Out of interest (I hope I don’t jinx my car!), but what proportion of the early Mk1s are likely to suffer from this, and does it just happen suddenly or over a period of time?
Cheers
All 1989 and certainly most 1990 cars (maybe into 1991) had the earlier type of crankshaft. For some, the nose wear had occurred after a cambelt change, leading to mechanics being blamed, but others occurred with cars that had never had a cambelt change. In principle, any MX5 NA/NB can get crank nose damage if the belt is changed badly.
You don’t hear of it so much now, so I suppose most of the affected cars have either had repairs, or have been condemmed. If you look in the FAQ, there is a thread about the affected engine number.
Cheers for that!
Or are still cracking on after 120k miles, 25k of that with a supercharger fitted. They don’t all fail.
So, in theory, if mine has had 2 cambelts in its life already, if it was going to go, it would have done by now…
Mine’s still going strong at about 110k too - and it’s a Sept’89 Roadster. 23 years young.
Mine’s still going strong at about 110k too - and it’s a Sept’89 Roadster. 23 years young. Used daily as well as for long haul hol’s.
That depends on how the belt was changed.
Members of the Miataforum noticed the first crank nose failures during 1994; these were on cars that were still on the original belt. But, Mazda introduced a fairly significant redesign of the crankshaft in 1991 (with rumours of an interim change never being substantiated). The reason for this change has never been stated, but the result was that crank nose damage is less likely (still possible, but it can be blamed squarely on the mechanic who replaced the timing belt). Mazda has never admitted there was an issue with the crankshaft. One of the Miataforum members, Lance Schall, picked up on the fact that Mazda issued an updated set of instructions for the timingbelt for the 323 B6T engine, but never for the Miata B6ZE. Cranknose failures are virtually unknown amongst the 323 community. A poll on Miataforum conducted amongst enthusiast owners (ie. the sort of owners who would be expected to be fussy) indicated maybe 20% were affected, but it was a small sample size, and those owners didn’t represent typical MX5 owners. And it wouldn’t include ex-Miata owners burnt by the experience of replacing a crankshaft.
If the reason Mazda changed the cranknose design was to improve reliability, I’d be interested to know how many failures would trigger such a change,18 months after a car was released. After all, Mazda wouldn’t knowingly release a deficient car.
There are at least two unofficial ways to change the belt on these early engines, maybe more, none of which adopted by Mazda. If I was to buy a higher mileage car, I might be feeling I was on borrowed time, and maybe the crank will be beyond even a Loctite fix. If I knew exactly how those belt changes were made, and a belt and braces approach was taken. I’ll probably be fairly relaxed. I wouldn’t touch an early car with an unknown history. But thats academic, as it will probably be rotten.
Its not a problem due to batches of crankshafts being defective, but due to a poor design, excerbated by poor assembly, whether in the factory or by the aftermarket. The design change must have reduced the chance of a mistake during assembly leading to a warranty claim.