-----BEGIN PRIVACY-ENHANCED MESSAGE-----
Proc-Type: 2001,MIC-CLEAR
Originator-Name: webmaster@www.sec.gov
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 TWSM7vrzLADbmYQaionwg5sDW3P6oaM5D3tdezXMm7z1T+B+twIDAQAB
MIC-Info: RSA-MD5,RSA,
 LNer/nSKuHiQ2SzF39ah1PR2xXPd8DRikswOfQfGmc66n+GgTUf7DXvS5pw6zZZ7
 K46a2ci97fvxSnJ30NXTrg==

<SEC-DOCUMENT>0001240602-04-000010.txt : 20041001
<SEC-HEADER>0001240602-04-000010.hdr.sgml : 20041001
<ACCEPTANCE-DATETIME>20041001134216
ACCESSION NUMBER:		0001240602-04-000010
CONFORMED SUBMISSION TYPE:	4
PUBLIC DOCUMENT COUNT:		1
CONFORMED PERIOD OF REPORT:	20040929
FILED AS OF DATE:		20041001
DATE AS OF CHANGE:		20041001

REPORTING-OWNER:	

	OWNER DATA:	
		COMPANY CONFORMED NAME:			RUNKEL SCOTT W
		CENTRAL INDEX KEY:			0001240602

	FILING VALUES:
		FORM TYPE:		4
		SEC ACT:		1934 Act
		SEC FILE NUMBER:	001-11703
		FILM NUMBER:		041057667

	MAIL ADDRESS:	
		STREET 1:		679 BLACKHAWK COURT
		CITY:			LAKE MARY
		STATE:			FL
		ZIP:			32746

ISSUER:		

	COMPANY DATA:	
		COMPANY CONFORMED NAME:			GENCOR INDUSTRIES INC
		CENTRAL INDEX KEY:			0000064472
		STANDARD INDUSTRIAL CLASSIFICATION:	CONSTRUCTION MACHINERY & EQUIP [3531]
		IRS NUMBER:				590933147
		STATE OF INCORPORATION:			DE
		FISCAL YEAR END:			0930

	BUSINESS ADDRESS:	
		STREET 1:		5201 N ORANGE BLOSSOM TRAIL
		CITY:			ORLANDO
		STATE:			FL
		ZIP:			32810
		BUSINESS PHONE:		4072906000

	MAIL ADDRESS:	
		STREET 1:		5201 N ORANGE BLOSSOM
		CITY:			ORANLANDO
		STATE:			FL
		ZIP:			32810

	FORMER COMPANY:	
		FORMER CONFORMED NAME:	MECHTRON INTERNATIONAL CORP
		DATE OF NAME CHANGE:	19880128

	FORMER COMPANY:	
		FORMER CONFORMED NAME:	MECHTRON GENCO CORP
		DATE OF NAME CHANGE:	19720411

	FORMER COMPANY:	
		FORMER CONFORMED NAME:	MECHTRON CORP
		DATE OF NAME CHANGE:	19690909
</SEC-HEADER>
<DOCUMENT>
<TYPE>4
<SEQUENCE>1
<FILENAME>primary_doc.xml
<DESCRIPTION>PRIMARY DOCUMENT
<TEXT>
<XML>
<?xml version="1.0"?>
<ownershipDocument>

    <schemaVersion>X0202</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2004-09-29</periodOfReport>

    <notSubjectToSection16>0</notSubjectToSection16>

    <issuer>
        <issuerCik>0000064472</issuerCik>
        <issuerName>GENCOR INDUSTRIES INC</issuerName>
        <issuerTradingSymbol>gnci</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001240602</rptOwnerCik>
            <rptOwnerName>RUNKEL SCOTT W</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>679 BLACKHAWK COURT</rptOwnerStreet1>
            <rptOwnerStreet2></rptOwnerStreet2>
            <rptOwnerCity>LAKE MARY</rptOwnerCity>
            <rptOwnerState>FL</rptOwnerState>
            <rptOwnerZipCode>32746</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>0</isDirector>
            <isOfficer>1</isOfficer>
            <isTenPercentOwner>0</isTenPercentOwner>
            <isOther>0</isOther>
            <officerTitle>Chief Financial Officer</officerTitle>
        </reportingOwnerRelationship>
    </reportingOwner>

    <nonDerivativeTable>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Common Stock</value>
            </securityTitle>
            <transactionDate>
                <value>2004-09-29</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>M</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionTimeliness>
                <value></value>
            </transactionTimeliness>
            <transactionAmounts>
                <transactionShares>
                    <value>20000</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>0.87</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>60000</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
    </nonDerivativeTable>

    <derivativeTable>
        <derivativeTransaction>
            <securityTitle>
                <value>Option</value>
            </securityTitle>
            <conversionOrExercisePrice>
                <value>0.87</value>
            </conversionOrExercisePrice>
            <transactionDate>
                <value>2004-09-29</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>M</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionTimeliness>
                <value></value>
            </transactionTimeliness>
            <transactionAmounts>
                <transactionShares>
                    <value>20000</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>0.87</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>D</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <exerciseDate>
                <value>2003-09-01</value>
            </exerciseDate>
            <expirationDate>
                <value>2010-09-01</value>
            </expirationDate>
            <underlyingSecurity>
                <underlyingSecurityTitle>
                    <value>Common Stock</value>
                </underlyingSecurityTitle>
                <underlyingSecurityShares>
                    <value>20000</value>
                </underlyingSecurityShares>
            </underlyingSecurity>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>60000</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </derivativeTransaction>
    </derivativeTable>

    <ownerSignature>
        <signatureName>Scott W. Runkel</signatureName>
        <signatureDate>2004-10-01</signatureDate>
    </ownerSignature>
</ownershipDocument>

</XML>
</TEXT>
</DOCUMENT>
</SEC-DOCUMENT>
-----END PRIVACY-ENHANCED MESSAGE-----