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Old 04-15-2005, 06:11 PM   #1
Brad_Olson
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1986 305 timing tab

My '86 305's timing tab is pretty dirty and all I can see are the "teeth"; the numbers are covered. I think I know what the teeth indicate but want to be sure so I know I'm setting the timing I think I'm setting.

Think of each tooth point as a high spot and the halfway point between 2 teeth as a low spot. There's one low spot that's wider and deeper than the others; I believe this is TDC. The first tooth counterclockwise from TDC is 2 BTDC, the next one is 6 BTDC, and so on. The low spots represent 4 BTDC, 8 BTDC, etc. Currently at idle the mark corresponds with the 2nd low spot, meaning the engine's initial timing is 8 BTDC.

Does this sound right? Thanks!

Brad
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Old 04-15-2005, 07:19 PM   #2
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I don't know how much this helps, but I believe the white mark was pointing at TDC when I took this pic.

http://www.slonaker.net/images/truck/TDC.jpg

I will be working on the truck tomorrow, and might be able to answer your question better then.

BTW, mine is an '86 with a 305 also.

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Old 04-15-2005, 08:53 PM   #3
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Thanks! According to the photo I'm correct about the location of TDC on the tab, so now all that remains is to verify that it's 4 degrees from tooth to tooth. If you could please check that tomorrow (as long as it's not an inconvenience) I'd really appreciate it.

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Old 04-15-2005, 08:56 PM   #4
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i wish i had a timing tab.....
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Old 04-15-2005, 09:01 PM   #5
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Quote:
Originally Posted by Prerunner1982
i wish i had a timing tab.....
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Old 04-16-2005, 01:22 AM   #6
boxrodz
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Brad -

Here's what I got for a timing tab for a 305. Maybe Slonaker will be able to confirm this. Hope this helps.
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Last edited by boxrodz; 04-16-2005 at 01:23 AM.
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Old 04-16-2005, 03:50 PM   #7
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is that 12 at the end?
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Old 04-16-2005, 08:42 PM   #8
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Quote:
Originally Posted by boxrodz
Here's what I got for a timing tab for a 305. Maybe Slonaker will be able to confirm this. Hope this helps.
Yes, quite a bit - thanks! So it looks like the teeth are 4, 8, 12, etc. and not 2, 6, 10 like I thought, which means I set my initial timing to 10 BTDC and not 8 BTDC. I drove it around a little bit like that today and I didn't hear any detonation w/89 octane so I'll leave it be for awhile.

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Old 04-16-2005, 08:58 PM   #9
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That is why I asked if that was 12, I to thought that was 10 and it is past that. So my is probably around 14-15 initial!
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Old 04-17-2005, 01:54 AM   #10
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You're welcome, Brad. (Sure is it tight where the tab is located.)

1986Silverado -
Yes, the last timing mark is a 12 (ie. 12 - 8 - 4 - 0 - 4).
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