2 little Indians

Hi Klippy how does the good lady like her kitchen?Atoms packed and ready to go. Just waiting for Marg to go to P.O. but it may not be this week Is there a special form for the customs declaration? I wrote the info on the box end but if there is a form /I'll have to ask Dennis the post master to do it as Marg is not good with forms.

Definitely a form to fill in. It looks like this:-


I will have to pay 20% Customs duty on the declared value, so be economical with the truth! The description should be something like 'secondhand engines for repair'

Well, I've finally got back to this, my sincere apologies.
To recap, neither engine will start and I've noticed serious differences in the amount of piston showing in the exhaust port.
With the cylinder removed I measure the amount of 'pop up'. ie, the amount of piston showing above the crankcase at top dead centre (TDC)
#1 2.17mm
#2 3.21mm
Serious differences there, which would seem to indicate that something got swapped along the line.
I then removed the back plates so I could remove the pistons and conrods. Since we already know that the pistons are not interchangeable I decided to measure the stroke (the amount the piston moves from it's lowest to its highest point)
#1 9.8mm
#2 9.16mm
That's an enormous difference! The I measured the pistons (with a micrometer of course)
#1 8.47mm
#2 8.47mm
Identical! To be sure I measured 4 or 5 times!

Back to the 'pop up' question, I then put #1 piston and rod into # 2 and #2 into #1, then measured the 'pop up'
#1 2.79mm
#2 2.35mm
Much better. I then made the assumption (yes I know assumptions are always the mother of all Fups) that since the pistons had been swapped the liners had also been swapped.
The engines have now been re-assembled and await testing.
As an aside, I thought these engines were .75cc but calculation shows #1 is .56cc and #2 is .52cc. Any comments on this, I'm off to make up some diesel.

Could they have been a sort of copy Klip? You know new smaller liners and turned down pistons in an attempt to restore compression.Just2 ps worth A thought ?

Klipkopwildlife wrote: Back to the 'pop up' question, I then put #1 piston and rod into # 2 and #2 into #1, then measured the 'pop up'
#1 2.79mm
#2 2.35mm
Much better. I then made the assumption (yes I know assumptions are always the mother of all Fups) that since the pistons had been swapped the liners had also been swapped.
The engines have now been re-assembled and await testing.
As an aside, I thought these engines were .75cc but calculation shows #1 is .56cc and #2 is .52cc. Any comments on this, I'm off to make up some diesel.

That's interesting. The reprint of the Engine Analysis of the Mills 75 in the 1952 Aeromodeller Annual quotes the bore and stroke as 0.33 and 0.52 inches respectively, which I make .73cc
Mike

That is a heck of a difference in pop ups App 10 difference have you missed the right button on the keyboard.Re capacity the engines are never exactly what they say even in full size .. e.g Atom 1.5 is 1,47 Javelin 1.5cc is 1.49actual and so on Daewoo Nexia 1.5 ltrs is 1497 cc I can;t recall exactly why this is but it's intentional.Something to do with how road tax was administered on Engine capacity.Probably to avoid the next higher Taxation class.

If Klippy's measurements are correct then are not Mills 75 copies but only "similar to" and quite a bit smaller.

Quorneng wrote: If Klippy's measurements are correct then are not Mills 75 copies but only "similar to" and quite a bit smaller.

Could be the case - I wonder if they varied? I remember back in the 70s when the 'Curry Mills', as some called them, appeared, some folk reckoned that they were well down on a genuine Mills for power - others disagreed. If some were only a bit over .5cc no wonder they were less powerful
Mike

Now that's a thought Well said

On reflection I seem to recall that Mills Bros were experimenting with smaller capacity motors and got as far as making a couple of prototypes. I think what you have in your hands are these prototypes History in the making If this is so.It might explain the differences between the two as well.

On reflection I seem to recall that Mills Bros ( sounds like another Gentlemens out fitter ) were experimenting with smaller capacity motors and got as far as making a couple of prototypes. I think what you have in your hands are these prototypes History in the making If this is so.It might explain the differences between the two as well.
I might have read this in model aircraft or Aeromodeller ( Heard at The Hangar Doors Perhaps)
in an editorial piece. If these are the experimental jobs the value could be enormous.Are there any numbers on them Klip? If not it looks like they could be the ones.I wonder where we could find the Mills original documentation.Would they have gone to India with the tooling I wonder. Anyway keep up the good work Klip

one tenor wrote: On reflection I seem to recall that Mills Bros ( sounds like another Gentlemens out fitter ) were experimenting with smaller capacity motors and got as far as making a couple of prototypes. I think what you have in your hands are these prototypes History in the making If this is so.It might explain the differences between the two as well.
I might have read this in model aircraft or Aeromodeller ( Heard at The Hangar Doors Perhaps)
in an editorial piece. If these are the experimental jobs the value could be enormous.Are there any numbers on them Klip? If not it looks like they could be the ones.I wonder where we could find the Mills original documentation.Would they have gone to India with the tooling I wonder. Anyway keep up the good work Klip

Just read the History of Mills engines written by Michael Hardinge son of the inventor/maker of mills engines. In this account he mentions his fathers attempt to make a very small engine. He says he thinks of .1cc he thinks but admits he could be mistaken .He saw the first and last flight in KK model which went O.O.S. and was lost.In light of this I may be right about these being experimental engines and being non ( so far ) starters I'll keep looking O.T.

Duh! A million apologies, how I could have made such a mistake after a lifetime in the business I just don't know! I measured the depth of the crank pin at Bottom Dead Centre (BDC)
#1 36.9mm
#2 36.24mm
Then I measured the crankpin depth at TDC (Top Dead Centre)
#1 23.95mm
#2 23.93mm
One minus the other gives
#1 12.95mm
#2 12.31mm
I then stupidly subtracted the diameter of the crankpin! Duh!
Using the correct figures (thanks Mike for pointing me in the right direction)
Capacity #1 = .847/2 x .847/2 x Pi x 1.295 = .7296cc
Capacity #2 = .847/2 x .847/2 x Pi x 1.231 = .6936cc
Ideally the stroke should be 13.3mm.

A result of sorts. I made up some new fuel using Diesel instead of Paraffin. #1 now starts and runs, #2 still doesn't want to ackle.