Ability to reverse the firing order on demand?

[stobl]

So I have a rather unique situation (I believe) that I’m curious if there is any solution using MS. I’ve searched through megasquirt documentation, searched the forums and was unable to find any relevant discussion. I have MS hooked up to an old car and motorcycle and was unable to find any sort of possibility in tuner studio

Simply put- is there a way you can tell the system to run the engine backwards? In essence, upon receiving an input (12v switch), can you have it reverse the firing order, or do a table switch with a different firing order?

I’m looking to convert an old outboard boat motor to a distributorless ignition to get rid of the points and rudimentary ignition advance. It’s a 1958 Mercury Mark 75 (6 cylinder 2 stroke) that uses points and two ignition coils (each runs 3 cylidners due to dwell time), and ignition advanced is achieved by the throttle cable rotating the distributor (not rpm or load based). 1950’s technology at its best. Ultimately I’d like to EFI this engine, but if I could just convert the ignition over, I would be extremely happy.

Now- the reason for the question is that this engine does not have a “clutch” system to reverse the propeller. To reverse, you pull the throttle to “forward-idle”, kill the motor, pull the throttle to “reverse-idle” then hit the starter button. The throttle control box has a series of switches in it that triggers one of two starter solenoids that rotates the starter based upon which direction you want to go. If you want to go forward, you put it in forward-idle, for forward-starter solenoid is sent power and the starter will rotate normally. If you want to go in reverse, you put it in reverse-idle position, that sends power to the reverse-direction starter solenoid, and the starter rotates the in the reverse direction- ultimately the engine runs “backwards.” As a 2 stroke motor does not have a camshaft or valves, it doesn’t care what direction it rotates.

My thinking on the solution would be a sort of table-switching feature using a 12v input. Using a signal from the throttle control box, upon receiving a 12v signal, the system would run the firing order in the forward direction. Upon receiving a different input (12v from the reverse setting), the engine would reverse the firing order- everything else would be equal.

Does this sound like a possibility? Is there some secret setting in tunerstudio I’m missing, or is this just a really weird request.

Thanks for the help!

[kjones6039]

or is this just a really weird request.

Pretty much............... (one mans opinion of course...)

You DO intend to stop the engine before reversing it don't you?

Ken

[billr]

Surely that isn't just a setting in TS, the coils all have to be "hard-wired" to their proper spark drivers. I think you could do what you want by using two CKP sensors and switching between the two "manually" in the same operation that reverses the starter, and using wasted-spark.

[racingmini_mtl]

Surely that isn't just a setting in TS, the coils all have to be "hard-wired" to their proper spark drivers. I think you could do what you want by using two CKP sensors and switching between the two "manually" in the same operation that reverses the starter, and using wasted-spark.

On a six cylinder, you would also need to reverse sparks B and C to have the correct firing order. I guess the manual switching of CKP sensors could also switch the 2 drivers.

As for a non-manual switching of firing order and not needing an additional CKP sensor, that is not trivial and would require coding this in the firmware. There has been one or two requests in the past of something similar but for a snowmobile where the reversing of the engine is actually done through spark timing and a slowed down but not stopped engine (I don't know the actual details).

Jean

[stobl]

You DO intend to stop the engine before reversing it don't you?

Ken

The actual normal method of going into reverse involves stopping the engine before starting it up again. They call these motors " dock busters" simply because if you need to get into reverse quickly, you're just going to hit the dock. Thanks all for the replies. I know it's kind of a unique situation. if it is somehow possible, I think I would just do a coil per cylinder to keep it "simpler."

The current Normal firing order is 1-6-4-2-5-3, so going in reverse I would need it to fire 3-5-2-4-6-1. I was thinking a manual switch with a voltage input that is always on when in reverse- and will be switched on when the engine is stopped, would be the best method for indicating when the firing order should be reversed. I'm more the hardware guy than the programmer, so I'm not too sure how much of a pull it would be to add a conditional loop in the firmware. (If 12v, then firing order=reverse, essentially)

Thanks for the responses. I at least have all winter to mull this over and wanted to get a head start. Worst case I can rig a distributor from a 6 cylinder Chevy to work, but then I'm curious if an ignition coil designed for a four stroke V8 around 6000-8000rpm might be at its limits when run on a 2-stroke six-cylinder doing about 7000rpm. I'll have to see if that's enough dwell time.

[stobl]

Take a look at this starting around 50 seconds in. Halfway between froward and reverse on the throttle handle is the dead/shutdown zone. Back is reverse, forward is forward. The button on top being the starter switch. The first time he tried to go in reverse, he isn't backwards enough on the throttle and shove the boat forward.

https://youtu.be/hU-hZOnvg1E

[440roadrunner]

ON A TWO STROKE there is no need to fiddle with the firing order. All you need do is change the IGNITION TIMING. If you change it far enough to the "opposite side' of TDC it will run in reverse

[cactus]

At least on a 4 stroke engine, don't you have to have a different cam to have the valve events happen in the right order if you ran backwards? even just considering a single cylinder, the piston would be rising and pushing out the intake, right?

[cactus]

Sorry, the reference to 2-stroke didn't stand out enough at first read.

[racingmini_mtl]

ON A TWO STROKE there is no need to fiddle with the firing order. ...

That's not true for a 6-cylinder: the firing order will change depending on the direction since the difference in degrees between cylinders is not symmetrical.

Jean

[440roadrunner]

ON A TWO STROKE there is no need to fiddle with the firing order. ...

That's not true for a 6-cylinder: the firing order will change depending on the direction since the difference in degrees between cylinders is not symmetrical.

Jean

Actually a 6 IS symmetrical, unless you are talking about the stupidly designed GM V6's which came out ?? about 1976 with the "odd fire even fire" nonsense

A straight six fires every 120 degrees.

But you may be partially correct because of the "I guess" the op wants to eliminate the distributor. It seems like if you use 1 coil to fire two cylinders it would work. All a 2 stroke "knows" is that every time the piston is 'up' it fires, unlike a 4 stroke, as there is no camshaft

[racingmini_mtl]

You don't see what I mean. If you look at the sequence of cylinder 1-2-3, you have 120 degrees between each firing (assuming that this is the firing order and ignoring cylinder 4-5-6). That also means there is 240 degrees between firing of cylinders 2 and 1 and between firing of cylinders 3 and 2. That's the asymmetrical aspect I'm talking about.

But that also means that if you reverse the engine direction, you are going to have to change the order from 1-2-3 to 3-2-1 or 1-3-2 if you start from 1. This still keeps 120 degrees between firing cylinders but not the same sequence. This has little to do with the fact that this is a 2-stroke engine but rather the split between crank throws. The fact it is a 2-stroke means you can actually run the engine in the reverse direction.

And yes, this is because the op is talking about running without a distributor. If you were using a distributor, the reverse firing order would be done by the distributor also running in reverse.

Jean

[stobl]

A straight six fires every 120 degrees.

A straight 6 two stroke fires every 60 degrees (360/6). Each cylinder has it's combustion event every revolution. A straight 6 4-stroke fires every 120 degrees. Also due to that, I would not be able to run wasted spark because no two cylinders are both on TDC. One would fire when the other is at BTC and that one has a clean charge in it. It would also ignite the charge in both the cylinder and the crankcase which wouldn't be good for anyone.

Yes, a single cylinder 2 stroke you can change the timing advance but you can't do that on multiple cylinders. However- Just fiddling with the spare distributor, there appears to be about 20-40* of slack in the connection between the rotor shaft and the drive pulley, so when run in reverse, the ignition advance changes to the correct side of TDC.

Ideally yes, I would like to eliminate the camshaft as it's a 1:1 ratio, belt driven and literally hanging off the side of the motor. Being 1:1 rotation with the crankshaft, there's really no need to keep it if a trigger wheel is put on the crankshaft. That's how i came to the thinking of a manual switched input to indicate reverse would tell MS which cylinder would be the lead-off one to fire upon seeing the tooth gap.

Sorry, now i'm starting to confuse myself. I'll see if i can snap a few photos of the motor this afternoon.

Blake

[elaw]

This isn't quite as elegant but what you want could be done in hardware.

Just build up a box with 3 DPDT relays and wire the relay coils all together to a "forward/reverse" switch near the operator's position. Wire the MS spark outputs to the common contacts on the relays, and wire the NO contacts such that each spark output gets routed to the correct ignition coil for one direction of running and the NC contacts to route the spark outputs for the other direction of running.

Note that one big drawback of this approach is it wouldn't provide any interlocking against changing direction when the motor was running.

[LAV1000]

You have to figure out a way to switch the ignition coils around.
If you use electronic coils its only some extra electronics.
Does anyone know how much mA there is needed to drive an LS coil ?

Same goes for the extra crank position sensor.

Since its a outboard motor I geus its a V6 ?

[elaw]

Same goes for the extra crank position sensor.

Ooh that's a very good point! This isn't just a firing order issue, the crank sensor needs to be accommodated too.

Although if the tooth #1 position is very close to TDC, you might be able to put up with retarded timing in reverse...

[LAV1000]

Same goes for the extra crank position sensor.

Ooh that's a very good point! This isn't just a firing order issue, the crank sensor needs to be accommodated too.

Although if the tooth #1 position is very close to TDC, you might be able to put up with retarded timing in reverse...

Or switch to second timing table.

When using electronics you need 12 and gates for the coils and 2 and gates to switch the crank position sensor.
Thats 4 times a 7408 type IC.
Don't know if there is an easier way beside Eric's relays.

[kjones6039]

Apologies for sticking my nose in earlier!

The only reversers I am even a little familiar with (from my Navy days) were mechanical.

Ken

[elaw]

I get a chuckle reading this topic.

I used to be a pretty hardcore Saab guy and I never owned one of those models but back in the early days they used to use 2-stroke engines. I guess once in a blue moon they would start up backwards and when you put it in gear and let the clutch out you could get a nasty surprise!

[LAV1000]

I get a chuckle reading this topic.

I used to be a pretty hardcore Saab guy and I never owned one of those models but back in the early days they used to use 2-stroke engines. I guess once in a blue moon they would start up backwards and when you put it in gear and let the clutch out you could get a nasty surprise!

Eh, blue moon due to the premix ???