i think you are referring to the \"short nose crank\" problem.. i personally dont know much about it but see here
http://www.miata.net/garage/crankshaft.html
i think the problem was corrected mid 91 as i have a December 91 and i dont have the short nose crank
Cheers
Ajay
engine issue
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If it is a \"short nose crank\" it is possible the problem will occur. It only happens if you stuff up the reassembly when changing the front main seal.
Easy way to tell a short nose from a long nose (which is different to a big nose) is to count the numbers of holes on the pulley (the crank pulley: central and down the bottom). If it has 4 holes (89-mid 91) you have the short nose. If it has 8 holes (mid 91-late 93) you have a long nose. The later model 1.6L engines (which never came out here in Aus) had big nose cranks IIRC.
Boags
Easy way to tell a short nose from a long nose (which is different to a big nose) is to count the numbers of holes on the pulley (the crank pulley: central and down the bottom). If it has 4 holes (89-mid 91) you have the short nose. If it has 8 holes (mid 91-late 93) you have a long nose. The later model 1.6L engines (which never came out here in Aus) had big nose cranks IIRC.
Boags

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Re:
Craig wrote:Meh...just get the 1.8 NA sold from late 93 through to 97!![]()
Problem solved!
Big nose 1.6s and even 1.8s have had crank keyway failures. Much rarer than the small nose 1.6s though.
(mine broke)
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My car has 260,000km on it now and I just replaced the front main oil seal. As part of this I bought a new bolt and woodruff key, then used some Loctite and torqued it properly. The keyway looked as good as new, so I think it is only if someone touches that bolt that you have to worry. I think the yanks make the problem out to be much bigger than it really is (or they have more dodgy mechanics over there).
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I have a short nose crank and mine is fine. I get the feeling that more people have no issues rather than have problems.
Ben
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