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dfwallis 
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 Topic: CA erratic spark
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?
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1952 CA13092
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steve(ill)
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Posted: 11 May 2025 at 3:36pm |
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i always suspect a weak condenser or coil when i have problems..
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Like them all, but love the "B"s.
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Stan R
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Posted: 11 May 2025 at 3:52pm |
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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.
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jaybmiller
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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
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dfwallis
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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.
Edited by dfwallis - 11 May 2025 at 4:55pm
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1952 CA13092
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Les Kerf
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Posted: 11 May 2025 at 4:59pm |
 dfwallis wrote:
Analyzing spark via a gtc505 analyzer. |
I am not familiar with that analyzer, is it an actual oscilloscope?
dfwallis wrote:
All 4 cylinders look horrible. |
Please describe "horrible". Is this at idle?
dfwallis wrote:
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. |
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.
dfwallis wrote:
... I think to get higher spikes, the dwell time must randomly increase?? ... |
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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Les Kerf
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Posted: 11 May 2025 at 5:04pm |
dfwallis wrote:
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. |
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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dfwallis
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Posted: 11 May 2025 at 5:22pm |
Les Kerf wrote:
dfwallis wrote:
Analyzing spark via a gtc505 analyzer. |
I am not familiar with that analyzer, is it an actual oscilloscope?
dfwallis wrote:
All 4 cylinders look horrible. |
Please describe "horrible". Is this at idle?
All speeds.
dfwallis wrote:
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. |
Do you mean that there are additional spikes other than the one, correct voltage spike?
I suspect these are additional spikes because the analyzer thinks the rpm jumps from 1040 to 5000.
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.
Yes, I have a masters in electronics.
dfwallis wrote:
... I think to get higher spikes, the dwell time must randomly increase?? ... |
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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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.
Edited by dfwallis - 11 May 2025 at 5:24pm
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1952 CA13092
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Les Kerf
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Posted: 11 May 2025 at 8:43pm |
dfwallis wrote:
... Does not seem to be any side to side distributor play, but there is up and down (in/out) play... |
jaybmiller wrote:
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 |
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.
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Trinity45
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Posted: 11 May 2025 at 9:26pm |
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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.
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DiyDave
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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...
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dfwallis
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Posted: 12 May 2025 at 7:29am |
DiyDave wrote:
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... |
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.
Edited by dfwallis - 12 May 2025 at 7:36am
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1952 CA13092
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ekjdm14
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Posted: 12 May 2025 at 8:54am |
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.
Edited by ekjdm14 - 12 May 2025 at 8:55am
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dfwallis
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Posted: 12 May 2025 at 9:24am |
Sorry for posting inside the quote...android ui sucks
ekjdm14 wrote:
What are the run symptoms from this? Spluttering/missing
Runs perfect for short bursts, then random misfires. Also seems to be some sort of cyclical change to timing once every few seconds...engine slows slightly similar to what occurs when you retard timing, then goes back to normal. This is only noticeable if you set timing to extra retard to begin with.
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.
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Edited by dfwallis - 12 May 2025 at 9:26am
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1952 CA13092
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ekjdm14
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Posted: 12 May 2025 at 9:55am |
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.
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orangeman
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Posted: 12 May 2025 at 2:42pm |
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I would check the play or displacement in the distributor shaft, possibly worn main shaft bushings? ~ Orangeman
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dfwallis
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Posted: 13 May 2025 at 1:54pm |
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I took the distributor apart and gave it a thorough cleaning. I didn't have a rebushing kit so stopped there. There is some marginal improvement...the centrifugal mechanism was highly gunked up, but only improved the advance/retard process...cylinder 2 and 3 waveforms are also slightly improved, but could partially be from changing point gap from 22 to 20...one manual says 22, one says 20...I'm leaning towards getting one from bnb while I work on other stuff...I had made a slow moving vehicle bracket, but I'll have to mod it...too close to the rockshaft mounted top link bracket when raised...I swear I measured it:(
Edited by dfwallis - 13 May 2025 at 2:13pm
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1952 CA13092
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dfwallis
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Posted: 13 Jun 2025 at 10:02am |
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Sent the distributor to B&B. Sun 504 tests showed the misfire and erratic dwell issues and mods were made and its now on its way back home. It appears the main problem was worn/pitted CAM/lobes (not end play). Replaced and tested with good spark all the way to 3200RPM (~where points float started). It may have worn in part due to lack of lubrication. The lubrication "wick" was there, but not consistently working, so that was also fixed. It's doubtful anybody ever lubricated it in 72 years.
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1952 CA13092
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steve(ill)
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Posted: 13 Jun 2025 at 3:49pm |
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very interesting about the cam !!!.......... and have heard many say that STEVE does excellent work !
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Like them all, but love the "B"s.
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CA13414
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Posted: Yesterday at 6:54am |
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Very interesting with everything you’ve done!
The trouble I’ve had with our CA is very much the same. Cylinders 2 and 3 quit working after the engine warms up. This was at an idle and full throttle. 2 was worse than 3, and there is no spark on #2 to the fingertip when touching the wire, my crude way vs your analyzer!! :-)
In sequence, I replaced the spark plugs first, then wires, distributor, cap, rotor, and the other day the magneto coil and condenser.
Replacing the magneto coil and condenser did the trick…… “thus far!!” Since it happened at an idle and full RPM didn’t seam to be floating and getting hot and cooling down was clearly causing the problem. My money was on the condenser but I can not explain why #2 and to a lesser extent #3 and not #1 or #4!?
I’m putting our little “Orange Dude” to work next weekend. That’ll be the test!
Dan
Edited by CA13414 - Yesterday at 8:28am
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Helping the aged survive and thrive! 1953 CA
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dfwallis
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Posted: Yesterday at 10:51am |
CA13414 wrote:
Very interesting with everything you’ve done!
The trouble I’ve had with our CA is very much the same. Cylinders 2 and 3 quit working after the engine warms up. This was at an idle and full throttle. 2 was worse than 3, and there is no spark on #2 to the fingertip when touching the wire, my crude way vs your analyzer!! :-)
In sequence, I replaced the spark plugs first, then wires, distributor, cap, rotor, and the other day the magneto coil and condenser.
Replacing the magneto coil and condenser did the trick…… “thus far!!” Since it happened at an idle and full RPM didn’t seam to be floating and getting hot and cooling down was clearly causing the problem. My money was on the condenser but I can not explain why #2 and to a lesser extent #3 and not #1 or #4!?
I’m putting our little “Orange Dude” to work next weekend. That’ll be the test!
Dan |
I just hope it's fixed. It's hard for me to imagine a CAM wear pattern happening that would give those results, unless it was pretty severely lop-sided. I polished up the CAM to try to improve it (pitting), but I did not check for roundness. When I set the points, I just picked one lobe and did not check if it had the same gap on other lobes. I'll try to be more thorough if there's a next time.
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1952 CA13092
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Les Kerf
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Posted: Yesterday at 2:05pm |
dfwallis wrote:
.... It's hard for me to imagine a CAM wear pattern happening that would give those results... |
I can.
It's called "bounce". The keyboards we use to type these messages have a built-in delay system known as "de-bounce" to help prevent multiple re-strikes; our mechanical distributor cam lobes have no such thing. Any roughness at the time of opening the points can easily cause this.
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Steve in NJ
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Posted: Yesterday at 2:54pm |
For those who were curious about this particular Distributor, here's the poop. It's very rare I change a cam. When I first ran that Distributor out of the box, the dwell was all over the place. First thing you think of is main shaft bushing. Not this time. Main shaft spun nice n' true. Up n' down, side to side all in spec. Looked good in the 504 too. Point Contacts were worn funny with a matching rub block which led me to a possible cam problem. Inspected the cam and one lobe looked almost round toward the middle. Installed a new NOS cam, ran it on the 504 again (same points) and the dwell straightened out quite a bit, but the misfire still was there. Put a new set of my points and condenser and ran it again. Misfire gone, dwell perfect, and full spark to all plugs. The ole' 504 said she was good ta' go! Should run pretty nice now. Let us know how she runs Gary. Steve@B&B
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dfwallis
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Posted: 22 hours 19 minutes ago at 3:50pm |
Steve in NJ wrote:
For those who were curious about this particular Distributor, here's the poop. It's very rare I change a cam. When I first ran that Distributor out of the box, the dwell was all over the place. First thing you think of is main shaft bushing. Not this time. Main shaft spun nice n' true. Up n' down, side to side all in spec. Looked good in the 504 too. Point Contacts were worn funny with a matching rub block which led me to a possible cam problem. Inspected the cam and one lobe looked almost round toward the middle. Installed a new NOS cam, ran it on the 504 again (same points) and the dwell straightened out quite a bit, but the misfire still was there. Put a new set of my points and condenser and ran it again. Misfire gone, dwell perfect, and full spark to all plugs. The ole' 504 said she was good ta' go! Should run pretty nice now. Let us know how she runs Gary. Steve@B&B
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Thanks, Steve! Kinda strange there was points wear. They were brand new and the engine probably hasn't run more than 4 hours since rebuild. I guess maybe they really WERE crappy quality.
Edited by dfwallis - 22 hours 16 minutes ago at 3:53pm
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1952 CA13092
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Les Kerf
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Posted: 17 hours 39 minutes ago at 8:30pm |
Steve in NJ wrote:
For those who were curious about this particular Distributor, here's the poop. It's very rare I change a cam. When I first ran that Distributor out of the box, the dwell was all over the place. First thing you think of is main shaft bushing. Not this time. Main shaft spun nice n' true. Up n' down, side to side all in spec. Looked good in the 504 too. Point Contacts were worn funny with a matching rub block which led me to a possible cam problem. Inspected the cam and one lobe looked almost round toward the middle. Installed a new NOS cam, ran it on the 504 again (same points) and the dwell straightened out quite a bit, but the misfire still was there. Put a new set of my points and condenser and ran it again. Misfire gone, dwell perfect, and full spark to all plugs. The ole' 504 said she was good ta' go! Should run pretty nice now. Let us know how she runs Gary. Steve@B&B
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And that's the difference between having the proper test equipment and merely stabbing around guessing!  |
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dfwallis
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Posted: 17 hours 32 minutes ago at 8:37pm |
Les Kerf wrote:
Steve in NJ wrote:
For those who were curious about this particular Distributor, here's the poop.(snip) Steve@B&B
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And that's the difference between having the proper test equipment and merely stabbing around guessing! |
Yeah, I may get me one of those...only about $4k...but I may never need one again at my age...:(
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1952 CA13092
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dfwallis
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Posted: 16 hours 44 minutes ago at 9:25pm |
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Should I get one of those super duper coils? I see a 40kv, a 55kv, and a 60kv option. Does that risk burning the points/plugs faster?
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1952 CA13092
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wjohn
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Posted: 15 hours 42 minutes ago at 10:27pm |
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Thanks for following up and letting us know what the issue was, and thanks to Steve for even more details. This is why this forum is great.
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1939 B, 1940 B, 1941 WC, 1951 WD, 1952 CA, 1956 WD-45
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Les Kerf
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Posted: 15 hours 5 minutes ago at 11:04pm |
dfwallis wrote:
Should I get one of those super duper coils? I see a 40kv, a 55kv, and a 60kv option. Does that risk burning the points/plugs faster? |
Complete waste of money. No, it won't hurt anything other than your bank account.
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Les Kerf
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Posted: 14 hours 58 minutes ago at 11:11pm |
dfwallis wrote:
...Yeah, I may get me one of those...only about $4k...but I may never need one again at my age...:( |
My last job before retiring was in the electronics engineering department at Encoder Products Company doing R&D work; we had lots of really cool test equipment that I sometimes wish I still had access to, but my pockets aren't deep enough and it is difficult to justify for a one-time use  |
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