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Thread: Busted engines and cambelts

  1. #1
    Senior Citizen Chief Engine Builder "Z" UTE's Avatar
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    Default Busted engines and cambelts

    Guys is there any way by looking at the cambelt to ascertain whether the belt was the cause of the failure or whether the belt slipped after the engine locked up?



    thanks, cheers Chuck.
    Last edited by "Z" UTE; 31-08-2014 at 11:43 AM.
    "What man can build, man can fix!"
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    Junior Member Automotive Encyclopaedia
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    Default Re: Busted engines and cambelts

    Belt loose enough to slip?? Guesstimate it'd take at least 2cm slack to do that, touch valves & stop, nothing more, or completely broken for an oil pump driven one..
    What does 'locked up' mean?
    What engine?
    'I've scrapped better.' John stated when asked about the car by the guy with the silver tipped cowboy boots!

  3. #3
    Senior Citizen Chief Engine Builder "Z" UTE's Avatar
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    Default Re: Busted engines and cambelts

    Yea, that was a fairly generic question, trying to see which came first the chiken or the egg.

    Case study: 1G-F? VVTi from a Lexus IS200.

    New cam belt, new cam seals, and crank seal fitted. Engine purred like a kitten, test drove perfectly. 18 hours later it was back in the shop with a broken valve preventing any further rotation in the appropriate power generating direction, to me locked up to all intents and purposes. First thing you check is the timing belt, it was out by 6 teeth, but was that a slippage causing the damage, or a result of the engine coming to a sudden stop. Could the inertia of the cams idlers and belt cause the skip.

    The mechanic is that pedantic he actually locks the cam shafts by various means before he removes an old belt, so misalignment is just not possible with this guy. Scratching my head as to what could cause this.


    your thoughts please guys.
    "What man can build, man can fix!"
    MS51Crown Coupe,
    GSV40R Aurion luxo tourer. One TA22 currently receiving some TLC prior to paint One RS56 Crown ute under construction, 2 x TA22's awaiting rebuilds. Toyota Crown RS47J ute in need of serious TLC. Toyota Crown Custom Wagon MS53 daily hauler stocko!

  4. #4
    she loves me coz im a Conversion King love ke70's Avatar
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    Default Re: Busted engines and cambelts

    I have had an engine spit the centre out of the oil pump pulley, that fucked the timing. 1ggte
    if the cams stopped turning but it was in gear I would believe it could slip the belt.
    But I am no mechanic...
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  5. #5
    Junior Member Backyard Mechanic jondee86's Avatar
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    Default Re: Busted engines and cambelts

    Theorizing... if the belt slipped in service the crank pulley would be advanced. If there was enough inertia in the cams etc to make the belt slip when the crank stopped suddenly, the crank pulley would be retarded. Tensioner not loose/broken ? Broken valve as in the head came off or ?

    Cheers... jondee86

  6. #6
    Junior Member Automotive Encyclopaedia
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    Default Re: Busted engines and cambelts

    I would think if its not a high km motor & you don't Rev the tits off it I would say there was probably to much slack in the cam belt when it was fitted, also depends on the tensioner set up too & some cant be left slack ..

    Has the head come off the valve or is it a bent valve stem & is it more than one valve ?? if the valve head is still attached to the stem I would say for sure that it jumped teeth due to incorrect fitment or as has been mentioned a cam belt idler pulley or oil pump drive pulley etc could have come undone ..

    I presume the mechanic pulled off the covers, were you there at the same time ? or if you pulled off the covers did you check the belt for slackness ??

  7. #7
    how much is Too Much Toyota JustenGT8's Avatar
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    Default Re: Busted engines and cambelts

    Seized tensioner? Looks like the culprit in my scenario....belt felt tight and there's still the possibility the belt delaminated, but it's also possible the tensioner wasn't quite doing it's job? New one going in regardless.
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  8. #8
    Junior Member Automotive Encyclopaedia
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    Default Re: Busted engines and cambelts

    Quote Originally Posted by "Z" UTE View Post
    ...broken valve preventing any further rotation in the appropriate power generating direction, to me locked up to all intents and purposes.
    Never seen one stop, inertia & the OK cyls. keeps them turning while turning everything in that cyl. into trash, then the piston falls apart completely, then the rod may come apart & jam up things.
    Cams have almost as close as you can get to zero inertia.
    Cam/s seized, possibly the result of his 'various means', and that did the belt.
    'I've scrapped better.' John stated when asked about the car by the guy with the silver tipped cowboy boots!

  9. #9
    Olde mechanic Carport Converter oldeskewltoy's Avatar
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    Default Re: Busted engines and cambelts

    1GF is belt drive of just one cam... with 2 tensioners...



    Looking at the belt shape... at the bottom it appears that besides the crank pulley, it is suppose to go around something else??
    Information is POWER... learn the facts!!

  10. #10
    Junior Member Automotive Encyclopaedia
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    Default Re: Busted engines and cambelts

    belt cover/s in place?
    Gravel/rock/whatever or left over/lost bolt/washer/tool in the cover could do it. Been done by them way too often but rarely at 18 hours.
    ***
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    Usual lock is just tightening down a piece of paper/cardboard on a journal.
    Last edited by allencr; 04-09-2014 at 02:55 AM.
    'I've scrapped better.' John stated when asked about the car by the guy with the silver tipped cowboy boots!

  11. #11
    Junior Member Grease Monkey
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    Default Re: Busted engines and cambelts

    I had a camshaft sieze on the G10 in my Suzuki Mightyboy. It stripped half a dozen teeth off the cambelt, and that was running at idle at the time.

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