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How do you identify a genuine Mills P-75 Diesel?

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How do you identify a genuine Mills P-75 Diesel?

Old 09-24-2009, 09:50 PM
  #1  
Dan Vincent
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Default How do you identify a genuine Mills P-75 Diesel?

I was making a display box for my Mills P-75 and was wondering how do you prove a Mills is genuine and not one of the many replicas.

My Mills has a serial number over the right beam mount.
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Old 09-24-2009, 10:09 PM
  #2  
Tee Bee
 
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Default RE: How do you identify a genuine Mills P-75 Diesel?

Can't really help ya with id but that's a neat display. Here's my old Deezil(late 40's from what I've been told). It was run several times on a test stand in the 60's, put into storage for many years, and then given to me. It was never flown according to the guy who gave it to me. It had belonged to his father and he would run it for his kids from time to time for entertainment. Long before video games.
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Old 09-24-2009, 10:12 PM
  #3  
Dan Vincent
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Default RE: How do you identify a genuine Mills P-75 Diesel?

Tee Dee,

If you have an original Deezil that actually runs you'd better treasure it.

So many of them had terrible fits and wouldn't run.

Consider yourself fortunate.
Old 09-24-2009, 10:43 PM
  #4  
SGC
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Default RE: How do you identify a genuine Mills P-75 Diesel?

DAN,
That looks to be a genuine Mills- not sure if the carb is tho(I think all Mills had a one peice machined carb/venturie , includeing the needle valve body)
From what I know,
Indian mills had india stamped inside the backplate, likewise Irvine had irvine, the Doonside has webs on the crankcase to shaft extension as does the russian copies.
Hope this helps
Stewart
PS mine has No's on both beam mounts - 2 aside, one peice carb assy with cutout arm- missing the spring.
Oh I think most genuine P75's also had a pin to limit the compression screw movement, yours is missing , does it have a small threaded hole for said pin ?
Old 09-24-2009, 11:43 PM
  #5  
Dan Vincent
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Default RE: How do you identify a genuine Mills P-75 Diesel?

Yes, there is a pin hole.

Mine is a P-75. P=Popular.

The S-75 had a spring for the air bleed. S-Standard.
Old 09-25-2009, 01:00 AM
  #6  
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Default RE: How do you identify a genuine Mills P-75 Diesel?

Dan your engine certainly looks a genuine Mills to me-BUT your front end is a bit suspect. The spinner nut looks too big, the prop washer too shiny and the prop driver is not right. The Mills 75 has a simple knurled face, flat disc prop driver with a truncated circle centre hole that matches the two flats on the crankshaft-yours seems to have a centre boss as well-which would be right for the 1.3 but not the 75. Either that or the spinner nut has a shank on it-a la ED Hunter-which is also incorrect for a Mills.
A genuine Mills should have the black crankcase (fairly dull, not glossy like the late model Indian ones) as a result of the chromate bath used to protect the magnesium crankcase alloy, a similar cast, treated backplate with two internal webs for a spanner to locate on for screwing in (most of the replicas have the more common diametrically opposed slots in the rim), no webs on the crankcase bearing housing, and sharp corners (no bevel) on the mounting lugs, plus serial numbersd stamped on the top surface of the mounting lugs-normally 2 digits on one and 3 digits on the other. Tank is a fairly thick perspex moulding which often crazes with age, and is retained by a couple of small tabs on the tank top bent over the rim of the tank.

Early Indians are grey, and have 'India' stamped in the centre of the backplate, a sharper tapered tank, and no stop pin hole in the head. Later ones have a black crankcase-which has a painted rather than treated look. Doonsides have 'made in Australia' and "Taipan' stamped on the backplate, plus a fully machined carb and tank top, a nylon tank retained with an internal circlip in the tank top, and a fairly heavy duty spring with properly ground ends, on the needle valve. The Mk2 Doonsides have webs on the case and a plain silvery crankcase, with anodised heads in a multitude of colours. The Russian-made Doonsides (effectively a Mk3-though they were never designated as such!) had a 3mm replaceable prop shaft stud-with a splined on prop driver-some were ABC cylinder technology as well.

Irvines had a serial number on the edge of the mounting lug, a taper mount prop driver and thicker shaft, and a male threaded tank which screwed into the female threaded tank top. The very last ones had a single ball race.

The exceptionally rare NZ made HPE Mills 75 replicas (there were only about 10 completed) had the tank top , needle valve block and venturi as a single unit casting, not separate machined components.

The first model Boddington Mills 75 looks quite a bit different from the Mills, so cannot be confused-the second model is a much closer replica, but I do not have one, so can't describe its key differences

'ffkiwi'
Old 09-25-2009, 07:04 AM
  #7  
qazimoto
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Default RE: How do you identify a genuine Mills P-75 Diesel?


ORIGINAL: Dan Vincent

I was making a display box for my Mills P-75 and was wondering how do you prove a Mills is genuine and not one of the many replicas.

My Mills has a serial number over the right beam mount.
Both my genuine Mills .75 have the words "Mills England" embossed on the cast backplate. This and the serial numbers on the lugs is my final test. The initial one is the look of the magnesium crankcase. These are like yours usually slightly corroded.

Ray
Old 09-25-2009, 07:21 AM
  #8  
Dan Vincent
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Default RE: How do you identify a genuine Mills P-75 Diesel?

ffkiwi,

Thanks for the detailed info.

I guess I'll take some more pictures to show the backplate and front end hardware.

The backplate just has two angled gussets to give a grip for removal.

This engine has really strong compression and should make a great runner.

I'm sure a Mills guy could make this engine look like new with little effort, maybe a good clean-up and new tank bowl.

The prop nut spinner is threaded and screws on to a threaded crank with shoulder.

I looked in my Mike Clanford book and see what you mean about the prop drivers. Could it be this is an early one and had different hardware on the front end?
Old 09-25-2009, 12:24 PM
  #9  
Dan Vincent
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Default RE: How do you identify a genuine Mills P-75 Diesel?

OK, took some more pics of the Mills.

The backplate does have Mills and England although it needs to be cleaned to bring it out.

The pin hole in the muff looks like there is a tiny screw in it. I'll have to find my tiny jewelr's screwdriver.

Here's a shot of the prop driver.
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Old 09-25-2009, 02:17 PM
  #10  
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Default RE: How do you identify a genuine Mills P-75 Diesel?

Dan other than the front end its the real deal. As I guessed earlier the prop driver and spinner nut are not kosher. The prop driver resembles the 1.3 one, with a centre spigot. Since it is likely to have a taper fit, this almost certainly implies that the crankshaft has a matching taper as well-which means the shaft is not original. This is not too surprising as Mills shafts are realtively easily broken in a crash-and invariably they snap off at the strees raiser caused by the two flats where the prop driver fits-leaving about 1/8" projecting from the case-if you're unlucky you lose the entire front end in the grass as well [been there, done that with a Doonside!] So it is quite likely that a previous owner had a shaft made up-and used perhaps some spare 1.3 bits to complete the job. Attached are some photos of an original Mills 75-note the spinner is non original-note the webs in the backplate, the small tabs retaining the tank, the sharp edges to the mounting lugs, and the prop driver. Now another pic with a group of Mills 75s:clockwise from top left: original english Mills(with correct spinner nut this time!), Irvine Mills (you can just make out the serial number stamped on the edge of the RH mounting lug-note also different prop driver and small 'acorn' type spinner), early (mid 80's) Indian Mills-note rounded head profile and more sharply tapered tank [this one should have a hex spinner nut but they strip easily!], Boddington Mills (made by CS)-quite different to all the rest, Russian made ABC Doonside Mills-high quality surface finish, webbed bearing housing,thicker, more parallel fin profile-thick alumium prop driver, and finally lower left an original Australian made Doonside Mills Mk2 -webbed crankcase, coloured head
Next some bits-top left an original Mills 75 prop driver (steel) and spinner-note the 'flattened circle' centre hole, next two complete carb assemblies-the first is a Doonside one-the steel circlip retaining the tank is just visible as a dark line inside the tank top, on the right an Irvine carb assembly-note the blacked needle, and beside that the rarely encountered long range tank which screws into the carb as a direct replacement for the smaller standard tank, if required, for longer run times in R/C models. Below this a broken 1.3 crankshaft-note the taper for the prop driver fitting
Finally, a shot of a 1.3 and 75 crankshaft-in particular note there is no taper on the 75 shaft, and one of the two milled flats for the prop driver seating is clearly visible.

A couple of other points: Indian Mills were manufactured using the original english tooling, jigs and fixtures from Mills Bros-so parts are interchangeable. The Australian made Doonsides were made by averaging measurements from a number of originals-there was a lot of variation in the originals. Parts may or may not be interchangeable-it will be pure luck if they do. Irvines were made to resemble the Mills 75 externally, but are quite different internally-NO parts are interchangeable with originals. The Russian Mills are probably metricated, but some parts may interchange with the Australian Doonsides. The Boddo Mk1 is unique. The Boddo Mk2 looks more like a Mills-but as it is made by CS is probably produced to metric dimensions.

ChrisM
'ffkiwi'
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Old 09-25-2009, 06:46 PM
  #11  
johnvb-RCU
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Default RE: How do you identify a genuine Mills P-75 Diesel?

Great info! Thanks Chris!
Old 09-25-2009, 07:34 PM
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Default RE: How do you identify a genuine Mills P-75 Diesel?

Thanks ChrisM ,
Great info, it apears mine is "almost" original, it looks to have been retrofited with an Irvine tank top and tank - not a bad thing, other than that all looks ok.
Stewart
Old 09-25-2009, 07:46 PM
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Default RE: How do you identify a genuine Mills P-75 Diesel?

A couple of afterthoughts from my previous posting-should you have the misfortune to break either an original, Doonside or an Indian Mills crankshaft, be VERY careful when you attempt to withdraw the broken shaft rearwards out of the crankcase. You will have seen that the prop driver in a couple of the photos in my previous post has moved forward on the shaft-this is typical-the fit is relatively loose on the two shaft flats and the prop driver merely sits in position, keyed by the two flats. There is no locking force retaining it there. This makes it easily removed-the down side of it this-and the point of this post-is that with time-the hardened steel prop driver raises tiny burrs on the edges of the crankshaft flats. If you attempt to withdraw the broken crankshaft, these burrs will invariably badly score the bronze bush of the main bearing, ruining it. Your only safe option is to carefully withdraw the shaft slowly-and if any resistance is felt as the flats portion of the shaft enters the main bearing-then STOP-get out a swiss file (or a points file if you still have one!) and dress the flats carefully until any burrs are gone, and you can withdraw the broken shaft safely. Be warned that this may take a lot longer than you think-I found this when treating the afflicted Mk2 Doonside previously mentioned-by hell that shaft was hard! Ironically-that engine has run happily for the past 25+ years with an Indian 75 shaft in it! Yes-one of those maligned 'about as much strength as a carrot' ones........
On a more positive note-there is someone on Oz who can drill and tap your broken Mills shaft for a 3mm screw, so all is not lost if you break a shaft. Unfortuinately the name of this nonpareil escapes me, since I have never needed his services. David Owen, SGC-one of you Australians must know..........

ChrisM
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Old 09-25-2009, 08:33 PM
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Default RE: How do you identify a genuine Mills P-75 Diesel?

I regard the Irvine carb and tank assembly as the best of the lot-the tank suimply unscrews for cleaning, degunging, or changing the fuel tube. A pity Irvine spares were so expensive when the engines were around. The Doonside is a pain because you have to chase the circlip out of its groove and prise it up and out to remove the tank-very positive retention-but hard to remove for cleaning, whereas the Indians and originals just retain the tank with the two bent tabs-eventually these break off-and your tank won't stay put. Here's a few more pics adding to the info pool-the first is the underside of the Russian Mills showing the serial location (the Russian Elfin replicas are marked similarly in the same location) -note that while the prop driver appears to have a centre spigot, this isn't actually the case the case-what appears to be an integral spigot is a separate bush for centre-ing the prop-necessary because of the small diameter of the 3mm stud. Worth it-you'll never break a shaft on one of these! Next a view of the Boddo series 1 carb and tank-which like the Irvine, screws in. [I've called it a series 1, to avoid calling it a Mk1-which might cause confusion. There WAS a Mk1 Mills 75 made in 1949-it looked very similar to the 1.3 in appearance, with a machined, not cast crankcase. The giveway was the acorn shaped tank. Expensive to manufacture it was quickly replaced-in 1950-by the classic Mills 75, which technically is the Mk2!) Note the solid metal tube fuel line-a nice touch. Finally a closeup of the Mk2 Doonside showing the serial # location on the lower right front of the crankcase-I assume the Mk1 Doonsides would have been similarly marked. This shot also shows a nice view of the prop driver properly seated on the crankshaft flats. For the record, only 1000 Doonsides were produced (give or take a few assembled later from remaining stocks of component by Ivor F.)-there were 250 Mk1's-which were exact copies of the original english one-black crankcases, plain silver head, sharp corners on the mounting lugs and no webs on the main bearing. These were available only to the original 250 subscribers who put up the money to fund the project (ca 1973)-which was initiated by Ivor F-who assembled tested and sold the engines. The actual components were manufactured by Gordon Burford, of Taipan engine fame-which accounts for the stamped backplate-see final pic. The wording reads 'TAIPAN.AUST.'After 250 had been produced the crankcase die was modified to produce the Mk2 crankcase-complete with bearing webs, and bevelled corners on the lugs. You could have your choice of plain, gold, red, green. blue or black cylinder head fins.
Finally (and someone is bound to ask eventually)-why 'Doonside' Mills? Well Doonside is a suburb of NW Sydney, Australia, close to Blacktown, and Doonside is where Ivor F lives.

ChrisM
'ffkiwi'
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Old 11-07-2013, 03:27 AM
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jmcalata
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Default Mills P 75

Hello, Do you know if this Mills P 75 is genuine original?

I see that compresion wrench and prop nut are different.

It has a carter hole (pore) repair with bronze.

Also I need a new plastic cowl tank.


Thanks
Jose
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Old 11-07-2013, 03:53 AM
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qazimoto
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Default

Originally Posted by jmcalata
Hello, Do you know if this Mills P 75 is genuine original?

I see that compresion wrench and prop nut are different.

It has a carter hole (pore) repair with bronze.

Also I need a new plastic cowl tank.


Thanks
Jose
So who's claiming that a Mills 75 dates from 1940?

Otherwise a genuine Mills will have a cast back plate with the two words "Mills" and "England" circumferentialy embossed on it.

The backplate metal should match that of the crankcase.

It should also have a serial number on the top side of each mounting lug.

Other identifying hints will become obvious if you read the thread above.

Good luck, Ray.

Last edited by qazimoto; 11-07-2013 at 03:55 AM.

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