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MG Midget and Sprite Technical - first gearbox tear down

I'm tearing down a ribcase for the first time.
I've got the first motion shaft sandwiched by the bearing on the front and the synchro cone on the inside. Haynes says to tap it out the front and the bearing comes out but the synchro cone keeps it from coming through. Is that cone supposed to get knocked off too? Tapping a metal rod from the inside per manual but not exactly sure how deep the rod should go. I guess I'm asking how to get either the cone off the inside or the bearing off the outside.
http://gallery.me.com/jvandyke#100290/SDC10106&bgcolor=black
J Van Dyke

try this link
http://homepage.mac.com/jvandyke/trappedfirstmotion.jpg

something about this site truncates the url and you get my whole gallery of photos, not just the MG stuff, too late to edit, a bit annoying really.
J Van Dyke

Have you removed the layshaft to alow the laygear to drop thereby giving clearance?
Sandy
SANDY SANDERS

Haynes is WRONG, WRONG, WRONG.

There is no way in this world that the first motion shaft can come out the front. It has to be removed through the gear casing after the mainshaft has been removed and the layshaft removed, allowing the laygear to drop down into the 'box.
Dave O'Neill 2

I do remember reading that in the Haynes manual the first time I dismantled a gearbox. I'm amazed it's never been highlighted here before...at least, not as far as I'm aware.

Obviously, you do need to remove the spring-ring from the bearing before removing the shaft.
Dave O'Neill 2

Yep, I got it. Popped the spring clip, tapped the front bearing back into the box, Haynes is wrong I guess.
Check out the gearbox gallery (don't know why I can't link straight to that gallery, click the top left one)
http://gallery.me.com/jvandyke#100290&view=grid&bgcolor=black&sel=10
Here's the deal (sorry to those who frequent other forums). Car popped out of 4th when I was driving it home from buying it. Put back, popped out again, wouldn't go back. Got home, went to drain the box, it was bone dry. I refilled and it didn't leak but 4th was toast. I swapped gearboxes and now that it's winter I'm tearing down the original one to see what there is to see.
I found what appears to be needle bearing bits in the drainage. There's scoring on teh layshaft but the lay gear roller needles look fine, there is however no evidence of a needle roller bearing between the first motion/input shaft and the third motion shaft. Nothing left there at all and the fork for 3/4 appears to be destroyed, the fork can't hold/push to engage 4th.
Wonder if these bits are worth saving or not. Maybe I can just replace the fork, bearings and such and have a spare box? Thoughts on the condition of the rest of the gears appreciated.
J Van Dyke

Not too bad. 1st a bit worn, and marks from debris on 1 & R. Main problem likely that the needle bearing broke up from bad assembly, bearing falls out of position and gets squashed when putting the 1st/3rd mo shafts in. then the pieces kept the 3/4 hub from going to the correct position; and/or bits jammed the hub so it was forced and held in gear by hand. That wore the fork out.
New fork, bearing and clean the hub out.
New other bearings.
New layshaft and bearings.
Clean everything really well!!!
Maybe not a perfect box, but serviceable.

FRM
FR Millmore

As FRM says, definitely rebuildable.

The laygear looks in very good condition.
Dave O'Neill 2

My guess is that it was <very> recently rebuilt, and they forgot to put oil in! Broke the bearing putting it together. Never saw a fork anything even close to that, even on really trashed boxes.

FRM
FR Millmore

Actually the engine/gearbox hadn't been worked on recently. The PO rarely drove it and when he did it wasn't very far. He only put 1995 miles on it between 1987 and 2007. I can ask him about it though to be sure. I think maybe it had been dry a long long time but was so seldom run and for such a short stretch it survived until I had it on the freeway for a while. After it dropped 4th I drove it another 50 or so in 3rd (not on the interstate anymore) and when home, found it dry, refilled and drove it a little more before pulling it out. That 50 miles in 3rd with no oil maybe what wore that fork into nothing. In hindsight, I should have checked the gearbox during inspection or soon after buying but a nice test drive with no evidence of leaks, well, I figured it was okay. After 4th went I should have checked the oil but, well, I didn't have a manual and didn't really think it was oil, figured it was pure mechanical issue at the time and nothing to do but nurse it home.
The carpet was glued down solid over the tunnel and it set in place in 1987. No one had checked or filled that thing while it was in the car since then. I had to tear it off to get at stuff.
J Van Dyke

"Recently" refers to miles, time is of no consequence! Probably rebuilt and never had oil. You lost 4th because it was already tostado.

FRM
FR Millmore

J, could you perhaps measure the dimensions of the bearing of the first motion shaft? My rebuilt gearbox pops out of the third gear and by coincidense I saw this thread on another forum and it seems that when you order
a first motion shaft bearing you get one from a smooth gearbox wich is narrower than one of the ribbed gearbox thus giving some play.Does somebody perhaps know how thick that spacer should be mentioned in the thread?

Here's the link : http://www.spritespot.com/phpBB3/viewtopic.php?f=14&t=3573&start=15

Sixth respond from the top

Many thanks in advance.

Pascal
pjw Seezink

Dave, which edition of the haynes manual is wrong? It was "revised" when the 1500 models came out, and they basically re wrote the whole thing in such a way that they corrected the misinformation from the first one, while omitting important information, and providing still more misinformation. Might be useful to know which one.
S.A. Jones

The edition that J Van Dyke has would appear to be wrong!

I have had numerous versions over the last 28 years, along with the 25+ Spridgets that I have owned.

The one that states that the first motion shaft comes out the front is most definitely wrong.

Also, there are several versions which give incorrect information for aligning the crankshaft and camshaft sprockets in relation to the distributor drive, resulting in the ignition timing being 180 degrees out.

Which edition do you have?
Dave O'Neill 2

I have both, plus a bently manual. I'm moving so I cant check. All in all the pre 1974 edition of the haynes manual is far better for a series engined cars. It uses tons of excellent illustrations left out in the later version. Of course it borrows heavily from the bently manual so its best going with the bently one.
S.A. Jones

I think the Haynes manual 'borrows heavily' from the original BMC factory workshop manual, so I'm presuming that Bentley did the same.
Dave O'Neill 2

Dave,
The BMC(Leyland) manual (reprint of 1973) is wrong as is the 'Autopress' manual - this even has an illustration of drifting forwards the F/M/S.
Did any of the very early gearboxes have a small gear that would have permitted this ? and hence taken foreward into later prints ?
Checked a parts r/case minor box and its not possible on that one.

R.
richard boobier

Richard

I've never dismantled a smoothcase 'box. I do have one somewhere, so I will have a look when I get a chance.
Dave O'Neill 2

Supposedly the first edition of the sprite and midget manual by haynes was the very first haynes manual ever, written by none other than hanyes himself. The illustrations were all taken from the BMC repair manual. I am sure he probibly used it as a source for information, but it claims to have been based upon a complete teardown and rebuild of the whole car.

The one that includes the 1500, however discards a good chunk of what was in the earlier edition apparently to save space. I'll have to give more detail after I unpack.
S.A. Jones

The 3rd 4th fork wear may be from driving it home w/o oil, but I suspect a PO kept their hand on the lever while driving applying constant pressure to the sides of the fork. I have a fork around somewhere that was worn almost through, it wouldn't shift into 4th as I recall.
J Bubela

My copy of Bently says the same "...drive the first motion shaft forwards out of the gearbox". My Haynes is a newer version as it has the 1500s in it. Yes the wear on the fork could be from hand pressure I guess.
I did get it all apart and there wasn't a single piece left of the needle roller bearing that is supposed to be between the first and third motion shafts. This probably failed due to lack of oil and the bits found they're way out? There were certainly bits floating around in there. I think with a new 3/4 fork it could be rebuilt. It is all bagged and tagged and sitting disassembled. Gear teeth all look pretty decent decent, laygear looks good.
J Van Dyke

Dave O'N,

I have an old frog sprite 1st motion shaft, today tried into the front of the bell housing and it does just pass through the bearing housing hole of a ribcase.

So its looks like Haynes was not updated for ribcases.

(assuming that bearing sizes did not change etc -don't have one on the frog shaft)

Richard.
richard boobier

Richard

Thanks for the update.

I still haven't had a chance to dig out the smoothcase 'box.
Dave O'Neill 2

This thread was discussed between 21/12/2009 and 16/01/2010

MG Midget and Sprite Technical index

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