Welcome to our resource for MG Car Information.



MG parts spares and accessories are available for MG T Series (TA, MG TB, MG TC, MG TD, MG TF), Magnette, MGA, Twin cam, MGB, MGBGT, MGC, MGC GT, MG Midget, Sprite and other MG models from British car spares company LBCarCo.

MG MGA - Ring Gear Wear

A few years ago when I restored my TD, I replaced the ring gear as it was badly worn. I just pulled my 18GA engine from my 60 MGA and noticed the ring gear shows some wear (see image). Do you think this amount of wear justifies repacing the gear? Thanks.

Joe Holtslag

I don't worry unless the wear is half the width of the tooth in the two regions of greatest wear. Never had a fail yet.

FR Millmore

That's not bad. Put it back in service.
Barney Gaylord

My ring gear showed about the same wear when I had my engine in for a rebuilt a few years back. I took a flat file and cleaned up the teath. Takes about a half an hour. My thought was, since the teath were worned this much they might catch (hold) the starter gear. After my quick file job, my rebuilder said it looked good and had no concerns.
Ray Ammeter

....and when that side is finally worn out you can always bolt on a high torque starter to engage on the other side!

Steve Gyles

If it's going to bug you, a new one is less than $40.
Del Rawlins

Thanks for the many responses. No it won't bother me to have a little gear wear as long as it works ok. As my father always said, "If it ain't broke- don't fix it." I like Ray's idea of using the flat file.

My big task now is to peruse the archives and try to convince myself that a new 5 speed is that much better than the MGA 4-speed and worth the money.
Joe Holtslag

5-speed conversion is never cost effective in fuel savings or reduced engine wear, but if you have a bundle of cash burning a hole in your pocket it is a nice luxury touch for quieter cruising. I just changed the final drive from 4.3 to 3.9, and it makes a nice improvement for casual cruising at normal highway speed. Way cheaper than a 5-speed, and can be installed in a few hours.
Barney Gaylord

I understand, appreciate, and have always thought 5th/OD gearboxes were a great thing in cars - even long before there were many - like 1960 - when I was planning a two speed rear axle for a flathead Ford powered Willys pickup. I would definitely install one, in MY car for MY use - stuff like crosscountry 10,000 miles in a month. But I absolutely cannot fathom why you would go to the expense and trauma of doing the conversion for the use most of these cars will ever see. If you are running lots of miles over 65-75mph, do it, otherwise keep the original.
For underpowered cars that need low ratio axles (stock T, Magnette), the 5th becomes more useful, but then you need to downshift, and many seem unwilling to do this on the highway.
For most people's use, some sensible low-end mods make more sense and are cheaper/less traumatic to the car. These are the same mods you will need to do when you overgear it so that the engine output is below power required to move the car at that speed.

FR Millmore

Gosh I love this board!! No, after the resto I will just be putting on a few hundred miles a year. Thanks for the advise FRM. I'll keep the 4 speed. (What was I thinking?--now I can afford leather seats!)

Barney, I like the idea about changing the gearing. I had the gears changed in my TD from 5.1 to 4.3. I was told changing the TD gears was beyond the skill level of a "weekend mechanic" so I took it up to a guy in PA (Geoff Love) who did it. Are you saying that I could buy some 3.9 gears and do it myself? Do you have the procedure on your site?

Here's my car now--might be a good time to do it...

Joe Holtslag

You can always rotate the flywheel 60 deg to get a fresh set of teeth at the resting point.
Art Pearse

Installing MGA 4.3 ring gear in the TD requires machine work, not for the faint of heart.

3.909:1 (43/11) was a factory optional ratio for the MGA (but extremely rare when the cars were new). There is also a part number for a matching speedometer, but I have never seen one and don't know anyone else who has ever seen on). It is the same basic rear axle and gears as used in the early MGB (1962-1967, not GT), given matching splines for sin gears to half shafts.

Installing early MGB 3.9 differential in MGA is a bolt in job, drain oil and swap the complete carrier. The complete photo tour is linked on my web site.
The link goes here:
Barney Gaylord

Connecticut is hilly not mountainous. But for what it's worth, I have a "normal" 1600 with both a 3.9 rear-end and a Hi-gear 5-speed. I don't consider it anymore under powered than our two modern vehicles, a 4 cylinder
Subaru Outback and a Ford Ranger with the small V-6. The MG is of course a lot more fun to drive.
David Werblow

This thread was discussed between 13/07/2012 and 14/07/2012

MG MGA index

This thread is from the archive. The Live MG MGA BBS is active now.