REPAIRS PAGE 14
CRANKSHAFT PULLEY PROBLEMS
Anybody had any problems with this pulley?
- if so let me know as I suspect it has a slight design weakness that could
possibly lead to failure. Hence my interest in feedback to see whether it really
has affected members or is it just a ‘one-off.
If it is just a ‘one-off - then I’m afraid it was me! The pulley on my N/A failed
recently, but luckily it was in a non-catastrophic way.
As such this might sound a trivial matter - but if it had totally disintegrated at high
rpm then it would have fired off shrapnel at about 200mph. In this case quite
apart from general flak damage to the engine bay innards, it could also sever
the high pressure fuel lines and cause a flash fire which would continue to be
fed by the pump. Also the driver is right in line with the pulley - and whilst
the bulkhead and seat back will provide some protection, I reckon that that a
sizeable chunk could still come through the seat back at a speed that could do a
bit of bodily damage!
To add insult to such injuries the engine will also almost certainly be U/S as the
crankshaft nose end could be damaged beyond repair.
Grim reading - but a possible event! A little precautionary checking is definitely
recommended here to avoid such nasty consequences.
It is fairly easy to do - grab the pulley and try to rock it as if you were trying to
simultaneously rock and pull it off the crankshaft. It should be absolutely
solid - any movement spells trouble and requires prompt corrective action - ie pulley change.
The cause of the problem is that the pulley looks somewhat under designed.
It is a conventional cast steel 4 spoke design - but it has a double drive rim (the 2nd
rim is to drive the a/c compressor if fitted.) This clearly adds extra weight
and it is ‘overhung’ -ie well beyond the crankshaft that is supporting it. This
might not sound like much when you’re looking at a static engine - but at 6500+
rpm it's a different ball game! At these rpm the engine is literally starting to
flex - both the block and the crank. (This phenomena is not unique to Mk1’s - it
is quite usual on high revving engines.) This is fine if the design is right -
but the pulley looks bog standard 4-AFE Corolla - which is way down on power and
revs. Add to this the fact that 2 of the spokes are tapped M8 (for a hub puller)
which makes them even weaker -then the design looks a bit marginal on a Mk1. The
crank flex at high revs causes the pulley to ‘wobble’, creating cyclical stresses on the spokes.
The failure mode on mine was fatigue across the 2 spokes with the M8 tappings -
which are points of weakness, and then the other 2 spokes were overloaded/and
also fatigued through. I was lucky - the cracks ‘interlocked’, leaving a loose
but roughly whole pulley. A slightly different cracking pattern could have
resulted in disintegration.
I didn’t actually notice any sudden major symptoms - just a tendency for the fan belt to
start to slip, and a slight increase in roughness at higher revs.
Having discovered it - I fixed mine by fitting a S/H pulley from
Fensport. Not that there is anything that says how long it will last -but at least it was
in one piece when I fitted it!
(The job wasn’t that difficult but it does need the right tools including a barring lever
to stop the pulley from turning when trying to undo the crankshaft nut - and its
on mighty tight! A suitable hub puller will also be needed to pull the pulley off the crank.)
Hopefully though it was one of those random ‘one-off events that isn’t a more general
problem. That's why I’m hoping I don’t get any feedback comments on this - its a
case of no news is good news!
ALAN JONES