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| How much should timing "jump around" at idle? https://slantsix.org/forum/viewtopic.php?t=45411 |
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| Author: | krytellan [ Fri Jun 24, 2011 5:17 pm ] |
| Post subject: | How much should timing "jump around" at idle? |
I know it's a bad thing when your timing moves around, but how much is too much. When I was last checking my timing, it would move around by about 2-3 degrees. To the point, actually, where at each cylinder fire it was essentially in another place, either by a little or a couple of degrees. I wanted to know know if this is something I need to be worried about. Anyone? |
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| Author: | wjajr [ Fri Jun 24, 2011 5:48 pm ] |
| Post subject: | |
Timing should be steady at idle on a stock engine ticking over about 700 rpm. If your rpm is much higher than say 750, a stock governor will start to advance. Probably what is happening is you may have a weak light spring in the governor that is allowing a little advance which in turn causes rpm to increase, at which point the stretched spring than pulls the governor weights back in and rpm drops. Before messing with distributor, make sure your idle rpm is set to factory recommendations, as well as the static timing or in other words initial timing. |
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| Author: | THOR [ Fri Jun 24, 2011 6:24 pm ] |
| Post subject: | |
The timing bopping around can also be a symptom of a slack timing chain. After awhile, the sprockets wear, and the chain stretches. This slack in the timing set causes the cam to fall in and out of sync with the crank at low rpm especially, due to firing impulses on the crank. Bill is right too, I've had a distributor cause this exact issue. It may be both. Take your distributor cap off, rotate the engine to TDC on the damper, and rotate the engine back and forth by hand. Measure how many degrees of rotation you get before the rotor moves. It should move almost immediately. ~RDE~ |
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| Author: | mc_ryan [ Sat Jun 25, 2011 12:16 am ] |
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Just to show how bad it can get... When I pulled the 318 out of my RV to put in the 318 I built I knew the old motor had a slack timing chain. So, I pulled the Distributor cap and moved the crank back and forth to see how bad it was. I could move the crank from 15 BTDC to 15 AFTER TDC before the distributor would move at all... lol I am baffled that it did not jump a tooth... |
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| Author: | krytellan [ Sat Jun 25, 2011 7:17 am ] |
| Post subject: | |
Thanks guys. I'll give the dizzy test a shot a bit later. I just spent some time getting everything shored up on the standard timing side. I got the idle a 725 as per hood spec and at about 14 BTDC (hood spec is 12 BTDC). It still jumps a bit with about 1-2 degrees in either direction. |
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