Gearbox play

[rcbowman]

Here's a question I really don't want to be asking:

How much play in the first motion shaft on the gearbox (the one that sticks out and fits into the flywheel on the engine) is too much?

I just pulled my gearbox for another issue and was cleaning things up preparatory to reinstalling, when I found the shaft wiggled. I am talking about a small amount of side-to-side play, but enough that I'm rather worried about it. The last time I had the gearbox off, three or four years ago, I don't think it had anything like this much play.

There have been no issues within the box itself, at least no perceptible ones. This was my first indication something was wrong.

So... Though I'm aware zero play is optimal, how much is tolerable? Do I need to drop everything and buy a new one, or put it back together and start saving up? I live an ocean and a continent away from the land of abundant moggy mechanics, so consulting an expert on this particular transmission/gearbox is not feasible.

While I'm at it, is it possible to replace the first motion shaft bearing, without entirely disassembling the gearbox? That is, can you just remove the front cover, pull the first shaft, press the bearing off, replace, and reassemble, thus buying only a bearing and a seal or three? The shop manual seems to imply you can't, but it isn't quite explicit anywhere I can see. I'm not a real machinist, but I have metalworking tools and experience. OTOH, even with the shocking cost of rebuilt ones at this distance from the UK, I am mightily intimidated by the idea of taking the whole box apart.

[bmcecosse]

The play you describe sounds ok to me. The front end of that shaft should be supported in the snug fitting 'oilite' bush in the centre of the flywheel. You may want to consider re-newing that if it looks worn. It is possible to renew the 1st motion bearing - but I really don't think it's necessary unless it feels 'rough' - or if the cage seems to have broken up. If you take the front cover off you should be able to eye-ball it and see if there is any damage.

[rcbowman]

Ah. Yes. I'll take a look at that bush/bearing. Good point.

If I take the front cover off the gearbox, do I need to buy and renew some oil seals?

[rcbowman]

Hmmm... My one not-too-far-off parts supplier will inspect it if I send it. Carriage costs would be minimal in this case. I'm not sure of their turnaround time or cost yet, though, so I'm still interested in hearing other opinions before I do that.

[bmcecosse]

If you take the bearing out - may as well fit a new one. I would just use it 'as is'. It will be fine.

[Kevin]

The front end of that shaft should be supported in the snug fitting 'oilite' bush in the centre of the flywheel.

As you have it apart renew the bush as a matter of course as it does help with 1st motion shaft alignment and is often overlooked they are only a couple of pounds and even with postage it shouldnt be much.

[rcbowman]

Yes, they're cheap enough. Only problem is time. I'd really rather get the thing put back together today, rather than wait for another part. Even coming from my local-ish supplier, it can be a couple of days if I'm not lucky. I should have thought about that bearing when I was ordering. Sigh.

[rayofleamington]

Play in the input shaft - yes as you already guessed, this is not a good thing to have.
However if the gearbox is NOT significantly noisier than it should be in 1st or reverse gear, then it's fair to say there is not too much to worry about. You can replace the bearing on this shaft without a full strip down (as far as I can remember).
However, the most important thing to replace to protect the input shaft bearings is the spigot bush in the back end of the crankshaft - as long as the input shaft is properly supported, it should last. Bear in mind that the input shaft holds the clutch disk concentric (or not if it is loose). If the spigot bush is worn it allows the clutch to run out (at many thousands of RPM) and quickly damages the input shaft bearing/s.

Ive dissasembled some Minors and found no spigot bush at all !! Needless to say they had some play in the input shaft. The one advantage to 'no bush' was that I didn't have to remove it before fitting a new one

If you can't get the bush before re-assembly, then this is a long shot, but... if you have a new bronze bush for the clutch relay shaft, they are the same diameter inside and out (you just need to cut the top hat part off).

[rcbowman]

Well, I've taken a look at the spigot bush bearing, and as near as I can tell it's in good shape. My finger is not a sufficiently precise measurement device, nor sufficiently sensitive to be sure there's no wiggle to those bearing cylinders/needles. But I can tell that they all roll smoothly.

I checked the one longshot on a possible local supplier, and they don't have the bearing. I'm inclined to just reassemble it. If the bearing were obviously worn or dying, I'd wait on another part.

Besides, I really don't feel like pulling the flywheel to replace that thing. It's not clear to me if I could get a bearing puller in there even if I had one.

[bmcecosse]

There is a trick that sometimes works to get it out - fill the hole with oil - then a piece of rod the exact size of the centre hole (or an old first motion shaft) is sat in the bush and tapped 'smartly' with a large hammer. With luck the hydraulic pressure will eject the bush - and a large spray of oil. Otherwise - it usually just gets hacked out. If the old one is there (as ray says - sometimes not to be found!!) and in good shape - just use it.

[rayofleamington]

if you wrap tape round a stick (e.g. valve grinding stick, or wooden spoon handle) to get the same diameter as the input shaft, this can be used as an indicator to show if the bush is badly worn or not.
(a finger isn't so accurate, but it would be the first thing I'd doo too )
The bush is in the back of the crank, not in the flywheel anyway, so no need to remove flywheel.
if it is close enough then I would also leave well alone.

For removing - I'd rather use grease than oil, and yes, that technique is praised by many.

[Kevin]

Well, I've taken a look at the spigot bush bearing, and as near as I can tell it's in good shape. My finger is not a sufficiently precise measurement device, nor sufficiently sensitive to be sure there's no wiggle to those bearing cylinders/needles. But I can tell that they all roll smoothly.

Right your spigot bush is the Midget style one with rollers in it the standard minor one is just a bronze bush, so if all the rollers feel smooth there should not be a problem hopefully.

[rcbowman]

if you wrap tape round a stick (e.g. valve grinding stick, or wooden spoon handle) to get the same diameter as the input shaft, this can be used as an indicator to show if the bush is badly worn or not.

Though this strikes me as more relevant to the bronze bush than the needle bearing, it seemed like a great suggestion. Being in the brassworking business, I found a brass rod my micrometer told me was just barely larger than the pilot of the input shaft, and the rod did not fit into the bearing, so I'm pretty satisfied with that test.

Thanks for help and reassurance, everyone.

[bmcecosse]

Of course! The bush is in the crank end stub - not the flywheel. Silly me. Also didn't know the Spridgets used a roller bearing in there - is it same for the Marina ?? And therefore does the Marina gearbox have the same diameter first motion shaft end as the Minor box ?