1926 Rover 9/20 2 seater parts wanted

[rob]

Hi I see you had posted on another forum querying the rear axle ratio for a 9/20? One of my owners manuals states it is 4.84 to 1.

Regards
Rob.

[jp928]

Rob,
Sorry I missed your post this long. Turning the propshaft with one back wheel stopped I came to 5.8, which dosent seem unreasonable when a 10/25 manual list top gear as 5.2. There is nothing in the 9/20 Maintenance manual I have giving diff ratio or gearbox ratios. A 9/20 having a lower numerical diff ratio , with less power would surprise me a bit, unless the tyres/wheels were smaller than the 10/25?
I now know the speedo turns/mile (2850 IIRC), and the alloy wheel that drives the speedo cable off the propshaft is stepped DOWN 4.8:1, and the tyres are 19x4.40; this gives a speedo cable turns/mile of (assuming 5.8 diff) of 870revs/mile. I intend to wait until I see what the speedo reads on the road before changing anything - the speedo people say they can splice a gearbox of any desired ratio into the cable if necessary.

I had an email response to an ad on Vintage drivers club recently, offering unspecified parts. When I asked what he had, responded with a picture, saying he was breaking that car up, what did I want. Sadly it was a picture of my car before I bought it, stolen off Flickr. Sent him off with a flea in his ear! Email was eric53lawrence@gmail.com.
Thanks
jp

[rob]

Hi sorry I missed this reply, I have 2 different factory owners manuals, one manual on page 17 states overall gear ratios of 16.44 for 1st, 8.57 for 2nd and 4.84 for top. Given that the gearbox goes silent in top gear one would assume like most other gearboxes of this era a 1 to 1 top gear ratio?? I remember reading once that you should jack up one side (with a none LSD) turn the wheel 10 times, count the tailshaft revolutions and divide this number by 10 for an accurate reading. The standard 4.50 x 19 tyres are 28" tall, the engines maximum power is at 3000 rpm, combine these figures with a 4.84 diff ratio and you come up with a maximum speed of 50 mph which is the same max speed the period road tests came up with. I don't think a 20 bhp engine would be capable of running past it's peak power revs on a level road. The technical drawing in the parts book is a bit blurry but it looks like a 6 tooth worm and a 29 tooth crown wheel, which would give 4.833 to 1?

Cheers Rob.

[jp928]

Rob,
apparently missed this post again! I have an old worm gear, and its got 5 teeth, and my parts book also shows 5 leads. My parts book shows a 30 tooth worm, which would give a 6:1 diff.The 10/25 book actually gives a diff ratio for that model of 5.2:1, which sort of makes sense for a bit more power.....Working on the basis of 6:1 for the moment.
thanks
john

[jp928]

When I look more closely at my parts book, the wheel has 26 teeth, worm is a 5 start , so that makes it 5.2, same as the 10/25. Possible.
Since cleaning out the radiator I now have a leak in a couple of places, so I am looking around for a radiator, or somewhere that makes cores I could afford. Couple of firms in UK say they can, waiting for an estimate now. People in NZ say they can do it, but word is they get the cores from UK.
jp