Wheel of Timing. Success at last!
04-28-2008, 08:19 PM
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Boost Pope
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Wheel of Timing. Success at last!
My crankwheel setup is finally just about finished. I bought a 4" 36-1 wheel from DIY, and built the adapter hub pretty much as I'd been describing in Ben's 60-2 thread, only without the big flange on the end.
The hub started as a 2.5" long piece of 2.75" diameter 6061 aluminum. This is the biggest piece of metal I can fit into the chuck on my lathe, and the smallest that was adequate to cover the area of the stock 4-bolt flange (the one that holds the pulley on) while leaving enough extra for me to take some material off the outside in order to true the hub.
Here's the finished product. This is the side that the wheel attaches to:
The four holes take four 6x70mm bolts that serve the original function of holding on the pulley and retain the wheel. The raised lip in the center is exactly 0.5", to center the wheel. Inside that is a 3/16" threaded hole which allows me to install a bolt, which is purely an affordance to allow me to turn the crank with a wrench. It serves no other function.
Here's the side that faces the crank pulley:
The major inside diameter is 38mm, to center the hub on the shoulder of the crank bolt, with a slight radius around the lip to help it slip over. Actually, I messed up and it's just a tiny bit larger than 38mm. I bolted it on as-is, and wound up with about .015" of runout, which I think I can live with. The minor inside diameter is about 30mm, simply because that's all I needed to clear the flats on the crank bolt, and I didn't feel like opening it all the way out. The fifth "odd" hole on the primary surface is to clear the alignment pin on the crank hub.
Here it is sitting in semi-final form inside the crank pulley, to give you an idea of how it goes together:
The overall height of the hub, after the facing operations, is about 2.1". Because the wheel is smaller than the pulley, it was necessary to stand it off a bit in order to provide space for the sensor.
I took it for a spin on the lathe, with the sensor clamped into the toolpost, to scope the output and get an idea as to what it looked like:
I don't have a scopecap (sorry) but it was pretty clean, and I judged the signal to be likely recoverable with much larger gaps than the manual says. Even at >2mm, I still had a decent looking signal. Interestingly, I found that the amplitude of the first tooth after the gap was higher than the others, and that the amplitude tended to increase with frequency.
Fabricating the hub turned out to be the easy part. It took me three attempts to build the damn sensor mount. The first time, I had it nearly finished when I accidentally cut the post too short. Of course, I hadn't bothered to tack-weld; that baby was really welded in good. So that part went into the trash.
For the second attempt I went slower, tack-welding and test-fitting at each step before laying down solid beads. The mount was absolutely perfect, until I tried to install the alternator belt.
For the third one, I used #2 as a template, but moved the post downwards and decided to make it a two-piece assembly that unbolts in the middle. The first half bolts to the block, then the alternator belt goes in, and then the second half bolts to the post.
I know, you can't picture it. Here:
And one with the mount removed, so you can see where it attaches:
The lower hole is for the oil pump bolt. The upper one is on the plastic timing belt cover. The lower hole is recessed exactly 10.2mm relative to the plane described by the surface of the upper one, so I cut a 10.2mm aluminum spacer to go behind the mount, through which the bolt passes.
For the moment, the car is still running on the CAS. I still need to build the input circuit for this and figure out the software. Due to the design of the sensor mount I don't have easy adjustability on it, so I'm hoping that as long as I stay with time-based cranking I can adjust the trigger angle to something other than 60° (just as we do with the CAS) to fine-tune the position.
The hub started as a 2.5" long piece of 2.75" diameter 6061 aluminum. This is the biggest piece of metal I can fit into the chuck on my lathe, and the smallest that was adequate to cover the area of the stock 4-bolt flange (the one that holds the pulley on) while leaving enough extra for me to take some material off the outside in order to true the hub.
Here's the finished product. This is the side that the wheel attaches to:
The four holes take four 6x70mm bolts that serve the original function of holding on the pulley and retain the wheel. The raised lip in the center is exactly 0.5", to center the wheel. Inside that is a 3/16" threaded hole which allows me to install a bolt, which is purely an affordance to allow me to turn the crank with a wrench. It serves no other function.
Here's the side that faces the crank pulley:
The major inside diameter is 38mm, to center the hub on the shoulder of the crank bolt, with a slight radius around the lip to help it slip over. Actually, I messed up and it's just a tiny bit larger than 38mm. I bolted it on as-is, and wound up with about .015" of runout, which I think I can live with. The minor inside diameter is about 30mm, simply because that's all I needed to clear the flats on the crank bolt, and I didn't feel like opening it all the way out. The fifth "odd" hole on the primary surface is to clear the alignment pin on the crank hub.
Here it is sitting in semi-final form inside the crank pulley, to give you an idea of how it goes together:
The overall height of the hub, after the facing operations, is about 2.1". Because the wheel is smaller than the pulley, it was necessary to stand it off a bit in order to provide space for the sensor.
I took it for a spin on the lathe, with the sensor clamped into the toolpost, to scope the output and get an idea as to what it looked like:
I don't have a scopecap (sorry) but it was pretty clean, and I judged the signal to be likely recoverable with much larger gaps than the manual says. Even at >2mm, I still had a decent looking signal. Interestingly, I found that the amplitude of the first tooth after the gap was higher than the others, and that the amplitude tended to increase with frequency.
Fabricating the hub turned out to be the easy part. It took me three attempts to build the damn sensor mount. The first time, I had it nearly finished when I accidentally cut the post too short. Of course, I hadn't bothered to tack-weld; that baby was really welded in good. So that part went into the trash.
For the second attempt I went slower, tack-welding and test-fitting at each step before laying down solid beads. The mount was absolutely perfect, until I tried to install the alternator belt.
For the third one, I used #2 as a template, but moved the post downwards and decided to make it a two-piece assembly that unbolts in the middle. The first half bolts to the block, then the alternator belt goes in, and then the second half bolts to the post.
I know, you can't picture it. Here:
And one with the mount removed, so you can see where it attaches:
The lower hole is for the oil pump bolt. The upper one is on the plastic timing belt cover. The lower hole is recessed exactly 10.2mm relative to the plane described by the surface of the upper one, so I cut a 10.2mm aluminum spacer to go behind the mount, through which the bolt passes.
For the moment, the car is still running on the CAS. I still need to build the input circuit for this and figure out the software. Due to the design of the sensor mount I don't have easy adjustability on it, so I'm hoping that as long as I stay with time-based cranking I can adjust the trigger angle to something other than 60° (just as we do with the CAS) to fine-tune the position.
Last edited by Joe Perez; 04-28-2008 at 08:58 PM.
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04-29-2008, 02:03 AM
#19
Boost Pope
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Posts: 33,019
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andLet me put it this way. If you have a sister who is is:
A- 25-35
B- Hot
C- Single
D- Has a 120 or better IQ (I'll also accept GRE/MCAT/etc), and
E- Keeps bugging you to hook her up with one of your Miata buddies,
then yes, we can probably work something out.
I am still contemplating doing a "group build" of these, if we can determine that a single design will handle all Miatas '90-'95, and can get enough commitments. If 10 people get on board, then it would probably cost ~$50-$60 each to get the hubs made. As for the sensor mount, you're on your own. I'm pretty sure that mine, for instance, wouldn't work with A/C.
Hell, I'll trade you. But seriously, thanks. I asked Matt Cramer at DIY if he had any thoughts as to what sensor I should use, and he suggested the one from a '91-'97 1.9L Escort. Bought one for $32 at NAPA. (It was $27 on their website. Always pisses me off how they do that...) And Reverant is right, you can probably get 'em cheaper elsewhere. I wanted to get it in my hands as quickly as possible however, since the sensor, to some degree, drove the rest of the design.
Ok... Let's just let that one go.
Ok, I admit I had to look up what a shuriken was. You coulda just said "ninja throwing star." Which is funny, because that's exactly what I thought when I first opened the box from DIY. I didn't realize from the picture on their website that the teeth were pointy. Most of 'em are flat. Still, produced a good signal on the scope and fits nicely on the engine, which is all that matters. The reason I went 4" instead of 6.5" is that my BOV sits right next to the pulley on the intake side, and I really didn't want to have to re-fabricate my inlet pipe.
Well, I've been having trigger issues with the CAS. Occasional mis-triggers resulting in stumbles, always in the same general RPM band (mid 4,000s). There's a whole thread about it- the one with the profane, all-caps title.
I spent weeks trying to design an input circuit that would clean up the signal, but to no avail. Maybe the stock ECU had a software debounce on the trigger inputs that the MS doesn't have, or maybe my CAS is just old and tired. Plus, I realized while observing my timing at high RPM that because the of the timing belt, the CAS jitters somewhat at high RPM. With the timing locked at 10°, I revved the engine slowly up to redline and observed it with a timing gun, and that damn mark was jumping around by more than 5° by the time I got to 6,000 RPM.
This way, I'm using all new hardware, a relatively known-and-proven design, and by triggering off the crank I should eliminate all jitter. We'll see in a few days once I get the VR circuit built- still trying to decide whether to use the R3.0 op-amp circuit, or the LM1815N-based one. I'll probably build both on a protoboard and compare them.
Mechanical stability. I don't trust four long standoffs to hold the wheel dead-steady when the crank is revving up and down.
Sensor answered above. I plan to eliminate the cam sync pulse altogether. The CAS will be physically left in place only to plug the hole in the back of the head. Remember- the CAS gives two CMP pulses per revolution, or one per crank rev. Therefore, it provides no more usefulness than a missing-tooth crankwheel. Both give only one locater pulse per crankshaft revolution.
I used split lockwashers, though locktite probably isn't a bad idea.
Remember, these are essentially the same four bolts that normally hold the crank pulley to the hub. Between the weight of the pulley and the stress of driving the alternator, water pump, power steering and A/C, I'm not worried about a little more rotational inertia.
As part of the design phase, I removed the crank pulley and measured the engagement depth of the four stock bolts- I think it was around 1cm. I then measured the stack-up of all the new parts, plus the pulley but minus the original retaining ring, and selected a set of 70mm bolts to provide the same engagement depth. The bolts themselves are class 10.9, and so are rated for 16Nm (12 ft/lb) which is at the high end of the factory spec. Thusly were they tightened.
We'll see how it goes. If my crankshaft decides to do the short-nose fandango, I'll be posting another thread with an obscene title.
Either Robert Jordan or Pat Sajak, depending on the cultural elevation (ok, the geekiness) of the reader. Thanks.
A- 25-35
B- Hot
C- Single
D- Has a 120 or better IQ (I'll also accept GRE/MCAT/etc), and
E- Keeps bugging you to hook her up with one of your Miata buddies,
then yes, we can probably work something out.
I am still contemplating doing a "group build" of these, if we can determine that a single design will handle all Miatas '90-'95, and can get enough commitments. If 10 people get on board, then it would probably cost ~$50-$60 each to get the hubs made. As for the sensor mount, you're on your own. I'm pretty sure that mine, for instance, wouldn't work with A/C.
Ok... Let's just let that one go.
I spent weeks trying to design an input circuit that would clean up the signal, but to no avail. Maybe the stock ECU had a software debounce on the trigger inputs that the MS doesn't have, or maybe my CAS is just old and tired. Plus, I realized while observing my timing at high RPM that because the of the timing belt, the CAS jitters somewhat at high RPM. With the timing locked at 10°, I revved the engine slowly up to redline and observed it with a timing gun, and that damn mark was jumping around by more than 5° by the time I got to 6,000 RPM.
This way, I'm using all new hardware, a relatively known-and-proven design, and by triggering off the crank I should eliminate all jitter. We'll see in a few days once I get the VR circuit built- still trying to decide whether to use the R3.0 op-amp circuit, or the LM1815N-based one. I'll probably build both on a protoboard and compare them.
Mechanical stability. I don't trust four long standoffs to hold the wheel dead-steady when the crank is revving up and down.
As part of the design phase, I removed the crank pulley and measured the engagement depth of the four stock bolts- I think it was around 1cm. I then measured the stack-up of all the new parts, plus the pulley but minus the original retaining ring, and selected a set of 70mm bolts to provide the same engagement depth. The bolts themselves are class 10.9, and so are rated for 16Nm (12 ft/lb) which is at the high end of the factory spec. Thusly were they tightened.
We'll see how it goes. If my crankshaft decides to do the short-nose fandango, I'll be posting another thread with an obscene title.
Either Robert Jordan or Pat Sajak, depending on the cultural elevation (ok, the geekiness) of the reader. Thanks.
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