Why don't old motorcycles need a distributor?

[postoak_imp]

I was just wondering about this. How did the pre-ECU bikes know when to send spark to a particular cylinder?

 

[SportsterDoc]

Wasted spark / dual fire ignition

 

[postoak_imp]

Yeah, I'm confused. A 4 cycle engine repeats every 720 degrees so there is a firing every 180 degrees on a 4 cylinder right? But how does the system know where to direct the spark?

If motorcycles didn't need distributors then why did cars have them?

 

[LongRanger_imp]

On many ‘70’s Japanese four-cylinder bikes, there were two sets of points, each driven off the crankshaft and each timed to open 360 degrees apart. Basically, that was the “distributor.” Each set of points allowed voltage to be sent to one of two different coils, each coil sending voltage to the spark plugs in two different cylinders (one on the compression stroke and the other on the exhaust stroke, thus a “wasted spark.”) Or something like that.

 

[postoak_imp]

Thanks, but why didn't cars use this same system?

 

[SportsterDoc]

My 1976 CB750F was dual fire, dual points, dual coil.
Dual points were replaced by a Martek 440 electronic ignition, as maintaining proper dwell with points was a nuisance.

The below link should provide a succinct pictorial explanation.

Wasted Spark Ignition

Prior to EFI (2007 up) Sportster's were primarily dual fire:

Coil Testing
Dual fire coil testing for Ironheads and Rigid EVO, (except for Spοrtster Spοrt 1998-2003)
Coil 31614-83A has two primary screw terminals (+ & -) with twin coil towers.
Primary resistance is measured from + to - terminals, at 2.5 to 3.1 ohms.
Secondary (high voltage) winding resistance is tested from coil tower to coil tower at 10,000 ohms to 12,500 ohms.

Single fire coil testing for Spοrtster Spοrt (1998-2003)
Coil 31646-99 has three connectorized primary terminals (- + -), referenced A (front) B (12 VDC) C (rear) and twin coil towers.
Primary resistance is from + to -, both B to A and B to C at 0.4 to 0.6 ohms. For the 1200S (dual plug heads), measure secondary resistance between both front coil towers and then between both rear coil towers at 11,700 to 12,700 ohms.

Single fire coil testing for carbed (ICM) rubsters, 2004-2006
Coil 31655-99 has three connectorized primary terminals (- + -), referenced 1 (rear) 2 (12 VDC) 3 (front) and twin coil towers.
Primary resistance is from + to -, both 2 to 1 and 2 to 3 at 0.5 to 0.7 ohms.
Secondary (high voltage) winding resistance is tested from coil tower to coil tower at 11,000 ohms to 15,000 ohms.

Single fire coil testing for EFI (ECM) rubsters, 2007 and up: Coil 31656-07 has 4 primary terminals, referenced, left to right, as A (+), B (+), C (rear) & D (front). A or B to D should measure 0.3 to 0.7 ohm and A or B to C should measure 0.3 to 0.7 ohm.
Secondary resistance: 3,000 to 4,800 ohms, tower to tower

Note: If resistance is lower than specified, that winding has partially shorted, bypassing part of the coil.

If resistance is higher, then corrosion or failing internal connections may be adding to the resistance.

 

[SportsterDoc]

wasted spark is correct. as said above, each coil is fired every 360 degrees of crank rotation. this means it fires near btdc on the combustion stroke, the next time that cyl fires is near top dead center of the exhaust stroke. in effect, the crankshaft itself is the distributor. so, the coil will fire cyl 1 and 4 at same time, and 2 and 3 at same time. however, cyl 1 may be on the power stroke, cyl 4 may be at the exhaust stroke.
the electronic ignition on the rd350 I posted is actually one for a japanese 4cyl.

now, another one forgot is overhead cam twins, such as cb350, 450, xs650, etc. these have points off the cam shaft in the head.

what I think your missing is that theres multiple coils, and that they are simply triggered at the motor, just in a more analog fashion. in lots of ways, more similar to modern car engines with coil on plug setups triggered by a crank sensor. hope this helps

Yes, as did my CB160, CL160, CL350, SL350 and CB360.

Sportsters ran points off the camshaft before a cam position sensor replaced points in the "nosecone".
Some riders got confused with setting timing, since Sportster cams rotate CCW, although the crank is CW.

 

[postoak_imp]

Thanks! This has been very informative.

 

[postoak_imp]

Okay, I understand the dual points and wasted spark setup but how is the relationship between the crankshaft position and the points opening established? Maybe it's too simple a question. There's a mark somewhere for TDC and the points plate is swiveled around so the points are closed at that point?

 

[GoldOxide_imp]

Great capture m_in_sc.

Man, those were the days - maybe some folks still dwell at the point.

 

[Lord Popgun]

Great capture m_in_sc.

Man, those were the days - maybe some folks still dwell at the point.

I see what you did there GO

 

[GoldOxide_imp]

Great capture m_in_sc.

Man, those were the days - maybe some folks still dwell at the point.

I see what you did there GO

I see what you did there GO
lol - I am sure many here at the Forum have had some bad days trying to set the timing on their ol' cage, or even a multi-cylinder two-stroker. I personally am glad for electronics, sans an "EM pulse burst" (but that thinkin' is pretty out-dated too).

 

[SportsterDoc]

theres typically a marker on the advance unit or the points cam in the case of a 4 stroke, which spins with the points rotor.. the rotor spins with the crank. then there's a fixed mark on the cases to time against. In the case of a SOHC CB750 for example, theres an 'f' mark on the alternator rotor to set timing at idle, then there a 'll' mark that lines up at full advance for each set of points. Pints '1' set cyls 1& 4, whereas '2' sets cyls 2&3. also, theres a 't' mark for top dead center, but thats used for setting valve clearances, etc.

so, in comparison to a car, imagine the timing marks on the damper AND the distributor in the same cover on the crank basically combined.





on cam driven units, there's usually a timing mark on the alternator on the crank.

Thanks for helping me remember why, when my 76 CB750F was only a year or two old, I replaced the dual points with a Martek 440 electronic unit!

I had a *Hawk engine analyzer at the time, but it was no help.

The dwell meter made point adjustment on GM motors very simple, since GM distributor caps had a lift-up door for access with an Allen wrench to adjust with engine running.

Thanks for the trip down memory lane.

*Manufactured on Nordhoff Street, in Chatsworth, walking distance from where I grew up. They also made good quality automotive gauges.

 

[SportsterDoc]

Great capture m_in_sc.

Man, those were the days - maybe some folks still dwell at the point.

I see what you did there GO

I see what you did there GO
lol - I am sure many here at the Forum have had some bad days trying to set the timing on their ol' cage, or even a multi-cylinder two-stroker. I personally am glad for electronics, sans an "EM pulse burst" (but that thinkin' is pretty out-dated too).

Nah, I gave away my timing lights long before I gave away the engine analyzer/dwell meter.

Just advance until it pings, then back off a degree or two.

Doing so involves test rides/drives, which takes time, but optimizes the timing, at least for that altitude.

Cycle Tuning Unlimited was under 1,000 feet elevation, so no need to further retard for altitude...in other words, no pinging issues with altitude changes.

Even with 300 HP (1982 Chev 350 V8) in my 1973 Datsun PL620, advancing timing at altitude made a noticeable difference...so, I left the distributor clamp just snug.

try 3 sets on a triple lol. . Not hard really, at all. martek was a big rd racer, he made ignitions for quite a while especially for the cbs, kz's, and rds, was an active member of the aircooled rd club last i heard.(about 5 years ago)

It was an optical unit-very reliable. I put close to 40,000 miles on that bike from 1976-1981 with only routine maintenance.

 

[SportsterDoc]

you have no idea how many people i have had to explain to that points gap controls dwell. ...

I may only be 47 but since i was broke most of my early days of motoring, ive learned the 'old ways', including polishing point faces on a lathe. still have a dwell meter as well. I've used it on electronic setups on occasion. (helps verify that air gap is set correctly )

Yep, dwell is measured in rotational degrees.
And most folks did not understand that the coil discharges through the spark plug when points open.
Or that the capacitor (condenser) is dual purpose.
When points open, it absorbs the voltage, saving point wear and when points close it discharges into the coil to facilitate quick enerization.
When the capactor was out of spec (typically 0.22 microfarad) which side had the tit and which side had the valley would indicate whether it was + or - spec.

I do not really miss points, but used them in 1982 on my V8 Datsun for reliability in remote areas.

i have to disagree, especially with 2 strokes that rev to 10k and other vehicles i have, timing is key to power and efficiency (including my 390 galaxie). But to each their own.

Disagree with optimizing timing for each individual engine, with all factors taken into consideration, such as fuel, altitude and even point gap/dwell, which affects timing? Timing is "key" and most factory settings are less than optimum. The disadvantage of running timing at optimum, is having to back off timing if running cheaper fuel.

 

[SportsterDoc]

well, I don't run cheap fuel, that's for sure. everything gets premium except the modern suv. and it definitely affects my older cars and bikes. I certainly do not run stock timing numbers, even on my stock (ish) 6-cyl 62 falcon. Thats the difference between tuned and maintained.

this is how important timing is. On a stock motored 73 kawasaki S2, i put on a dynamic timing control module, tuned in a curve and with NO PORTING put down 59 RWHP with a 45 degree power curve on the dyno graph. Chambers, timing, and jetting, thats it. the timing was the key. out of a 347 cc aircooled motor. Prior i was in the mid to high 40s at the rear wheel. I could go on and on, but i think my 'point' has been made.

No, what is your point?
I am recommending optimizing timing over stock (when feasible) and it seems that you are, also. So, what is the disagreement?

well, I don't run cheap fuel, that's for sure. everything gets premium except the modern suv. and it definitely affects my older cars and bikes. I certainly do not run stock timing numbers, even on my stock (ish) 6-cyl 62 falcon. Thats the difference between tuned and maintained.

this is how important timing is. On a stock motored 73 kawasaki S2, i put on a dynamic timing control module, tuned in a curve and with NO PORTING put down 59 RWHP with a 45 degree power curve on the dyno graph. Chambers, timing, and jetting, thats it. the timing was the key. out of a 347 cc aircooled motor. Prior i was in the mid to high 40s at the rear wheel. I could go on and on, but i think my 'point' has been made.

Sometimes there is not much choice.
Stovepipe Wells in Death Valley only sells 87 octane.
If timing is optimized for performance/fuel economy, it may need to be backed off, although at close to sea level, it may be OK.

 

[SportsterDoc]

well, I don't run cheap fuel, that's for sure. everything gets premium except the modern suv. and it definitely affects my older cars and bikes. I certainly do not run stock timing numbers, even on my stock (ish) 6-cyl 62 falcon. Thats the difference between tuned and maintained.

this is how important timing is. On a stock motored 73 kawasaki S2, i put on a dynamic timing control module, tuned in a curve and with NO PORTING put down 59 RWHP with a 45 degree power curve on the dyno graph. Chambers, timing, and jetting, thats it. the timing was the key. out of a 347 cc aircooled motor. Prior i was in the mid to high 40s at the rear wheel. I could go on and on, but i think my 'point' has been made.

My grandparents 63 Ford Falcon was an amazingly durable vehicle. It survived my teenage years. They had it for about 35 years.

170 cu in straight 6 (110 HP/), 2 speed FordoMatic. I took them in it on a 6 week 10K mile trip when I was 16. Nevada was memorable, as there were no speed limits between towns. It cruised at 85+ and got about 23 MPG.

A lot of firsts that year:
Self adjusting brakes
Transistor radio
Heater was stock, no longer an extra
No side view mirrors or seat belts
Padded dash and padded sun visors

I thought you were disagreeing with my point. I misread. we are saying the same thing.

LOL
No worries
I am sure I have done the same

 

[SportsterDoc]

Now that we are agreed that we both agree...
Advancing timing, without interfering with the piston(s) approaching TDC, maximizes burn time, which is best for not only power, but also fuel efficiency.

 

[max]

Advanced spark timing was explained as follows to me years ago;
If you want a woodpile to burn at twelve o'clock you don't light it at twelve, it will peak burning 10 minutes later, you light it at ten minutes to twelve, it will burn at maximum rate at twelve.
Same with a fuel mixture.

Does a modern ecu actually have a p.i.d. for the ignition timing and can you see it change in live data?

 

[SportsterDoc]

p.i.d?

if you want to get REAL weird, i'll again reference 2 (fairly modern) strokes, the timing starts low, then advances till peak torque, then retards again at higher revs because the dynamic compression goes up at higher rpms. makes for interesting tuning days.

Max, Popgun and Peter are the electronic gurus on this forum (that I know of).

Max is referencing a proportional–integral–derivative controller, which is a common PLC (programable logic controller) with algorithms.

PLCs are very common in industrial automation.

The automation company that I retired from three years ago closed three months thereafter and I think this is the only active link left on the web:

RFID-equipped workcell provides complete traceability

Max, thanks for taking me down memory lane for a moment.