Pulley Wobble/Short Nose Crank questions

[Bob K]

Hi Zorruno,

Wot is the "short crank nose problem" you refer to?
My MX5 is an early 1989 and I'm concerned! My car also suffers from a buzzing/metalic rattling noise on deceleration in the lower gears. I hope this is a loose exhaust heat sheild and not something in the gearbox or is it related to the "problem"?

I would appreciate your comments.

[Shermio]

Although I know nothing about the NA MX-5s here is a good thread on what it is and if you do a search on the NA forums you will have a better answer

90-91 Short Crank Nose Prob

Photo of what it is on a 94

And do a search here!

[Vince]

Hi Bob, for what it's worth, here's my opinion. The Americans seem to make a big issue out of it, bigger than it needs to be I think. If you read the article that Shermio just sent thru, they reckon it only affects about 1% of early cars, 89-91s, but some of the photo's are of 93+94s which theoretically should'nt cause a problem! I would'nt worry too much about it, it may cause a problem at some stage, it may not. There are hundreds of early MX5s running around in NZ without any problems, in fact we've got two of them, an 89 and a 90, and we bought the second one knowing about the supposed short crank problem. I don't see it as an issue.
There is someone in Auckland who has I understand, repaired a couple by building up the crank nose and remachining, while the engine is still in the car, something the Americans say can't be done! The name Taylors rings a bell, but I'm not sure, someone on this list will know who it is, as it has been discussed at length several times in the past. If your car's running fine, I would'nt worry about it. You could get hit by a bus one day, but you don't lie awake worrying about that do you?
Cheers,Vince.
 

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[Fletch]

I've been hanging around the US mailing list and forum for about ten years now....

That 1% number was only ever a wild guess, and it was a wild guess over 8 years ago when the artical originally appeared. Since then, only more have failed. How many? Who knows?

I know of at least 5 short-nose failures just in Auckland.

Thats not a huge number, but its enough to be of concern. But theres no need to panic. There is a well known and documented preventative maintenance proceedure, and following it will reduce your chances of the crank-nose failure to essentially zero.

Fletch.

[Bluesgeek]

Personally I would recommend anyone with an affected model to strongly keep an eye out for pulley wobble, I had to repair mine a year or so ago.

[Fletch]

I would suggest replacing the bolt and using loctite BEFORE you detect any pulley wobble.

Fletch.

[Growler]

I have done 5 engine swaps for various members now because of the crank problem.
The main problem is the cam belt pulley keyway being too short and flogging out. (It either flogs out the keyway on the crank or keyway on the the pulley).
You can fix them but it generally is a short term remedy. You can pick up second hand engines for around $500 - $750 (92' onwards) and an engine swap takes me about 15 hours by myself.

Growler.

[Bluesgeek]

I would suggest replacing the bolt and using loctite BEFORE you detect any pulley wobble.

Fletch.

indeed