Nemet – Lynx

[duncan webster 1Participant @duncanwebster1]

Hi all,

I'm building my first petrol engine, having had enough steam engines for a while. I've battled against the drawings in 'Best of ME vol 6' which are truly awful. The original magazine drawings were much easier to understand. I suspect the problem with the later ones is that the linescale on hidden detail is wrong, hence what should be dotted lines comes out solid, but ME deny all knowledge. Now to my question (perhaps the first of many!). There is no mention of recommended spark plug. Hemigway sell Rimfire 1/4 * 32, but internet search brings up both the Rimfire in short and long reach versions (from US, still much cheaper than Hemingway), and also a chinese plug at only ~£8. Anyone got any advice? I'm also thinking of using what is described as 'universal ATV' coil, which is ~£9, again anyone got experience of this?

[JasonBModerator @jasonb]

On the actual drawings from Malcom Stride the hidden detail is dotted and the centre lines are black not red and the traditional long dash- short dash. If it bothers you a lot you can always buy the drawings from MHS which will also be larger at A3 rather than the A4 in the mag.

The head drawing says counterbore the plug hole to suit the plug so you can go either way, the short is more common. Minimag are a bit cheaper than Hemmingway on the plugs. Don't forget you may get stung for VAT, Import Duty and Post office charges on items from the US.

Julian at Minimag also does coils but not as cheap as the motorcycle/ATV ones though they are neater and smaller. I've used the ATV ones to make Buzz coils and they work OK though tend to prefer the Minimag ones as they can be hidden more easily. They also have a neat silicon plug wire which looks better than a 6/7mm standard plug wire on a 1/4" plug

J

 

Edited By JasonB on 17/04/2014 17:13:59

[Neil WyattModerator @neilwyatt]

Back in days of yore, people used to wind their own coils for magnetos, ignition and radio etc.

With modern neodyminium magnets I'm sure a magneto could be made very tiny.

Would there be any interest in an article on making a coil winding machine in MEW?

Neil

[doubletopParticipant @doubletop]

Neil

Coil winding? there is no need do that at all these days, for a quick easy and cheap way just get hold of an ignition coil for most modern cars. The Subaru coil I used has drive circuity inbuilt that can be driven by a TTL chip. Albeit it needs 12V supply. The bit that needs a little thought is the interface between the hall sensor and the coil unit.

Duncan

Depending on what you plan to do with your Lynx the Chinese 1/4×32 plugs on Ebay will be fine. If like me this is a new area for you I can't imagine you plan to stick your engine in an aircraft and trust it to fate so it will spend most of its life on a shelf looking good.

While you are on Ebay be aware the Chinese ignition systems, although very good and cheap they are designed to have the sensor on the crank and not the camshaft as the timing will be wrong for a four stroke, So something like a minimag (which costs more than twice as much as a complete Chinese CDI) and a Gerry Howell TIM6 will probably be the easiest way to get yourself up and running.

There are many ways of skinning this Lynx

Pete

[Neil GreenawayParticipant @neilgreenaway71611]

Hi Neil,

I remembered there was an article some time ago as a work colleague was interested in this area of coil winding – turns out a lego machine was designed and article published in Autumn 2011 issue, but with a view to using this as a prototype for a more commercial version – perhaps this might be useful for an update on what happened – did it go commercial?

Neil

[JasonBModerator @jasonb]

Neil, Alan Thatcher who usually shows a couple of Hit & Miss engines at the MEX makes hios own mags, the latest is down to 1.75" x 1.5" x 0.75". This is a slightly larger one.

I've also got a coil sitting here that is about the size of five pound coils in a stack.

J

[duncan webster 1Participant @duncanwebster1]

Thanks to all who have replied. As a result I've bought a Chinese plug and an ATV coil, both from UK suppliers,

As an amusing aside, I once bought a tangential toolholder from US. The postman eventually arrived demanding VAT, which I was expecting, and a £20 handling charge which I thought outrageous. I told him I wasn't prepared to accept it and he should return it to supplier from whom I would request a refund. This caused complete brain overload, he thrust it into my hand and went away muttering. I wouldn't rely on it working again.

When I eventually get it running I'll post some pictures. Thanks again to all who replied.

Neil, there was an article on coil winding recently in ME, not for HT coils tho'

Duncan

[Roderick JenkinsParticipant @roderickjenkins93242]

There seems to be a flat charge of £8 to collect the fees. I've just bought a milling cutter from the US that attracted £4 for VAT but adding the handling charge totaled £12. I believe anything over £15 now incurs a charge. There could be import duty as well, it depends what it is and where it comes from.

Worth bearing in mind even though the pound is stronger against the dollar.

Rod

[Neil WyattModerator @neilwyatt]

Hi Pete,

Home made coils might appeal to those making scale models, especially magnetos which need no battery at all.

Jason,

It wouldn't be the box with 'magneto' written on it, would it?

Neil

[doubletopParticipant @doubletop]

Neil

Reflecting on my post last night it occurred to me that some might wish to make their own coils. A was aware John had done a thread on making a magneto a few years back. The peril of late night posting after a few Pinot's

I also realised I had forgotten to add that there are also pitfalls with using these 'pencil' coils from modern ignition systems. Although they can be triggered by a TTL signal they need a 2-3ms pulse and fire on the falling edge. That means the triggering circuit needs to preempt when to fire the trigger pulse and it will be at a different point depending on the revs. So it needs a 'smart' trigger circuit which these days means a micro controller.

For those interested in going that route there's a whole saga over here that also includes home made micro controlled CDI HV circuit that uses the igniter coils from gas stoves. Although appearing to be a solution those coils can’t be used independently as the primary requires 240v pulse. The CDI design includes a 400v inverter.

There is probably a series of ME articles that could be produced on this subject but my experience is limited to the Chinese CDI and the DIY micro controlled systems. I have no experience a TIM6, Minimag coils, Magnetos, distributors or the Megasquirt that some have used on multi cylinder engines.

As I said many ways of skinning this cat.

Pete

[doubletopParticipant @doubletop]

With new posts to this thread I've started thinking about the subject again. I had used one of these and thought I had problems with it that's why I went down the DIY route. However, that diversion has helped my understanding of how these thing work

These ignition systems are designed to have the sensor on the crankshaft so they can measure the time/rev and work out the proper timing for the to fire the spark. As the Lynx is a four stroke with the sensor on the cam the rev interval is twice what it should be and the timing will be wrong. However, putting two magnets at 180deg on the timing disc will ensure the correct time/rev is input and the firing point correctly calculated. OK you'll be firing at on all the revs with a wasted spark but any car ignition systems run wasted spark these days.

You'll see them on Ebay for $75 but the best source is HobbyKing, this one is only $35

**LINK**

The plug cap is the wrong one for 1/4×32 plugs but the proper caps can be obtained from Ebay for $8

**LINK**

HobbyKing do many different versions other than RCeXl, I also Have two Phoenix units from them. I've purchased from both sources without any problems. (well there is one problem with HobbyKing, once you've found them you keep going back for more toys! Take a look around at the amazing stuff they do at unbelievable prices)

Its all in the box 2.5"x1.5"x1.25" and by far the cheapest and most compact solution to get you running.

A further thought, I saw quoted somewhere "Most ignition problems can be traced to the carburetor"

Pete

[duncan webster 1Participant @duncanwebster1]

My coil off a mini motorbike has not worked out, gets really hot and no sparks, so yes I'm interested in an article on how to wind ignition coils!

[duncan webster 1Participant @duncanwebster1]

I'm slowly moving forward, delayed by making things for other people. Bad idea. Anyone know where I can buy valve springs without suffering the minimum order charge problem. Lee Spring do a LCM 080 CG 02 M but it is smaller wire diameter and hence lower rate. Flexo have a £18 +vat minimum which is a lot for 2 springs!

[Keith LongParticipant @keithlong89920]

Duncan

HPC (of gears fame) show a good range in both stainless and music wire. Don't know how their overall prices compare but could be worth a look.

Keith

[Roderick JenkinsParticipant @roderickjenkins93242]

Winding your own springs is very straightforward. Choose the gauge of spring (music/piano) wire and the i.d. of the spring. Find a bit of MS steel to act as the mandrel and drill a cross hole to anchor the wire. Mount a bit of bar in the lathe toolpost so that the top of the bar is at centre height and file a V groove into the bar top surface.

Set the lathe up for screw turning to the desired pitch. Without engaging the lead screw turn a couple of close turns.

 

Then engage the lead screw and turn the spring to the required length

Now disengage the lead screw and add a couple more turns

Snip off the wire at both ends and you have a spring with closed ends

Now touch each end of the spring on a grindstone and you have a completed spring

I turn the mandrel by hand for this process and you might need to do a little experimentation with the spring mandrel diameter. I've used this method on 3 engines now and the springs have fulfilled their purpose admirably. Spring/Music/Piano wire is available from the usual ME suppliers.

Hope this helps,

Rod

Edited By Roderick Jenkins on 04/07/2014 17:28:14

[Steve WithnellParticipant @stevewithnell34426]

This is me winding the valve springs for the Nemett –

 

Steve

Edited By JasonB on 06/07/2014 10:27:31

[duncan webster 1Participant @duncanwebster1]

Thanks to all who replied on springs. I'm definitely going to have a go at winding some, but not this time, I want to get on. I rang Flexo, and they did me a deal, still very expensive, but by the time I'd drive to the nearest piano wire supplier and buy the wire not that bad.

For the record, Lee Springs will now sell minimum 5 off any one item at the catalogue price if you order on line, which is not bad at all. Unfortunately they don't have an equivalent spring.

[nipperParticipant @nipper]

Hello. Sorry to get onto this forum very late but I am building the Lynx and come to the part of ordering the pulleys and belt from HPC gears. An order for the 2 pulleys and 2 belts came to £49, which was bad enough, but then the cheapest shipping cost was £9.60. This for a few items in the smallest jiffy bag. I rang them and pointed out the post office will ship a small parcel for £2.90 but they would not budge. Any suggestions as to where I can get it all at a sensible price.

[doubletopParticipant @doubletop]

Nipper

HPC have always been expensive for our needs. Try belting on line just Google them.

Pete

[doubletopParticipant @doubletop]

**LINK**

[nipperParticipant @nipper]

Hi Pete. Many thanks for the reply I have ordered parts from the company on the link and have reduced the cost from £59, and this may not have included VAT, to £21 including VAT. Now I may be able to afford the ignition system. I will press on and it should be finished by next Spring, unless a railway engine gets in the way.

[Peter SpinkParticipant @peterspink21088]

Good evening all.

Always wanted to build an IC engine so about make a start on the construction of this one.

A couple of points – I'd rather like to use valve inserts in the head rather than seating the valves in the ally. Was hoping to look at the pics earlier in this thread but they're long gone. Any chance of them being resurrected?

Secondly, am I missing the obvious – how do you get oil into the crankcase?

I'm sure there'll be other questions en route but any help much appreciated!

[JasonBModerator @jasonb]

Probably easiest to unscrew the breather and fill through that hole

[nipperParticipant @nipper]

Hi Jason. I have long finished the Lynx and it has run but is too big, too heavy and underpowered to do anything with . I put a oil filler plug an the rear cover. I did fit bronze valve guides but had a real problem getting the valves to seal and get good compression. One major problem with the engine, for me anyway, was setting the tappet clearance, you cannot get feeler gauges in there and there is no adjustment anyway. I looks good on the shelf. Best of luck David Murray

[Peter SpinkParticipant @peterspink21088]

Thanks David, useful info but not a great endorsement!p

I think quite a lot have been built successfully so worth giving it a go.

Not too bothered about usefulness – getting it to run at all would be a major achievement for me!

Regards,

Peter

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