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Can this cause a misfiring engine? |
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1958 rambler super 
AMC Addicted 
Joined: Dec/10/2020 Location: Victoria BC can Status: Offline Points: 1201 |
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 Topic: Can this cause a misfiring engine?Posted: May/05/2023 at 10:55pm |
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Would an unbalanced contact pattern of the points opening and closing as the distributor shaft revolves cause a misfire?
Edited by 1958 rambler super - May/05/2023 at 10:57pm |
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ramblinrev
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Joined: Dec/28/2008 Location: Wisconsin Status: Online Points: 11528 |
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Posted: May/05/2023 at 11:08pm |
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Not sure what you are asking. If the distributor shaft bearing is worn, and the cam wobbles, I can see that creating some uneven spark. If the distributor and point set are in good shape, there should be no issue.
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74 Hornet Hatchback X twins (since 1977)
62 American Convertible (still worth the $50 I spent in 1973!) AMCRC #513, AMO #384 70 AMX 360 4-speed (since 1981) |
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mtrosclair
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Joined: Feb/05/2022 Location: Metairie LA Status: Offline Points: 486 |
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Posted: May/06/2023 at 9:36am |
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Is there play in the distributor bearings?
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1963 Rambler Classic 550
Originally a 196, this one has a 199 from a 69 American. |
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mstrcrftr
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Posted: May/06/2023 at 9:42am |
no, its normal.
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1958 rambler super
AMC Addicted
Joined: Dec/10/2020 Location: Victoria BC can Status: Offline Points: 1201 |
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Posted: May/06/2023 at 7:25pm |
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I have taken the distributor apart several times, but never taken it apart far enough to see the bearings, BUT! I have oiled the shaft of the distributor, so that should count for something.... and I can't remember ever noticing any wobble.... And I've handled it and inspected its performance many times and never noticed any wobble....
(this is the original distributor for the engine) (is there any newly manufactured distributors that can be used with the 195.6 engine? I think I've read that newly manufactured HEI distributors can be used with the larger engines 199-232 sizes... Unless I'm wrong about that fact)
Ok, picture this, the distributor is out of the engine and in your hand, the cap is off and your looking inside, the rotor is off and can see the condenser and the points and the little bumper thing that is attached to the edge of the points that rides along the octogon shaped surface of the shaft of the distributor... You turn the helical gear at the other end of the distributor that interfaces with the same type of helical gear of the cam shaft and watch the top of the distributor shaft that the rotor sits on start to spin.... the bumper of the points slides along the octogon shaped edges and opens and closes the points, and you see that sometimes the points open a little further then other times as the shaft is rotated by your hand. Would this inconsistency cause a misfire? Does that indicate a worn distributor? The reason I'm asking specifically about this is because I believe there is a misfire in my engine and I've never been able to chase it down, the timing HAS to be excluded from the list of causes, I've followed people's directions for setting timing to the letter and these folks have been working on the AMCs and these engines in some cases since the 1960's... So they can't be wrong.... The only remaining causes of a misfire after consulting a complete list of possible types of misfires and their causes that I haven't faced is a mechanical problem inside the engine, or a worn distributor.....
Edited by 1958 rambler super - May/06/2023 at 7:38pm |
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1958 rambler super
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Joined: Dec/10/2020 Location: Victoria BC can Status: Offline Points: 1201 |
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Posted: May/06/2023 at 7:56pm |
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Doing a google search ievcome across an amc forum post that a guy from Sooke bc (just down the road from me) is asking about a new distributor to choose, some of the forum members were telling him about thier experiences with trying hei and having no luck and going back to points.... The same guy also said
"oh, and check your vacuum advance" And this is something I would like to start asking about. could something have gone wrong with the vacuum advance in my distributor that could cause a misfire? The PO had done something fishy with it, I can definitely tell... the case of the vacuum advance looks like he used pliers to pull and force it apart and then close it back together again, it's all messed up...
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troutwilly
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Joined: Sep/14/2007 Location: Carriere, MS Status: Offline Points: 994 |
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Posted: May/06/2023 at 11:42pm |
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Not sure a faulty vacuum advance would cause a stumble or even if a vacuum leak would. But get/borrow a hand held vacuum pump and pull a vacuum on the advance unit and, 1. see if it moves, 2. see if it holds the vacuum. That'll tell you if its good. Assuming you now have your distributor out of the car, jiggle it around and see if it seems like the bearings are worn/loose. If its wobbling too much it could cause some issues. Also see if it moves up and down in the housing much. That could be fixed with some shims between the gear and the housing. You say you can see differences in the points opening on different lobes, so re-install your distributor. You'll have to re-set the timing. Pull the plugs so the engine rotates easy by hand (wrench on the front pulley bolt). Turn the engine easily and check your points opening at the peak of each lobe with a feeler gauge. If they're really that different you may be able to set them at a happy medium as close as possible to specs. When I think I have a cylinder not doing its job I use my timing light (inductive) and move it from plug wire to plug wire and watch the flash patterns to see which one is not firing evenly. Try that. If you find a lazy one, check its wire good and the cap at that wire. Could just be a defective wire or cap.
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Bill O.
70 AMX |
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1958 rambler super
AMC Addicted
Joined: Dec/10/2020 Location: Victoria BC can Status: Offline Points: 1201 |
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Posted: May/07/2023 at 6:14pm |
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I remember doing this test for the vacuum advance...
If you suck on it and plug the hole with your tongue, and it sucks on your tongue and you here the air gett sucked into the advance when you pulled your tongue off it, then the vacuum adv is good.... So that's what I did and it seemed good. I did buy a new vac advanc from galvins, but when I got it, It was obviously a original part, still had the super old box too... So I never used it... Didn't think 64 year old rubber inside it was a good idea.. Also, new wires, new coil, new rotor, new cap, new points, new plugs... FYI (plugs and points gapped properly to specification) I've looked with the timing gun flashes but really couldn't tell if there was a cyl that was flashing out of rythym... I looked for so long I started to go crazy! I think it's a good idea to check the dist another time and focus on the job of the alt, but I'll get back to this later,
Edited by 1958 rambler super - May/07/2023 at 6:56pm |
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wittsend
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Posted: May/08/2023 at 10:21am |
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It sounds like the points cam has uneven wear (as you describe it). That will change the dwell time for the coil charge as well alter the firing timing on those cylinders affected - to some extent.
Rotate the distributor with the points on the highest position. Measure all six points individually with a feeler gauge. They should measure very close to each other. This is best done with the distributor out and held gently in a vise. That will tell if the points cam is worn..., or bushings are worn and for some reason the wear is showing itself only at certain positions. Bushing wear can usually be felt by holding the distributor and trying to move the gear to the side. The advance mechanism also can wear on the shaft it (partially) rotates on. So check that for wear independently.
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'63 American Hardtop
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1958 rambler super
AMC Addicted
Joined: Dec/10/2020 Location: Victoria BC can Status: Offline Points: 1201 |
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Posted: May/08/2023 at 5:20pm |
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Thanks guys for the input....
I did email a distributor rebuilder but they never answered, so I moved on... This misfire has been going on since the first start up, man I'm getting burned out. Another thing that came to mind was the timing.... Maybe the engine builder didn't arrange the timing chain the right way and maybe the valves aren't opening/closing at the right time... There's a way to check, I saw it in the tsm.... Rotating the engine while checking the 6th cylinder on its turn to fire, check and see if at tdc the exhaust valve is opening (or closing, not too sure, I'll have to do a fact check on that...)  Edited by 1958 rambler super - May/08/2023 at 5:56pm |
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1958 rambler super wrote: