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MG MG Y Type - RING GEAR TEETH

Hi,

Getting to all the bits Ive not looked at for 20 years now....my starter ring gear appears pretty worn so I have been looking at a replacement.

My YA has a 7 1/4" clutch and I thought it would have the early TD 120 toothed (10 3/8" ID) ring gear...

wheras it has the 93 toothed (10 1/4" ID) TB/TC ? ring gear.....is this right for and early YA?

Thanks
Rob King

Rob

The question is not so much as which is right for an early or late car ... but more about what starter motor do you have and how many teeth are on that as it is about the ratio of one to the other as much as anything I believe ... but stand to be corrected.

Paul
Paul Barrow

Rob, there is a new 93 tooth TC ring gear on ebay now for about $60.00. Just do a search on MG TC ring gear.
Hope this is the one you need. Larry
Larry Brown

The Y type was introduced with ring gear 93 teeth and ID 10 1/4", starter 10 teeth.
In 1949, with the introduction of a smaller starter motor, at eng XPAG/SC/14023 the ring gear was changed to 120 teeth and ID 10 5/8, starter 9 teeth.
In 1951, with the introduction of the 8" clutch, at eng XPAG/SC/16916 the ring gear ID was increased to 10 3/4".
The Y, or YA, became the YB in late 1951, after the introduction of the 8" clutch, so the Y (YA) had all three types.

Hope this helps.
PS, would rotating the ring gear by 90 deg solve the problem?
R A WILSON

Thanks for your contributions guys.

...Mr Wilson, you seem to have clarified the situation for me...

I have a 1949 YA its original engine number was 13041 so it looks like 93 teeth is okay.

The starter is an M418G with 10 teeth.

Rob
Rob King

There are three types of ring gear:

93 teeth to go with early starter motor (M418G)with 9 teeth on pinion for the 7 1/4 in clutch

120 teeth to go with later starter motor (M35G)with 10 teeth on pinion again 7 1/4 in clutch

120 teeth to go with later starter motor with 10 teeth on pinion but larger flywheel for 8 in clutch

The same flywheel was used for the 7 1/4 in clutch so you can use either a 120 teeth ring gear or the 93 teeth ring gear provided you use the appropriate starter motor. In essence there were only TWO types of flywheels...not three...one for the 7 1/4 in clutch and one for the 8 inch clutch. Try asking NTG (Mike Green) or another suppliers.

The M35 G later starters are a lot cheaper and more readily available than the earlier M418G.

I feel confident I am correct as I had this problem too. The later starter is much easier to fit or remove and is mounted with two bolts instead of three with the earlier starter.
D MULLEN

Rob King himself states that his 93 tooth ring gear, fitted to a flywheel for a 7 1/4" clutch, has an ID of 10 1/4".
The "same" 7 1/4" clutch flywheel, with the 120 tooth ring gear had this diameter increased to 10 3/8". (Sorry, I put 10 5/8" before). This was done so that people could not fit the wrong ring gear if they needed to replace it.
Thus there are two flywheels for the 7 1/4" clutch, albeit very similar.
The flywheel for the 8" clutch was larger, which meant that the flywheel fitting diameter had to be increased to 10 3/4", but they managed to use the same 120 tooth ring gear with it's ID increased to 10 3/4".
Thus three flywheels and three ring gears, which cannot be mixed.
R A WILSON

In fact Rob also mentions the 120 tooth, 10 3/8" ID, ring gear for the 7 1/4" clutch, indicating slightly different flywheels.
R A WILSON

I still maintain that there were only two flywheels and that you can fit the 120 tooth ring gear to the flywheel that took the 93 teeth ring gear provided you change to a later starter motor. Ring NTG or any supplier of flywheels and they only supply two flywheels not three...please check this out....if you can find them I will bow to your greater knowledge. The slight difference in diameter is due to measuring errors when assessing diameters of the flywheel by enthusiasts....I may be wrong so check with an MG supplier of flywheels.
D MULLEN

I have to admit I am intrigued - my dimensions come from measuring different flywheels, but that was some years ago (although I do not think matters would have changed). I have looked at the specifications given by several ring gear manufacturers - only one gives the ID of the 93 tooth ring, and 10.343" is given (which could be a typing error for 10.373"). Perhaps Rob could recheck his measurement, and if any reader has a flywheel with a 93 tooth ring gear, perhaps they could also supply a measurement.
I will check with NTG (now MGbits4U), but I will ask them to measure the ID of a 93 tooth ring gear, preferably S/H, and the same diameter on a S/H TB/TC flywheel if they have one. There may be other reasons why they only supply two flywheels.
Brown and Gammons do say that the bare TB/TC and early TD flywheels are identical.
I wonder if we will find both sizes for the 93 tooth ring gear, and Morris/MG made a change without telling anyone - it has happened before.
R A WILSON

David Lawrence says the early Y type 7 1/4" flywheel was not changed when the ring gear changed.
R A WILSON

The engine on my YB is a YA gold seal one with 7 1/4 in clutch....it had originally a 93 teeth ring gear with the M418G starter....I have changed it to the 120 teeth ring gear and fitted the M35G starter..a much better system as the starter is much easier to fit..getting the larger M418 G starter off is a pig of a job. Also you can get a M35G starter for under £50 new. I suspect the slight variation in measurements of 7 1/4 clutch flywheels is down to transcription errors and it being difficult to accurately measure. Let us know if this proves correct. Cheers .
D MULLEN

That's the puzzle - I would have taken my measurements with vernier calipers. I am thinking of opening a book, with 1p on offer - only one bet to be accepted.
R A WILSON

Should have explained - the bet could be that the 7 1/4" clutch flywheel ring gear ID was changed.
R A WILSON

My bet..is that there were only ever two flywheels. ...ten pounds to a charity of yout choice if I am wrong and 1p if I win so thats odds of 1000 to one in your favour..seriously the very small difference in 7 1/4 diameter clutch flywheels is nothing in comparison with the circumference. We'll see!
D MULLEN

Oh dear - I have just measured two 93 tooth ring gears and one TC flywheel, and the mating diameter is 10 3/8". So 1p has to go somewhere!
I am puzzled as to where I got my dimension, as it seems rather exact, and the reason for the non-existant change seems reasonable.
R A WILSON

Just glad its now confirmed that there were only ever 2 flywheels.This means of course that owners of 7 1/4 in clutch types can convert from the 93 teeth ring gear and older type heavy M418G starter motor to the later 120 teeth ring gear and use a modern M35G starter.
D MULLEN

This thread was discussed between 21/05/2013 and 05/06/2013

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