340 timing chain stretch tolerance

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    Author Topic: 340 timing chain stretch tolerance  (Read 2842 times)

    Offline miketyler

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    340 timing chain stretch tolerance
    « on: July 13, 2005 - 07:05:33 PM »
    I started fitting the front end back together on the 340 and found the chain to be a bit more loose than I think it should be. The book shows 3/16" slack movement as allowable between the crank and cam. That seems absurd - maybe I am not reading this right. I have less than that but when the engine is turned CW and the chain pulled taut on one side the other side is so loose that I have about 1/2" of deflection. WTF? Is that acceptable?

    Also coming into play here again is the crank gear I mentioned in a previous thread. I noted that it seemed "loose" on the crank where it would slide on and off a little too easy for a nice machined "slip" fit. Now I notice that it does have a little free rotation on the crank. Looking more closely it appears that much of the free movement is attributed to the crank key being loose in the keyway. This cant be right. The keyway looks fine and doesnt look to have been boogered but the key almost looks like it has been machined along the upper edge. I will try and post a pic of this.

    can anyone comment on this? Would a new chain be nice and tight compared to what I have now or ?             
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    Offline Mr. 6pak2go

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    Re: 340 timing chain stretch tolerance
    « Reply #1 on: July 13, 2005 - 07:46:07 PM »
    mine fits very loose to i hope its normal!! well see next week when i fire her up!!
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    Offline Chryco Psycho

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    Re: 340 timing chain stretch tolerance
    « Reply #2 on: July 13, 2005 - 08:31:12 PM »
    the Key may be worn from years of load & need to be replaced , if the block has been align honed the crank is moved closer to the cam in the block &  can cause the chain to be loose , Short chains are available to compensate for this .! engine I did had to use a gear drive to fix this problem as event he short chain was loose
    « Last Edit: July 15, 2005 - 12:54:19 AM by Chryco Psycho »
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    Offline Mr. 6pak2go

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    Re: 340 timing chain stretch tolerance
    « Reply #3 on: July 14, 2005 - 07:16:43 PM »
    thanks chryco!!  :thumbs:
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    Offline miketyler

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    Re: 340 timing chain stretch tolerance
    « Reply #4 on: July 15, 2005 - 05:38:04 AM »
    I dont think my engine has been align-bored/honed but if it was, wouldn't the cam to crank center-to-center distance be marginal? Only like .010"-.030"? Check out my key - I mic'd the crankshaft imbedded portion and it came up to .185". Shouldn't it be closer to .189" (3/16")?  Also, see attached and you can see the gear and balancer wear marks I was talking about. This car had a new harmonic balancer installed when I got it. The old one was included in a heap of other parts and was cracked at the hub. Unusual damage I would think.  If new crank key and chain doesn't reduce the slack, has anyone tried one of these tensioners?



     

     
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    Offline miketyler

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    Re: 340 timing chain stretch tolerance
    « Reply #5 on: July 15, 2005 - 05:57:36 AM »
    Quote
    mine fits very loose to i hope its normal!!


    6pak - is your chain new?
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    Offline Chryco Psycho

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    Re: 340 timing chain stretch tolerance
    « Reply #6 on: July 15, 2005 - 08:56:21 AM »
    I would definatly replace the Key
     you could try a dufferent chain as the one you have may be poorly made ,
     Those tensioners are a good idea 
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    Offline Mr. 6pak2go

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    Re: 340 timing chain stretch tolerance
    « Reply #7 on: July 15, 2005 - 01:26:54 PM »
    no my chain is not new it is the orininal one that came on the motor!! the only thing i replaced was the pistons,rings cam and all gaskets and seals!! the heads and intake are different but hte block is all stock!!
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    dodgetkboy78

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    Re: 340 timing chain stretch tolerance
    « Reply #8 on: July 16, 2005 - 11:28:50 PM »
    Quote from: miketyler on July 15, 2005 - 05:38:04 AM
    I dont think my engine has been align-bored/honed but if it was, wouldn't the cam to crank center-to-center distance be marginal? Only like .010"-.030"? Check out my key - I mic'd the crankshaft imbedded portion and it came up to .185". Shouldn't it be closer to .189" (3/16")?  Also, see attached and you can see the gear and balancer wear marks I was talking about. This car had a new harmonic balancer installed when I got it. The old one was included in a heap of other parts and was cracked at the hub. Unusual damage I would think.  If new crank key and chain doesn't reduce the slack, has anyone tried one of these tensioners?



    Yup, use them all the time! They work great, well worth the money!
    Also, get a new chain, and make sure it is a "true roller"

     

     
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