Timing tabs and damper TDC lines SBC
(→The three most common locations for the timing mark on the damper) |
(→The three most common locations for the timing mark on the damper) |
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==The three most common locations for the timing mark on the damper== | ==The three most common locations for the timing mark on the damper== | ||
The exact years of the type of damper timing marks overlap one another, depending on the exact application. | The exact years of the type of damper timing marks overlap one another, depending on the exact application. | ||
| − | + | These clock positions don't seem to make sense. The keyway is located at the same position as the the No. 1 cylinder crank arm. So when the keyway is inline with the midpoint of the No. 1 cylinder, the piston is at TDC. Looking at the front of the engine, the key way is at 1:30 (or 45 degrees from vertical). If the timing mark is at 2 degrees or 10 degrees to the left (CCW), the marks would be at 1:29 and 1:20, respectively. | |
#The pre-1969 damper has the TDC line on the outer ring at the 2:30 o’clock position- or 2º before the keyway centerline- i.e. the line is to the LEFT of the keyway, looking at the front of the damper or engine. The keyway is seen in the ID of the damper nose. Includes a majority of the 2.30" small journal main engines and the 1967-69 2.45" large journal engines. | #The pre-1969 damper has the TDC line on the outer ring at the 2:30 o’clock position- or 2º before the keyway centerline- i.e. the line is to the LEFT of the keyway, looking at the front of the damper or engine. The keyway is seen in the ID of the damper nose. Includes a majority of the 2.30" small journal main engines and the 1967-69 2.45" large journal engines. | ||
#The damper used from 1969 to about 1995 (some 1978-86 GM automobiles do not use the 2 o'clock position balancer and associated timing cover where there is some overlap usage e.g. G-series vans which retained the 2 o'clock balancer while the passenger car and C/K light duty trucks transitioned over to the 12 o'clock position which used a centrally located timing pointer spot welded) has the TDC line at the 2 o’clock position- or 10º before the keyway. You'll find that aftermarket dampers are the 10º type, as are the bolt-on tabs sold by the aftermarket, unless they're adjustable. The 2 o'clock position was reintroduced during the 1987 model year trucks with the 8" balancer (only with the LO5-optioned 350/5.7L).<br>{{Note1}}This includes the SBC 400, although the 400 damper is counterweighted because the engine is externally balanced, and the 1985-present 4.3L V6 with its respective 6.75" damper (raised outer lip) that has both a 2 o'clock and a 4 o'clock position (for some vans eg. G-series, Express, and Astro/Safari). Do not mix and match internal and external balanced dampers (also applies to 1996-up Vortec applications (4.3L, 5.0L, 5.7L) since the balancers have a shorter snout to clear the pressed on crankshaft position sensor used with the associated plastic timing cover. <br>{{Note1}}Using the Vortec balancer with a non-Vortec engine will result in misalignment of the crank pulley with the rest of the accessories, e.g. power steering pump, alternator, water pump. | #The damper used from 1969 to about 1995 (some 1978-86 GM automobiles do not use the 2 o'clock position balancer and associated timing cover where there is some overlap usage e.g. G-series vans which retained the 2 o'clock balancer while the passenger car and C/K light duty trucks transitioned over to the 12 o'clock position which used a centrally located timing pointer spot welded) has the TDC line at the 2 o’clock position- or 10º before the keyway. You'll find that aftermarket dampers are the 10º type, as are the bolt-on tabs sold by the aftermarket, unless they're adjustable. The 2 o'clock position was reintroduced during the 1987 model year trucks with the 8" balancer (only with the LO5-optioned 350/5.7L).<br>{{Note1}}This includes the SBC 400, although the 400 damper is counterweighted because the engine is externally balanced, and the 1985-present 4.3L V6 with its respective 6.75" damper (raised outer lip) that has both a 2 o'clock and a 4 o'clock position (for some vans eg. G-series, Express, and Astro/Safari). Do not mix and match internal and external balanced dampers (also applies to 1996-up Vortec applications (4.3L, 5.0L, 5.7L) since the balancers have a shorter snout to clear the pressed on crankshaft position sensor used with the associated plastic timing cover. <br>{{Note1}}Using the Vortec balancer with a non-Vortec engine will result in misalignment of the crank pulley with the rest of the accessories, e.g. power steering pump, alternator, water pump. | ||
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