Suprise 4A failure.

[Hen]

So I was quietly driving down a highway minding my own business when suddenly my engine cuts out (smallport 4AGZE in a Sprinter). A few lights come on in the dash so as I roll to a stop beside the road I think maybe one of the main fuses has gone.

However when I pop the bonnet it looks a little worse, both accessories belts are missing and it looks like the crank pulley is swinging free. So now I suspect a loose pulley.

But a little closer inspection shows that the crankshaft has broken right at the front of the engine. The timing gear and crank pulley are still firmly attacehd to the crank, it's just the crank is no longer attached to itself, as shown in the photos below. When I stopped it was only the plastic lower timing cover that kept the pulleys attached to the car.





And I have no idea what caused it. No (unusal) sounds beforehand. It had oil and water, cams still turn by hand, can't check if engine turns until I drop the box. Only thought is that maybe years of a too tight SC belt eventually took it's toll, but it sounds far fetched.

Anyone willing to suggest possible causes?

And also I want to let everyone know that Jez and Fergus (aka rallystanza and inertia) went ridiculously out of their way to help me out once things broke. Without hesitation they both took their entire Saturday arvo to run round town and deliver a car trailer over an hour out of town. So a big thanks to both of them.

Hen

[mr2gze]

Wow I cant say Ive seen that before.

I cant remember if you had a larger pulley or not?

edit. Pics look like it was a larger aluminum one?

[roadsailing]

shit!

i know clayton had issues with his crankshaft nose, but that was with a damaged key and munched out slot in the crank pulley, had to get a new one.

have you ever had issues with timing?

that crack looks old to me (rusty all over) but its hard to tell from a photo.

i'm tipping fatiigue over a long period of the time, baybeye the crank got knocked when they unloaded it off the overnight container from japan?

[brett_celicacoupe]

holy sheet!

could it be possible the crank pulley had been loose for some time?
it could have then enlarged the pulley hole slightly. this would put the stress on the outer opposit side of the shaft and inner adjacent side.

a kind of exaggerated pic but demonstrates the point. that inner contact may have slowly weakened the shaft in one point. and the continuous twisting would have been bad



have you inspected the pulley hole surface and the broken crank piece?


thats just my idea of a plausible cause

[thechuckster]

get some closeups (macro lens) and send to oldcorollas for opinion?


dumb questions:
does the crank still turn (e.g. starter motor)?
does the crack start from the keyway?

[Hen]

Brett, that's sort of the idea I had, but suprisingly the crank pulley bolt was still tight on the crank when it broke. I needed to get onto it with a socket to loosen it. Maybe not as tight as it should be (ie, not a total bitch to loosen) but definitely not loose.

It had been happy and untouched for three and a half years before deciding to take it's bat and ball and go home.

Yes it's a slightly bigger pulley. The biggest you can fit with the timing marker in normal position (bent a little for clearance). It made 10-11psi.

It's funny that the crank stub looks rusty. As you can see it's not like I wash it or anything. All broken parts are still in the back of the car and will be inspected more closely later. Other projects have taken priority unfortunately.

Hen

[oldcorollas]

from here (hard to tell from the pics but..) it looks like fatigue, growing from crack starting from the keyway..

there's like a "crescent" of fresh broken metal... that would have been the last bit that failed suddenly..

[RobertoX]

^^ just what I thought, it looks like its been happening over a long period of time due to the rust. There appear to be some beach lines (rusted) at the top of that pic originating from the keyway (this indicates fatigue, from a change in loading condition) and as you follow it clockwise it is very shinny which is possibly a bit of 'burnishing' where the fractured metal surfaces rubbs together and buffs it up as the shaft bends around a lot at the small piece holding it together. Then the final fracture is the dull clean metal part on the bottom left

is a tad hard to tell from that pic though

[30psi 4agte]

That is a absolute ripper!


I agree fatigue is the prob cause, possibly from the larger pulley and like you said mabe the belt was abit tight.

[oldcorollas]

so is this going to be more of a problem on GZE's than GE's?
any idea how tight the belt is in terms of tension?

would it be worht setting up an idler of some sort on the other belt to provide an opposite force.. to try and even out the force on the crank?

or go to toothed belts to reduce the tension required?

[30psi 4agte]

I think the toothed belt is the best possible way to go when S/C but space and cost is always a factor with this type of mod.

There is deffnate merrit in trying to create an idler setup to distribute the load evenly. Depending on how the S/c belt is setup it may require quite some tension to stop it from slipping..... esp when the pulley is Oversize like hens.

OC: "so is this going to be more of a problem on GZE's than GE's?'

Sorry mate cant answer that one this is the first snapped crank spout on a 4a i have seen.

Snapped cranks
GZE......1
GE........0

[stradlater]

Too much boooost bro. ;-)

[TooF]

ouch,

my gze tore the key out of the crank and hence munched up the keyway but nothing quite that dramatic.

[TA-022]

dang .. did it dosse?!

[4agte]

i vote keyway failure