CA erratic spark
Printed From: Unofficial Allis
Category: Allis Chalmers
Forum Name: Farm Equipment
Forum Description: everything about Allis-Chalmers farm equipment
URL: https://www.allischalmers.com/forum/forum_posts.asp?TID=206666
Printed Date: 12 May 2025 at 2:25pm
Software Version: Web Wiz Forums 11.10 - http://www.webwizforums.com
Topic: CA erratic spark
Posted By: dfwallis
Subject: CA erratic spark
Date Posted: 11 May 2025 at 3:33pm
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Analyzing spark via a gtc505 analyzer. All 4 cylinders look horrible. Cylinder 1 and 4 have the best signals but 2 and 3 are spiking randomly. All have a peak voltage of around 6kv, but 2 and 3 have extra random spikes to 9kv. Suspect random short circuit through cap or wires or other...all is new. My brother says it behaved the same in the 80s. It is running better with new venturi in carb, corrected spark plug gaps. I think to get higher spikes, the dwell time must randomly increase?? Does not seem to be any side to side distributor play, but there is up and down (in/out) play. Suggestions? ------------- 1952 CA13092 |
Replies:
Posted By: steve(ill)
Date Posted: 11 May 2025 at 3:36pm
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i always suspect a weak condenser or coil when i have problems.. ------------- Like them all, but love the "B"s. |
Posted By: Stan R
Date Posted: 11 May 2025 at 3:52pm
| Last electrical tune-up was in the 80's? I'd throw in new points, condenser, wires, cap and rotor in it. And go from there if still problematic. I'm sure your time is worth more than the cost of these items. |
Posted By: jaybmiller
Date Posted: 11 May 2025 at 4:18pm
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Distributor shaft float? Yep, I’ve seen that a dozen times on old CA tractors. That’s your gremlin right there. New cap, new wires won’t fix it till you take out the slack. Re-bush or swap that dizzy ------------- 3 D-14s,A-C forklift, B-112 Kubota BX23S lil' TOOT( The Other Orange Tractor) Never burn your bridges, unless you can walk on water |
Posted By: dfwallis
Date Posted: 11 May 2025 at 4:48pm
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Stanr...Those are all new...completeish rebuild...from the waveforms, I think the coil is fine. I think more likely erratic points...the analyzer also gets confused with lots of extra pulses, declaring rpm 5000 instead of 1040 momentarily...cylinder 2 and 3 mostly. ------------- 1952 CA13092 |
Posted By: Les Kerf
Date Posted: 11 May 2025 at 4:59pm
I am not familiar with that analyzer, is it an actual oscilloscope?
Please describe "horrible". Is this at idle?
Do you mean that there are additional spikes other than the one, correct voltage spike? When the points open, the electro-magnetic field in the coil collapses; the resulting 'flyback effect' induces a voltage in the secondary windings of the coil. This voltage increases until the spark is able to jump the gap. It is not unusual to have variations in the firing voltage as an engine runs; I would not be alarmed seeing 6-9kV ranges.
No. The required firing voltage was higher on that particular event. In order to fire at all, the dwell had to be at least 'adequate'. The first two things I would want to know is what each cylinder has for compression, and next would be to hook up a vacuum gauge and see what that looks like. Also, do you have any way to take analyzer readings under load? That would be most interesting.
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dfwallis wrote:Posted By: Les Kerf
Date Posted: 11 May 2025 at 5:04pm
You posted this while I was composing my previous answer. Your points might be bouncing around, also poor grounding can give fits. The breaker plate needs to be well-grounded to the outside.
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Posted By: dfwallis
Date Posted: 11 May 2025 at 5:22pm
Cylinder 1 and 4 do not experience the additional spikes to 9k or more at all. Gtc505 is a scope of sorts. I have images but too painful to edit and upload on android. ------------- 1952 CA13092 |
Posted By: Les Kerf
Date Posted: 11 May 2025 at 8:43pm
After ponderizing about this for a while I believe jaybmiller is right. The vertical play in the distributor shaft can make the points chatter about due to the spiral gears causing the shaft to advance and return rapidly. |
Posted By: Trinity45
Date Posted: 11 May 2025 at 9:26pm
| I had problems with my B, thought it was points, then change the coil and the cap, lastly replaced the condenser and that fixed my problem. |
Posted By: DiyDave
Date Posted: 12 May 2025 at 4:43am
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Check the insulator block that carries the points wire through the side of the distributor for cracks, and to see if the points wire has one ear grounding the points at that point... ------------- Source: Babylon Bee. Sponsored by BRAWNDO, its got what you need! |
Posted By: dfwallis
Date Posted: 12 May 2025 at 7:29am
I will check...there was a grounding issue that I fixed...got shocked adjusting timing while running, touching the housing, but did not change the behavior when I fixed the grounding (paint). I did check that the points plate is grounded. ------------- 1952 CA13092 |
Posted By: ekjdm14
Date Posted: 12 May 2025 at 8:54am
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What are the run symptoms from this? Spluttering/missing randomly? I've not scoped the signal but believe I'm having a similar issue on the redneck B & (timing "fluttering" all over the place due to slack in it's ignition timing chain setup, needs a new bit of chain. So could be caused by the lash in your distributor in your case Also, if the condenser is new new & not NOS then perhaps switch back to the previous one/a known good one. Modern parts are/were trash last I checked.
------------- Stuck Farmer |
Posted By: dfwallis
Date Posted: 12 May 2025 at 9:24am
Sorry for posting inside the quote...android ui sucks
------------- 1952 CA13092 |
Posted By: ekjdm14
Date Posted: 12 May 2025 at 9:55am
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Not a problem, posting from a 'phone must be a real PITA! This is kinda like mine now I think about it, acts like it was going to clear up and then back to misbehaving. thought I was losing fuel initially but pretty sure it's timing slop. Would certainly attend to the distributor on your tractor, especially as Jay has experience of this being a cause. ------------- Stuck Farmer |