<?xml version="1.0"?>
<ownershipDocument>

    <schemaVersion>X0202</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2007-02-15</periodOfReport>

    <notSubjectToSection16>0</notSubjectToSection16>

    <issuer>
        <issuerCik>0000740761</issuerCik>
        <issuerName>BUCYRUS INTERNATIONAL INC</issuerName>
        <issuerTradingSymbol>BUCY</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001236637</rptOwnerCik>
            <rptOwnerName>KRUEGER KENNETH W</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1></rptOwnerStreet1>
            <rptOwnerStreet2></rptOwnerStreet2>
            <rptOwnerCity></rptOwnerCity>
            <rptOwnerState></rptOwnerState>
            <rptOwnerZipCode></rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>0</isDirector>
            <isOfficer>1</isOfficer>
            <isTenPercentOwner>0</isTenPercentOwner>
            <isOther>0</isOther>
            <officerTitle>Chief Operating Officer</officerTitle>
        </reportingOwnerRelationship>
    </reportingOwner>

    <nonDerivativeTable>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Class A Common Stock, Par Value $0.01 Per Share</value>
            </securityTitle>
            <transactionDate>
                <value>2007-02-15</value>
                <footnoteId id="F1"/>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>F</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
                <footnoteId id="F1"/>
            </transactionCoding>
            <transactionTimeliness>
                <value></value>
            </transactionTimeliness>
            <transactionAmounts>
                <transactionShares>
                    <value>2265</value>
                    <footnoteId id="F1"/>
                </transactionShares>
                <transactionPricePerShare>
                    <value>51.06</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>D</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>17835</value>
                    <footnoteId id="F2"/>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
        <nonDerivativeHolding>
            <securityTitle>
                <value>Class A Common Stock, Par Value $0.01 Per share</value>
            </securityTitle>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>10050</value>
                    <footnoteId id="F3"/>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </nonDerivativeHolding>
        <nonDerivativeHolding>
            <securityTitle>
                <value>Class A Common Stock, Par Value $0.01 Per Share</value>
            </securityTitle>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>2400</value>
                    <footnoteId id="F4"/>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </nonDerivativeHolding>
    </nonDerivativeTable>

    <footnotes>
        <footnote id="F1">Reflects the portion of the shares of &quot;base&quot; restricted stock that vested based on performance through December 31, 2006 that were retained by the Company in payment of applicable tax withholding obligations, calculated at a price of $51.06 per share, which was the closing price of the Company's common stock as of February 15, 2007 (the date the vesting was confirmed by the Company's Board of Directors).</footnote>
        <footnote id="F2">Grant to reporting person of &quot;base&quot; restricted stock under the 2004 Equity Incentive Plan.  The &quot;base&quot; restricted stock vests on December 31, 2009, but vesting is accelerated to 25% on December 31, 2006, 2007, 2008 and 2009 in the event certain financial performance criteria are met.</footnote>
        <footnote id="F3">Grant to reporting person of &quot;premium&quot; restricted stock under the 2004 Equity Incentive Plan.  The &quot;premium&quot; restricted stock partially vests in an amount between 20-25% on December 31, 2006, 2007, 2008 and 2009 in the event certain financial prformance criteria are met and all partially vested shares fully vest on December 31, 2009.</footnote>
        <footnote id="F4">Grant to reporting person of restricted stock under the 2004 Equity Incentive Plan.  The restricted stock vests on December 31, 2010.</footnote>
    </footnotes>

    <ownerSignature>
        <signatureName>Kenneth W. Krueger</signatureName>
        <signatureDate>2007-03-05</signatureDate>
    </ownerSignature>
</ownershipDocument>
