WestfieldMX5

Are the crank wheels on both engines the same (NA / NB)?
I think I might have a NA crank wheel + plate on my NB engine. The engine came without one so I just bought 'any' crank wheel assembly I could find. Now I'm starting to wonder if that's a good thing, seeing as the crank signal edges are different.
Anyone have a pic of both so I can compare?

richyvrlimited

iTrader: (1)

There is no crank plate on the NA, all of the engine position is determined by the CAS

jsisco

iTrader: (7)

96 and 97 do have a crank wheel, and if I remember correctly it is the same.

EDIT: now I'm not sure. I know the sensors are different, but I think I remember the same nubs on both when I did my engine swap.

Joe Perez

iTrader: (8)

This is what the NB wheel looks like:

If I recall correctly, the "odd" hole around the central cutout is straight up when the crank is at #1 TDC. (There's a locating pin that passes through it)

Joe Perez

iTrader: (8)

The part numbers are different, according to Mazda.

'97 is B6BF-11-408B or B3C7-11-408, whereas '01 is BP4W-11-408.

No idea whether they interchange.

richyvrlimited

iTrader: (1)

I have a 96 it's not got a crank wheel. The crank wheel didn't appear till the NB.

jsisco

iTrader: (7)

So there was a difference between 96 and 97 then. I was under the impression they were the same, because the crank sensor was required by OBDII spec to detect mis-fires which was all it was used for in the 97. My 97 did have a crank wheel for sure. It looked like what Joe pictured, but I don't know for sure if the nubs were in the same place. I know for a fact the sensors are not interchangeable.

Joe Perez

iTrader: (8)

The crankwheel was introduced in mid 1995 for the '96 model year on US-spec cars. It was part of the misfire detection system for OBD-II. The sensor used was a variable-reluctance unit (two wire plus shield) and was not a primary sensor. It's sole function was to provide ultra-accurate tracking of crankshaft speed, by measuring the time elapsed between pulses, each pulse corresponding to one power cycle. If a discrepancy was sensed (ie- the time for a certain pulse pair exceeded that for the leading and trailing pairs by a certain threshold) then a misfire was understood to have occurred. After the crankwheel was added, the black/white wire was removed from the ignition coils (as it was now redundant) and the tach began to be fed by the ECU.

The CAS continued to be used as the primary triggering device throughout the NA production run, disappearing in '99 when a sensor was added to the intake cam to provide the CMP signal, and the crank sensor was changed from VR to a hall-effect sensor (three wire, open-collector.)


Here is the crankwheel sensor on the '96 FSM wiring diagram:


And here is the wheel itself from the '97 parts catalog:

jsisco

iTrader: (7)

f_devocht: I need to take a trip out to the shop tomorrow, and I will try to get some good pictures of the 97 wheel. I've got the 99 wheel on my car so I can't really compare them together.

richyvrlimited

iTrader: (1)

Told me!

Never knew that though Joe, I appreciate the detailed explanation!

Machismo

iTrader: (1)

96's most definately have the wheel and trigger. I've thrown codes from hitting debris and moving the trigger out of wack. I don't know if they are interchangeable though.

j_man

Here is some info on all that - pulley, wheel & boss:

The crank wheel has nothing to do with the pulley. It has to do with the boss. If you need the wheel, you use the thinner boss. If no wheel is needed - you use the thicker boss.

The pulleys are independent from that (trigger wheel and boss) and are interchangeable ('94 - '05). There are two types of pulleys though (and are not year bound) - cast and stamped. One comes with a spacer for the bolts and different length bolts IIRC. So, depending on which pulley you get, use the matching bolts and spacer.

'94-'95 Miatas come stock with the thicker boss and no crank wheel.
'96-'05 Miatas come stock with the thinner boss and crank wheel.
The '96-'97 trigger wheel is used for misfire detection, the '99-'05 wheel is used for the crank position detection.

Pictures:

http://picasaweb.google.com/mx5files...WheelsCompared

The teeth on both '96-'97 and '99-'05 trigger wheels are positioned similar but the '99 one has 2 degrees advance and a little bit different shape ('99-'05 wheel is a circle, the '96-'97 one is not). So, the leading edges in the signal could be 2 degrees shifted, but they could be not either depending on the sensor positioning, etc.. Not sure about the trailing edges or whether the signal is inverted - I've never scoped a '96-'97 one).

Btw, a brand new OEM trigger wheel costs $6 at Mazdaspeed Motorsports

j_man

Interesting info! I newer knew the '96-'97 used a VR one. That explains the weird shaped teeth/wheel. Wow, I was lucky I used a '99 sensor for my NA crank wheel conversion then I was wondering should I use a '99-'05 crank sensor or a '96-'97 along with the '99 trigger wheel. Either sensor was a direct bolt on to my '94 oil pump, but in the end I just ordered a '99 one just because it didn't have a metal bracket. It's been working flawless.

Joe Perez

iTrader: (8)

J_man, wonderful info!

I wonder if the pulley boss from a '96-'97 would fit onto a longnose 1.6?

I ask because while my 36-1 setup works fabulously, it seems that the rather complicated welded steel mount I made for the sensor has slightly more flex in it than I'd like. It's been on for a little over a year now, and there is evidence that the sensor has been coming into contact with the teeth, as a slight groove has been cut into the face of it

Since I have no other projects on my plate right now, I'm seriously considering converting to MS3 once it's shipping, largely out of boredom. That would be a perfect time to convert from a VR sensor to a '99 sensor as well. I guess I'd have to come up with some way to mount a sensor on one of the cam gears as well, as I'd be going 100% sequential at that point.


Worst-case, I guess I could just turn down a 1.6 pulley boss in a lathe by the thickness of the wheel. (I miss my lathe...)

WestfieldMX5

J_man, thanks man. Very good info!

j_man

You're welcome

j_man

Huh? Why not just use the cam sync signal from the OEM cam sensor (the one at the back of your intake cam)? This way you won't have to worry about mounting.

richyvrlimited

iTrader: (1)

cos he binned it

Plus if you're going to do it you may aswell use the more accurate trigger!

j_man

You've misunderstood what we're talking about. That's for syncing an engine cycle. It can't be more accurate than it already is.

Joe Perez

iTrader: (8)

Well, the short answer would be because I threw it in the trash after removing it. Getting a clean signal out of that thing had been the bane of my existence for some time, and the primary reason I built the 36-1 setup in the first place.

I guess I would get another one, I just really enjoy not having anything back there.

If I do go this route, I'll probably copy the early NB setup.

Actually, I wonder if I could put a sensor straight down through the top of the valve cover and trigger off of one of the cam lobes? That would be ****.