Short nose 4 slots
Big nose 8 slots
Problems with LWSC engines
It was thought that this affected a minority of engines, and was down to poor maintenance, however this was somewhat undermined when the crank of John Cookson’s (MX5OC Tech Whizz) own 89 Roadster went:
His response (and current thinking:
You will mainly be interested in this if you have an early (pre-Spring 91) car - but I am starting to receive reports which may make it relevant to later 1.6 engines and even 1.8 - I’m sure you will hear more about why)
What is LWSC syndrome?
Failure of the drive between crankshaft and cam pulley (and auxiliary pulleys) resulting in, initially loss of some power, and ultimately, all power!
What causes it?
Very simply, the crankshaft pulley bolt comes undone.
But the real question is, why?
This is my idea, so I offer it along with all the other theories that abound. Firstly, I do not now believe that it is a maintenance issue, as is the common opinion, although poor maintenance (in particular, incorrect torque settings on the crankshaft pulley bolt) could cause it. I believe that hundreds, and possibly thousands of early engines have failed due to poor production tolerances. Basically, the crankshaft pulley is a poor fit on the end of the crankshaft. It is too loose. It should be a very tight fit, but even new pulleys on an unworn crankshaft end can be moved laterally by a detectable (and measurable) amount. In my case, there was 5 thou (ins) clearance between a new pulley and the crankshaft.
Therefore, when the bolt is tightened, the pulley cocks off to one side. This results in out of balance forces on the pulley due to rotational imbalance - the pulley assembly is very heavy, and drives a lot of kit - alternator, water pump, power steering pump, aircon pump (and sometimes a supercharger!) as well as two camshafts with 16 valves. And there’s a big inertial force every time you start the engine. These forces all combine to hammer away at the bolt, all the while trying to undo it. Eventually, it bows to the pressure, and loosens. The bolt is dry (ie not “Loctited”, so it unscrews easily once started.
Now the real damage starts. The crankshaft does not extend the full depth of the pulley bore, and because the pulley bore is a poor fit on the shaft, the pulley starts to wobble on the end of the crankshaft. The key (incidentally a Feather Key, not a Woodruff key as it is universally described) now takes all the drive of the crankshaft on the pulley, unaided by the clamping force of the bolt. It wears - quickly. As it wears, it eats into the drive face of the key slot in the crankshaft, and the key itself begins to disintegrate. The wear on the drive face of the slot in the crankshaft allows the pulley to rotate slightly anticlockwise relative to the crankshaft, effectively retarding valve opening, resulting in very gradual, and for a while barely noticeable, loss of power.
But we are told not to take the pulley off even when changing the cambelt, so all this goes on hidden from view.
Eventually, one of three things happens. The crankshaft nose breaks off, or the keyway tears out, so that there is no longer a drive face. Either of these two is terminal, and the only possible practical repair would be to fit a new crankshaft. This is uneconomic in most territorities, as good condition used engines are readily available at much lower cost - so you replace your engine. Or, and this is what usually happens, the key eventually wears to such a degree that it falls out into the void between the end of the crankshaft and the bolt. Drive to the camshafts then fails at once, and the engine stops.
Why doesn’t this happen to every engine (re Bob Hall’s comment - some engines…high mileage…this is testimony) ?
Because of production tolerances. Some pulleys are probably fairly tight on the crankshaft - if the pulley bore is at or near its lower limit, and the crankshaft nose it at or near its upper limit. If the pulley is tight on the shaft without the bolt, the imbalance forces will be much less, and the clamping effect of the bolt will be less critical.
So what do you do now?
Don’t take it to a Mazda dealer. Their solution so far has been to either fit a new pulley, bolt and key and reassemble and hope for the best. Sometimes they suggest glueing the key into the crankshaft slot, and indeed most remedies for the problem described on the Internet are variants of glueing. These courses of action are doomed to failure, IMHO. Amazing adhesives are available, but most of them depend on extremely stringent conditions in which to work, and/or stringent material specifications. The capabilities of adhesives do not extend to fastening ill-fitting keys into worn slots in high-force internal combustion engine conditions - or to anything else involving steel parts in engines.
Unfortunately, the remedy requires engineering, or at least fitting skills. Firstly, find a time-served engineering fitter. Supply him with a new crankshaft pulley and bolt (and incidentally replace the crankshaft oil seal while it is exposed).
He must then make a stepped key out of “key steel” - available from engineering suppliers and designed for the purpose. This key is wider where it fits into the crankshaft slot - in my case the slot was worn 20 thou (ins) (about 0.5mm) wider than its standard measurement of 5mm (sorry for mixing units). Furthermore, the side of this part of the key must be profiled to fit the wear pattern on the worn face of the crankshaft slot. That is the bit that requires the real skill. The other part of the key fits into the standard slot (5mm or so) of the pulley slot. In other words, the key is L-shaped rather than square (or rectangular - whatever) (But when the slot is at the top of the crankshaft, the base of the L extends to the left rather than right as you look at it, because it is the face of the crankshaft slot to your left which wears (I will produce an illustrated version of this which will be clearer))
Next he must fit the pulley to the crankshaft with a shim. Mine required a 2-1/2 thou (ins) thick piece of shim steel (again, designed for the job and available from engineering suppliers) inserted into the bore of the pulley to make it a tight push fit onto the crankshaft. But it mustn’t be too tight - otherwise the shim will just push out or ruck up at the back of the pulley. Selecting the correct thickness of shim requires accurate measurement of the clearance and careful trial and error. The shim must extend all the way round the pulley bore from one edge of the key slot round to the other edge - a full ring apart from the slot. The shim should be the full depth of the crankshaft penetration into the pulley bore.
On assembly, a little Loctite “Bearing fit” should be used where the new key fits the slots in crankshaft and pulley. The pulley will need to be partly pushed on by hand, and partly drawn on by the bolt - if it can be pushed on all the way by hand it is too loose. Use Loctite Thread lock material on the threads of the bolt.
To tighten the bolt, a tool needs to be made to lock the pulley and crankshaft while the bolt is tightened. It is easy to make a tool to bolt to the face of the pulley and brace to an engine component. (In my case we used the alternator lower bolt as the brace point) It is not possible to get an accurate torque setting against the “mush” of clutch, transmission backlash and tyres, so don’t just depend on putting it in gear. The torque must be set accurately to the range 80-87 ft lbs (110-118 Nm). This setting is critical, and the wrench must be calibrated. (NB the setting only applies to early engines, but so does the detail of the whole of this piece)
Later removal of the pulley will require the use of an extractor. (9/01)
Does the 4 slot against the 8 slot rule still apply. Our car chassis number is somewhere in the middle of all this but the pulley definately has 8 slots. The bolt at present can not be undone by hand… Do you think 14 deg, intake mods, exhaust mods compound the problem?, and what about really hard driving such as track days ?? (9/01)
AFAIK the 4 slot v 8 slot rule is correct. (It was Richard Ducommun who pointed this out to me, and I’ve looked at quite a few cars since.) I don’t think N/A mods on this side of reason will significantly affect things. Driving a supercharger might, because it adds more load to the pulley. But I haven’t heard that supercharged cars are any more prone to failure. On the other hand, most s/c cars are mollycoddled weekenders (by which I mean a high ratio of maintenance to mileage!) that only do a few K miles each year (ducks quickly). I think it’s mileage that kills the crank/key. I’m not sure I’ve completely convinced Sheila that it was pure coincidence that it failed at Silverstone. It could have happened anywhere! So, er - well I suppose hard driving does add stress. But who has a 5 and doesn’t drive it hard?. One day it’ll be a small metal cube anyway. So enjoy it while you can! (9/01)
I don’t think that it is a good idea to mess with the bolt unless you replace it. I think its tensile strength is marginal and it is prone to stretching - and that will be fatal.
And most people don’t have a calibrated torque wrench.
I simply don’t have enough evidence about later engines yet. Anyone who has replaced a cam belt on a 91-94 1.6 - how tight was the pulley on the crankshaft - did it just fall off when you undid the bolt, or did you need to extract it?
Later engines have a tighter, stronger bolt, so it is less likely to come undone, and the crankshaft nose penetrates the pulley bore to nearly its full depth. These two factors make the problem much less likely on later engines, or at least much less likely to develop rapidly - I think.
Also the cam belt needs replacing at 60K miles, so you take the bolt out and re-torque it. And that bolt, being stronger and tighter can stand more abuse and the torque setting is much less critical - maybe not the FT standard, but anyway - it doesn’t need a calibrated torque wrench.
Mazda did, to give them their due, address the problem fairly smartly. How did they know about it? (9/01)
I have heard first hand of one or two cases of cranknose wear on post-91 engines in the UK; but this DOES seem to be down to poor maintenance practices, rather than an inherent design flaw.
A good article on LWSC problems on Miata.net