Results of only one set of points.

[pooch]

My bus came with only one set of points, obviously the breaking side.

It also came with detonation damaged pistons.

With the bus diff ratio, it would have been spinning high revs most of the time and also pulling very hard.

Would the much lessened dwell somehow contributed to a weak spark which in turn could have caused the piston damage?

[Bruce Lancaster]

Just to be 100% clear...the points you have are on the USA driver's side, Australian passenger side??

[koates]

Hi, I would think that if only the TIMING set of contacts were fitted inside your distributer and were adjusted correctly then your engine should run very well. Would not be the cause of detonation and damaged pistons. The second set of contacts if set correctly would enable the coil primary winding a slightly longer time to build up voltage for a hotter secondary voltage to the spark plugs. Of course in either case the distributer should be set up correctly for ignition timing. Fuel quality (octane) and correct mixture is also a factor here. You have not stated what year vehicle you have. Regards, Kevin.

[pooch]

Originally Posted by Bruce Lancaster

Just to be 100% clear...the points you have are on the USA driver's side, Australian passenger side??

Yes...USA driver's side.. the breaking points only... prob 23 degrees of dwell with this one set.

And i have stated what the engine is in , a bus which is very heavy and a diff to suit.

High revs ,heavy load. I have not measured the diff ratio yet but the bus weighs about 4.6 tons.

The engine must be working hard.

This bus I gather has not driven since 1969 and this is way before the unleaded we have these days.

Just wondering why the engine innards seem so perfect original bore no lip but has detonated piston top rings and lands .

[BUBBAS IGNITION]

Pretty common myth with the flatheads.

Some removed the dwell set of points thinking there was some hidden power there for some reason. On a helmet or crab the contacts are set at 27 degrees each ( 22 degrees for a crab with small indivudal points) and over lap to obtain the total of 36 degrees of dwell. The drivers side open the circuit and causes the ignition coil to fire, thus controlling the timing...
When one set of points is removed the short dwell needs to be adjusted to the needed 36 degrees.
This also changes engine timing 2 degrees of crankshaft per one degree of dwell! Using 36 degrees minus the correct setting of 27 degrees (spec for strap point on a helmet) would be 36-27=9 degrees x 2 or 18 degrees retarded spark timing!!!!!!
Small later individual points would be worse at 36 -22=14 degrees x 2 or 28 degrees of retard !!!!!!!!!!



Note revised this post after actually running one on a tester..

[pooch]

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Bubba, how did they alter the dwell with one set ?

This is a crab.

The points have not been touched yet, just the dissy pulled apart to check innards.

I thought if it only had the breaking points and set at .015, the timing would be correct just the dwell would be short, and at high revs/high load, this would only contribute to a weak spark ?

[BUBBAS IGNITION]

Originally Posted by pooch

Bubba, how did they alter the dwell with one set ?

This is a crab.

The points have not been touched yet, just the dissy pulled apart to check innards.

I thought if it only had the breaking points and set at .015, the timing would be correct just the dwell would be short, and at high revs/high load, this would only contribute to a weak spark ?

Actually it wouldnt run very well at 22 degrees of dwell. Especially is it was using a six volt coil etc. The coil needs a little more dwell and when dwell is added on a single set the timing would suffer.

[pooch]

How is the dwell altered on a single set, so I can look and see what they may have done ?

[BUBBAS IGNITION]

Originally Posted by pooch

How is the dwell altered on a single set, so I can look and see what they may have done ?

With the two mounting screws loosened you would turn the dwell adjusting screw causing the gap to open and close. Next one i do i will verify what this range is in degrees maximum????????

[pooch]

I must be still missing something.

I figure to increase dwell, you have to have a minimal point gap and this would retard the ignition .

[koates]

pooch, Set the contacts at .012" which will increase the dwell just a little. Base Ignition timing (advance & retard) can be adjusted somewhat on the sliding scale on the side of the dist housing. Really need to test this on a timing fixture or better still on a distributer test bench to see exactly what it is doing. Would be an interesting exercise to play around with. Back in the day these single point base plates were sold for the Ford V8. I think Flathead Ted in NZ did make some in more recent times. Regards, Kevin.

[JSeery]

Originally Posted by pooch

How is the dwell altered on a single set, so I can look and see what they may have done ?

Pooch, are you understanding the relationship between points gap and dwell? The dwell is altered by changing the points gap. Changing the points gap both changes the dwell and the timing. Like koates pointed out it is going to be difficult on a carb distributor to determine where it is at without checking it on a timing fixture. Is there a reason to not just change it back to the original two points setup or just replace the distributor?

[Hoop]

The original question was whether or not pre-ignition or detonation could cause the described damage.

Simple answer ... yes.

Here's a very good link:

http://www.contactmagazine.com/Issue...ineBasics.html

Further, as JSeery correctly suggests, "just change it back to the original two points setup or just replace the distributor." Pooch probably does not intend to continue using the set-up he found but was curious about the damage.

Talking about operating with just a single set of points is a great discussion even though it really isn't recommended.

[Hoop]

As an aside:

"When one set of points is removed the short dwell needs to be adjusted to the needed 36 degrees.
This also changes engine timing 2 degrees of crankshaft per one degree of dwell! Using 36 degrees minus the correct setting of 27 degrees (spec for strap point on a helmet) would be 36-27=9 degrees x 2 or 18 degrees advanced spark timing!!!!!!
Small later individual points would be worse at 36 -22=14 degrees x 2 or 28 degrees of advance !!!!!!!!!!
Assuming that the helmet has 20 degrees of spark advance at 2000 rpm add the 28 degrees." Bubba

Are we saying that increasing the dwell INCREASES the advance?

[pooch]

Yes, this whole thread is being thrown around somewhat.

The original Q was........Would the much lessened dwell somehow contributed to a weak spark which in turn could have caused the piston damage?

I know over advance will cause detonation .

Using one set of points, the BREAKING ones , set at .015 will still give a correct timing spark, just the dwell is reduced a lot.

Dwell is only TIME, so with a slow revving engine, it would not matter much.

Obviously this bus has a high revving hard working engine.

I guess the result of a short dwell and high revs would rersult in a weak spark.

Even though the timing is correct, I was wondering if a weak spark alone would cause detonation ?.

I will be fitting 2 sets points when it goes back together.

[Hoop]

In the link above, read the section "Muddy Water." .... maybe.

[Jack E/NJ]

Pooch>>>this whole thread is being thrown around somewhat.>>>The original Q was>>>if a weak spark alone would cause detonation?>>>

I agree Pooch. And I think you already know the answer. 8^) Jack E/NJ

[FlatheadTed]

I don't profess to know all there is to know about the subject but have run single points for years now and like them ,a lot more forgiving ,I think .The smaller the gap the greater the dwell ,the points I use you get a maximum 28 Deg dwell from a single points set with a modern coil they produce a nice strong spark and work good .As far as I can tell Ford used the twin points because of the limitations of the 8 lob cam and possibly coil that did not produce the hot spark needed at high revs . he 8BA had singles points maybe because of coil efficiency it was possible by then , I don't think the piston marking can be blamed on the points ,setting the timing wrong or a lean mixture may do .With singles You still need to time them in , what J seery and others said does apply ,you first set the dwell (eg points gap ) then time them to open at 4 Deg BTDC (eg advance plate) on the side of the distributor ,Ted

[Hoop]

Two things.

Can weak spark cause detonation and/or pre-ignition? If the cylinder is fouled by deposits that result from weak spark misfires, the hot spots could cause pre-ignition which will result in the damage described. Very possible, but of course not certain.

Second .... Ted is correct. We had a recent discussion on "Distributor Dwell" which included coil efficiency and likely improvements in modern coils. Ford changed the dwell when going from the early helmet to the later helmet. I have always suspected that they thought the gap was too close ... this would result in the gap closing with wear ... perhaps leading to the points failing to perform properly. More gap would allow for more room for wear ... my theory.

As the gap closes, dwell increases, and timing advance is retarded, not increased.

As far as running single points rather than dual, there is no real reason to abandon the 2 point set-up. The distributor is reliable and not anywhere nearly as complicated as some folks think. If you want to try it ... experimenting is great.

I recently posted ... which puts Ted and me on the same page:

"Dwell is about TIME ... it is correctly expressed in degrees but it still relates back to time.

Why 36 degrees?

It all has to do with how long it takes for the coil to saturate with enough power to adequately fire a spark plug. If you think about it, how rapidly the plugs are firing is one consideration ... the other consideration is the capability of the coil.

The spec is written to insure adequate spark at max rpm. That's about 240 sparks per second, if my math is correct.

The coil has to be able to supply those sparks. MAYBE it is more powerful, or maybe less. The specified dwell is determined by that requirement.

However, what if you never exceed even, say, 2500 rpm? Is 36 degrees of dwell important?

"Skip" and G.M. sell coils that are generally accepted as the "go to" coils. But, we do not know what the coils are really capable of in terms of how rapidly they can re-saturate the coil. All we know is that they work. Maybe that's all we need to know.

Setting the points to spec determines the ability of the distributor to supply the power to fire the plugs ... point gap also helps determine the timing of when the spark is delivered. Spark timing in most cases, those not running max rpm, is more critical than dwell, considering few of us really know how much dwell (time) we really need or what our coil can deliver.

Changing the gap on the L.H. points changes the timing ... changes in advance make more of a difference in "normal" driving than a few degrees of total dwell. Especially when, again, we have no idea of our coil's capability."

[BUBBAS IGNITION]

Hoop, Good post , notice i revised my orginal post after running a couple ina test this week......