OHC Minor Crownwheel and pinion

[Sam Christie]

I am looking for a good matched crownwheel and pinion for my M-type - the same as the set fitted to the OHC Minor. A complete diff would do.Can anyone help ? Phone Sam Christie 02890768124 or email s_christie04@yahoo.co.uk

[Toby]

Is this the same as sv minor and 8? I believe the 8 diff fits the M, due to the speed at which the mg stallholder at Beaulieu buys up 8 diffs then doubles the price!!!

[Trevor Wilkinson]

The Minor and Eight diffs I think are the same.
The diff on my car has a dipstick, which I am pretty sure was only introduced on the Eight.

[Toby]

Yes, the 8 has a dipstick but i thought it fitted the sv minor. If you have one of those on your minor then it only fits the sv, not the ohv or m type???

[Sam Christie]

I understand that the OHC ratio is 4.88:1 (9/44) - see the Technical Section - but Morris 8 and SV Minor are different and if fitted to an M would produce great acceleration but a much lower top speed. This is a pity because Morris 8 crownwheel and pinion sets are reasonably easy to find.

[David Whittle]

I understand that the OHC ratio is 4.88:1 (9/44) - see the Technical Section - but Morris 8 and SV Minor are different and if fitted to an M would produce great acceleration but a much lower top speed. This is a pity because Morris 8 crownwheel and pinion sets are reasonably easy to find.

I believe, in reality, the difference is almost un-noticeable between the original OHC ratio and the Morris 8 one! Or so the late John Peckham says in some literature passed on to me with my Minor. He restored Minors & M types and often fitted Morris 8 Diffs!
Regards
David

[DF9053]

The Sports and Vintage MG place does 9/44 crownwheels and pinions, well they are in thier catalogue, my price list says they are £450 so I can see why less expensive alternatives are used.

Do the later MG ones fit? Say from a J or P type?

Where can Morris 8 ones be found?

Cheers
Jeremy

[Toby]

Try Terry Ferguson (Fergusons) in Lincs or Dave Parrish. Sorry no details for either until next classic motor monthly arrives. There's also a guy in Yorks and in Jersey. I may have one or two in my autojumble stock if the MG guy didn't have the last ones when he raided our stall for Morris MGalike bits! Postage would be dear though , unless collected at Beaulieu in May (if I've got any) . They are fairly abundant in classic motor monthly ads and the Morris Register newsletter or autojumbles . Expect to pay around £60.00 for a fair one? £100.00 plus, once they're on the MG stall!!!

[Ian Grace]

By coincidence, I had an e-mail today from John Stubberfieled, Peter's father:

"Hello Ian and a happy new year to you. I am tasked with getting the diff back together as Peter is in Brighton and I should quite like to get the Alvis back to her home garage.

Have you any suggestions for torque setting on the diff bearing caps? A rough check with the torque wrench when we dismantled suggested about 30 ft lbs. I should not be popular if I broke something! Also, what do you reckon the oil level should be?

I think the combination of castle nuts and split pins are the work of the devil! How did they ever fit them quickly in production, or did they just tweak up the nut to the next available hole and ignore such niceties as torque settings? I suppose they were not lying on their back in a cold garage! Self-locking nuts are very tempting, but why bother with a vintage car if you want it to be easy."

[Toby]

Oh dear the list grows! wheels, chips, cogs, split pins and castle nuts. Mind you I suppose that except for chips, it all comes under the wheels category.

[Sam Christie]

The subject of why a 9/44 crownwheel and pinion is better on an M-type has come up on the MG Triple-M Forum -

Reply (1)
One of the features of an M-type is their ability to get along the open road. Their lightness (and lively engine) enables them to cope admirably with their relatively tall rear axle. Changing to 8/43 would be a seriously retrograde step.What you will get is an M type which could climb Everest in 2nd gear!

Reply (2)
I am the first to champion lower overall gearing - but the last thing an M Type needs is revs.

You will be able to start in 2nd gear (even on a 3 speeder) and you might be able to gain valve bounce in top.

But seriously leave the gearing where it is - the engineers at MG knew what they were talking about!

However - if you plan competition use that is a different matter - then you start gearing the car to maximum revs at the end of the longest straight (on an 8-43 that would be suitable for Ben Nevis).......END OF REPLY

......Perhaps the lower ratio is fine for saloons but not ideal the very light M-type ?

Sam

[Ian Grace]

Absolutely right - if you have an open Minor and its on tune, it needs a 9/44 to get along at is advertised top speed of 50+. if you have a saloon and a big family or are lugging coal, then go for the SV 8/43. Similarly for any trials work, use the 8/43 or even a 7/37. Also, remember that the 8/43 and 7/37 have fatter and therefore stronger teeth on the pinion and so are more robust for trials work.

Unfortunately, good original 9/44's with all their teeth are like hen's teeth - I only have an 8/43 in the Bed-Pan and I could also do with a 9/44 for it if anyone has a spare set.

[David Whittle]

IMHO If you fit 400 x 19 decent tyres (as fitted at the factory), like Blockleys, the results of the Morris 8 diff gives very adequate road performance in my standard Minor! Any higher gearing would be awful on the light car rallies and trials. As it is some of the road hills in Wales require maximum performance in 1st to concour, and on some Welsh countryside top gear is a luxury seldom encountered! Perhaps owners in the Fens need higher gearing but most of the LC&E folk need the stronger lower diff!

My car keeps up with all the other Minors when out and about! Cruising at about 38/42 MPH

[DF9053]

What is the actual difference in road speed between the diffs, in decimals the ratios are 4.89 (9/44), 5.375(8/43) and 5.28 (7/37)

So with a 4.00x19 the 4.89 diff gives approx 16.2mph per 1000 rpm, the 5.28 diff 15.2 mph. So at 2000 rpm on car is doing 32.4mph whilst the other 30.4mph

With 3.50x19 tyres you get 15.8 mph and 14.6 mph per 1000 rpm for the same two diffs. Resulting in 31.6 and 29.2mph at 2000 rpm.

So pick your diff's and tyres to suit your uses and location! 5 up in a saloon living in Wales you need all the help you can get the other day I got overtaken by a tractor!