This data has been gathered from old out-of-print material. While we make every effort to be accurate, the information shown is to be used for general reference only. It is always best to have the original service or operator's manual for your tractor before attempting any tuneup.

There is a legend at the bottom of the page describing some of the terms used here.

Model	Point Gap	Spark Plug Gap	Timing Mark On	Spark Occurs	Firing Order	Int. Valve Clearance	Exh. Valve Clearance	Comments
WC,WD,WD-45,WF	.020	.030	FLY	TDC	1-2-4-3	.010H	.010H	For intake & exhaust valve clearance, WD-45 set at .012H
U,UC	.013	.035	FLY	TDC	1-2-4-3	.010H	.010H
H-3	.020	.025	FLY	TDC	1-2-4-3	.010H	.016H
G	.020	.025	FP	NOTCH	1-3-4-2	.010H	.010H
D-19	.022	.025	FP	TDC	1-5-3-6-2-4	.015H	.020H
D-10,D-12,D-17	.022	.025	FLY	TDC	1-2-4-3	.013H	.013H	Spark plug gap for LPG is .020. Int. & Exh Valve clearance for Ser. No. D-10 (3501) D-12 (3001) & Up is .009H and .015H
C,CA	.020	.030	FLY	TDC	1-2-4-3	.010H	.012H
B,IB,RC	.020	.035	FLY	TDC	1-2-4-3	.010H	.010H
A	.020	.032	FLY	TDC	1-3-4-2	.012H	.012H	Point gap is for Fairbanks. Set Splitdorf .012-.015
D-14,D-15	.022	.025	FLY	LINE	1-2-4-3	.009H	.015H	Point gap is for D-15 only, set D-14 at .020. For spark, LPG set center. For Int. & Exh. Valve clearance, D-14 set at .013H

Legend
TDC - Top Dead Center FP - Crankshaft Fan Drive Pulley Exh - Exhaust Int - Intake ATDC - After Top Dead Center BTDC - Before Top Dead Center
Data collected from an old Niehoff tune-up chart.

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