Additional Crank Trigger Wheel

[TuckerE30]

I am interested in adding an additional crank trigger wheel to my engine so that I may utilize MegaSquirt. The BMW M20B27 I'm targeting has its own crank trigger wheel and sensors in stock configuration, but they appear to be incompatible without significant MS source code modification. Does the GCR allow the addition of a crank wheel and sensor? Just the trigger wheel or sensor? Thanks.

This would be for a BMW E30 325e running in ITA.

9.13.D.1.e
Any ignition system which utilizes the original distributor for spark timing and distribution is permitted. Internal distributor components and distributor cap may be substituted. Crankfire ignition systems are prohibited unless fitted as original equipment.

[JoshS]

I see no rule that would allow you to ADD a crank sensor.

You can replace the sensor per rule 9.1.3.D.1.a.6, but it's not clear to me whether or not that wording also allows you to substitute the trigger wheel. In my opinion the intent was to allow you to substitute both the sensor and the wheel, but I'm not sure that we got the wording fully right there.

[JeffYoung]

Rule actually says stock sensors can be substituted with any equivalent units.

I believe what you are doing is within the intent of the rule - you are using an equivalent unit to perform the function the stock one did.

There may be a hypertechnical argument that you can't add a wheel, you have to substitute, and to be 100% legal you may want to see if you can do that. However, I am convinced that what you are doing is within the intent of the rule.

[Andy Bettencourt]

It does not say you can add a second crank trigger wheel. You can replace your OEM CTW with a different one, but not add a second one. The rule clearly states IMHO that there are only two types of 'sensors' that can be added (in addition to what came on the car).

Why can't the original CTW be replaced with one that is compatible with MS?

[chuck baader]

Tuckere30..contact me directly [email protected]

[TuckerE30]

I'll try to explain the stock setup and hopefully it will make some sense.

The stock M20B27 crank trigger wheel is made up two sensors actually. One sensor counts all 120 flywheel teeth and one sensor is just for a a positioning key attached to the side of the flywheel.

The closest trigger wheel style that megasquirt is compatible with is a missing-tooth style where there are a number of teeth (like 30 or 60) with one or two missing. I could try to modify my flywheel by knocking off a tooth or two, but I am afraid that I'd end up breaking off additional teeth due to the added stress during starting. Basically, I didn't see an easy way to add a crank trigger wheel to the backside of the engine.

Later BMW M20 motors come with a missing tooth crank trigger wheel on the front of the engine which is compatible with MS.

I think I should be covered with regards to adding new crank trigger sensor since I currently have two and could just move and replace one.

[Eagle7]

The stock M20B27 crank trigger wheel is made up two sensors actually. One sensor counts all 120 flywheel teeth and one sensor is just for a a positioning key attached to the side of the flywheel.

The closest trigger wheel style that megasquirt is compatible with is a missing-tooth style where there are a number of teeth (like 30 or 60) with one or two missing. I could try to modify my flywheel by knocking off a tooth or two, but I am afraid that I'd end up breaking off additional teeth due to the added stress during starting. Basically, I didn't see an easy way to add a crank trigger wheel to the backside of the engine.

Would a dual wheel configuration work with this?

[tderonne]

You can change pulleys, right? Is an allowed pulley performing an illegal function if it happens to have teeth on it? The substituted sensor is arguably legal - save for being in a different location.

You'd think with meagsquirt, someone would have done the code (and maybe they have above?).

[Andy Bettencourt]

I'll try to explain the stock setup and hopefully it will make some sense.

The stock M20B27 crank trigger wheel is made up two sensors actually. One sensor counts all 120 flywheel teeth and one sensor is just for a a positioning key attached to the side of the flywheel.

The closest trigger wheel style that megasquirt is compatible with is a missing-tooth style where there are a number of teeth (like 30 or 60) with one or two missing. I could try to modify my flywheel by knocking off a tooth or two, but I am afraid that I'd end up breaking off additional teeth due to the added stress during starting. Basically, I didn't see an easy way to add a crank trigger wheel to the backside of the engine.

Later BMW M20 motors come with a missing tooth crank trigger wheel on the front of the engine which is compatible with MS.

I think I should be covered with regards to adding new crank trigger sensor since I currently have two and could just move and replace one.

Not knowing the exact config, you state you have two sensors. Replace 1 or both of those sensors with a sensor that performs the smae function that can talk with your ECU. Done. Just don't ADD any that weren't there before.

Modifying your flywheel by taking teeth out is not legal. And if anyone wants to argue that it could be considered balancing - save your keystrokes!

[TuckerE30]

Thanks Andy, but your suggestion still means that I have an incompatible crank trigger wheel that MS can't understand even if it has the correct sensor. Thanks to everybody else as well for their assistance.

From the responses so far it seems there isn't a clear consensus.

With regards to why MS hasn't done this already, this configuration was just used for a few years on BMWs before the common missing-tooth style was adapted. Most people who use MS will switch to the later motors (with updated crank trigger wheel) and not use the "eta" motor that we use in ITA. Actually this BMW motor comes with 3 position sensors total with one on the front that is not used during runtime and is only for diagnostics?!?

[chuck baader]

"Assemblies can be changed/updated" which would allow the change of the engine wiring harness, as an assembly, to a later version using a stock 60-2 trigger wheel....IMHO. Chuck

[ericblois]

"Assemblies can be changed/updated" which would allow the change of the engine wiring harness, as an assembly, to a later version using a stock 60-2 trigger wheel....IMHO. Chuck

but the later version is on a car that is named in the next class up ITS. so if you update to that sesnor wheel wouldnt you also have to run in the other class?

[Andy Bettencourt]

but the later version is on a car that is named in the next class up ITS. so if you update to that sesnor wheel wouldnt you also have to run in the other class?

It doesn't work like that...but, if that version of the crank trigger wheel (ctw) was not available on any version of the car on the spec line (meaning e/es from 84-87), then it is indeed illegal. Same goes for a wiring harness. If it's from another model, it's not legal to UD/BD.

I trust Chuck has a legal solution he can explain to you/us if he chooses to share his secrets of speed!

[JeffYoung]

Plus, as someone mentioned above, pulleys are free, so you can make a trigger wheel out of it, or add one, there. The sensor is a different story but if you are simply substituting it for a sensor that used to be on teh flywheel, I think you are ok.

But talk to Chuck. He knows these cars.

[ericblois]

you are correct Jeffyoung with pulleys be free "n. Alternate water pump, alternator, power steering, and crankshaft
pulleys of any diameter or material may be used. Type of
accessory drive (e.g., V-belt, toothed belt, etc.) shall remain as
stock." so i can put what ever crank pulley i want on so i can put the newer motors crank pulley on that also has teeth. i belive both the bmw motors the one in the 84-87 325e and the newer ones use the same part number sensor on the front crank pulley just different pulleys. so i think it would be ok to run MS with the crank sensor after choosing to replace your crank pulley. since the car already has a crank sensor in that location. BTW i too race an ITA e30 325