Gearbox Like Butter
Turbo Mini Forums

I'v been rebuilding the gearbox slowly over the past week or so with relative success, apart from breaking a bearing which cost £40 to replace and today I started to put it all back together.

Everything was going swimmingly until the 3rd motion bearing retainer. Was going round each of the three bolts slowly doing each up so as to not crack the casing by too much pressure in one spot over another.

Then, doing the third bolt up it all just went soggy and soft. Removed the retainer to find the bloody things cracked.

There must have already been a crack or weakness there before because i had barely even put the bolt under any tension at all more than finger tight before it went jammy.



What to do? Can i continue with only the two bolts and a knackered third or is a whole new box case in order?

Edited by carts60 on 16th Jul, 2011.

I have replaced a casing for just that, but then, I am anal

Those bolts shoud only be done up to about 18lbft which is naff all, and easily less than hand tight if your a bit of a brute

question is, if your engine is going to be anything other than a standard motor, would you risk it? I certainly never, and I have known others not to either, but then it 'might' be ok, but if the gearbox failed knowing that this damage was present, how would you feel then?

I think its going to be a personal choice, but my advice would be either replace the case, or at least have it welded, drilled and tapped, which might end up being more expensive depending on who you know.

What could be the possible repercussions of trying the box with the current problem? Either with a bodge job on the thread on using only 2 bolts instead of the 3?

I'm not trying to skimp around the problem, but i'd like to at least know what my options are.

And im anything but a brute lol

Anybody have a spare gearbox case kicking about?? :)

If there were two threads left diagonally opposite i might chance it, but not like that.

I'd rip the broken bit off and see if there is enough meat to get a helicoil in, if not I'd find another case.

Righto!

Just to confirm helicoiling is where you drill out the old thread, re-tap a larger thread then put in an insert which contains the original thread??

Cheers chaps

yep thats right.

Can someone please confirm its an M7 thread? I'v been to the garage to check and i'm fairly sure it is, but i dont have a tap to quickly run into the hole to make sure...

Its 5/16 UNC

Well im glad i asked that question! lol Literally had my finger on the buy button

edit*****

Sorry posted in the wrong topic

Edited by Sprocket on 16th Jul, 2011.

You might find that a timesert would be best in this case (punn not intended) as they are solid instead of being a coil.

Something like this...

http://cgi.ebay.co.uk/Classic-MINI-Wurth-T...D-/130341080629

https://www.facebook.com/pages/Fusion-Fabri..._homepage_panel

www.fusionfabs.co.uk



1/4mile in 13.2sec @ 111 terminal on 15psi

Only problem is i'v got to go all to Warwickshire to get it fitted, by which time petrol will have cost more than a new case.

I'v ordered a helicoil kit so i'll give that a go first

1 - damage may have been instigated by the way you took the bearing out (read the early post on this subject)

2 - that photo looks very much like a helicoil has already been fitted - shadow round the left hand side, and especially because the thread is broken in a completely different place to the place the casting is broken on the right hand - so someone may have already fitted the wrong metric one (and fitted it very badly).

Schrödinger's cat - so which one am I ???

It seems to me that you used these bolts to press the bearing in? Not the way to do it. I suggest you investigate how to work properly on gearboxes before you continue.

Looks to me that it needs welding and a time sert putting in after the repair, i only use helicoils when the thread is stripped, not destroyed.

Edited by carts60 on 17th Jul, 2011.

I have seen this a good few times normally caused by crud at the bottom of the thread hole, when you tighten up the bolt presure is caused and it has to go somewhere( exit stage left) I would simply drill all the way through the main web tread a bit deeper and use a longer bolt this is simply a bearing retainer and only serves to stop the outer race from turning. If you put the other 2 bolts in at the right torque and you can get a bolt to pull 11nm in that hole with a bit of locktite then I would not worry for one minuite

I'd have it welded before any helicoiling was done...