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Thread: blacktop 20 valve 4age, Interference engine?

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    Member _sawyer_'s Avatar
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    Default blacktop 20 valve 4age, Interference engine?

    Hey everyone,
    Im getting my sprinter build underway soon and ive acquired a blacktop 20 valve 4age (cheap) which had a cam belt snap on it.
    Its had a new one fitted but still but still has no compression (im expecting the worst)

    After many searches on the web and this site resulting with conflicting answers, my question is,
    For people who have owned one and maybe had this experience, are they an interference engines?

    And what can be the extent of the damage if a belt does snap?

    I am praying that the engine has been sitting around to long and the lifters need bleeding

    Thanks!

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    Moderator Sam-Q's Avatar
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    I don't think you will get a straight answer on this. I free spun an engine and I had what every much felt like the valves touching the pistons, however I could not take the head off to check.

    20V engines don't have lifters...
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    the 16v engines are non-interference, but cant say on the 20v sorry

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    silvertops are non-interference (if i remember correctly, don't quote me)
    while blacktops are. a friend snapped his belt and the valves bent =(. i've also heard stories of scarring pistons, and bent rods =(

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    Moderator Sam-Q's Avatar
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    I tottaly agree with the above. My silvertop with 8500 revs with a 0.8mm TRD gasket was still non interference so I completely give that the thumbs up.

    Mikeyee sound like your friend have confirmed what I have suspected for a while- there just isn't deep enough releifs in the pistons to allow room for the valves at the wrong time
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    hey sam, could the question over interferance on a blacktop be dependant on the timing at the time of belt snappage?

    so blacktop a snaps a belt at rev 2000 no damage,
    blacktop b snaps a belt at 7000 with full advance???? hence a little bit too much on the smaller reliefs?

    hence two scenarious and two answers?
    RIP Carly - a smile to light the world.
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    Moderator Sam-Q's Avatar
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    Quote Originally Posted by fantapants View Post
    hey sam, could the question over interferance on a blacktop be dependant on the timing at the time of belt snappage?

    so blacktop a snaps a belt at rev 2000 no damage,
    blacktop b snaps a belt at 7000 with full advance???? hence a little bit too much on the smaller reliefs?

    hence two scenarious and two answers?
    possibly yes but not due to the advance, morso the rod stretch- the higher revs the more chance of it touching.


    Now back to the original post- whats the worse case scenerio? well my friend managed to wreck his head, pistons, valves and block by the valves touching
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    Moderator Sam-Q's Avatar
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    and thread cleaned
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    Senior Member Vezza's Avatar
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    I've personally replaced a timing belt on a 20V BT and can confirm that it's definitely an interference engine, no doubt about it. Which surprised me as I was under the assumption it wasn't.

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    Senior Member Vezza's Avatar
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    Quote Originally Posted by Sam-Q View Post
    it could be that it wasn't enough to actually cause damage, it is possible to touch valves for a little while before the damage sets in depending on how severe it is.
    But I guess it would depend on the position of the cams when the belt broke, could be lucky and at low rpms.

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