Anyone know how to use a Tach-Dwell meter?
07-01-2006, 03:08 PM
#1
Pro
Thread Starter
Anyone know how to use a Tach-Dwell meter?
Hello, I picked up a old Craftsman meter a yard sale today for a dollar but I dont realy know how to hook it up.All it is is a meter and a pair of clamps like jumper cables except one clamp is black and the other green.Where do you attach the clamps?Thanx for the help.
07-01-2006, 03:48 PM
#2
Le Mans Master
For the Dwell function, the Green clamp goes to the (-) terminal
on a coil. The Black clamp goes to a good ground. Older Craftsman
testers had Red and Black leads.
I do not know of a use for this kind of Dwell function on an HEI,
only for a points-style ign. Someone else might.
Does the meter indicate that it can be used as a Tach, Ammeter,
Voltage or other type of tester?
.
on a coil. The Black clamp goes to a good ground. Older Craftsman
testers had Red and Black leads.
I do not know of a use for this kind of Dwell function on an HEI,
only for a points-style ign. Someone else might.
Does the meter indicate that it can be used as a Tach, Ammeter,
Voltage or other type of tester?
.
07-01-2006, 07:22 PM
#4
Originally Posted by Slalom4me
For the Dwell function, the Green clamp goes to the (-) terminal
on a coil. The Black clamp goes to a good ground. Older Craftsman
testers had Red and Black leads.
I do not know of a use for this kind of Dwell function on an HEI,
only for a points-style ign. Someone else might.
Does the meter indicate that it can be used as a Tach, Ammeter,
Voltage or other type of tester?
.
on a coil. The Black clamp goes to a good ground. Older Craftsman
testers had Red and Black leads.
I do not know of a use for this kind of Dwell function on an HEI,
only for a points-style ign. Someone else might.
Does the meter indicate that it can be used as a Tach, Ammeter,
Voltage or other type of tester?
.
Remember that the duty cycle is a measurement of the relationship of the on-time and the off-time. Place the dwell meter on the four cylinder scale; again, do not be concerned with how many cylinders the engine has that you are working on. Connect your dwell meter to the wire on which you want to read the duty cycle, and observe the reading. Multiply the reading by 1.1"
07-01-2006, 08:48 PM
#5
Pro
Thread Starter
What about the Tach feature?What do I connect the clamps to? I want to check the accuracy of my digital dash tach since I am setting my minnimum idle speed.Thanks
07-01-2006, 09:01 PM
#6
Instructor
Member Since: Jun 2002
Location: 80/680 junction Ca.
Posts: 231
Likes: 0
Received 0 Likes
on
0 Posts
Same attachment as stated above, should have a switch for tach or dwell, just flip it to tach.
If you do ever use it to set the dwell of points remember, the larger the points gap the lower the dwell and the smaller the gap the larger the dwell.
If you do ever use it to set the dwell of points remember, the larger the points gap the lower the dwell and the smaller the gap the larger the dwell.
07-01-2006, 09:22 PM
#7
Racer
Member Since: Jun 2006
Location: Elkton MD
Posts: 408
Likes: 0
Received 0 Likes
on
0 Posts
Tach/Dwell Meter
These units were a boon for the old point type ignitions. But DO NOT hook them up to an electronic ignition. Most electronics will be blown out and rendered useless if the dwell function is activated. The rpm function is Ok but depends on an analog resistor calibration. So it's really rinky dink compared to today's tachometer technology.
The old point type ignitions used a cam follower on the distributor to control the angle thru which the spark was applied. The cam follower was a bakelite (pre-plastic) material that would wear with time. The point gap could be set with a micrometer or more accurately with a 'dwell meter'. If the cam follower wore a little, the points had to be reset (on my old 327 that was about 4000 miles) to control the gap and therefore the dwell angle. The spark timing was also affected by the 'dwell angle'. Many adjusted the timing (cam angle that firing ocurred) after a few thousand mile but should have adjusted the 'dwell'. If the 'dwell' were adjusted, the timing would also be brought back into specification.
Think about it. The spark has to begin at a certain time in relation to the cam/crank angle so the flame/pressure can apply to the downward stroke of the piston. And the spark has to continue long enough to burn the air/fuel mixture. The spark beginning has to occur earlier at high rpm's so the pressure is high at the correct instant. So the dwell set the length of the spark, and the timing set the start point. The timing was an invariant (angle of the distributor relative to the cam/crank) but the dwell varied depending on the point cam follower wear.
So a dwell meter was a real god-send.
Nostalgic huh?
The old point type ignitions used a cam follower on the distributor to control the angle thru which the spark was applied. The cam follower was a bakelite (pre-plastic) material that would wear with time. The point gap could be set with a micrometer or more accurately with a 'dwell meter'. If the cam follower wore a little, the points had to be reset (on my old 327 that was about 4000 miles) to control the gap and therefore the dwell angle. The spark timing was also affected by the 'dwell angle'. Many adjusted the timing (cam angle that firing ocurred) after a few thousand mile but should have adjusted the 'dwell'. If the 'dwell' were adjusted, the timing would also be brought back into specification.
Think about it. The spark has to begin at a certain time in relation to the cam/crank angle so the flame/pressure can apply to the downward stroke of the piston. And the spark has to continue long enough to burn the air/fuel mixture. The spark beginning has to occur earlier at high rpm's so the pressure is high at the correct instant. So the dwell set the length of the spark, and the timing set the start point. The timing was an invariant (angle of the distributor relative to the cam/crank) but the dwell varied depending on the point cam follower wear.
So a dwell meter was a real god-send.
Nostalgic huh?
07-01-2006, 11:45 PM
#8
Team Owner
Member Since: Jun 2005
Location: Northern, VA
Posts: 46,106
Received 2,481 Likes
on
1,944 Posts
St. Jude Donor '15
"In honor of jpee"
Good explain and post, Raid man. Thanks! I forgot how to use a dwell tach, it's been that long.
07-02-2006, 11:24 AM
#9
Le Mans Master
The revelation for me on reading IRAraid's post was 'oh my gosh, it is
possible that a majority of people on the C4 forum have never used
this instrument'.
But enough about aging.
Nice post.
.
possible that a majority of people on the C4 forum have never used
this instrument'.
But enough about aging.
Nice post.
.
