Swifty's build of Nemett Lynx

[gus]

Hi Paul,

I am following behind and watching with great interest. Prepping up before cam cutting is still ongoing.
RT beefed up and graduated with engraving cutter. This is my very first time using engraving mill and doing a great job but table is graduated in 10 degrees div plus the 45 degree. After this will do dry run on paper on the cam profile.

 

[doubletop]

I can't believe it only took you half an hour to get it started!! Maybe the double magnet trick is worth doing, regardless of the wasted sparks, I may give it a try

VIDEO REQUIRED PLEASE
​

Pete

 

[Swifty]

Pete, I was most surprised that I had it going in such a short time. Because the camshaft is only going at half the speed of the crankshaft, there is no additional waste of spark with the 2 magnets. Even with a single magnet on the crankshaft there will be one wasted spark per cycle at the top of the exhaust stroke.

When I was cranking it over, I had the carburettor open about half way and slowly opened the needle valve until it started. I primed it first by holding my finger over the intake and drawing the fuel up.

I have to borrow a video camera off one of my sons to enable me to post a video. In the meantime, I'm finishing off the fuel tank and stand, so hang in there it won't be long.

Paul.

 

[gus]

We are patiently waiting for video.

Speed Controller Device came in so looks like cam cuttting delayed.:wall::rant:
Space in the foot pedal box is crammed but I think I can get it snugly.Now on the Computer Desk.Windfall $$$$ about to come and have $$$ to travel.

 

[doubletop]

Pete, I was most surprised that I had it going in such a short time. Because the camshaft is only going at half the speed of the crankshaft, there is no additional waste of spark with the 2 magnets. Even with a single magnet on the crankshaft there will be one wasted spark per cycle at the top of the exhaust stroke.

.

Paul

Sorry wrong way round mate. With two magnets you'll get a spark at every TDC, on compression and exhaust. With one magnet you'll only get a spark at the compression TDC.

Not that it matters some of the modern car ignition systems use one coil for a pair of plugs so one is doing wasted spark on the exhaust stroke while the other is firing on compression.

Pete

 

[Swifty]

Pete, I'm going to have to disagree with you, with one magnet attached to a flywheel directly on the crankshaft of a 4 stroke motor, the piston is at TDC twice per cycle, once on the compression stroke and once on the exhaust stroke, (ignoring spark advance) it fires every time it hits TDC. When I say cycle, I'm referring to 2 revolutions of the crank, inlet - compression = 1 rev, power stroke - exhaust = 1 rev.

Paul.

 

[Swifty]

Just to make sure that I didn't have it the wrong way around, http://en.m.wikipedia.org/wiki/Wasted_spark

Paul.

 

[Swifty]

I'm still thinking about the Rcexl CDI system, I assume that it is made for use on 2 and 4 stroke engines. On 2 strokes it definitely has to fire every revolution, but on 4 strokes it only really has to fire on every second revolution. This leads me to comment about a digital sensor that plugs into the ignition module to show engine revs (you do have to multiply the figure by 10 to get the correct revs). I assume that the system counts the number of "sparks" to work out the RPM, if this is correct, it will definitely need a spark every revolution to work out the correct RPM.

When I look at Brian Rupnows latest engine, he has the points working off the camshaft, so only gets a spark every second revolution, perfect for a 4 stroke engine.

Paul.

 

[johnny1320]

Would you not multiple by 2 Paul?

 

[Brian Rupnow]

On many of my engines the ignition points run off a cam on the crankshaft. That is whats's known as the "waste spark" system. the extra spark occurring on the exhaust stroke does no harm.

 

[johnny1320]

Yes I agree Brian no harm using waste spark, I use it on my turbocharged methanol drag bike, makes around 500hp 1428cc

 

[SixSixSevenSeven]

Many full size production engines going into cars used to use wasted spark setups anyway. Really not a huge issue. I think its a bigger issue whether or not it fires during combustion than whether it also fires during exhaust.

 

[Swifty]

Would you not multiple by 2 Paul?

On the Rxcel site, they state that the multiplier is *10. I assume that if the display shows 300, the actual speed is 3000RPM.

Here are the specs.

1. Use PIC16f628a microcontrollers
2. Do not need batteries - powered from the ignition
3. Standard FUTABA plug(Black-Negative Red-Positive and White-Signal)
4. Uses high-brightness LED digital tube.
5. Input voltage range:3.5V-8.4V
6. Current consumption 25mA-60mA
7. Mini tachometer indicates up to 30000 rpm
8. Actual RPM= Display Digital *10
9. Body Size: 41mm L x 17mm W x 12mm H
10.Window Size: 30mm L x 15mm H
11.Weight:8.5g (0.3OZ)

Paul.

 

[Swifty]

I finished the fuel tank and stand today, it's mounted up on the temporary board with the engine. I will have the video camera tomorrow, so with a bit of luck, hopefully I will have the video of it running soon.

Paul.

 

[doubletop]

Pete, I'm going to have to disagree with you, with one magnet attached to a flywheel directly on the crankshaft of a 4 stroke motor, the piston is at TDC twice per cycle, once on the compression stroke and once on the exhaust stroke, (ignoring spark advance) it fires every time it hits TDC. When I say cycle, I'm referring to 2 revolutions of the crank, inlet - compression = 1 rev, power stroke - exhaust = 1 rev.

Paul.

Paul

We're at cross purposes I was talking about 2 magnets on the camshaft to deal with the camshaft running at 1/2 crank speed. With a single cylinder you'll only need a single magnet on the crank. I won't go into multi cylinders as that depends on the configuration inline, flat or V and is a whole other subject beyond these CDI systems.

These CDI systems are intended to replace glow plugs making a glow engine a two stroke. So no camshaft and the sensor mounted on the crank. You'll have seen that from the parts and the instructions that came with it. By putting the sensor on the crank on a four stroke it will still work but with a wasted spark. But that doesn't matter.

By putting the sensor on the cam a with our engine the ignition will fire at TDC but the timing will be wrong as these units work out the advance based on engine speed. (actually pulse interval). Putting a second magnet on the cam will fix this problem, again with a wasted spark, again we don't care.

The rev counter module gets its signal from the sensor and displays RPM/10 basically to enable the unit to display RPM for high reving engines I understand 25000RPM is possible with some. The units display would be pretty useless anyway as it will jitter so much you won't be able to read it. If you want the correct display you'll need the second magnet on the camshaft otherwise it will be displaying half speed,

Pete

 

[Swifty]

Hi Pete, I think that we both have the same thoughts in our heads, just putting it across different ways. I have ordered a tachometer, they don't cost too much, more out of curiosity than anything else, the second magnet on the camshaft will, as you say, give me the correct reading to multiply by 10 to get the RPM (so long as I can read it).

One advantage that I see of this type of ignition system is, that it can readily be disconnected and used on other engines, so long as the spark plug is the same. I may buy another in the future to suit a bigger spark plug. Once I have an engine finished and running, more often than not, it just sits on the shelf, so why not reuse the ignition.

Paul.

 

[Swifty]

At last we have a video of the engine running, it's not completely finished yet, I still need to polish it a bit, get some "O" rings to hold the fuel tank on and mount it up properly on a nice board. The carburetor still needs some tweaking, you should be able to hear it speeding up as I lean up the mixture screw, I haven't started to play with the idle mixture yet. The carburetor is only held on to the manifold with some loctite 515 sealant, I will have to find something more permanent.

[ame]https://www.youtube.com/watch?v=pJEFec-pBUE&feature=youtu.be[/ame]

Paul.

 

[Swifty]

I forgot to mention in my last post that I'm running the engine on shellite now (Coleman fuel). There is no noticeable difference to running it on petrol, except it doesn't smell the place out now.

Paul.

 

[doubletop]

Hi Pete, I think that we both have the same thoughts in our heads, just putting it across different ways. I have ordered a tachometer, they don't cost too much, more out of curiosity than anything else, the second magnet on the camshaft will, as you say, give me the correct reading to multiply by 10 to get the RPM (so long as I can read it).

One advantage that I see of this type of ignition system is, that it can readily be disconnected and used on other engines, so long as the spark plug is the same. I may buy another in the future to suit a bigger spark plug. Once I have an engine finished and running, more often than not, it just sits on the shelf, so why not reuse the ignition.

Paul.

Paul

As you say the tacho's are cheap and they help you understand what the engine is doing. There is a patch available to make it display the units but its not official and there's no way back.

http://www.bittnar.info/en/tachometer-rcexl-alternative-firmware/

The units also trigger on one pulse so help with setting up the sensor trigger point.

I've used RCExcel and Pegasus and there are others out of China. There's no difference as far as I can tell. The usual case of one design and many clones. Hobby King have good prices if you are prepared to change the plug cap. I've got those off Ebay.

Like you once the engine is running it gets cleaned up and put on the shelf, but I do like to think I can get it out and give it a run without too much bother,

Pete

 

[doubletop]

Paul

Wow!!! That's the best running version I've seen. Even Malcolm Strides doesn't sound that sweet.

Well done!!!

Pete