identifying modified short nose crank?

[emilmh]

Hey guys,
Just a quick one. I'm looking at buying an mx5. It is an import and built in 1990. From factory it came with short nose crank, but a visual inspection of the crank shows it to be a long nose (8 slot) crank.

The question: Is there a way to know "what" has been done? For example: Is it possible to put a long nose crank pulley onto the short nose engine? or does it mean that the whole engine has been changed to a long nose engine? (Given the age of the car, it seems completely plausible that the engine may have been swapped at some time in its life) Can I do some form of check by comparing engine and vin numbers?

Any help would be appreciated.
Cheers,
Emil

[StanTheMan]

as far as i'm aware the pulley is not interchangeable.

[Juffa]

Hey guys,
Just a quick one. I'm looking at buying an mx5. It is an import and built in 1990. From factory it came with short nose crank, but a visual inspection of the crank shows it to be a long nose (8 slot) crank.

The question: Is there a way to know "what" has been done? For example: Is it possible to put a long nose crank pulley onto the short nose engine? or does it mean that the whole engine has been changed to a long nose engine? (Given the age of the car, it seems completely plausible that the engine may have been swapped at some time in its life) Can I do some form of check by comparing engine and vin numbers?

Any help would be appreciated.
Cheers,
Emil

It is also possible that the crankshaft was replaced, but as you have said a replacement engine is more plausible. Does the engine number match the registration details of the car? If the engine was swapped without notifiying the state authority then the number won't match. If they do match it might be that the state authority was notified, assuming that the engine has been changed. For a final confirmation, try a Mazda Dealer. The dealer might be able to confirm if the engine number is the original one against the VIN?

J

[Matty]

FYI, the 8-slot is a "big nose", not a long nose. The long nose was an interim fix, same diameter as the short nose, but .. uh... longer. And not as strong as the big nose.

It's most likely an engine swap. To change the pulley you need to (pull the engine,) change the crank, (line bore the block and change all the bearings), change the timing pulley, woodruff key, bolt, water pump (I think) and oil pump.

[jerrah]

And how many slots does a big nose have?

[emilmh]

Hey guys.
Thanks a lot for your information. It is greatly appreciated. The car has only had one owner since importing and the engine swap would have been done in japan, so all registration/complicance in australia would have been done with the new engine number.
If engine is the original should the number match the car vin? So they are matched durring assembly? I would think it unlikely that the numbers and consequently the engine and car body would be matched due to manufacturing processes/inefficiencies.

Cheers,
Emil

[madboy]

I have a 90 roadster as well, has an 8 slot pulley, I was under the impression that at some point in 1990 they changed to this crank/pulley. As for using the VIN to gather info on the car, forget it. Unless you know someone in Japan who can search their records because Mazda dealers will not be able to give you any info on it.

I had this issue when replacing the cam belt on mine, I wanted to replace the woodruff key and the pulley bolt. We could not find the correct key so I reused the one that came out as it was in perfect condition and we had 2 goes and getting the correct bolt.

[Steampunk]

I have a 90 roadster as well...

You have or you HAD?

If the former, then welcome back to the fold

[madboy]

I have a 90 roadster as well...

You have or you HAD?

If the former, then welcome back to the fold

still have m8, I lost my job in May and lost interest in a lot of things very soon after, still no job but working myself back into sanity again

[rodent]

I believe my first NA6 had a build date somewhere around October or November 1990. Came stock with a big nose crank in it.

[GS]

Theres a good summary on the NA6 crank pulley on the big forum. Although as its a US writer you have to translate his references to the model years affected:

http://miata.net/garage/crankshaft.html

Does anyone know if Mazda fitted any long noses as a dealer service item in Australia?

A SUMMARY OF THREE DIFFERENT CRANKSHAFTS

There are 3 crankshafts for 1.6 liter engines. Some people mention "short" and "long" when they really mean "short" and "big". Watch for this when you search archives. The crankshafts are the short nose, long nose, and big nose (Figures 1, 3, and 5 respectively). The short nose is fitted on early cars, the long nose is available primarily as a service part for those cars before the VIN cut in 1991. The long nose crankshaft is directly compatible with a short nose engine with no additional parts swapping required. The short nose and long nose use the same pulley bolt and torque. After the VIN cut, the big nose crankshaft is fitted with a bigger bolt. The nose of this crankshaft is larger diameter so a different engine front cover/oil pump is needed. The new oil pump has a bigger hole through the georotor to fit over the larger crankshaft. The big nose bolt has a larger threaded diameter, large shoulder diameter, and higher tightening torque. All of the bolts have 21mm heads.

Also the short nose crankshaft uses the lower timing belt cog as a structural member, that is the cog is bolted to the crankshaft, the accessory pulleys (one v-belt and one serpentine) are bolted to the cog. The timing belt cog, in addition to its timing belt rotational duties, must support the rotational and bending forces of the accessory belts. After the introduction of the big nose crankshaft, the timing belt cog has only one job, to rotate the timing belt. Mazda introduced an additional part they call a "pulley boss" (Figure 5). The pulley boss is a sturdy cast hub that forms a mounting flange on the front of the crankshaft. It is bolted to the crankshaft. The timing belt cog is bolted to the back of the boss and the accessory pulleys are bolted to the front of the boss.

[emilmh]

I actually ended up buying the car that I mentioned in the start of the thread, and it is "overdue" for a timing belt change. Everytime I think I understand the whole which crankshaft is which, I read it again, then question myself. Figuring out what to do with the crankshaft is the only thing which is holding me back getting all the parts i need for a timing belt!!
I have read all the recommended articles on crankshafts, but I don't think they are as obvious as the authors seem to think.

So to recap, I have a 1990 car with an 8 slot pulley. If I understand correctly this is known as the BIG nose crank?
When I do the timing belt I plan on replacing the crank shaft seal, which requires removal of the timing belt pulley/bolt and woodruff key. To be on the safe side I would like to replace the pulley bolt and woodruff key.
Essentially what I would like to know is:
* What size/type bolt do I need? (I get the impression sometimes that there are 3! different blots for small nose, big nose and long nose. How do you differentiate between the different bolts?)
* What torque is required for the bolt? (I believe 80-87 footpounds? Is this correct for 1990 with an 8 slot pulley??)
* Is the woodruff key the same? (I haven't heard anything about this being different, so I assume it's the same)

Any confirmation on these issues would be greatly appreciated.
Cheers,
Emil

[adamjp]

* What size/type bolt do I need? (I get the impression sometimes that there are 3! different blots for small nose, big nose and long nose. How do you differentiate between the different bolts?)

Go to Mazda, there are two bolts listed for the NA6 MX5 engine. Choose the younger of the two bolts.

* What torque is required for the bolt? (I believe 80-87 footpounds? Is this correct for 1990 with an 8 slot pulley??)

That is mentioned on the web - google is your friend.

* Is the woodruff key the same? (I haven't heard anything about this being different, so I assume it's the same)

No, but you should be able to re-use your existing key. It is not necessary to replace it. If you must replace it, again get the younger one from Mazda.

[emilmh]

* What size/type bolt do I need? (I get the impression sometimes that there are 3! different blots for small nose, big nose and long nose. How do you differentiate between the different bolts?)

Go to Mazda, there are two bolts listed for the NA6 MX5 engine. Choose the younger of the two bolts.

* What torque is required for the bolt? (I believe 80-87 footpounds? Is this correct for 1990 with an 8 slot pulley??)

That is mentioned on the web - google is your friend.

* Is the woodruff key the same? (I haven't heard anything about this being different, so I assume it's the same)

No, but you should be able to re-use your existing key. It is not necessary to replace it. If you must replace it, again get the younger one from Mazda.

When you say "younger" wouldnt that be the small nose?? (with me having the big nose, wouldn;t that make it the wrong part?)
I have googled heaps and read heaps on miata.net after the right torque. As i said I'm quite sure its the 80-87 foot pound. (but the vaugness comes with the 4 slot and 8 slot small/big nose difference) I'm basically after some confirmation, as a lot of the information is not in a solid straight forward answer, but reliant on piecing together lots of different sources or topics from within the one piece of info.
I also thought the woodruff key was prone to wear. If thats not an issue, i will just forget trying to get it and just get a new, pulley bolt as insurance (also a new bolt increases the accuracy of the torque due to lack of corrosion and junk etc on an old bolt.

[adamjp]

Sorry, I always understood younger to mean 'less old', 'born later'. Another way to put this is that you want the bolt from the later VIN series, not the early VIN series.

You must have a new bolt anyway. They are unforunately a one-use bolt.