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Restoration & Repair Tips Board


Author  [Modern View]

08-17-2012 16:56:20

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I have a 172 cui engine that I suspect needs a condenser. The one on it does not have any markings. How can I test if it's actually weak or kaput. And, if it is, are all 6V condensers the same? or do various engines use different values of capacitance?

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08-18-2012 08:56:57

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 Re: Condenser in reply to JMOR, 08-17-2012 16:56:20  
"To add even more to that: Heck the coil will still fire even if theres NO condensor at all."

BUT so weak that many engines won't run on THAT little spark........most of the energy went into the arc across the points. Yes, best if right on, but not critical as in bearing clearances, valve gaps, etc. more like horseshoes. :)

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John T

08-18-2012 12:37:59

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 Re: Condenser in reply to JMOR, 08-18-2012 08:56:57  
You sure got that right, yep it will still fire a spark (even with NO condensor) but indeed as I noted its a weak one. Still it would sure tickle the old ticker if you had hold of it OUCH lol We agree, its best if the condensor value is "right on" plus the points will last longer...

Fun chat, take care now

John T

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John T PS

08-18-2012 05:38:48

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 Re: Condenser in reply to Unruh, 08-17-2012 16:56:20  
To add to 36 Coupes excellent comment, if the condesnor value isnt close to the correct capacitance, you will observe like a pit/crater on one set of the contact points versus a build up on the other point. If however the capacitance is the correct value, while theres still normal burning and carbon, you wont see the pits versus build ups so much i.e. even wear on BOTH sides. That has to do with the condensor being the correct value to correspond to the coils inductance.....

So while she can still fire with the incorrect capacitance value, its best for spark quality and points longevity if its correctly sized and not several factors off correct.


Hope this helps

God Bless yall

John T

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36 coupe

09-02-2012 03:01:14

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 Re: Condenser in reply to John T PS, 08-18-2012 05:38:48  
The post on the 28 Chrysler came up when I turned the computer on this morning.I looked in my Ford Service Manual page on condenser capacity.Ford used 10 different part numbers on condensers before 1938.Most were in the .20 to.25 range, a few were.30 to.34 mfd.The condenser used on the 4 cyl Model B had a capacity of .45 to .63 mfd.Test was to be done at 250 volts.low capacity shortened point life, high capacity limited high speed performance.I have 6 nos condensers that test at .25 mfd.A note in the manual says I got it in april 1956.The ohmmeter test is null and void.I never used it.I have a model B nos condenser that tests at .50 mfd.Nos means new old stock in auto parts.

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36 coupe

08-18-2012 03:36:44

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 Re: Condenser in reply to Unruh, 08-17-2012 16:56:20  
The meter test wont catch a condensor that has leakage.Condensors operate at 200 to 300 volts when the engine is running.Condensors with leakage always test off rated mfd.

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08-17-2012 20:50:00

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 Re: Condenser in reply to dan mcdonald, 08-17-2012 16:56:20  
Quoting Removed, click Modern View to seeVirtually all have used 0.2 to0.3 microfarads and it is not critical. They will run even if off by a factor of 10 or even greater. Points life will be best if dead on value, but that isn't a big deal. So, hunt for one that physically/mechanically fits & be happy.

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John T

08-18-2012 05:05:30

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 Re: Condenser in reply to JMOR, 08-17-2012 20:50:00  
To add even more to that: Heck the coil will still fire even if theres NO condensor at all. If the condensor value is too large she may not fire at all,,,,,,,,,If its too small she can still fire but the sparks weaker and the points burn up sooner. Of course, if its shorted theres NO spark

The condensor rating is computed based much on the inductance value of the coil which accunts for the diffrerence in values for different cars trucks n tractors which may have different inductance rated coils.

For sure, diferent values of condensors will still "work" (see above) while its still better if they are at least somewhere near the correct size to correspond with the coils inductance value......

Hope this helps, best wishes n God Bless

Fun chat for us sparkies at least

John T

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John T

08-17-2012 19:11:21

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 Re: Condenser in reply to Unruh, 08-17-2012 16:56:20  
To REALLY test it for capacitance and leakage you need an actual capacitor tester. An old fashioned analog ohm meter can tell you if its bad (like its shorted out) but even if it passes, that dont mean its good under actual operating conditions. To steady state DC it should read an open circuit (once charged) and if it reads a short its BAD and will kill the spark.

Yes different vehicles can use different values of condensors and its best to get the right one. It can still spark, albeit weak, if theres no condensor at all and the points would burn up sooner, but again if its a dead short theres no spark.

John T

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08-17-2012 19:27:09

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 Re: Condenser in reply to John T, 08-17-2012 19:11:21  
Thanks, John, for the additional direction. Yes, it does have spark; but weak which makes me suspicious of it. My v/o meter is digital, but I'll do what I can.

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John T

08-17-2012 19:42:50

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 Re: Condenser in reply to Unruh, 08-17-2012 19:27:09  
With my oldddddddddddd Simpson 260 VOM I can set her to the R X 10,000 scale,,,,,,,,discharge the condensor,,,,,,,then attach the meter and watch the needle start to swing over to low ohms (as condensor draws current to charge up) but then KICKBACK back over to high infinty ohms once shes charged up. If the needle dont initially start over to low ohms shes not drawing current and charging and then if it dont kickback towards infinity she may be shorted or leaking........

If you dont have a capacitor tester its time for a substitution test (if you can find the right one with correct capacitance etc) n see if that helps

John T

John T

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08-17-2012 18:22:28

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 Re: Condenser in reply to Unruh, 08-17-2012 16:56:20  
Check with an ohm meter. If shorted it's bad. If it shows ohm meter increasing let it build, then reverse leads and it should drop back to zero and then build again. If so chances are fairly good that it's ok, unless it fails after operating awhile. If it shows open it's no good.

Only sure test is to replace with a known good one. New does not mean it's good.

Condenser doesn't care if system is 6 or 12 volt and doesn't care if positive or negative ground.

A good auto parts should be able to cross reference one to your tractor or engine.

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08-17-2012 19:01:46

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 Re: Condenser in reply to rvirgil_KS, 08-17-2012 18:22:28  

Actually, it's a 1928 Chrysler with that 172 cid 4 cyl. Napa doesn't have a book that goes back that far, so I was "fishing" for what value, if there is one, that I could use. I once heard that one for a "H" Farmall will work,but how would I know if it's right?

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36 coupe

08-18-2012 03:44:17

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 Re: Condenser in reply to Unruh, 08-17-2012 19:01:46  
The Farmall condenser measures .15 mfd.most autos use .25 mfd.The wrong value will cause metal transfer on the points.

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08-17-2012 19:25:24

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 Re: Condenser in reply to Unruh, 08-17-2012 19:01:46  
In the ignition systems there is room to go bigger or smaller as for MFD of a condenser. Take the old one in and find one that fits and your most likely to be ok. But it is not common for a condenser to go bad and they can and will last decades

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