Flathead cam timing specs

	FLATHEAD CAM TIMING SPECS	www.virtualindian.org
April 2000	Compiled by Guy	Home / Archives / Cam timing

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Make	Model(s)	IN open	IN close	EX open	EX close	Overlap	Lift	Ignition Advance
		BTDC	ABDC	BBDC	ATDC			BTDC
J.A.P.¹	175, 250, 350 sv	15^o	50^o	50^o	20^o			40^o
J.A.P.¹	500, 600 sv	16^o	65^o	65^o	25^o			40^o
J.A.P.¹	1100 sv	16^o	65^o	65^o	25^o			38^o

Indian	741	10^o	60^o	60^o	10^o		0.460"³	7/16" / 40^o
	3 1/16" Stroke	0.037"	0.625"	0.625"	0.037"

Indian	45 Scout	10^o	60^o	60^o	10^o		0.460"³	7/16" / 37.5^o
	3.5" Stroke	0.050"	0.730"	0.730"	0.050"

Indian	Bon. Scout²40-on	34^o	60^o	60^o	34^o			5/8" / 45^o
	3.5" Stroke	0.359"	0.730"	0.730"	0.359"

Indian	74 Chief	10^o	60^o	60^o	10^o		0.400"³	1/2" / 36^o
	4 7/16" Stroke	0.060"	0.795"	0.795"	0.060"

Indian	74 Bonne. Chief²	30^o	60^o	60^o	30^o		0.475"³	5/8" / 40^o
	4 7/16" Stroke	0.400"	0.795"	0.795"	0.400"

Indian	74 Chief, Schunk²	__^o	__^o	__^o	__^o		0.560"³	5/8" / 40^o
	4 7/16" Stroke	____"	____"	____"	____"

Indian	80 Std Chief	10^o	60^o	60^o	10^o		0.400"³	11/16" / 39^o
	4 13/16" Stroke	____"	____"	____"	____"

HD	45	__^o	__^o	__^o	__^o		0.313"	1/4" / 30^o
	3 13/16" Stroke	____"	____"	____"	____"

HD	UL 89" Hot Rod	55^o	65^o	53^o	37^o		0.450"	29^o
	4 3/4" Stroke						[0.375"Std]

NOTE: THIS CHART NEEDS VALVE TIMING & IGNITION ADVANCES CONVERTED FROM FRACTIONAL INCH SPECS TO DEGREES (USING STROKE).

COROLARY NOTE: FRACTIONAL INCH CAM SPECS MUST BE CONVERTED FOR STROKERS!
NOTE: LOOKS LIKE 741 CAMS CAN BE REGROUND TO HAVE 0.54" LIFT W/O WELDING

NOTE: VALUES XX ARE AS PUBLISHED, (XX) IS CALC’D

1. From July 19, 1945 Motor Cycling magazine article by Phil Irving, reprinted in Restoring & Tuning Classic Motorcycles
2. From 19^th Edition of Q&A, published by Antique Cycle Supply.
3. Per Jerry Greer's Catalog, pg. 10:

741 & Sp. Scout Std Chief Bonn Chief Schunk Chief

Lobe Height 1.615" 1.510" 1.575" 1.635"

Base Circle 1.155" 1.110" 1.100" 1.075"

Calc’d Lift 0.460" 0.400" 0.475" 0.560"

	741 & Sp. Scout	Std Chief	Bonn Chief	Schunk Chief
Lobe Height	1.615"	1.510"	1.575"	1.635"
Base Circle	1.155"	1.110"	1.100"	1.075"
Calc’d Lift	0.460"	0.400"	0.475"	0.560"