fiery

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I recently picked up an "as new" Irvine Mills .75, with box and papers, from a forum contributor. After settings were found, starting was as easy as it gets. One choke, two flicks, and it starts. Every time. Hot (back off compression 1/4 of a turn first, then increase when running) or cold. Just like a Mills should.

Compression (piston seal) on this Irvine Mills .75 is excellent.

A minor issue with it. There is too much "fore and and aft" crankshaft play. I will relieve the prop driver very slightly. It needs to be set back towards the case. About one millimetre.

Recycled Flyer

A hardened steel washer or shim maybe easier to take the play out as duplicating the exact angle the crankshaft has is going to be difficult, and unecessary in the end.

fiery

My Feedback: (2)

After more thought, I was thinking the same thing. O.S. do just that on many of their plain bearing engines.

AMB

Fiery I did this on one of my PAWs however used a brass one thinned it down by rubbing on emory whick was on a flat surface , piece of glass martin

ffkiwi

Cox International have shim thrust washers for the various models of Cox (TD 049/051, Killer bee, Queen Bee and TD 09) that used them. Fairly thin too at ca. 10 thou. You'd still (probably) have to reduce the OD a bit to fit the Irvine. IIRC the Killer Bee thrust washer is the smallest diameter of the Cox offerings.

ChrisM
'ffkiwi'

aeroland

Hello fiery,

Just joined Club Mills and picked up on your Irvine Mills .75 excessive crankshaft end float problem. That would suggest that something is seriously wrong. Normal Irvine Mills .75 end float is ~ 0.010" (0,25mm). Excessive end float will cause the conrod ends to wear oval, the crankpin to scour the back plate and the resulting debris in the engine will cause bore wear.

Short term expediency is to pack the float out with a washer behind the prop. driver. Long term is to correct the problem. What serial no. is your engine please? Early Irvine Mills I have been told were made entirely in the UK. Later ones were made in Taiwan. Have dismantled and rebuilt both and the Taiwanese built ones usually have issues.

The Irvine Mills .75 design secures the prop. driver to the shaft taper on taper. To achieve a controlled end float requires precision in manufacturing. If as I suspect the taper in the prop. driver is not machined deep enough then this can be remachined to fit. Either I or others skilled in model engines can do this for you.

Regards - Jon

fiery

My Feedback: (2)

Welcome to the diesel forum at RCU Jon.

There is a further problem with the above Irvine Mills .75 engine. It will not turn more than 4,800 rpm on my Tornado nylon 7x4 propeller. It should do about twice this.

I will disassemble it. I suspect that the cylinder or piston are 180 degrees out. Piston and contra-piston fits are superb.

** EDIT **

There is no serial number on the Irvine Mills .75 anywhere.

Engine as acquired was unrun NIB and overall presents very nicely.

A further matter.

If anyone has a tip on how to unscrew a fuel bowl when locked solid from either old castor oil residue or factory preserving oil it would be much appreciated. I am starting to think I prefer the original Mills "tab" securing method, despite the weakness of the tabs, or the "snap" fitting of the Russian "Z" version.

There is no pressing need to remove the fuel bowl on this engine. However numerous specks of workshop debris are lining the inner walls of the bowl. I would like to wipe the debris off.

I am thinking of drizzling WD-40, or a penetrating oil, on the screw thread of the "upturned" bowl, and leaving for a few days to soak in, and hopefully loosen it.

aeroland

G' Day Fiery,

Oh dear! 5,000 rpm on a 7 x 4 means a problem. I test run Mills .75's on a white nylon Taipan 8 x 4. Depending on engine type and condition 7,250 rpm is typical. Irvine Mills are usually quicker than genuine Mills by ~ 500 rpm.

If you unscrew the carb. assy. and look into the crankcase the two cylinder holes should be in the centre of the venturi hole. If you have two holes or a slot at the upper edge the cylinder is in the wrong way round. Bring the piston to BDC and if you see an edge uncovering and can see into the cylinder then the piston is the wrong way round. It has a step at the top which must always face the front of the engine.

Next with the carb. assy. off unscrew the needle and spring and look through the venturi. Should be a hole ~0.125" dia. right through. If someone has unscrewed the spray bar the hole could be partially closed off. Common fault on genuine Mils P75's when the early thin type tank top broke. By way of explanation the Mills venturis were drilled through the spray bar on assy. Retightening for a loose tank top will also cause the mismatch problem.

Contra piston could be too loose and riding up and down on the piston when hot. You would need to unscrew the cylinder jacket to check for this. Take care turning the engine over with cylinder jacket removed as the contra piston can be blown out and lost. Lastly check for good crankcase pressure. In a well fitted engine nice and clean and oiled the piston should bounce up slightly against crankcase compression until the transfer ports are opned. At that point a little puff of gas should be heard and resistance to turning the engine through BDC should cease. If you can hear a hiss as the piston descends check for where its coming from. Irvine Mills uses a paper backplate gasket, genuine Mills a red fibre washer. Gas can be coming from the back platejoint, down the crankshaft or up past the piston and out the exhaust ports. In the case of genuine Mills also through the corrosion holes in the magnesium crankcase!

With the cylinder jacket off pull out the cylinder and looking into the crankcase check to see if congealed castor oil is blocking the transfer port. Also check the holes/slots in the cylinder for the same blockage. To refit Mills .75 Mk II cylinders I use of piece of hardwood carved to fit right through the exhaust ports. Taper it slightly. This holds the cylinder from rotating whilst retightening the jacket. When done wriggle out the stick and blow any wood fibres clear.

Regards - Jon

fiery

My Feedback: (2)

Inspection process under way.

Tank bowl unscrewed without drama after a "zen moment". Firstly, tank lid was heated with a hair dryer. Purpose - to soften gummy oil residue. Then, fingers devoid of oil residue (unlike at the field) actually achieved some purchase on the bowl.

Debris and gum removed from threads and inner bowl.

Carburettor securing nut was then loosened, and the assembly removed. Photographs show no issue with carburettor venturi or intake port.

It looks like a full strip down of this wee beast is required. Partially blocked transfer passage or transfer port holes are suspected.

I will post again once the culprit is identitfied and problem sorted.

aeroland

Ah yes,  the Achilles heel of screwed tank bowls!  Really good idea to clean out thread in both tank top and bowl before neglecting the engine for some years.   I found this out same way as everyone else.   

fiery

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Here is a new offering for the club. The new CS 0.82 cc. In R/C and F/F versions. Image is taken from the CS Engines web site.

Looks like a "series II" of the Boddo Mills.

There is also a claim by a contributor on another site that a 1.6 cc in-line twin version of this engine will be offered very soon. I may contact CS (Peng Han) to verify.

ffkiwi

Other way round Dereck-this was the first version of the Boddo Mills-which CS are obviously keeping in production. Now a twin would be fun. I suppose since the CS Oliver Tiger twin has been fairly well received, CS are looking at something a bit more suited to the vintage flier. After all there are a few Mills based in-line twins out there-I think Mike Crisp has produced the odd one from time to time....

ChrisM
'ffkiwi'

fiery

My Feedback: (2)

Hi Chris

Was the Boddo Mills always 0.82 cc?

I know that the late Mr Boddington did sell some Boddo Mills "twins". Some left over Boddo engines were recently offered for sale on Uk 8bay.

I have not heard any bad reports about them. I'd say they were carefully inspected before sale.

Hopefully the new CS Navo "twin" will be as good, or even better. Having an R/C throttle option will add to it's market appeal.

ffkiwi

I'll measure mine up and see..........I think his son is dealing with the vestiges of the Boddo Mills project stock-0.5s, 75, 1.3s and the in-twin 5cc Oliver

CJM

earlwb

I think of all the model airplane engines that have been made over the years that the Mills type of engine has to be the best one ever done.
If you get a decent engine, they run OK, start easily, fly planes OK and are just plain lots of fun too.

aeroland

Earl,

fiery

My Feedback: (2)

Irvine Mills shown above:

1. Cleaned internally. It's transfer ports were gummed up.

2. Thrust washer installed.

I am looking forward to re-running it.

fiery

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Had some fun re-running in the Irvine Mills .75 Replica shown above. Good performance on a Master Airscrew 8 x 3, and (just for fun) a Master Airscrew 6 x 4.

For ease of starting and moderate load, the Master Airscrew blue 8 x 3 propeller is ideal.

As to speed, mid 7,000 rpm's for the 8 x 3 propeller were the norm. Mid 10,000 rpm's were sustainable for the 6 x 4 propeller once dialled in.

Best running needle setting is 2 1/4 turns out from closed.

Overall it runs well and starts very easily. With compression unchanged from best running setting, open needle 1/4 of a turn to richen, give it two choked primes, and a small port prime. Three smart flicks and it's away. Every time.

All starts were by hand only. Electric starters are not recommended nor required for these engines.

Video:

http://www.youtube.com/watch?v=KbSn-...ature=youtu.be

Stills:

aeroland

Ha!  A pleasing result.  

fiery

My Feedback: (2)

CS "Boddo" twin and single.

A report on the running characteristics of the twin would be interesting.

ffkiwi

Fiery-Hmmn-any indication on price?

CJM

fiery

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Chris .. this one could be yours

http://www.ebay.co.uk/itm/DB-mill-75...item337d0309a8

But hurry ... it's available for a limited time only

ffkiwi

Could be expensive collecting it in person though..................

CJM

fiery

My Feedback: (2)

That crankcase on the CS "Boddo Twin" looks bulky, and heavy.

fiery

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Ed Carlson emailed me to advise that he has CS "Boddo Mills" .75 engines available. Current price is USD $95.00, plus shipping.

www.carlsonengineimports.net/CHINA.html

This engine is better priced than buying from CS directly, where the engines are listed for USD $122.99 plus shipping.

Recent reports are that the CS Boddo Mills is quite acceptable in finish and performance.

It is the engine on the right, not the traditional Mills replica.