HobbyKing.com New Products Flash Sale
Reply
Thread Tools
Old May 21, 2012, 08:54 PM
Registered User
Joined Jan 2008
1,208 Posts
I have Aurora Mills 75 and 1.3. They took a bit of breaking in, but now start and run as one would expect. The compression screw on the 75 is loose and I've been holding it while running on the bench. I've been intending to re tap and put in a setscrew. However, I have been contemplating trying park flier sort of RC. I read of the idea of moving the compression screw as a throttle. This would work with my 75, I think. So I'm not going to get excited about fixing it.

I think I read in an Aeromodeller that some of the early Indian Mills were superior runners compared to the originals.
Jim Thomerson is offline Find More Posts by Jim Thomerson
Reply With Quote
Sign up now
to remove ads between posts
Old May 21, 2012, 10:36 PM
Registered User
earlwb's Avatar
USA, TX, Grapevine
Joined Dec 2008
13,338 Posts
Quote:
Originally Posted by Jim Thomerson View Post
I think I read in an Aeromodeller that some of the early Indian Mills were superior runners compared to the originals.
It figures that some people would have all the luck. The magazine probably got a "cherry picked" engine to review.

I would simply make a small locking lever for the adjustment screw. No sense getting all that fancy making it up better.

Actually they seem to work fairly well using the compression screw as a throttle of sorts. The problem though is when you are increasing the compression it might take more force than the servo can provide.
earlwb is offline Find More Posts by earlwb
RCG Plus Member
Latest blog entry: My new Gaui X5 Rc Helicopter
Reply With Quote
Old May 22, 2012, 04:37 AM
Sticks, Tissue & old Diesels
brokenenglish's Avatar
France, Centre, Amboise
Joined Nov 2011
1,682 Posts
Quote:
Originally Posted by Jim Thomerson View Post
I have Aurora Mills 75 and 1.3. They took a bit of breaking in, but now start and run as one would expect. The compression screw on the 75 is loose and I've been holding it while running on the bench. I've been intending to re tap and put in a setscrew. However, I have been contemplating trying park flier sort of RC. I read of the idea of moving the compression screw as a throttle. This would work with my 75, I think. So I'm not going to get excited about fixing it.

I think I read in an Aeromodeller that some of the early Indian Mills were superior runners compared to the originals.
Jim, when you say the compression screw is loose... This shouldn't be a problem... Do you actually mean that the contra-piston is loose?

RC throttles exist for the Mills .75 and 1.3. I've also read that the Tarno TD 049 throttle fits a Mills .75.
Using compression adjustment in flight seems unrealistic to me. A servo arm in linear motion couldn't apply more than about one quarter of a turn on the screw, and this would probably by insufficient for worthwhile throttling.

It seems to me that, whenever a new repro is released, there's always great enthusiasm about its quality and performance...
Remember when the CS Tigers were first produced. I remember reviews (Australian, I think) claiming that they were "at least as good as the originals"... After a year or two, everyone realizes that this is nonsense, and that the repros are way below the quality of the originals.
I've owned one Doonside and two Irvine Mills that all had the cylinder rotation problem. They would run OK for a minute or two, and then the cylinder would rotate and the engine would no longer run.
I've also owned several Indian Mills that were all good runners with no particular problem.
The bottom line is that the originals are best (the only ones that are reliably trouble-free), and my own preference would be for the Mark I.
brokenenglish is offline Find More Posts by brokenenglish
RCG Plus Member
Old May 22, 2012, 06:49 AM
Registered User
DeeBee1's Avatar
United Kingdom, England, Brighton
Joined Apr 2007
1,138 Posts
Quote:
Originally Posted by Jim Thomerson View Post
The compression screw on the 75 is loose and I've been holding it while running on the bench.
Jim, last Aurora Mills I bought has a small spring running outside the comp. screw (see awful sketch attached!). I assume this is to try and stop the thing uncompressing itself - seems to work. The other Auroras I've had didn't have this spring.
DeeBee1 is offline Find More Posts by DeeBee1
Reply With Quote
Old May 22, 2012, 07:57 AM
looking up down under
scruffy1's Avatar
Australia, NSW, Fairlight
Joined Feb 2008
1,484 Posts
wow, what a blast from the past

as per my memory, ivor f. (aka ivor stowe) produced a run of "doonside mills" with the assistance of gordon burford - two great australian legends of modelling

i had the job of being ivor's gofer in the scramble at the 1976-7 bunbury nats, where i chased his mills powered model for the event

i was too young and impecunious to buy one after i blew my $ on a dc dart 0.5cc that i still have today (along with a collection of taipan diesels )
scruffy1 is online now Find More Posts by scruffy1
Reply With Quote
Old May 22, 2012, 10:35 AM
Sticks, Tissue & old Diesels
brokenenglish's Avatar
France, Centre, Amboise
Joined Nov 2011
1,682 Posts
Quote:
Originally Posted by DeeBee1 View Post
Jim, last Aurora Mills I bought has a small spring running outside the comp. screw (see awful sketch attached!). I assume this is to try and stop the thing uncompressing itself - seems to work. The other Auroras I've had didn't have this spring.
Other engines (Micron 2.5R) had such a spring as standard, without actually needing it. Whether it works or not depends on just how loose the contra-piston is, and how tight the comp screw threads are in the head, but the fact remains that a properly fitted engine shouldn't need a comp screw lock...
brokenenglish is offline Find More Posts by brokenenglish
RCG Plus Member
Old May 22, 2012, 10:51 AM
Registered User
DeeBee1's Avatar
United Kingdom, England, Brighton
Joined Apr 2007
1,138 Posts
Quote:
Originally Posted by brokenenglish View Post
but the fact remains that a properly fitted engine shouldn't need a comp screw lock...
Agreed. I had a PAW 55 where the needle valve and the comp screw both used to adjust themselves due to vibration. Needle valve was easy enough to tighten, but the comp screw was a pain.
DeeBee1 is offline Find More Posts by DeeBee1
Reply With Quote
Old May 22, 2012, 11:02 AM
Registered User
Joined Jan 2008
1,208 Posts
On my Mills, it is about a quarter turn range from just right to slow undercompressed, and doesn't take much to turn it. I may try the spring idea.
Jim Thomerson is offline Find More Posts by Jim Thomerson
Reply With Quote
Old May 22, 2012, 05:13 PM
Registered User
fiery's Avatar
Hervey Bay, Queensland, Australia
Joined Mar 2008
559 Posts
Doonside Mills .75

My understanding is the Doonside Mills replica had it's cylinder pinned to prevent rotation when tightening the cylinder jacket.
fiery is online now Find More Posts by fiery
Reply With Quote
Old May 23, 2012, 08:00 AM
Registered User
earlwb's Avatar
USA, TX, Grapevine
Joined Dec 2008
13,338 Posts
Some people will discover that the 8x3 props usually have a hole in the center that is too large for the engine, so they can't center the prop correctly. What I have done in the past was to use some short lengths of heat shrink tubing and put the tubing on the crankshaft shoulder and heat shrink it, to build it up to center the prop better.

More recently I made some small metal spacers to fit into the rear recess on the Master Airscrew props. If you use that rear molded in recess you don't have to balance the props or anything as that is what the factory used to set the props up in the first place.

The basic method was to chuck up a piece of aluminum in a lathe, then drill the center hole with a slightly undersized drill bit. What I did was drill a hole in some scrap aluminum and check the crankshaft shoulder fit on the hole and get a drill bit to match that just right. Then I machine down the outside to be a snug fit on a MA propeller. Then I used a cut off tool to cut the short spacer off the rod. You might have to chase the small part across the floor when it comes loose so be prepared for that too.






earlwb is offline Find More Posts by earlwb
RCG Plus Member
Last edited by earlwb; May 23, 2012 at 09:20 AM.
Reply With Quote
Old May 23, 2012, 10:18 AM
Registered User
DeeBee1's Avatar
United Kingdom, England, Brighton
Joined Apr 2007
1,138 Posts
Nice job earlwb, I use a short piece of fuel tube screwed onto the prop shaft and then push the prop onto that. It works but your idea looks much more professional.

Can you start selling the inserts so we can buy them? - I've never found a prop that comes with just the right hole for a Mills .75.
DeeBee1 is offline Find More Posts by DeeBee1
Reply With Quote
Old May 23, 2012, 11:01 AM
Sticks, Tissue & old Diesels
brokenenglish's Avatar
France, Centre, Amboise
Joined Nov 2011
1,682 Posts
Quote:
Originally Posted by DeeBee1 View Post
I've never found a prop that comes with just the right hole for a Mills .75.
That's probably because you're using modern propellers.
Modern thinking dictates that (say) an 8x4 corresponds to a .15 size TBR engine, and the modern G/F and C/F props are made based on that assumption.

Really, if you want to use old engines (which is all I use), you need a good stock of old props. For example, the KK, DC, Topflite and Tornado props of the sixties were sold with holes that suited the older engines, i.e. the original hole in a KK, DC or Topflite 8x4 fits a Mills fine... and you have to ream it out a bit for an ED Bee or an Amco!
The thought has never occurred to me, as I only use old wood or plastic props, but I don't think I'd like to fly an original Mills .75 with a carbon prop...
brokenenglish is offline Find More Posts by brokenenglish
RCG Plus Member
Old May 23, 2012, 11:31 AM
Registered User
earlwb's Avatar
USA, TX, Grapevine
Joined Dec 2008
13,338 Posts
Quote:
Originally Posted by DeeBee1 View Post
Nice job earlwb, I use a short piece of fuel tube screwed onto the prop shaft and then push the prop onto that. It works but your idea looks much more professional.

Can you start selling the inserts so we can buy them? - I've never found a prop that comes with just the right hole for a Mills .75.
Thanks
I need to think about it. I also need to check to see if the spacer inserts work Ok on my other Mills engines and replicas too. I don't know how close they all followed the specs, so to speak. Some of the different engine replicas may have used different crankshaft sizes.
earlwb is offline Find More Posts by earlwb
RCG Plus Member
Latest blog entry: My new Gaui X5 Rc Helicopter
Reply With Quote
Old May 23, 2012, 11:39 AM
Registered User
DeeBee1's Avatar
United Kingdom, England, Brighton
Joined Apr 2007
1,138 Posts
Quote:
Originally Posted by brokenenglish View Post
Really, if you want to use old engines (which is all I use), you need a good stock of old props.
Yeah you're right, although I've never had a problem running any of my vintage engines with newer props and it's only the smaller ones that have the smaller prop shaft. Bit of a pain having to fit a bit of fuel tube but it doesn't take long.

No problem with my old Cox engines as you can still get the props!
DeeBee1 is offline Find More Posts by DeeBee1
Reply With Quote
Old May 23, 2012, 11:59 AM
Sticks, Tissue & old Diesels
brokenenglish's Avatar
France, Centre, Amboise
Joined Nov 2011
1,682 Posts
One of the best props for gentle Mills flying is the Cox 8x4 TD15 prop.
I thought of Cox props after my post. They all have small holes because all Cox engines (except the Conquest I think) use the hollow shaft prop/bolt principle.
I often use the old TD15 props on old diesels around 0.75 to 1cc.
In any case, the props I mentioned frequently come up on eBay, and often new.
brokenenglish is offline Find More Posts by brokenenglish
RCG Plus Member
Reply


Thread Tools

Similar Threads
Category Thread Thread Starter Forum Replies Last Post
Discussion didn't someone build and fly a Coro Delta with small diesel engine earlwb SPAD - Simple Plastic Airplane Designs 15 May 27, 2011 09:56 PM
Discussion Help on Mills Diesel Assembly NX-687 Engines 2 Dec 22, 2008 03:46 PM
Wanted Mills 75 Diesel Tag1260 Aircraft - Fuel - Engines and Accessories (FS/W) 3 Feb 28, 2006 07:54 PM
Mills 0.75 Diesel RC mlbco 1/2A Planes 10 Apr 02, 2005 09:20 PM