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    what do crankshaft corks do

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    8 replies
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    • Member since
      May, 2008
    what do crankshaft corks do
    Posted by eltigre on Sunday, July 20, 2008 4:54 PM

    got my answer thanks

    • Member since
      May, 2008
    Posted by eltigre on Thursday, July 24, 2008 9:28 PM
    I've been wondering for quite awhile now what the corks in the crankshaft lightening holes do on my old polaris triple. Any help would be great because I have the bottom end apart and wondering if I should leave them in or out. I've repeatedly googles and searched forums and the only reference I could come across said "whatever you do remember to put them back in" but didn't say any more. I guess what I'm hoping is that it will not harm the engine to put it together without otherwise I have to find some which is like chasing a greased pig. One person recommended having the crank rebuilt and at that time it could be threaded for nylon plugs. I don't think I want to go that far as it is in superb condition.
    • Member since
      July, 2005
    • From: Coon Rapids MN.
    Posted by Riley on Friday, July 25, 2008 10:21 AM

    I believe it is to take up volume inside the case

    Riley

    P.J.H. Racing

    • Member since
      May, 2008
    Posted by eltigre on Friday, July 25, 2008 11:50 PM
    I've heard that but any idea why they are used for that? I mean what's wrong with volume? thanks
    • Member since
      May, 2008
    • From: Vesper, WI.
    Posted by Ruppsforever on Saturday, July 26, 2008 10:36 AM
    They are used to stuff the crankcase.  Which in term pushes more fuel charge up through the transfers.  More compression.  There are better ways to stuff a case.  Cork adds rotating weight to the motor. Which could be good or bad.
    The most powerful force on earth: The Rupp Magnum
    • Member since
      May, 2008
    Posted by eltigre on Saturday, July 26, 2008 1:26 PM
    I understand what you are saying. I just wonder if I can put it together without the stock corks and be alright. I saw a reference on the net somewhere say "whatever you do don not forget to reinstall" or something of the sort. thanks for your help
    • Member since
      May, 2008
    • From: Vesper, WI.
    Posted by Ruppsforever on Sunday, July 27, 2008 10:17 AM
    If it runs good with them in I'd put them back in.  You might notice the difference.
    The most powerful force on earth: The Rupp Magnum
    • Member since
      May, 2008
    Posted by eltigre on Monday, July 28, 2008 12:08 PM
    The issue is that some of them were damaged/dislocated when I got the motor and I don't have a source for them. I ran it without them and it seemed great but now the motor is out and was just trying to figure out the exact logic and importance of them so I know what I'm getting into if I don't find more to put in. Thanks again for your help.
    • Member since
      July, 2005
    Posted by Dr.Crank on Tuesday, August 05, 2008 10:06 PM
    Run the cork for base compression.Press them in a little below flush,paint over them with shalack or urethane like you would clear coat a piece of wood.Some cranks have lead.Melt wheel weights, stand crank on end and pour melted lead in hole with a piece of copper on botom side.Some use soft plugs-cover with Devcon.Wash out bearings,check them dry-with no oil.Dont spin with air!Degree crank twin is 180-180 triple is 120-120-120.Make sure crank is true .001-.002.A true crank makes more power and the clutch works better.PM me if you need help.It all starts with a good crank-no hammering on ends!

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