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AMC backfiring

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akimmet View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote akimmet Quote  Post ReplyReply Direct Link To This Post Posted: Jul/11/2018 at 10:53am
Originally posted by AMC-304 AMC-304 wrote:

I dont know, i can fix a chevy in my sleep, but this amc....


There is nothing specific to an AMC that makes them harder to get running. Keep at it, you will get it figured out.

The description of your problems all appear to point to some sort of valve or ignition timing problem.

Did you pull the timing gears when you had the timing cover off?
Both the upper and lower gears are indexed with a key, make sure the keys haven't sheared.

Are some of your valves hanging open? Check lifter pre-load. The correct method of setting and checking pre-load is diffrent depending on what rocker arm setup you have. Since AMC have used several different kinds of rocker arms over the years, we would need to see a picture of your heads and rocker arms to identify what you have.

Do you have a flat cam? While this is unlikely, it is always a good idea to make sure all of the valves are opening.

Are both distributor gears in good shape?

If your distributor has a GM HEI cap on it, you definitely have an aftermarket dist on your engine. Some of these early aftermarket GM HEI cap distributors were very poorly made, and will be nothing but trouble. They were made by welding or pinning together mismatched housings. The newer billet housing HEI distributors on the market aren't quite so bad, and most are now acceptable quality.

Are you absolutely certain your engine doesn't have a reverse rotation cam? Make sure valve timing events match the firing order. Since both distributor gears are removable on a AMC V8, it is possible someone before you may have swapped in the incorrect dist gears.

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PHAT69AMX View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote PHAT69AMX Quote  Post ReplyReply Direct Link To This Post Posted: Jul/12/2018 at 11:57am
Well when you find out what the problem is please be sure and let us know, ok ?
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AMC-304 View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote AMC-304 Quote  Post ReplyReply Direct Link To This Post Posted: Jul/13/2018 at 5:00pm
Well let me state that I haven't had a motor give me fits like this, and reading up on it it seems to be just like a chevy small block even the firing order is the same...The valves are operating correctly, I had the valve covers off and they are the non-adjustable type. the gears on the dist. look good. both the crank and the dist. turn clockwise so I dont think it turns backward. So I just dont want to throw parts and money at it! I want to get it running and make sure the impeller works! if it doesn't we will make the derision then. So my question to you is I have read all over the internet dirfferent ways to set the dist, I've always get to tdc compression and then drop the dist pointed to #1 cylinder. the start installing the spark plud wires with #1 alittle before the #1 cylinder and continue the firing cw....
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Boris Badanov View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Boris Badanov Quote  Post ReplyReply Direct Link To This Post Posted: Jul/13/2018 at 7:11pm
Try a compression test.

Yes, the firing order on all AMC V8s are the same as the SBC
1-8-4-3-6-5-7-2

Check to be sure that the phasing of the rotor and cap are correct.
That is a little before the "contact" at rest and a little after it at full advance.

Gremlin Dreams
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Post Options Post Options   Thanks (0) Thanks(0)   Quote PHAT69AMX Quote  Post ReplyReply Direct Link To This Post Posted: Jul/13/2018 at 7:19pm
Yes, Distributor turns Clockwise.  Yes, kinda like a SBC...
Can only think of "basics"... just stating the obvious is all... no "judgement" involved...
#1 cylinder is drivers side front, that side is 1, 3, 5, 7
#2 cylinder is passenger side front, that side is 2, 4, 6, 8
What Distributor?  A stock AMC Delco type?  Points or what?
Pull Distributor, get motor to Compression on #1, align Dampener Mark and Pointer
Cap is Keyed to Distributor Housing, Front & Center is "normal" position for #1 Cap Post.
Put Cap on Distributor and use tape or a marker and mark Housing with Cap #1 Post position.
May want to confirm the Points or whatever are at a "fire point" when the
Rotor Button Tip points to the Housing mark that matches the Cap #1 Post.
Although a Delco Type Distributor, the AMC & Chevy Point Plates *are different* ( pic )
Remove Cap, pre-align Oil Pump Drive in motor, stab distributor (there is a Distributor GASKET)
so that the Rotor Button Tip ends up Pointing at housing #1 Cap Post Mark.
Turning the Distributor CCW Advances the Timing.
Install the Plug Wires... ? cross fingers ?
It will be interesting to see what was awry once it fires ups...




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Post Options Post Options   Thanks (0) Thanks(0)   Quote AMC-304 Quote  Post ReplyReply Direct Link To This Post Posted: Jul/13/2018 at 9:19pm
I think i told you its a gm hei.....maybe not...
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Post Options Post Options   Thanks (0) Thanks(0)   Quote AMC-304 Quote  Post ReplyReply Direct Link To This Post Posted: Jul/13/2018 at 9:25pm
See im getting the drawings you sent. Ok the engine is at tdc. Installing the dist. Rotor pointing at #1 cylinder, and it shows the #1 spark plug at the front of the dist...so whats up with that??
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Post Options Post Options   Thanks (0) Thanks(0)   Quote mmaher94087 Quote  Post ReplyReply Direct Link To This Post Posted: Jul/13/2018 at 9:54pm
Question: knowing this is a boat motor; Has the starter been replaced by the prior owner? This might sound off-the-wall, but.... I'm still hung up on the fact that all these remedies have not produced a fix.
Mike
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Post Options Post Options   Thanks (0) Thanks(0)   Quote AMC-304 Quote  Post ReplyReply Direct Link To This Post Posted: Jul/13/2018 at 10:21pm
I dont know if the starter has been reppaced...but that being said, every once in awhile it does drag....
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Boris Badanov Quote  Post ReplyReply Direct Link To This Post Posted: Jul/14/2018 at 8:00am
Compression test to spot a hanging or burnt valve.
Gremlin Dreams
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