NUT-LUG 1427493 - Caterpillar

3406 (9HB, 2DC, 4FD, 90U, 55X),
3406B (6TB) Industrial;
3406 (91U, 56X),
3406B (4TB) Marine;
3406 (75Z),
3406B (2WB, 3SF, 4RG, 4JK, 4PM) Generator Set EnginesReference: See the article titled "Timing Procedure Aid" in this issue.Alignment of the timing gear marks on the above engines occurs as follows:
* After aligning the 3406 front timing marks it is necessary to turn the engine over 42 revolutions. This will get the timing marks on the crankshaft and cam gears to line up again.* The crankshaft gear (8) and the front or large idler gear (7) marks line up every 21 revolutions.The number 21 is the denominator of the lowest term of the fraction obtained by figuring the number of crank teeth (numerator) over the number of the large idler gear teeth (denominator) or 80 over 105. To reduce this fraction to it's lowest terms, factor the numerator (16 and 5) and the denominator (21 and 5) and divide by the common factor(s). In this example 5 is the only common factor. If 80 is divided by 5 , equals 16. If 105 is divided by 5, equals 21. This equals 16 over 21 which means that every 21st revolution the same teeth will line up.
* The camshaft gear runs at half the revolutions of the crankshaft gear. The camshaft gear marks will line up every 2 crank revolutions.On the 3406A/3406B/3406C it takes 21 × 2 or 42 revolutions for the crankshaft gear (8) and front or large idler gear (7) and the rear or small idler and the cam gear marks (3) to align.
For the 3406E Engine, the same 42 revolutions are required for the crankshaft gear (8) and front or large idler gear (7) and the cam gear (3) and timing gear housing (2), marks or pin (5) to align.
3406 Front Gear Timing. 3406, 3406B/3406C left view. 3406E right view. Timing marks shown in magnified circles. (1) Magnified view of k timing mark. (2) timing gear housing. (3) cam gear. (4) Alignment every 42 revolutions. (5) alignment pin. (6) Alignment every 21 revolutions. (7) large idler gear. (8) crankshaft gear.