Backfire after rebuild - JeepForum.com
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post #1 of 17 Old 05-06-2021, 05:00 PM Thread Starter
atrusler
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Backfire after rebuild

Ok, I'm way out of my comfort zone trying to get the distributor/timing set properly on my newly refreshed 360. (cleaned completely inside & out, new gaskets, etc) Just finished getting everything back together and installed back in the chassis and now tackling trying to get it started again. I took out the #1 spark plug and put the finger of a rubber glove in while I turned the crank. When the glove popped out, I made a small turn to line up the HB line to TDC. Have the distributor installed and wires in the proper order 1-8-4-3-6-5-7-2. When I crank it and give it some gas, it will catch and give a huge backfire. I have new spark plugs that were suppose to be the correct size but I suspect they are a tad too short (just ordered a set of the Champion's that were in there before my rebuild). Would this cause the issue? I put in the old plugs and it seemed to try to catch but had the same backfire issue. Also, I see that only 2 of the plugs look to have fired, or show evidence of the backfire (?). I obviously have something connected wrong and/or I'm not identifying the #1 cylinder correctly. At this point, I'm beyond my skill set so any thoughts or suggestions are greatly appreciated.

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post #2 of 17 Old 05-06-2021, 06:22 PM
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Did the backfire occur through the carb or the tailpipe? If it backfires through the carb it's likely a too lean fuel mixture. Otherwise (tailpipe) could mean too rich.

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post #3 of 17 Old 05-06-2021, 06:37 PM
Axhammer
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It sounds like the distributor is 180 out. When the piston blows the glove out, it should be at TDC on the harmonic balancer, like you described. The rotor in the distributor should be pointing to the #1 spark plug wire. If it’s 180 out it will be pointing at the #6 spark plug wire. If this is the case, remove the distributor and reinstall the distributor with the rotor pointing to #1. I normally set it up so the rotor is slightly before the #1, for the initial start up of a fresh engine.

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post #4 of 17 Old 05-06-2021, 07:04 PM Thread Starter
atrusler
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Thanks Axhammer. I spoke to a friend and he suggested the same thing. going to try rotating it 180 and see how it goes. Appreciate the responses.
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post #5 of 17 Old 05-06-2021, 11:54 PM
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Don't do anything until you confirm that #1 is a TDC at the top of the compression stroke. Do you you did before but put your finger over the hole and you should feel the compression while a friend cranks the motor over with a wrench on the harmonic balancer. When you get the timing mark lined up (assuming you have the correct balancer and pointer) pull the distributor cap and be sure the rotor is pointing in the correct direction to spark plug #1.

Next be sure that all the wires go from the cap to the correct plug.

I recently had to tear a head off my son's 1966 Mustang to replace a head gasket. I gave him the job of numbering the plugs wires with making tape to make it go back together faster. It was dark when we finished the project and when it started it was backfiring and not sounding very good. It is a mechanical lifer cam and I adjusted all the valves so all sorts of bad thing started going through my head like maybe I had the cam in the wrong position when I adjusted one of the exhaust valves. ...anyway, I started looking and it seems my son mixed the tape up and had wire #3 numbered as #4 and wire #4 numbered as #3. It makes a difference... Swaped the plug wire locations and it ran as expected...
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post #6 of 17 Old 05-07-2021, 07:43 AM
pedal2themetai
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HI Tho I'm with the others on 180* out.. That's an easy one to mess up..
Did you replace the timing gear and chain set? and if you did did you line up the dots .. dot to dot, cam at 6 and crank at 12?
good luck
tim
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post #7 of 17 Old 05-07-2021, 09:06 AM
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I have seen people get the motor at top dead center and then not understand which way the rotor should point and actually have the rotor pointing 180 out. Look for the little metal contact on the end of the rotor that should contact the electrode in the distributor cap for the #1 cylinder that you want to lineup. I think HEI distributors are fairly obvious with their design as far as the rotor shape.
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post #8 of 17 Old 05-07-2021, 09:07 AM
katwalk27
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Seems to me the rubber glove might pop out somewhere in the middle of the compression stroke before it gets to TDC. I usually stick my thumb over the hole and crank it to determine when the compression stroke just begins. I then get a flexible piece of wire and stick it into the sparkplug hole so that I can feel when the piston gets to TDC. Then, I stab the distributor in and go through the timing process. I have had a couple of engines where I found out the timing marks on the HB were not exactly right, so I always find TDC this way to eliminate the variable of incorrect timing marks. Good luck
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post #9 of 17 Old 05-07-2021, 10:27 AM
StoneTower
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This is why I said "(assuming you have the correct balancer and pointer)". Depending on the engine, some people use a dowel or carefully use a screwdriver (as the piston nears the top of the stroke) to see exactly when the piston reaches TDC.


You just want to be sure the piston is near the top of the stroke so you do not jam the screwdriver or dowel sideways in the cylinder. Personally I would never use something metal. You need something rigid so you can see when the piston stops moving up just before it starts going down.
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post #10 of 17 Old 05-07-2021, 12:48 PM
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Quote:
Originally Posted by StoneTower View Post
This is why I said "(assuming you have the correct balancer and pointer)". Depending on the engine, some people use a dowel or carefully use a screwdriver (as the piston nears the top of the stroke) to see exactly when the piston reaches TDC.

https://www.youtube.com/watch?v=bd1AMuI0Eec

You just want to be sure the piston is near the top of the stroke so you do not jam the screwdriver or dowel sideways in the cylinder. Personally I would never use something metal. You need something rigid so you can see when the piston stops moving up just before it starts going down.

I have found one of the bigger zipties works pretty well too.
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post #11 of 17 Old 05-07-2021, 01:48 PM
StoneTower
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I like the Ziptie idea, I think I would put the locking end in the cylinder to be sure that the small end does not get jammed in between the cylinder and the piston. That would be really bad.

Quote:
Originally Posted by katwalk27 View Post
I have found one of the bigger zipties works pretty well too.
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post #12 of 17 Old 05-08-2021, 05:43 AM
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I just use one of those compression testers that screws in.


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post #13 of 17 Old 05-08-2021, 02:28 PM Thread Starter
atrusler
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Thanks for all the info guys, going to work on this over the weekend and will let you know how it goes!
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post #14 of 17 Old 05-08-2021, 04:43 PM Thread Starter
atrusler
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OK, you guys rock. got it running. Now just need to get the timing set but we're back in business. The video was a big help.
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post #15 of 17 Old 05-08-2021, 06:20 PM
StoneTower
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So tell us exactly what the problem was and how you solved it. We are Jeep junkies and we need to know...
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