Member postings for Peter Wood 5

Geoff.

Thanks for the link to Adrians Model Aero Engines. An interesting site and the article by Ken Croft was really helpful. Full of useful tips such as using Turps as a lubricant in the lapping process.

I made the cylinder lap he described but found that it tended to expand at the end as the grub screw was tightened which is exactly what you don't need so I have reverted to Adrians design which gives a parallel expansion along the laps length.

Now for several hours of patient work on the liner.

Peter

A photo of the two Firefly's I have built. I have had no success in getting the top one to run. I have not tried the front version as it currently contains an early attempt at the cyl /piston assembly.

Basically I don't seem to be able to get a fit of the piston in the liner to give good compression. My attempt at using a piston ring did not work (probably because I did not temper the ring).

I suspect that the venturi on the commercial carb is too large as well and the poor crankcase vacuum is not sufficient to draw fuel.

So the next (and probably final) step will be to make a new cylinder/ liner for the front version with the design carb adopting all the excellent advice I have been offered on this thread

Hi Danny

The observations on using diamond lapping paste may be the explanation for the problems I have been experiencing. When I was trying to start the engine I noticed that the unburnt fuel that was coming out of the exhaust was black as were the residues inside the engine when dismantled.

I have read the article on making rings with interest but wonder whether I really need to go to all the trouble of annealing the ring for a simple engine like the Firefly? Why wont my approach of making the ring marginally oversize work in a simple engine like this. It just needs enough power to lift a Flair Cub into the air.

Anyway I have run out of Meehanite for the moment so will have to take stock whilst I decide whether to have another go at lapping.

Thanks for the comments.

Peter

Has anybody modified this design to use piston rings?

I have had two attempts to get a piston / cylinder combination with good compression. After hours spent hand lapping with the technique described by Ramon in Model Engine Maker and following Geoffs advice I achieved what I thought was a reasonable fit. Not as tight as a commercial engine but there was a plop when flicking it over. However as soon as I tried to start the motor, using a starter it quickly lost compression.

In desperation, I have just turned up a piston ring out of cast iron. It is 0.08 mm larger diam than the cylinder diameter, 2mm wide and 1.3mm thick. it was split with a diamond cutting wheel.

A groove was turned in a discarded undersize piston about 3mm from the piston head, 2.1mm wide and 1.7mm deep.

The ring was easily expanded by hand to fit in the groove and then the piston was slid into the cylinder and the ring pushed into the groove whilst pressing down.

A bit of lapping with 1200 paste was needed but now it feels good.

I need to make a new gudgeon pin before reassembling and testing tomorrow.

Any observations why this should not work?

Peter

I have now almost completed my second Firefly with beam mounts, cylinder head cooling fins and the designed carburettor. My first has an ASP 46 carb.

However that has raised a question in my mind.

In a commercial RC carb the barrel rotates in a spiral groove which effectively allows more fuel to flow through the needle valve as the throttle is opened thus keeping a constant mixture.

However in the Firefl design, the amount of fuel going to the carburettor is fixed throughout the carb barrel rotation by the remote needle valve. Does that mean that the needle valve has to be adjusted (in flight) for each throttle opening?

Colin

Brilliant thanks very much - just what I needed.

Les

You were spot on about the wiring confirmed by Colins diagram.

Tomorrow I will reconnect and test.

Thanks again to both

Peter

Les

Thanks for the comments. The Emergency switch, micro switch (chuck guard) and reversing switch are indeed in series. By on/off I meant the start/ stop buttons.

I agree that it is unlikely that the live in would go to 5T3 or 6T3 as I have confirmed that they are paired coil controlled contacts. However the live spade connector is a male and the contactor is the only device employing them and all the other terminals are done up tight. The boards both have female spade connectors on input wires. So I am at a loss as to where it should go.

The three way reversing rotary switch is barrel shaped with three terminals on each quadrant so it is proving tricky to sort out. All the inputs have crimped bullet type connections.

I am still hoping to get a wiring diagram from Amadeal.

Thanks again.

Peter

Just before Christmas my mill blew a fuse when I stopped it as usual by opening the chuck guard. I replaced the fuse and this time it blew as soon as I started the motor.>>

Amadeal have been very helpful in suggesting a series of tests which have eliminated the motor and filter board as the likely culprits. The control board shows no signs of burnt components so I started to look elsewhere. Inside the control box on a rail on the side is a black cube which I have established is a LC1K09 mini contactor. On removing it I discovered that there was a black wire with a spade connector hanging free. This is the mains live supply. The terminal clamps on 5T3 were unscrewed so I assumed that it was that terminal the wire had come from. However on further inspection I discovered terminal 6T3 was also fully unscrewed but had nothing attached. So the question now is where should the wire connect to and was that the reason for the blown fuses?>>

I have attached a photo of the contactor and the wire inputs. Can anyone help identify what each the terminals are for or supply a wiring diagram for the AM25LV or one of its clones?

>>>>

Aaaaah. Misunderstood the picture. I thought it was vertical not horizontal.

After my breakthrough with the old knurling tool i will give your broaching method a try. Thanks again.

Peter

Jason

Just tried the knurling technique with an old rusty tool I had in my scrap box./Worked like a charm. Thanks

Peter

Jason

Thanks. I missed that thread. The use of a vertical knurling tool is a great idea. I have previously made prop drivers for larger engines for friends by tilting the mill head at 45 deg and just making grooves across the face but I felt this needed proper radial knurling.

However not having an arbor press I am not keen on using my mill or Myford in that role.

Geoff.

Milling the keyway in the crankshaft is not a problem. Thinking about it I have made internal keyways as required on the prop driver by drilling the correct size hole on the joint line of the crankshaft hole and a temporary plug. Then it is just a matter of squaring the hole with careful filing.

Meanwhile I am still contemplating a split tapered collet as was made in the RCME build article.

Peter

I am now making a second Firefly learning from the mistakes on the first and adding cooling fins to the head and beam mounting.

On the first one I used a commercial prop driver but this time I want to make my own.

Two questions.

How do I drill a hole with a flat. Jasons excellent thread does not mention this part.

Would I be better making a tapered split collet to secure the driver on the prop shaft?

Secondly how do I mill the radiused grooves on the driver face?

Peter

I recently purchased a face end mill from Banggood after watching a video review. The finish on ali was not as good as I got with my fly cutter but more importantly it seriously overloaded my WM18 mill.

I am now wondering if I can use it with just one or possibly two inserts instead of four?

Ian

An OS # 8 would be a good starting point. I use them in most of my 2-stroke aero engines.

Peter

Keith

I think you are right. I used 7/32 silver steel for the crankpin. I did not want to turn this down but was also scared of drilling the hole in the crankweb too large and having to start again. So I drilled the hole 13/64.Obviously too tight!!

Next time I will take a 7/32 reamer to the 13/64 hol but not take it all the way through. Also I will freeze the pin first and possibly heat the crankshaft with a hot air gun.

Geoff

I am going to make another piston. Like you I got carried away with Jasons brilliant reamer design having already made the piston. Also I had three attempts at the con rod eventually rounding the ends with filing buttons, but was pleased with the final result.

At present it has a prop driver and carb from an ASP 46 until I know it runs when I will make a new one.

Perhaps a photo later although it is not exhibition standard.

Peter

I have just completed my Firefly relying heavily on Jasons build thread. Thanks Jason.

Since I have plenty of spare material left I am thinking of making another but this time with beam mounting lugs and learning from some of my mistakes.

One of the most difficult tasks was pressing the silver steel crankpin into the crankshaft web as it kept going off square in the mill vice.

In the RCME article by Frank Payne he suggests using a roll pin for the crank pin!

Has anybody any experience of this method?

Peter

Thanks for the info. Not sure what I will use them for but I will hang on to them now.

When i returned from holiday yesterday I found this tool ( and two similar ones) on my doorstep.

Can anyone tell me what they are used for.

Peter Wood

Edited By Peter Wood 5 on 14/04/2018 12:21:05

Oh ******** !!

I thought it was to balance the oil nipple cut out opposite. Learn something every day.

Anyway no great problem as I don't think I have ever used the locking pin.

Thanks John for solving my problem.

Peter

I am sorry - I really did not intend to re-ignite the whole pro-con tacho debate again.

I just wanted to know whether the weight of the sensor magnet on the large belt pulley would seriously upset the balance.

Anyway I have done some calculations and reckon that the centrifugal force of a 1g magnet, 50 mm from the centre revolving at 600 rpm is 0.02 kg.f.

I am going to stop worrying.

Peter