I am thinking a slight miss match or maybe a foreign object. (a roller bearing from a lifter or a gearbox bearing?)

It reminds me of the JP cam gears in my old HQ, the steel driving gear stripped and the alloy driven gear chipped some teeth. These cam gears needed careful bedding in before they were capable of tanking any real load.

I had a good look at the gears today, the pinion looks to be through hardened, unusual for a gear. The teeth have all just broken off, they don't look like a fatigue crack then break.

I'd say the gearbox housing broke because a broken pinion tooth got caught in the crownwheel on the way out.

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DrMini- 1970 wasaMatic 1360, Mk1S crank, 86.6HP (ATW) =~125 @ crank, 45 Dellorto (38 chokes), RE282 sprint cam, 1.5 rockers, 11.0:1 C/R.

I concur doc!

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1969 Cooper "S"
1967 Mini Deluxe
1973 Clubman Van (the fleet spare)
1978 ex 1275 LS ("Wizard" Eaton Supercharged)
2015 HSV GenF GTS(occasional drive & tow car)
2019 MINI F55 Cooper S

This is very interesting, any chance of some more Photos Maybe square on to the teeth,
Also I would be very interested in knowing any part Number that may be on the Crown Wheel,
It is interesting to note that rover done away with using four bolts in the bearing retainer, This was done I understand To stop the gearbox case cracking in that area. which happened more often when bigger wheels were fitted, I would ask Kev, if this is worth any thought when choosing You next Case

_________________
" A Hundred Years From Now It will not Matter what my Bank Acount Was,
The Sort Of House I Lived in, Or The Kind Of Car I drove ... But The World May Be A Better Place
Because I was Once Important In The Life Of A Child"

Just as a matter of interest Kev, Did You ever come across the problems caused when a Borg warner crown wheel was mixed with a BMC pinion or visa versa.
very rare today but a bit of a problem back in the day, Just interested in what You
may have experienced

_________________
" A Hundred Years From Now It will not Matter what my Bank Acount Was,
The Sort Of House I Lived in, Or The Kind Of Car I drove ... But The World May Be A Better Place
Because I was Once Important In The Life Of A Child"

hi michael
im assuming this diff was a new one, if so they are aftermarket and not correctly heat treated, i know that link automotive initially used a few of these c/w and pinions on there supercharged minis and had exactly the same problem (stripped teeth),from what i understand they will only use original/genuine units which of course are no longer availiable .
cheers josh

John, I have never matched odd pinions and crown wheels, any I strip from a box I cable tie together as a set.

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DrMini- 1970 wasaMatic 1360, Mk1S crank, 86.6HP (ATW) =~125 @ crank, 45 Dellorto (38 chokes), RE282 sprint cam, 1.5 rockers, 11.0:1 C/R.

Hi Josh
Yes I purchased a new CW and pinion set from a UK mini specialist with the expectation it would last longer than 12 months. I now have another CW and pinion set from hopefully a better supplier, but only time will tell.
I am continually surprised at the sub standard parts being supplied from the UK
Probably why this topic will e around for some time to come

_________________
1969 Cooper "S"
1967 Mini Deluxe
1973 Clubman Van (the fleet spare)
1978 ex 1275 LS ("Wizard" Eaton Supercharged)
2015 HSV GenF GTS(occasional drive & tow car)
2019 MINI F55 Cooper S

Indeed I find more and more crap arriving, I have started sending it back which is a pain in the backside.. Minisport UK are the worst to deal with for returns, no problem taking money off my card yet to try and put it back on they seem to have all sorts of problems!

_________________
1965 Riley Elf
1974 Ex Army Moke
1997 Rover Cooper
2002 JCW Cooper
2003 JCW Cooper S

Yes Mate I think we all do , I am Sorry Kev I was talking about New Gears

_________________
" A Hundred Years From Now It will not Matter what my Bank Acount Was,
The Sort Of House I Lived in, Or The Kind Of Car I drove ... But The World May Be A Better Place
Because I was Once Important In The Life Of A Child"

".....yet to try and put it back on they seem to have all sorts of problems!"

Assuming the parts arrive - and fail - before you the CC payment is due you just advise the bank that the parts are not as advertised and refuse to pay that portion of the card bill when it arrives....

The bank generally doesn't pass the money to the supplier until you cough up - so you let the supplier know that you are refusing payment and ask what they want to do.

Its not you responsibility to send back a defective item....

Cheers, Ian

Here's another couple, more grist for the mill.

1. Aftermarket spin-on filter housings.
Thread for the pipe nipple in the original Mini housing was 1/4BSP.
The ones masquerading as replacements now (I think from Minis***** UK, but bought local this week) have what appears to be an M14x1.5 tapered metric thread in them.
Their website says it is a 1/4 NPT tapered thread but this size tap rattles around in it.
This is the 2nd new one I've found like this.
If you screw an original Mini 1/4 BSP flare nipple (or any other 1/4 BSP one) in there, it sort-of fits, but really there is only the innermost thread or 2 holding it. It falls 1/4" into the hole before any threads engage.

I'm putting a fitting in for a Pirtek hydraulic hose, it looks like I'll be tapping the housing out to 5/8 UNF (same size as the block fitting) like I did before.
More work, on NEW parts to make them serviceable. Sorry, not good enough.

2. Minispares 1.5:1 forged rockers, C-AHT436
I was warned that the valve lift on currently sold ones (unlike those sold years ago) was all over the place, so after bolting a set on a fresh motor, I checked all the lifts. I used a fresh RE13 cam and checked each rocker in turn on the #1 exhaust valve position (easy to test and remove each time from there).
With .019" rocker clearance, they ranged from .416" to .438" lift and I wondered WHY...?
a. All the adjusters were .020" undersized on the threads and loose in the rockers.
b. 7 of the 8 adjusters were bent in heat treatment.
c. All 8 nuts were loose on the threads (est 50% thread engagement).
d. The nuts only touched the rockers at 1 point, because where they seated on the rocker was not machined square to the threads.

After replacing all 8 adjusters and nuts with A+ ones, and machining the top of the rockers square where the nut sits, the lift range improved to .419" - .433", with most in the range .424+ - .430".
Worth using now after this work, but not perfect.

I now wonder how good the cheap roller tip ones are, eh... watch this space...

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DrMini- 1970 wasaMatic 1360, Mk1S crank, 86.6HP (ATW) =~125 @ crank, 45 Dellorto (38 chokes), RE282 sprint cam, 1.5 rockers, 11.0:1 C/R.

Thanks doc this is the sort of information we need. There has been far too many thousands of dollars wasted on inferior crap products sold as replacement parts. This should be made a sticky like on other car forums I frequent so folks know what not to waste their hard earned cash on.

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1965 Riley Elf
1974 Ex Army Moke
1997 Rover Cooper
2002 JCW Cooper
2003 JCW Cooper S

Doc "were bent in heat treatment."
I wonder if that is why the layshaft that I bought from them was bent like a banana. I did get a replacemnet though, six months later and numerous emails later.

My new minilife wheels arrived from said mini supplier, after having the tyres fitted I found that 2 of the wheels had very loose centre caps. After playing musical caps I found it was the actual wheels, the ridge had been miss machined! After lots of emails, calls and false promises I got 2 New wheels and a tyre thrown in FOC to use so I can use as spare ob one of the faulty wheels! Was a yoko 032 too!

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New from the UK and wanting a NICE little British car!