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Vibration damper slippage |
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george w 
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 Topic: Vibration damper slippagePosted: Oct/23/2016 at 5:21pm |
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How common is it that a vibration damper outer ring slips throwing off the timing mark calibration ? The car in question is my 69 AMX with the 343 / automatic.
When it does slip in which direction does it shift ? Toward retard or advance ? When I set my timing at spec, TDC, the car stumbles badly at WOT, but as soon as I back off a bit it's fine. Advancing the timing about 10 to 15 degrees (estimated)corrects the problem completely.The vac. advance is working properly and the engine is completely stock. Plugs,ignition, etc are in good order. There appears to be no play in the distributor and the dwell angle stays rock steady at 30 degrees. Second question, how much difference does the dwell angle make ? Is it better to set it at the lower spec of 29 degrees or the higher at 31 degrees ? |
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Long time AMC fan. Ambassador 343, AMX 390, Hornet 360, Spirit 304 and Javelin 390. All but javelin bought new.
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304-dude
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Joined: Sep/29/2008 Location: Central Illinoi Status: Offline Points: 9082 |
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Posted: Oct/23/2016 at 5:43pm |
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Dwell is a measurement of points opening and closing, not degrees in timing. You can have a vacuum or diaphragm leak, or carb adjustment issue rather than timing effecting WOT. Usually a ping condition occurs when timing is off, or be very slow to pickup speed under load.
If the ring slipped, it would put the timing in retarded position. As the torque of the engine will cause the ring to act as if it wants to be stationary, thus eventually shifting behind in direction of the rotation of the crank. As long as you have a steady dwell between 29 to 31 you are good. There should not be much difference in how the engine will operate within the dwell settings. |
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71 Javelin SST body
390 69 crank, 70 block & heads NASCAR SB2 rods & pistons 78 Jeep TH400 w/ 2.76 Low 50/50 Ford-AMC Suspension 79 F150 rear & 8.8 axles Ford Racing 3.25 gears & 9" /w Detroit locker |
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WesternRed
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Posted: Oct/23/2016 at 7:33pm |
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Quite common for the balancer ring to slip.
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6PakBee
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Posted: Oct/23/2016 at 8:19pm |
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Dwell is the angular rotation of the distributor when the points are closed. More dwell is better than less as you have more coil saturation time. But practically speaking, a couple degrees won't make a noticeable difference. You really want to gap the points at the wide end of the range as the gap will close with rubbing block wear.
As to the harmonic damper slipping, the best way I know of to determine if slippage has occurred is to use a cylinder stop made from an old spark plug. WITH THE BATTERY DISCONNECTED, rotate the engine until it goes solid against the stop. Mark the damper at the TDC mark on the cover. Rotate the engine in the opposite direction until it again goes solid against the stop. Mark the damper again at the TDC mark on the cover. Your actual TDC point will be in the middle of the two marks. Use this point in the middle to time the motor. The '68-'70 Mopar 340's were notorious for slipping dampers. It got so bad that I'd check TDC on a 340 as a matter of course before trying to time one. |
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Roger Gazur
1969 'B' Scheme SC/Rambler 1970 RWB 4-spd Machine 1970 Sonic Silver auto AMX All project cars. Forum Cockroach |
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AMC Okie
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Joined: Sep/09/2015 Location: Okmulgee Okla Status: Offline Points: 327 |
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Posted: Oct/23/2016 at 8:23pm |
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Would the damper slipping give a pulsating vibration to the engine?
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69 "GO PACK AMX"
73 Javelin 43,000 mile,origanl SURVIVOR 68 Javelin parts car 39 Ford coupe 48 Chevy coupe 2004 Dodge 1500 Rumble Bee 2005 Pontiac Solstice Charlie S. |
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304-dude
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Posted: Oct/23/2016 at 8:30pm |
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A loose damper, unbalanced flyweel or flex plate, or bad accessory dragging on the engine.
If your ring was loose, it would spin off or be offset from the balancer hub. You would see the hub protrude from the ring, instead of being flush. |
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71 Javelin SST body
390 69 crank, 70 block & heads NASCAR SB2 rods & pistons 78 Jeep TH400 w/ 2.76 Low 50/50 Ford-AMC Suspension 79 F150 rear & 8.8 axles Ford Racing 3.25 gears & 9" /w Detroit locker |
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Bruce Clarkson
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Posted: Oct/24/2016 at 8:09pm |
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There are folks like The Damper Doctor who will rebuild these. They did fine on my 67 343. Mine was considerably off and you could see it had slipped.
Bruce Clarkson |
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Bruce Clarkson
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mstrcrftr
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Posted: Oct/24/2016 at 8:13pm |
yes |
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