Timing tabs and damper TDC lines SBC
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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 1:26 and 1:10, 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 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. | |
| − | + | #A third timing mark was used from 1978 to about 1986 (carbureted engines) and nearly all 1984-1995 (except for 1985-present 4.3L V6 and van (Astro/Safari, G10, 20, 30 and P-series box vans) applications with some overlap use e.g. C/K series trucks, marine/industrial, passenger car). It is at the 12 o’clock position- or 40º before the keyway. These dampers have a thicker ring unlike the 2 o'clock position balancers. This damper uses a timing cover that has the tab welded on at about the 12 o'clock position - the timing covers with this setup had either the 6.75" (305 and pre-1985 90 degree V6) or 8" (350/5.7L only). The 1987-'95 balancer (LO3/LO5) or 1969-'80 balancer will fit if used with the associated timing tab (GM 12551537 for 6.75", 88960604 for 8") and front cover. Professional Products lists the years for this type damper line as being 1984-1995 and is a 6-3/4” diameter damper. | |
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==Relocating the damper line== | ==Relocating the damper line== | ||
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===Checking the outer damper ring for movement=== | ===Checking the outer damper ring for movement=== | ||
| − | [[File:Damper line.jpg|left|400px]]Draw a sharpie line as shown in the image below. When the timing light is pointed at the TDC line, the sharpie line will also be seen. By revving the engine and running it at different speeds, if the outer ring is loose, the line on the outer ring will be seen to move independently of the line on the inner hub. | + | [[File:Damper line.jpg|left|400px]]Draw a sharpie line as shown in the image below. When the timing light is pointed at the TDC line, the sharpie line will also be seen. By revving the engine and running it at different speeds, if the outer ring is loose, the line on the outer ring will be seen to move independently of the line on the inner hub. Over time the line may be seen to have separated as the outer ring has moved independently of the inner hub. |
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===Part numbers=== | ===Part numbers=== | ||
*The p/n for plastic cover '''with''' sensor hole is: p/n10244600 | *The p/n for plastic cover '''with''' sensor hole is: p/n10244600 | ||
| − | *The p/n for plastic '''without''' sensor hole is: p/n12552557 | + | *The p/n for plastic '''without''' sensor hole is: p/n12552557 (EDIT: new number for cover with out the sensor hole is 12562818) |
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| + | ==Resources== | ||
| + | *[[Determining top dead center]] | ||
| + | *[[Estimating timing chain wear]] | ||
[[Category:Engine]] | [[Category:Engine]] | ||
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