Second set of points, B points, rpm speed sensor tacho
Jan 17, 2021 16:59:55 GMT -5
cp9800 and Ramblin' Russ like this
Post by wayne on Jan 17, 2021 16:59:55 GMT -5
B points: In the following, what the B points do is factual. Partially cut ignition on over run. Components named are also factual. The rest is my opinion. If you feel you cannot tell the difference between your dual point bike and a single pointer, read on. Yours probably aren't working.
Rotary engines have poor engine braking. To overcome this, race cars often cut the ignition entirely on overrun (I've been trackside in the ‘70’s before I even knew what a B point was and noticed this on racing Mazdas). However, Suzuki knew this leads to excess carbon and prematurely contaminated seals leading to sticking etc. If the ignition is left on, the rotor is reluctant to decelerate. In an RE5 you can feel it below 3000 rpm and especially below 2500 on overrun as a jerky, loping bike. Suzuki also spoke of backfiring on overrun. So they came up with a compromise.
The compromise is the B point system. It fires the rotor every second face on overrun instead of every face. The A points I believe are grounded out when the B's become active. This assists the deceleration of the rotor, gives some engine braking and keeps the engine cleaner. As a consequence the loping and jerkiness on over run is also reduced. Suzuki used the "engine cleaner" in their explanation of the bike’s systems. It's sort of true. It's cleaner than NO ignition on overrun, but it's still dirtier than leaving the rotor firing every face.
The system consisted of a speed relay (under the fuel tank, looks like a flasher/blinker relay), a vacuum switch (behind the radiator and either a metal bell housing or a black plastic block), an rpm sensor in the M model tacho (the A model tacho is not equipped with this so you won’t get proper functioning if you try and retrofit to an A) and in the points housing right side of engine, the single lobe points cam and B points.
Why did they remove it for the A model? Cost, so many additional components? Or were they having warranty issues with sticking seals? I suspect the former. I don't think RE5's were racking up enough miles to cause warranty claims due to carbon buildup. Why did they order the M models disabled? One of our members who worked for Suzuki says they were disabled because the later model vacuum switch on the M"s (black plastic version) were unreliable. I suspect that it was also to make all the bikes run and feel the same as the A model no longer had them. I think the B points make the bike just a bit nicer to ride and they didn't want talk about how the old M model rode a bit better than the A. And their disabling does lead to a cleaner engine in the long term.
The B points make no "performance" difference. But they are icing on the cake. They make the bike much nicer around urban streets. If I was blindfolded, I could tell by the bottom of my street whether I'm on the M or the A purely by the feel and sound of the B point system.
In short, if you don’t have them or they’re disabled, you don’t need them. It’s also likely that if you appear to have B points installed, they’re not working. Dealers sometimes disabled them by snipping one wire and leaving all components in place. If your bike escaped the disabling, they still may not work. If the vacuum switch (behind the radiator) is a metal bell like the 2nd throat carby actuator, it’s very reliable. If it’s the later M version black plastic, it’s most likely failed and your B points won’t work.
See below the video for more B point information.
Which set of points are which? In the genuine RE5 parts catalogue the points are shown incorrectly (page 26). The book shows the right side labelled #3 and in the description says "POINT, contact (B)". That's not right, arse about.
The Right side points, the deeply recessed ones, are the A points and do the business of a normal set of points. The left side points are the B points and if connected, only fire the rotor every second face on overrun. You can tell which is which by simply looking into the the points housing and rotating the engine by pushing down on the kickstart lever (hey, if I can do it...). You'll see the deeply recessed one on the right opens twice as many times as the one on the left. IE the right side are your "driving" points, the A set.
The tacho sensor in the M is a simple mechanism. A metal disc of varying diameter rotates on the same shaft as the tach needle. It has a couple of "slices" taken out of it. At one point on its circumference where the radius is large, a disc segment passes through a U shaped device (some sort of Hall effect sensor). That goes into a tiny electronics box and wires out the back of the instrument tub.
When the disc segment is between the sensor, the circuit to the B points is open and they don't operate. As the RPM increases, the disc rotates with the needle until that segment clears the sensor, that part of the B point mechanism is now closed with the potential to make a circuit (remember it's also reliant on high vacuum so it alone won't activate the B points).
As the needle and disc rotate to higher rpm the radius of the disc near the sensor has reduced enough to clear the sensor completely (so the sensor sees nothing) leaving the B point circuit closed and ready.
The disc segment is cut so it's passing through the sensor from idle to 1700 rpm. Regardless of all other conditions, the B point circuit doesn't work in that band. Above 1700 rpm the segment clears the sensor and the B points are ready to work when the vacuum sensor behind the radiator senses an overrun condition (high vacuum). As the rpm reduces on overrun, the B points continue to work until, at 1700 rpm, the segment enters the sensor and cuts out the circuit returning the engine to firing on every face on overrun.
Looking from above the "U" block sensor is clear to see. You're looking at the thin metal disc edge on:
Note the rpm needle at idle. Behind the "4" on the tacho face you can see there's a segment of the disc in the gold/brown sensor:
Due to parallex, the tach needle doesn't look it but it's at 1200 rpm, book idle. The disc segment is still in the sensor:
Once again parallex but that's 1700 rpm. You can see the edge of the segment leaving the sensor:
Now it's well clear at higher rpm:
Well into the rev range you can now see the remainder of the disc is smaller in radius and continues to clear the sensor leaving the points potentially active:
The magic box:
Rotary engines have poor engine braking. To overcome this, race cars often cut the ignition entirely on overrun (I've been trackside in the ‘70’s before I even knew what a B point was and noticed this on racing Mazdas). However, Suzuki knew this leads to excess carbon and prematurely contaminated seals leading to sticking etc. If the ignition is left on, the rotor is reluctant to decelerate. In an RE5 you can feel it below 3000 rpm and especially below 2500 on overrun as a jerky, loping bike. Suzuki also spoke of backfiring on overrun. So they came up with a compromise.
The compromise is the B point system. It fires the rotor every second face on overrun instead of every face. The A points I believe are grounded out when the B's become active. This assists the deceleration of the rotor, gives some engine braking and keeps the engine cleaner. As a consequence the loping and jerkiness on over run is also reduced. Suzuki used the "engine cleaner" in their explanation of the bike’s systems. It's sort of true. It's cleaner than NO ignition on overrun, but it's still dirtier than leaving the rotor firing every face.
The system consisted of a speed relay (under the fuel tank, looks like a flasher/blinker relay), a vacuum switch (behind the radiator and either a metal bell housing or a black plastic block), an rpm sensor in the M model tacho (the A model tacho is not equipped with this so you won’t get proper functioning if you try and retrofit to an A) and in the points housing right side of engine, the single lobe points cam and B points.
Why did they remove it for the A model? Cost, so many additional components? Or were they having warranty issues with sticking seals? I suspect the former. I don't think RE5's were racking up enough miles to cause warranty claims due to carbon buildup. Why did they order the M models disabled? One of our members who worked for Suzuki says they were disabled because the later model vacuum switch on the M"s (black plastic version) were unreliable. I suspect that it was also to make all the bikes run and feel the same as the A model no longer had them. I think the B points make the bike just a bit nicer to ride and they didn't want talk about how the old M model rode a bit better than the A. And their disabling does lead to a cleaner engine in the long term.
The B points make no "performance" difference. But they are icing on the cake. They make the bike much nicer around urban streets. If I was blindfolded, I could tell by the bottom of my street whether I'm on the M or the A purely by the feel and sound of the B point system.
In short, if you don’t have them or they’re disabled, you don’t need them. It’s also likely that if you appear to have B points installed, they’re not working. Dealers sometimes disabled them by snipping one wire and leaving all components in place. If your bike escaped the disabling, they still may not work. If the vacuum switch (behind the radiator) is a metal bell like the 2nd throat carby actuator, it’s very reliable. If it’s the later M version black plastic, it’s most likely failed and your B points won’t work.
See below the video for more B point information.
Which set of points are which? In the genuine RE5 parts catalogue the points are shown incorrectly (page 26). The book shows the right side labelled #3 and in the description says "POINT, contact (B)". That's not right, arse about.
The Right side points, the deeply recessed ones, are the A points and do the business of a normal set of points. The left side points are the B points and if connected, only fire the rotor every second face on overrun. You can tell which is which by simply looking into the the points housing and rotating the engine by pushing down on the kickstart lever (hey, if I can do it...). You'll see the deeply recessed one on the right opens twice as many times as the one on the left. IE the right side are your "driving" points, the A set.
The tacho sensor in the M is a simple mechanism. A metal disc of varying diameter rotates on the same shaft as the tach needle. It has a couple of "slices" taken out of it. At one point on its circumference where the radius is large, a disc segment passes through a U shaped device (some sort of Hall effect sensor). That goes into a tiny electronics box and wires out the back of the instrument tub.
When the disc segment is between the sensor, the circuit to the B points is open and they don't operate. As the RPM increases, the disc rotates with the needle until that segment clears the sensor, that part of the B point mechanism is now closed with the potential to make a circuit (remember it's also reliant on high vacuum so it alone won't activate the B points).
As the needle and disc rotate to higher rpm the radius of the disc near the sensor has reduced enough to clear the sensor completely (so the sensor sees nothing) leaving the B point circuit closed and ready.
The disc segment is cut so it's passing through the sensor from idle to 1700 rpm. Regardless of all other conditions, the B point circuit doesn't work in that band. Above 1700 rpm the segment clears the sensor and the B points are ready to work when the vacuum sensor behind the radiator senses an overrun condition (high vacuum). As the rpm reduces on overrun, the B points continue to work until, at 1700 rpm, the segment enters the sensor and cuts out the circuit returning the engine to firing on every face on overrun.
Looking from above the "U" block sensor is clear to see. You're looking at the thin metal disc edge on:
Note the rpm needle at idle. Behind the "4" on the tacho face you can see there's a segment of the disc in the gold/brown sensor:
Due to parallex, the tach needle doesn't look it but it's at 1200 rpm, book idle. The disc segment is still in the sensor:
Once again parallex but that's 1700 rpm. You can see the edge of the segment leaving the sensor:
Now it's well clear at higher rpm:
Well into the rev range you can now see the remainder of the disc is smaller in radius and continues to clear the sensor leaving the points potentially active:
The magic box:
