouldnt cause more harm, if something is amiss.

    If the ignition was timed correctly, and was running well prior to this event, checking static ignition timing should confirm valve timing if you check it carefully. One belt tooth is about 30 degrees crankshaft rotation, so verify your looking at the correct marks.
     
  6. rolindsay

    rolindsay Formula 3

    Jul 14, 2006
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    Rick Lindsay
    Step 1: Verify that the cam belt for the offending bank is actually moving. Mine wasn't. :-(

    rick
     
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  8. joeyy

    joeyy Karting

    Nov 11, 2003
    190
    long island
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    joe
    thanks for the glass is 1/2 full scenario. i pulled the cover and checked the cam timing . it looks as though the ex cam has jumped. after a comp test i have one cyl that has 60psi and could be the suspect that has me pulling that head. i will do a lealk test tomorrow and will hope for the best. how hard is pulling the head in the car? is there a way to jack the front of the motor to possibly give more room? is there a trick? anything will help at this piont.
     
  9. blainewest

    blainewest Formula Junior

    Aug 26, 2005
    721
    Kelowna, BC
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    Blaine W
    Joey...sorry to hear about the exhaust cam...but am I to understand that this car still runs with out any major metal on metal sounds etc.? If the camshaft has only jumped one tooth then maybe it could be (I think) that the shaft may not be off enough to have caused physical contact between valve and piston. If you're sure the timing on the cam shaft is out then I would remove the offending belt, set the shafts to where they should be, put new belt on, turn crank by hand, if ok then you might run the compression and leak down tests. That should tell you if the head needs to be pulled. Good luck ,and keep us posted.

    I'd be very interested to hear what you think the cause of the skipped tooth was. Was your belt old, loose, installed improperly, is the affected camshaft spinning freely (ie is it seizing up?)...what?
     
  10. joeyy

    joeyy Karting

    Nov 11, 2003
    190
    long island
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    joe
    thanks for the input. i did a leakdown test and #7 leaks over 80% (Bent ex).
    i haven't found any reason at all why it jumped. the belts are only 3 years old with no sign of deterioration or hardening.
    i drive the car frequently and had no problems with it up to this point. with belt covers on it is unlikely that a small stone or something found its way onto the belt but nothing is impossible.

    how do I post pictures to this thread? i will try to put some on so all can see what i am looking at.
     
  11. BigTex

    BigTex Seven Time F1 World Champ
    Rossa Subscribed Owner

    Dec 6, 2002
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    hit "manage attachments" in area below post window, then you can "browse" your hard drive....
     
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  13. cavallo_nero

    cavallo_nero Formula 3

    Nov 3, 2003
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    on my last major service, we replaced the cam sprockets - 78 308. the originals are plastic, and were pretty worn down - maybe that is how your belt jumped a tooth. just a thought
     
  14. Rifledriver

    Rifledriver Two Time F1 World Champ

    Apr 29, 2004
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    When the belt slips it changes valve timing on all cylinders on that bank equally. If the cam timing was off enough to cause one exhaust valve to bend it would have bent all exhaust valves on that bank. When you take it apart you should look to see the cause of the bent valve with an eye towards considering the bent valve and whatever caused it as the initiating event not the result.
     
  15. Steve King

    Steve King F1 Rookie

    Feb 15, 2001
    4,366
    NY
    I agree with Rifledriver on this. If you slipped the timing you would take out all of the valves and not just 1. Also you might find that either you burned this valve because the clearance was not checked and the valve was tight or you could have a broken valve spring .
     
  16. rolindsay

    rolindsay Formula 3

    Jul 14, 2006
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    Agreed completely. If you're taking it apart this far, pull both heads and do a valve job. It's false economy to do otherwise.
     
  17. Artvonne

    Artvonne F1 Veteran

    Oct 29, 2004
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    I think what RD is trying to say, if I follow his reasoning, is that the belt most likely jumped when the valve did something. Since you were hearing an obvious tappet type sound, it may have been a stuck valve, and this may in turn have strained the load on the cam rotating, and the belt slipped.

    I equally agree on both heads and valve job. Pull the motor out, freshen it up, clean and detail, and baby will be ready for many more happy miles.

    I have a shop I trust rebuilding a set of heads for me, going with Ferrea valves, havnt decided yet whose springs to use, but either way its getting new ones. It might seem expensive up front, but it is truly cheap insurance.
     
  18. joeyy

    joeyy Karting

    Nov 11, 2003
    190
    long island
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    joe
    #15 joeyy, Nov 15, 2006
    Last edited by a moderator: Sep 7, 2017
    i think you guys are on to something. after more testing i confirmed the fact that only one cyl is dead. so the although the cam timing is off it is not enough to be a catastrophic faliure. it also looks way too tight to try to do this repair w/ the engine in so it will have to come out.
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  19. Rifledriver

    Rifledriver Two Time F1 World Champ

    Apr 29, 2004
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    The head will come out pretty easily in the car but the pistons will not. If you feel there is a good chance of piston damage might as well take it out. If on the other hand you have reason to think it is just a bent valve and the head has been off in the last few years it should come out easily.

    If there is no valve clearance you probably have a broken valve in which case the piston will be history. If you have big valve clearance it may just be bent.

    I only say that because I hate to pull 308 motors when I dont have to. I have had the heads off in the car many times.
     
  20. joeyy

    joeyy Karting

    Nov 11, 2003
    190
    long island
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    joe
    the clearance on that valve is 20 thou.(hopefully just bent) i think it is usually set @ 10-13. plus i am a nut and always get caught up in that dreaded might as well do it while we are here syndrome. so if the engine is out i am thinking of some dyno time!!!!!
     

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