Gearbox- rebuild or not?
Turbo Mini Forums

Hi,
Im rebuilding my 998 engine in the new year and im wondering if a gearbox rebuild is necessary or not, its hopefully going to be a 998 turbo and aiming for around the 100bhp mark. The thing is ive never actually drove the mini so i havent a clue of the condition of the box, I havent rebuilt an engine before so its all new to me but would a rebuild sort out any problem that i could have with the gearbox,
Minispares have a bit of a discount these days so want to get it now while its cheap, that is if its definiately needed, Another thing, is this the correct rebuild kit.
http://www.minispares.com/Product.aspx?ty=...id=37117&title=
Its a 86 mayfair i have so its A plus.
Any help appreciated.

A job worth doing is a job worth over doing

Rebuild it!

Edit, also worth adding a 4 pin diff while your at it.

Edited by minimole23 on 2nd Dec, 2011.

I supose a rebuild is the way to go,
Already have a minispares cross pin diff added to my long list.
Speaking of diffs, do i need to replace any bearing or anything when fitting a cross pin diff.

A job worth doing is a job worth over doing

It would be a shame to put a nice rebuilt engine on a used gearbox, especially if you don't know the condition, for peace of mind and your future plans its a no brainer imo.

Ya, i know what you mean but my thinking behind it was it would be a balls if i rebuilt the gearbox and it turns out theres something wrong with it, would a rebuild allow me to check for any abvious faults.
Im beginning to think a rebuild is a must, might as well i supose,

A job worth doing is a job worth over doing

So two of these (http://www.minispares.com/Product.aspx?ty=pb&pid=37231&title=)
, a cross pin diff and locktabs and the diff should be sorted,
Is that rebuild kit the one i want
Cheers

On 2nd Dec, 2011 Tom Fenton said:

On 2nd Dec, 2011 jdisel said:
I supose a rebuild is the way to go,
Already have a minispares cross pin diff added to my long list.
Speaking of diffs, do i need to replace any bearing or anything when fitting a cross pin diff.

You will need a pair of diff brgs, and also 3 off locktabs for the crownwheel bolts.

A job worth doing is a job worth over doing

On 2nd Dec, 2011 jdisel said:
Ya, i know what you mean but my thinking behind it was it would be a balls if i rebuilt the gearbox and it turns out theres something wrong with it, would a rebuild allow me to check for any abvious faults.
Im beginning to think a rebuild is a must, might as well i supose,

Yes i moved to the darkside

Instagram @jdm_brett

a rebuild it is so. Ill check out that dvd.
Cheers

A job worth doing is a job worth over doing

Good call mate and its peace of mind as well, its horried thinking your gearbox is about to shit itself!

Personnally I would strip it and see what it needs before spending over £100 on a rebuild kit, but I have rebuilt boxes many times. If you know what youre looking at you will be able to assess whether all the bearings actually need replacing or not - same with baulk rings - you could save a fair few quid by just changing the ones that are necessary, you will ofcourse need all new gaskets though.
Most of us find you cannot go wrong if you follow a Haynes manual

Edited by paul wiginton on 4th Dec, 2011.

I seriously doubt it!

Get a metro haines manual. They are cheep and have a detailed gearbox rebuild guide in them. It's not difficult, just a little fiddly until you get used to it.

I think ill just go for a full rebuild and put my mind at ease,i wouldnt mind ripping it up and getting my head round how each part works anyway,
Ill keep an eye out for that book too, might be worth a read.
Thanks again for the help
Another question, if a change my standard one to an x pin one, is changing the bearings a common thing to do or are the origional ones usually good.

A job worth doing is a job worth over doing

in my opinion, if you are confident enough to assess the wear or damage to the original bearings, and are happy they are in good order, i'd use the original bearings where possible. The first and third motion shaft bearings being the important ones. As a matter of course I would replace the roller bearings in the laygear with genuine new items (not the ones Minisport sell) and where budget allows, a competition or Swiftune layshaft. Otherwise, again, it comes down to how confident you are at assessing the parts for wear or damage.

I try and only replace parts that really do need to be replaced, and try to find good used original ones instead of new. I might be the only skeptic, but I'm not sure of the quality of the parts available these days, what with all the bad and nasty things used in processes to manufacture these parts being banned, removed or replaced with something less suitable.

The first secont and third gear mainshaft needle rollers don't normally pose a wear problem and can be used again in most cases. Its important to ensure the end journal on the main shaft where the first motion shaft pilot bearing runs is in good order, as well as its sister journal on the inside of the first motion shaft itself. any wear or pitting there and its a new first motion shaft and main shaft, since this is one of the highest stressed areas of the transmission, which can allow the gears to push appart (marginally) under load in any gear except fourth.

The old style 'two part' diff bearings are, in my opinion, better than these new caged bearings, but again whether you can re use them comes down to how well you can assess them for wear or damage.

You will get all other wear parts, new with a Minispares cross pin diff, you only need to find good condition diff output shafts and crownwheel. If your original diff has lots of play in it (wiggle the pot joints when they are still on the box and pull in and out) chances are the output shafts will be worn, the bush in the crownwheel, and the bushs in the diff side covers will also be worn.

Don't let this put you off in any way, since the transverse A series gearbox is far from complex, but you do need to follow the haynes book very carefully, and if you still are unsure about anything, you know you just have to ask.

It also pays to have more than one gearbox you can use to build one good one 998 boxes are usually better, but 998 engines are now starting to fetch a premium, if you're just buying it for the gearbox

if i was to replace just the worn bearings, is there any fear that a couple thousand miles down the line the ones i didnt change would need replacing.
Ive never tinkered with engines before so dont know a thing about checking bearings or anything. Is it straight forward enough.

A job worth doing is a job worth over doing

im a fan of 'if its done 100kmiles and looks as good as new there is probably another 100k left in it'

when i did mine i bought every bearing because i wanted a 100% new box
in reality the little bearings that sit under the gears on the 3rd motion shaft the old ones looked better than the new ones i had to put in, 2 out of 3 old ones went back in

ones i would recomend looking at and replacing
diff output bearings x2
1st motion bearings x2( on in box one in drops case) (38)
3rd motion double roller (19)
and the 2 on the layshaft (2 - 4)

found these articles there of the older box but roughly the same

http://www.7ent.com/pages/articles-tech-ti...ansmission.html

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Edited by Brett on 10th Dec, 2011.

Yes i moved to the darkside

Instagram @jdm_brett

You'd know all about that, with 150nanas on top of a completely standard helical box.

In the 13's at last!.. Just

Cheers for the link
Would the rebuild kit listed below replace all the bearing you mentioned brett.
Just out of interest, hows your box holding up to that sort of power.

Im just getting a list of a few things i need for the rebuild so im planning on making an order with minispares tonight while the sale is on, just want to make sure the parts i have are suitable and if there actually the right ones, im not too sure if the clutch kit is right,
this is a copy of my shopping cart,
http://i1226.photobucket.com/albums/ee420/jdisel1/ii.jpg
I know theres loads of other bits to get, i just want to get the more expensive bits now to save me a bit of dosh in the long run.So if these any other obvious parts, shout,
Any help would be great

Oh ya, what cam followers would be the best, would the stand ones do the job or are the ones with the holes be better and what about a duplex timing set, do minispares do any performance ones, Another thing, these a valve spring missing on my 12g295 so would it be worth just getting a full set new, I also need a few tools for the rebuild, just wondering what sort of things i might need, I know i need a set of taps, callipers, dial guage,but other that that im a bit lost.

Edited by jdisel on 10th Dec, 2011.

A job worth doing is a job worth over doing

we'll see how I get on in the coming year then

On 11th Dec, 2011 minimole23 said:

On 10th Dec, 2011 jdisel said:
Cheers for the link
Would the rebuild kit listed below replace all the bearing you mentioned brett.
Just out of interest, hows your box holding up to that sort of power.

Well I would not be happy putting more then 120 though even a well reconditioned helical box.

Bang, grind followed by 'oh bollocks' I think!

On 11th Dec, 2011 Sprocket said:
we'll see how I get on in the coming year then

On 11th Dec, 2011 minimole23 said:

Bang, grind followed by 'oh bollocks' I think!

On 11th Dec, 2011 Sprocket said:
we'll see how I get on in the coming year then

Edited by Sprocket on 11th Dec, 2011.

there you go, 60k miles. The transmission is already pre stressed

A 998 couldn't stress a plastic gearset