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MG Midget and Sprite Technical - Gearbox springs at front of laygear

I'm back from a lengthy detour in rebuilding the gearbox in my 1971 midget. From my last post in late September I learned I had a laygear with teeth in good condition for a car with 113k miles, but the inside was just too damaged to be used as is.

A very helpful mechanic at my work cleaned up the inside and fitted bearings with a tad larger OD. He had to use two end to end as they were exactly half the length, but I'm confident I now have a usable laygear.

My next step is to test fit the laygear, with the new hardened layshaft from Moss, and the existing thrust washers. I'll measure the end float to see if I need a different rear thrust washer.

But I have questions about where the front thrust washer meets the case. There are three sorry looking springs. I can't find them in any of the many illustrations I have available, and not in the Moss offering. Are there supposed to be four? Can I use a spring illustrated elsewhere to replace them? Should I be concerned about what damaged them?

The surface around the springs seems quite chewed up. As long as the end float at the rear is in spec, should I be all right?

Couldn't find anything in the archives about this.

I appreciate any advice. Thank you.



Mark 1275

This image shows the area a bit better.

Thanks for looking.


Mark 1275

Hi mark

Never seen this in all the gearboxes I have stripped. Looks like a modification by someone. The face is badly chewed up and should be nice and smooth. Whats the condition of the large thrust washer?
If you can tidy it up and get the end float within tolerance then you should be ok. The springs don't do anything and can be removed
Bob Beaumont

I know nothing about such things in the gearbox, but my interpretation of that is that the 4 springs were fitted at some time each with a small ball bearing as someones's attempt to provide some sort of pre-loading onto the thrust washer. But there has been too much clearance and first the ball bearings and then the missing spring have worked their way out between the casing and the thrust washer, causing that damage to the alloy surfacing in the process.

Maybe you could find a thin steel shim that fits the recess and use something like a bearing adhesive to secure it to the alloy to provide a fresh surface for the thrust washer to turn against?
GuyW

Mark

As Bob said, there's a reason you can't find a reference to them anywhere - they shouldn't be there.
Dave O'Neill 2

Thank you for the prompt replies. Not the answers I expected.

The surface of the front thrust washer is actually pretty good compared to the lunar surface of the case. I have it packed up to go back to my work, but I'll post an image later. It might be something also out of the ordinary.

I've packed it up because I ran into another problem this afternoon. I was so confident I'd start making progress today, but I'm in for another delay.

The two, new half-length bearings are actually just a bit oversized in the length, so the bearing stands proud of the laygear by about 0.017". My rear thrust washer is only 0.121", but I can't get it in. I hope my friend at work has some suggestions. Seems there might be a few paths forward. I could use just one bearing and maybe fabricate a spacer. I could take a few thousandths here and there, including the rear washer, to get the end float into the correct range.

But, for now I'm temporarily stuck again.

Those holes for the springs sure are strange. I'm just going to pretend they aren't there.
Mark 1275

Mark
As others have said the springs don't exist- I'd remove them. As for the proud bearing I'd want it to be flush. Could 17 thou be machined off the roller bearing, say 8 thou from either end or 4 thou off each end of the two bearings?
Bill Bretherton

I'm not sure about ball bearings. It would be like herding cats, trying to fit the laygear, shims and ball bearings all in one go.
Dave O'Neill 2

Probably right Dave. But just springs bearing against the back of the thrust washer? That seems a bit odd, and doomed to failure. Which it did of course!

GuyW

I was thinking the same thing about trying to take a bit off each end of the bearings, and maybe even a few thousandths off the rear thrust washer. I'll let my friend help with that decision.

This shows the side of the front thrust washer that rides against the case, where those springs were.

The flip side has a parabolic slot like the rear washer, which I assume are for oil passages.

Does this look like it should? It's a little abraded, but I also chose the picture that most accentuates the rough surface.

I'll also post a bearing image next.




Mark 1275

Here's a stock image of the bearing used at the front of the laygear. It's a Slovakia HK 1612. Looks like there might be enough meat at the ends to take a little bit off.

Maybe I can get by with just one of these bearings at the front.


Mark 1275

Those holes in the thrust washer don't look right, either.

I wouldn't be tempted to use just one bearing. You already have considerably less length of needle roller, due to the extra width of the bearing casing.

One option would be to counter-bore the centre of the thrust washer to clear the bearing, although that would mean needing to insert the laygear into the casing complete with thrust washers. I don't know how possible that would be.
Dave O'Neill 2

I don't know much about the A-series boxes, but just for info, the 1500 box has three little springs that push against the laygear thrust washers, just like this.

Malc.
Malcolm Le Chevalier

Malc
That reinforces what I have been thinking i.e. a PO has modified the 1275 box. I suppose you want the thrust washers to be fixed, ideally, otherwise they'll tend to rotate and wear the g/box casing which they seem to do in my limited experience, although I presume the oil groove is there to prevent wear.
Bill Bretherton

Again, of no particular help, but maybe of interest. The 1500 thrusts have tangs on them to stop them rotating in the housing.


Malcolm Le Chevalier

I would replace the large thrust washer. It has oil grooves on both sides and yours appears to have worn away on one side. I would not mess about with the needle roller bearing but focus on getting the laygear installed with the correct end float with thrust washers on both ends. Given the wear on the casing it may need an additional shim to get within the tolerance.

The rib case gear box is not the strongest of items but if the bearings and laygear are in good order and the oil changed regularly then they will provide a reasonable service.
Bob Beaumont

If you have concerns about the modifications to your gearbox and the reliability of them, perhaps an other case may be a better way to go. I can help you with that if you are interested. John
J Bubela

Mark,

Those bearings HK 1612 are drawn cup needle roller bearings so the shell is quite thin. I think a better fix rather than removing material from the outer shell would be to deepen the bore in the laygear so they can be pressed in flush.
David Billington

Much appreciate all the responses.

Some good news today. I brought the laygear assembly back to my friend at work. He's a capable guy, and if I understood him correctly the two bearings he installed should have totaled 26mm in length. The new one from Moss was 27mm, so the doubled up bearings should have had room to spare.

He just pressed them in further, and I should be good to go. (On Saturday I tried tapping them with a rubber mallet, but I guess I was just too tentative.) Very glad we didn't need to alter the bearings.

Next chance I get to spend time in the garage I should be able to make some progress, and I'm looking forward to it.

I will replace the front thrust washer.

Thanks for your offer, John. If I can't get the correct end float I may be in touch.
Mark 1275

As Malcolm has stated the Triumph gearbox used in midgets and Morris Marinas (1.8)uses this idea of 3 springs on the lay gear,the reason for these springs is to slow down the lay gear when you dip the clutch to aid selection of reverse gear,
Andy Tilney

This thread was discussed between 28/01/2018 and 30/01/2018

MG Midget and Sprite Technical index

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