1985 GMC Short Bed Timing Marks

GMC
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SNOWMAN6058
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  • 1 POST
I have a 1985 GMC Short bed pickup with a 305 in it. Trying to read the timing mark directly under the water pump is unreal. I took off the fan and water pump pully, all the belts, shroud. It has 4 V notches. Where is "0" and 4 degrees BTD? There is a very wide notch towards the drivers side. Is that zero?

Thank you,
snowman)
Mar 26, 2006 at 9:06 AM
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BURRBRIAN
  • ✓Experienced Mechanic
  • 158 POSTS
Hey snowman, I'm not positive that gmc and chevy use the same, but if they are tdc (0) is the second point- not notch- from the drivers side going counter clockwise.4 degrees before would be the next point, the v-notch in between would be 2 degrees.See how it goes? The first point would be 4 degrees after.next point 0, next point 4 before.This is on chevy but should work for you.And your right-It's a royal pain@$^##$ to see sometimes! I don't know about wide notch unless someone has filed it .Look closely and clean it off real good and you might find
0 marked on it. hope you get it. Burr

Me again, a little more checking around and I see that on some the wide notch is indeed 0 then it still goes 4 degrees for every point from there.later
Mar 26, 2006 at 12:32 PM
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Suggested Repair

Clean the timing tab thoroughly and look closely for a stamped 0. On many of these tabs the wide notch toward the driver's side is 0 (TDC); from there each point is about 4 degrees, so the next point counterclockwise is about 4 degrees before TDC and the V-notch between points is about 2 degrees. Confirm the marks on your tab, since layouts vary and a wide notch may have been filed.

Conversation Summary

The owner of a 1985 GMC short-bed pickup with a 305 cannot clearly read the timing tab under the water pump. It has four V-notches and a wide notch toward the driver's side, and the owner asks which mark is 0 and which is 4 degrees before TDC. The expert says Chevy-style tabs often place TDC at the second point from the driver's side going counterclockwise, with about 4 degrees between points, and later notes that on some tabs the wide notch itself is 0. The advice is to clean the tab and look for a stamped 0.

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