What's a dwell meter ?

[slick4x4]

Went out to move one of my grain trucks , to ready for harvest....
My son had tried to start it , the day before....
No gas to the carb he thought, so we filled tank & blew in tank
DAM IT ! ... I left the key on , he says.....
Swapped batteries and tried it..... No start.....
Tilted up the cab, looked down carb throat... Getting gas , I see....
Let's check for spark.... He climbs in tilted cab, I hold wire.... No spark
(I'll tell you here... This is a 73 gmc.... 350 engine)
I love this old girl... First grain truck I bought....
So we pulled the cap... Yep... Points are fried...
From leaving the key on ? ... Well, yea.... That probably finished them , I say
To town & got new points
... 3 years ago I could read the smallest print... Not anymore...
And I didn't have my glasses....
I explained to him how to 'set' the gap
He got them in & we put it together..... No spark.....
I need a dwell meter I tell him..... What's that ? He says
So we go to the old shop , and dam if it wasn't right where I put it
A long time ago... 7-8 ? Years ago ?
Blew the dust off and hooked to the coil... No dwell...
You sure they are closing ? I ask.....
I open the little window in the cap & adjust them a bit.... Here we go !
Started right up !
..... Why do they call it a dwell meter ? He asks me....
Hell if I know, I say
Then I wondered why it WAS called a dwell meter.....
I try to know these things...... But if I dont....
I'm not going to dwell on it

[foodstick]

I thought I heard dwell was the time they were open and between contacts thats the dwell time... so little auto knowledge sticks in my mind when it comes to motors


I could pass tests in shop, and forget it the next day

[bobenhotep]

Dwell is how long the points are closed. It is measured in degrees of rotation. So, if the points stay closed for 30 degrees of distributor rotation, it has 30 degrees of dwell.

Dan

[Toyz]

Without, err, dwelling on the matter; ignition "dwell" refers to the amount of rotation during which the points are closed, allowing the coil and condenser to saturate as much electricity as possible. Note that this is also speed dependent, as time also enters the equation. Thus the reason for dwell setting to spec being more important than actual point gap. Worn distributors may cause varying dwell from cylinder to cylinder. One of the advantages of electronic ignition systems is better control of dwell. And Dan's explanation reveals why four and six cylinder applications normally have more dwell than V8's.
However, I suspect it is just as you noted; your curiosity has already driven you to find a better explanation than what I offered. Part of that is due to the fact that long ago, when I actually attempted to teach such things, the concept of electricity and ignition (among young mechanics), was not as well founded as in these times. Don't even get me started on microfarads!
Paul

[Toyz]

And, if the worn distributor becomes problematic in the future; yours is one of the few applications for which I would heartily recommend the ubiquitous HEI distributor. It's not a great system by today's standards, but it is a vast improvement over point ignition! One of these days, I'll reveal a rather personal story involving dwell and an accompanying HEI!
Paul

[slick4x4]

I put about 750 miles a year on it
It sits quietly 11 months & then gets the living snot ran out of it
I'm lucky I don't have more problems from then sitting
Owned it 25 years and never touched any of the fuel system

[Toyz]

Man, that's a lot of trips to and from the escalator!
Paul

[slick4x4]

Man, that's a lot of trips to and from the escalator!
Paul

Took me a while to figure that one out.....
And I'm on the inside of that inside joke !

[kstones63]

Dwell is just because that is what my Dad told me it was. I never really thought about what it actually meant.

Here is the next one to ponder.
What does the cam shaft specs mean when it says, advertised duration at 0.050 lift?

I used to know this but I have to think about it anymore. Years ago, I helped a neighbor kid with this for his auto shop class and he was the only person in class that got it correct.

Kevin

[slick4x4]

Does that mean it will stay lifted at least .050 for a determined amount of rotation ?

[kstones63]

Does that mean it will stay lifted at least .050 for a determined amount of rotation ?

No, not there yet.

[Toyz]

Subscribed!
Paul

[Gary Seymour]

The advertised duration at .05 lift is the amount of rotation, degrees, the cam will turn from .05 lift when opening the valve to .05 lift when closing the valve. Actual valve lift off the seat would be multiplied by the rocker arm ratio.

[Toyz]

So far, Pat's answer is the most accurate, although evidently not what Kevin is getting at!
Paul

[mercuryv8]

The advertised duration at .05 lift is the amount of rotation, degrees, the cam will turn from .05 lift when opening the valve to .05 lift when closing the valve. Actual valve lift off the seat would be multiplied by the rocker arm ratio.

Sounds about right to me.

Nic

[Toyz]

Only off by 50%!!
Paul

[Alan Mclennan]

AH Spit!...I thought the Dwell meter measured how many buckets of water you took out of the well!

[Toyz]

Good point, Macca; Pat is probably more familiar with d'well meters, anyway!
Paul

[kstones63]

I might be getting my facts a little confused.
My understanding is that the duration at 0.50 lift is the amount of time that the intake and exhaust valve are open at the same time as the exhaust is closing and the intake is opening.
Like I said, it has been a long time since I had any dealings with this stuff.
And besides that, I have slept since then.

Kevin

[slick4x4]

Good point, Macca; Pat is probably more familiar with d'well meters, anyway!
Paul

I have a d well meter...
Also a "A" "B" "C" well meters....
Pump that water you know