Effect of Large Point Gap?

Ian Curtis

Ian Curtis

Senior Member
Hi All,

My truck had been sitting for several months, for the winter/brake job. That's all done now, and the first trip around the neighborhood it got real hot, real fast. In the previous two years, I've never once had an overheating problem, and don't even spit water with a completely full radiator.

Obvious culprit for a hot engine is timing. The point gap was .030... After adjusting the points back down .020 & re-timing, the over-heating is gone & everything is back to normal. Would a large point gap cause over-heating, or was it likely that both the point gap was way too big & the the timing was too advanced? There were never any knocking and there was never any obvious difficulty in starting it.

Just curious...
 
If the points gap is too wide, the timing is retarded. Late timing can cause an engine to run hot. You may have hit the nail on the head.
 
Synchro909 said:
If the points gap is too wide, the timing is retarded. Late timing can cause an engine to run hot. You may have hit the nail on the head.
Click to expand...

Ahhh... I guess I hadn't put two and two together that retarded timing also caused overheating, I was just thinking it was being way too advanced and getting the heat from knocking... Thanks!
 
I believe it is the other way around. A large point gap will advance the timing. Either you couldn't hear the knocking or you have another problem.
 
wmws said:
I believe it is the other way around. A large point gap will advance the timing. Either you couldn't hear the knocking or you have another problem.
Click to expand...

Maybe we're about to start a side issue on this thread but the way I understand it is thus: If the plug fires when the points open, a wide gap will mean that the distributor shaft (and therefore the motor) have turned further for the cam to lift the rubbing block and open the points. That would result in late timing.
Maybe others will confirm/contradict this.
 
Here is a diagram. The French don't understand a word I say so you are on your own there.

AngleCame.jpg

Middle one, wider gap, opens quicker.
 
"Reducing the point gap ... retards the timing. Conversely, enlarging the gap will advance the timing."

From Marcos web page on how to time the A.
 
This is getting out of control, with all the "what ifs"---Just set the points to .020, set the timing properly & use your spark lever properly.
Bill W.
 
BILL WILLIAMSON said:
This is getting out of control, with all the "what ifs"---Just set the points to .020, set the timing properly & use your spark lever properly.
Bill W.
Click to expand...

I drove a mid 60's car for years and once I took it to the local mechanic for something to do with the distributor. He took one look at it and recoiled in horror.

He said "I don't understand THAT thing mate, that was made before I was born!".

It's not rocket science.
 
Wider gap rduces dwell , the time that the points are closed giving time for the coil to charge .

Not so critical on a 4 cylinder, but very critical on a V8 with 8 lobes .

Wider point gap will also wear the rubbing block quicker, because of higher spring tension and longer duration on the cam .

Wider gap advances igniton, given that the timing is set at the correct gap, and then widened after.
 
Seems a little odd the points gap got to .030 with the car sitting, as you didn't have a overheat problem before storing it, I think something else is wrong.
 
mshmodela said:
If you think about it, a larger gap will take a bit longer time for the spark to jump... a time delay...
Click to expand...

Spark does not jump the open gap....the spark you see is when the points make contact its completing a circuit to ground which causes the arc or when the circuit to ground is broken by the points opening. The wider the gap the more it advances the timing unless one adjusts the cam to compensate for it.
Hope this helps
 
pooch said:
Wider gap rduces dwell , the time that the points are closed giving time for the coil to charge .

Not so critical on a 4 cylinder, but very critical on a V8 with 8 lobes .

Wider point gap will also wear the rubbing block quicker, because of higher spring tension and longer duration on the cam .

Wider gap advances igniton, given that the timing is set at the correct gap, and then widened after.
Click to expand...
Interesting tidbit, Pooch,
The Bosch points for a Volvo 4 cyl & the inline 6 cyl looks the same & fits perfectly, BUT, the spring pressure is considerably GREATER on the 6 cyl, to prevent point float @ higher RPM's.
Bill Old
 
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