7 replies to this topic

[alex-cooper]

Whilst driving along a gentle left hand bend in a 40limit (being rather sensible!) there was a large bang, quickly noticed I had no oil pressure, stopped the engine and got out to find my sump had dumped it's contents onto the road.
The engine is a stage 4 mini mpi, using the standard box and diff. The engine was new 2000miles ago, at the same time the box/diff was inspected and everything seemed to be in good order.

Has anyone seen this damage before? Is it likely to be a blown diff?
Is it true you are unable to replace just half of the diff casing due to them being a matching pair?
Will the engine need to be removed to get it sorted?

Many thanks in advance!

[alex-cooper]

Sorry struggled to upload a photo, please see my later post with the photo

[Cooperman]

The engine will almost definitely need to be removed and probably lifted from the gearbox.

The last time I had this, a crownwheel bolt had come loose and the head broke off, the crownwheel then forcing it through the bottom of the gearbox casing. You need to see where the actual hole is before proper advice can be given.

The gearbox casing and diff cover are machined as a matched pair. However, the mis-match is only of consequence in terms of the mating faces for the diff output covers. Where it is machined to clamp the diff bearings is not really an issue - well, I've never found it so. The problem can come with slight oil leakage when the diff output covers are bolted up. You can lightly linesh out some slight amount of 'step', then use a quality gasket sealant to make a good seal.

The purists will tell you this is not possible (hey are all rich enough to afford a complete replacement gearbox casing) but I can confirm that it is no problem and I've done it on rally cars which have damaged diff covers and have never had any issues.

 

Edited to add:

 

Just seen the photo. You need a new diff casing, but before that you need to strip it out after taking out the engine, to find out what caused this. That is an unusual failure mode and something inside must have broken up.

You might get away with leaving the engine on the box.

Edited by Cooperman, 06 May 2014 - 11:43 PM.

[Tupers]

I saw the picture in you're other thread and you're differential pin has removed it's self from the diff and torn through the housing. I've seen it a couple of times but bother were young lads doing J-turns in car parks. 

 

You're lucky the diff case will need replacing along with the diff pin and some other diff components but you wont know the full extent until the gearbox is out and stripped down. 

[Tupers]

Check out the link to an exploded diagram of a diff on the Mini Spares site. Clicky
 
Once the diff is removed I'm sure you'll find the roll pin that holds the diff pin in place (number 11) has snapped and allowed the diff pin (number 10) to fly through the diff car hence the long hole. 
 
Personally I would be splitting the engine off the gearbox to make sure I got any pieces of stray casing or pin out. 

Edited by Tupers, 06 May 2014 - 11:58 PM.

[alex-cooper]

Brilliant, thanks for your replies. I shall start removing the engine.
Do you have any advice on what diff is best to replace it with? 4 pin?
The mini is only used for fun and I will probably split the box off the engine to fit different pistons to allow my to also fit my charger at the same time.

[Cooperman]

The X-Pin diff is the answer to high wear rates on the diff pins in high powered engines.

Not necessary in an 850 or 998, but a really good idea for a 1275, especially if modified.

I'm the only person I've heard of who has managed to break a X-Pin!

[Alex_B]

Ahh excellent fun when the diff decides it no longer enjoys being a diff! I had the same issue last summer, doing about 50 it felt like I went over a large bump in the road and caused the car to jump, turned around and drove past where it happened and couldnt see anything. Got back home to see oil pithing out the bottom of the engine and on further inspection it was a tiny hole in the diff casing where the roll pin had failed and went out the casing. 

I ended up using a complete diff from another engine and had the lot swapped in three days before a car show and had no issues with a non matched diff casing in 10 months of driving since. 

But I would recommend checking the gearbox carefully if you are splitting the engine and box, I found a lot of aluminium shards in mine where the diff pin had partially pulled out and taken some casing with it!