Irvine Mills .75 replica

Hi Guys

Following my Mills adventures, I've found another Irvine one :



This one has a remarkably low serial number (0036)

The vendor selled me what seems to be a VA Mini Mills 0.4 (larger than a Pee Wee so I assume this is the 0.4 cc variant ; but could be a 0.25 cc assuming diesels are larger than glow engines for the same displacement - if anyone has some dimensions for comparison...)



Unfortunately the engine is clogged, and furthermore the sleeve is not well aligned with the crankcase : one of the 2 intake ports is partially hidden... so I need to dismantle this little beast, but I don't now how to remove the "muff" in a clean way (without scratches). Any experience would be appreciated.

Vincent

The only way to safely remove the muff is to use a leather strap, or a plumber's type strap wrench.
I'm surprised that the liner is misaligned as I thought that Irvine fixed that issue. My original Mills has chunks taken out of the sides of the con-rod due to a rotated liner.

Read this about the cylinder liner repair, I got one and needs this done but i just have not had the nerve I guess? http://modelenginenews.org/cardfile/m75.html Getting old sucks use to bee i would get in there and DO IT .

Your small Mills is the VA .4cc version-the best one to own-the 0.25cc has a number of issues associated with it, and few were as good as they could have been. Quite apart from the difference in size, the 0.25 is readily identifiable by having two holes at the exhaust opening rather than the oval 'racetrack' shape of the 0.4cc model. easily spotted and identified.--it looks like the numeral '8' lying sideways.

ChrisM
'ffkiwi'

ffkiwi wrote:Your small Mills is the VA .4cc version-the best one to own-the 0.25cc has a number of issues associated with it, and few were as good as they could have been. Quite apart from the difference in size, the 0.25 is readily identifiable by having two holes at the exhaust opening rather than the oval 'racetrack' shape of the 0.4cc model. easily spotted and identified.--it looks like the numeral '8' lying sideways.

Thank you for identifying the model! However, as the liner is misaligned, I will have to dismantle it before trying to run it.

Vincent

Grosvince wrote:

ffkiwi wrote:Your small Mills is the VA .4cc version-the best one to own-the 0.25cc has a number of issues associated with it, and few were as good as they could have been. Quite apart from the difference in size, the 0.25 is readily identifiable by having two holes at the exhaust opening rather than the oval 'racetrack' shape of the 0.4cc model. easily spotted and identified.--it looks like the numeral '8' lying sideways.

Thank you for identifying the model! However, as the liner is misaligned, I will have to dismantle it before trying to run it.

Vincent

I wouldn't bother-looking at the exhaust opening it is fairly close-and if it has been previously run like that you will upset the fits to a degree by relocating the liner. From memory-both my examples are in models and not easily accessible as I write this-there is no positive location for the liner, unlike in some Mills 75 replicas-which use a pin engaging in the liner flange-(the original Doonside of 1973 was the first to do this) the VA is like the originals-just screw the head down and hope. In practice-the best you can do is use a piece of wood which is a snug fit in the exhaust ports and push it through both before tightening up the head. This at least allows you a reasonable chance of keeping the alignment as the head tightens down on the liner flange. Without some form of mechanical locking, the liner will rotate slightly as you do the head up tight.

I would though remove the backplate before doing anything and check the rod-the clearance slots in the liner (put there to allow for rod angularity clearance at 90 degrees of crankthrow) can foul the rod if the liner is too far out of alignment. Forget about aligning the intake port-it is the alignment of the exhaust ports that matters-as these are the ones that relate to the conrod cutouts below. Having just gone down to the garage and checked one of mine-the intake port is not fully aligned in the venturi opening whereas the exhaust ports are-and this is what matters. It makes no detectable difference to the way the engine runs.If it's any comfort the original ones use a pair of holes in a horizontal figure 8 as the intake and transfer ports-and it was rare to find these fully aligned either.

ChrisM
'ffkiwi'

On my Currie Mills (Aurora) I have done exactly what Chris said about using a dowel in the exhaust ports to keep the liner close to being in alignment.
Never had really any problem doing it that way as I tightened the beehive head down onto the liner.

sosam117 wrote:On my Currie Mills (Aurora) I have done exactly what Chris said about using a dowel in the exhaust ports to keep the liner close to being in alignment.
Never had really any problem doing it that way as I tightened the beehive head down onto the liner.

I usually use a short length of spruce, rounded off at the edges-the key is not to use anything hard, or reach for the nearest screwdriver or steel tommy bar to do the job, lest you burr the cylinder. If you have the skills and equipment-at the very least a Dremel and a pinvice for small diameter drills-there is merit in installing a pin in the case to engage with a matching slot in the liner flange. I've done this to some of my non Doonside Mills-I may have done it to some of the other engines such as the VA's as well....I'm fairly sure the MP Jets have it done during manufacture...

ChrisM

I have used my Dremel tool to drill small holes for a pin and 1/2 the time I break off the small drill while drilling the hole.
Now with the broken drill (if it is sticking out) becomes my location pin.

sosam117 wrote:I have used my Dremel tool to drill small holes for a pin and 1/2 the time I break off the small drill while drilling the hole.
Now with the broken drill (if it is sticking out) becomes my location pin.

Yep-you have to use a delicate touch-IIRC the original Doonside used a tiny length of .010 or .012 control line wire-so that's a damn small drill to drill the hole with...I use a pin vice or a small spiral jewellers push drill to do the drilling-I tend to use something metric mostly since I don't have much in the way of those 60-80 number drills-a 0.5 mm works for .020 wire-a few 10 thou undersize-and you have to tap the wire in-which helps it stay put. I just use the dremel with a thin cutoff disc to cut the small slot in the liner flange

CJM

Hi Guys,

Some sun eventually here in France. I've got a try on the Mills .75, on a Boddington design, the Mills Beam. This plane flies well under engine power, but glide like a cloth iron. But I love the sheets&sticks design (some sort of a 2CV of a plane - the 2CV is a post-WW2 minimal french car)



The engine seems wanting to run at constant speed, but you can greatly improve the duration of the tank by tweaking needle valve and contra-piston.

https://outerzone.co.uk/plan_details.asp?ID=7793

Indeed, some serious fun !

Vincent

Very neat indeed, I love the fact your using a diesel. I powered a few free flight planes with my converted diesels from Cox engines. I was getting runs that were too long. I still loved hearing it though.

The tank is very tiny (maybe 2-3 ml) but the runtime equals a well tuned Babe Bee with a 5 ml tank.

I will make an external tank for RC flying.

Regards

It Looks Great Vincent I looked at the pic on Outerzone

Thank you, I've just seen Outerzone used my pic as the main pic on the Mills Beam page !

Surprise Surprise !! Thats cool i thought you put the address in there for that

Grosvince wrote:The tank is very tiny (maybe 2-3 ml) but the runtime equals a well tuned Babe Bee with a 5 ml tank.

I will make an external tank for RC flying.

Regards

I assume you are not aware that there is a larger tank made for the Irvine Mills specifically to give a longer run for R/C use?   whilst hard to find there may well be a few left with some UK stockists such as Steve Webb models-the 'long range tank' has about twice the capacity of the standard tank and is a direct screw in replacement onto the normal Irvine 75 intake assembly

ChrisM
'ffkiwi'

Hi guys,

A little video of the beast taken at our airfield :



I'm not very proud of my rear wind landing

The tank is very tiny for RC usage !

Regards,
Vincent

She looks to fly very well , and it states it not a good glider but flys well under power , So you got it right ! Thanks for sharing and Yes a little longer would bee better .

Aurora of India. Made a 1.0cc version.  It went through a tank of fuel in seconds.

VA from Russia made .25cc and .4cc versions in gray and black finishes.  Even an RC carb for the 25cc.

I made the boxes for my engines.

I have a Mills p.75 tryed to run it a couple time with no luck , I think my diesel fuel mix was off ... Then I read where they had problems with the liner moving and needed a mod. so it sets till then . You do make some nice display boxes wonder if @rsv1cox has seen them he has repaired a few of his boxes in the past .

getback wrote:I have a Mills p.75 tryed to run it a couple time with no luck , I think my diesel fuel mix was off ... Then I read where they had problems with the liner moving and needed a mod. so it sets till then . You do make some nice display boxes wonder if @rsv1cox has seen them he has repaired a few of his boxes in the past .

Well the mills 75 is about the easiest starting diesel ever made-so something was definitely off...either your fuel, the compression setting or something. The piston liner fit is so good they last virtually indefinitely. The conrod is a bit of a weakpoint, given its length, and the need for liner clearance-plus the previously mentioned risk of someone putting the liner in 180 degrees pit of alignment-thus mixing up the inlet and transfer ports-which results in messed up timing. The best mod-as carried out by ivor F with the Doonside Mills replica is a tiny slot in the cylinder flange into which a small diameter pin pressed into the top of the crankcase fits in reassembly. This eliminates any possibility of liner rotation and incorrect orientation-and removes the problem of the liner bottom chewing the rod if the clearance slots are misaligned. FWIW I am gradually doing this mod to all my mills 75-original or replica...exempting the Doonsides which already have it done ex factory. Peace of mind for very little effort!

ChrisM
'ffkiwi'

I too have acquired one of these engines

I am still researching about it which has directed me here of all places

May I ask please, rear cover, mine seems to have two shirt angled webs
Within the rear cover outer hole, a flat bar being used to unscrew the cover via these webs.

The tank plate has two alloy *tabs* to retain the tank which is missing.

The compression screw is T shaped rather than L and the stop pin in the head is missing .

Numbers seen from above between engine bearer holes are, Port side, 41, and starboard side, Either 765 or 785, the 5 being smaller than the other two digits, slightly smaller. Engibe intake at rear.

Crankcase is black. If it's sand cast, it's been done well .

Engine will be very gently cleaned to preserve black coating, and reveal any other markings/numbers .

I have yet to read this complete thread....

What would, if anything, the rear cover webs indicate please ?

She will be run up eventually after checking for any rod/liner clearance issues, re ranked ( not sure how yet ) and fitted to a 2, maybe 3 channel "tomboy"........ I also need to get/make a domed prop nut .