[ROVERNET - UK] Diff ratio check

Alan Gale agale at iinet.net.au
Fri Nov 25 01:30:39 GMT 2005

Barry -
Well that's what it is **supposed** to be, but then my engine is 
supposed to be a rover 10 - but in the rebuilding we found it had been 
bored out to a 12 at some stage (prompting some gasket exchanging). 
So I am not taking anything for granted!  The gearbox has 10hp stamped 
on it, so that seems original.

However in the meantime i have worked out that it is a 4.88-1 diff - one 
wheel in the air turns twice for just under five turns of the prop 
shaft, which according to "how stuff works" and a couple of restoration 
and idiots' guides is the best way to check.
Reckon the best thing is to run the car as it is for a few months after 
assembly, let the engine run in and then consider options depending on 
how she performs.  Unrestored she was surprisingly eager (much more 
lively than the Cyclops); so expect her to be a very strong car.  She is 
very lightweight (very easy to push around in the garage, unlike the 
bloody Crossley).
Options therefore include:
1) a longer crown wheel and pinion (say 4.0 - 1) - will take some expert 
advice on this
2) an overdrive unit
3) no change at all. (Why try to make it something she is not?)

According to my maths, the engine will be revving at 3750 rpm at 60 mph 
(the book says I get 16mph/1,000 revs) which is a bit much for direct 
poured big ends and I am more interested in having a comfortable highway 
touring speed (ideally able to cruise at 60-65) than have a fast takeoff 
at the lights (which will never be an option without remaking the gear 
clusters to produce a special close ratio box.  A little overdrive unit 
is appealing, but screams of modernity. 
I think if anything needs doing, I will go for a crown and pinion 
makeover (a lot more cosmetically appealing and a 1930s possible 
I am told that if it is the original rover 10 diff, there is not another 
one that can be used as a swap because of splinal conflicts.  I have a 
spare diff and spare gearbox to experiment with, so there is plenty of 
time to muck about without taking the car off the road.

Thanks for the input and advice, as ever.

Alan G.

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