T's and others w/distributors

Topics Last Day Last Week Tree View    Getting Started Formatting Troubleshooting Program Credits    New Messages Keyword Search Contact Moderators Edit Profile Administration
Model T Ford Forum: Forum 2010: T's and others w/distributors
Top of pagePrevious messageNext messageBottom of page Link to this message  By Gary H. White on Wednesday, August 18, 2010 - 01:28 pm:

Read an article on another vintage car site about the accuracy of dwell meters. Four dwell meters were tried on a distributor with a point gap of 18 degrees. Results were:

Dixon 1501.... 37 Degrees
Dixon 1376.... 28 Degrees
Dixon Pro Tester 10.. 32 Degrees
Sears 244.21032.... 34 Degrees

Authors thought Sears was most accurate as it allowed zeroing at rest and with a charge applied. I have 3 or 4 dwell meters so next time I tune up one of my distributor cars I'm going to do some comparisons.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Ricks - Surf City on Wednesday, August 18, 2010 - 01:50 pm:

I don't expect you'll get those numbers from a T .. . Looks like numbers from a six.

As long as you're in the ballpark, and not revving over 5,000, I doubt those numbers, if accurate, would matter.

The early Atwater-Kent Uni-sparker had snap action points, so the current draw varied directly with rpm. They claimed up to 2,000 miles on a set of dry cells. I'd bet NIH and royalties kept Henry from adopting the Uni-sparker as standard for the T, rather than buzz coils and that heavyweight low tension magneto. Even the high tension magneto like on the Model K would have been better technically, and it doesn't need any battery at all.

rdr


Top of pagePrevious messageNext messageBottom of page Link to this message  By Royce Peterson on Wednesday, August 18, 2010 - 04:42 pm:

How old is that article? Do any of those companies still sell dwell meters? All the Sears Automotive centers closed around here long ago. We don't even have the Sears Roebuck store any more, just a smaller store called a "Sears Express".


Top of pagePrevious messageNext messageBottom of page Link to this message  By Gary H. White on Wednesday, August 18, 2010 - 05:40 pm:

They were trying out the dwell meters on a '31 chevy 6. Don't know the age of the article but a lot of us are still using older equipment. Dwell meters are like tube testers. Except for us vintage technitions, there isn't much market for them. Sears stores exist in larger cities and they still have catalogs. (My Sears tool catalog didn't list dwell meters, only fault analyzers.) I got a Sears multi-tester off ebay and have a couple older dwell meters picked up at garage sales. Usually set points then check with dwell meter but think I'll check them out against each other before relying on the first one I pick up. Just thought I'd offer this info for those relying on their dwell meter to set point gap. It may not be accurate.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Seth Harbuck - Shreveport, LA on Wednesday, August 18, 2010 - 06:51 pm:

My thoughts:

Dwell angle means a bunch in an eight-cylinder engine that needs to rev to 6,000 rpm without ever missing a lick.

A four-cylinder engine that never sees half that needs no more than setting the points by gap - the gap specified by the distributor manufacturer because points cams have different profiles.

I set the points in my '64 Mini by gap and it runs miss-free well past 6,000 rpm. I've even added 1.2 ohms of ballast which increases the primary resistance from 2.8 ohms to 4 ohms and it's still happy well past 6,000 rpm.

A model T with a six volt system should run fine with a 12 volt coil and no ballast resistance. Points will last much longer this way.

Seth


Top of pagePrevious messageNext messageBottom of page Link to this message  By Harold Schwendeman on Wednesday, August 18, 2010 - 11:54 pm:

Gary & Seth - My thinking might be a bit "off" on this, but my thought has always been that where a dwell meter really shows it's worth is when adjusting points on a vehicle with a lot of miles on it. If the distributor is in good shape, setting point gap with a feeler gauge will suffice, but if the distributor shaft bushings are worn, the point gap on a running engine can vary from the static setting by feeler guage. This happens when the slight torque necessary to drive the distributor torques the shaft slightly out of line in the worn bushings, which of course can alter the effective point gap.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Seth Harbuck - Shreveport, LA on Thursday, August 19, 2010 - 06:24 am:

Well, in that case, the dwell meter might allow you to get the correct average dwell angle but the problem hasn't been corrected and the cylinders still have different firing points.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Steve Hughes on Thursday, August 19, 2010 - 10:13 am:

Seth: Since a coil is just a transformer, then wouldn't running a 12 volt coil on 6 volts (ie. half the primary voltage) cut the secondary voltage in half as well? I would think that would result in a weak spark.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Seth Harbuck - Shreveport, LA on Thursday, August 19, 2010 - 10:54 am:

The current in the primary starts at zero when the points close and rises over time. At high engine speeds there isn't much time before the points open and the coil must be designed to have adequate primary current at all speeds.

So, what I'm saying is that at low engine speeds like in a T, even a 12 volt coil will reach high enough current before the points open to provide adequate spark.

Also, the arc-over voltage of a spark gap of 0.030" in compression pressure of only some 50 psig is way lower than the open circuit voltage of the coil, so there should be plenty.

The open-circuit voltage may be much lower in this scenario, but I think still plenty.

A 3 ohm primary 12 volt coil will saturate at 2.4 amps at 7.2 volts. Plenty for good spark, I believe.


Top of pagePrevious messageNext messageBottom of page Link to this message  By CharlieB on Thursday, August 19, 2010 - 10:59 am:

Used to set the GM V-8's (with the allen head adjustable points) at 30 deg. dwell.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Steve Hughes on Thursday, August 19, 2010 - 11:27 am:

Seth: Thanks for the followup. Yes, I had forgotten about the core going into saturation. That certainly changes it from standard "transformer" operation. If the core is in saturation and the points open collapsing the field, it doesn't matter what voltage got it into saturation.


Top of pagePrevious messageNext messageBottom of page Link to this message  By leefrostpierce on Thursday, August 19, 2010 - 01:23 pm:

What should the gap be and the dwell for a 4 cyl engine? I forgot


Top of pagePrevious messageNext messageBottom of page Link to this message  By Seth Harbuck - Shreveport, LA on Thursday, August 19, 2010 - 01:39 pm:

Lee,

Both depend on the points cam profile somewhat but 0.016" and 45 degrees will usually be just fine.

Seth


Add a Message


This is a private posting area. Only registered users and moderators may post messages here.
Username:  
Password:

Topics Last Day Last Week Tree View    Getting Started Formatting Troubleshooting Program Credits    New Messages Keyword Search Contact Moderators Edit Profile Administration