Swifty's build of Nemett Lynx

[doubletop]

I've often thought about using one way bearings (sprag bearings). When I make a multi cylinder engine, I will use a permanent starter motor with sprag bearing.

Paul.

Paul

One of these helio starters from hobby king

Modified with a few bits of silver steel to become

Pete

 

[Brian Rupnow]

Swifty--I like that dipstick very much.---Brian

 

[Swifty]

Pete, that sure makes a nice starter.

Brian, thanks for you comment on the dipstick, I hope that it will solve one of the problems that you mentioned about not knowing how much oil is in there.

 

[Swifty]

I fiddled around with the breather tube and fittings today, I plan to thread the top of the fitting that screws into the crankcase then make a cap for it, I will use an O ring as an olive to grab the tube. The way it is now will be fine for a test run.



I have mounted the motor on a temporary board for the time being, the 360 deg graduated disc is one of a pair that I have had for years, I knew that it would come in to use one day, perfect for setting the timing.



Paul.

 

[Swifty]

I still have to get some tube to make the exhaust pipe, but that won't delay me starting the engine. This morning I set the cam timing and the ignition timing, it was straight forward using the degree wheel. I also put 35ml of engine oil in the crankcase, I intend to use a makeshift fuel tank for the initial attempt to start the engine.

I am using an Rcexl electronic ignition module, ever since it arrived in the mail, I was confused, as it has no earth lead coming out of the box. After googling for a while, I found the answer. The high tension lead for the spark plug has a metal sheath around it, this together with the metal spark plug cap acts as the earth. With that problem solved, I only have to hook up the ignition and temporary fuel tank and attempt to start the engine. Other things are stopping me from doing this at the moment, but by this time tomorrow I hope to have a runner.

Paul.

 

[doubletop]

..............

I am using an Rcexl electronic ignition module, ever since it arrived in the mail, .............

Paul.

Paul

You'll need to read my write up on the ignition systems on my build thread. These modules expect the sensor to be on the crankshaft and not on the camshaft as on this engine .

The camshaft is running at half the speed of the engine and the ignition unit times the pulse interval to determine the speed and then calculates the advance it needs to apply. With the sensor on the cam it gets the advance calculation wrong.

The worst time is when its starting. The ignition system is set up with the sensor at 27deg advanced. It gets the sensor pulse and waits for and interval the equivalent of 27deg to fire at TDC. However, as the cam is running at half speed the interval is calculated as twice as long as it should be and the ignition is fired at 27deg after TDC.

It will work to some extent but it one thing you are going to need to deal with to get it to run. With the three variables Carburation, Compression and Ignition, and you'll be chasing your tail like Brian. If you are going to run with a flywheel then just fix the magnet to that and find a way of mounting the sensor.


Pete

 

[Swifty]

Thanks for the advice Pete, looks like I will have to rethink it a bit.

Paul.

 

[Swifty]

Pete, could you please post a link to your build thread, I'm having trouble finding it.

Paul.

 

[Swifty]

Paul

The camshaft is running at half the speed of the engine and the ignition unit times the pulse interval to determine the speed and then calculates the advance it needs to apply. With the sensor on the cam it gets the advance calculation wrong.

Pete

Hi Pete, surely the easiest thing to do is use 2 magnets on the camshaft, 180deg apart. That way the CDI will get the correct amount of pulses.

Paul.

 

[Brian Rupnow]

Here is a link to Doubletop's Bobcat build.
http://www.modelenginemaker.com/index.php?topic=1796.0

 

[Swifty]

Thanks Brian.

Paul.

 

[Swifty]

I made a new magnet holder today, it has 2 magnets 180degrees apart, so seeing that the camshaft rotates at half the engine speed I should now be getting a signal every rotation of the crankshaft. I've had one attempt to start it, it pops a bit and fights with the drill that I am using for a starter, but won't take off yet. The compression is not all that great at the moment, the piston and rings appear to be a good seal, whenever I had the head off I held the palm of my hand over the cylinder and it certainly had good suction. I have lapped the valves in a couple of times, but they still must be leaking a bit.

There is a good spark, so I will just play around a bit more, if I can get it firing a bit more the valves may seat a bit better.

Paul.

 

[Swifty]

Woo Hoo! That didn't take long, I now have a runner woohoo1. I was so excited that I grabbed my iphone and took a video. The valves are already seating better, giving more compression. I have stopped and started it a few times, it is still blowing out a bit of smoke as I oiled the cylinder and piston when I assembled it. I still have to make an exhaust pipe, I picked up some 3/8" stainless tube this morning, but I still have to make up a tube bender. I will post a video later when I can grab my sons HD camera.

The engine revs reasonably well, but needs a bit more attention to getting the mixture correct, it seemed to idle well.

Paul.

 

[Cogsy]

Half an hour between posts and you got it running! Wow, that was easy . It's a great looking engine and I can't wait to hear what it sounds like.

 

[gus]

Please post video.

Taking my sweet time prepping for the cam cutting.Also taking a break.

 

[AussieJimG]

Congratulations Swifty, there is nothing like the putter of a little feat to make the heart beat faster.

Jim

 

[Swifty]

I spent a few hours today making a bender for the 3/8"stainless tube that I purchased to make the exhaust pipe, I have plenty of pipe for trials as it was only sold in 6mt lengths. I made the 2 wheels different sizes so I can interchange them for different bend rad's. I will make provision for a longer handle later as it took a bit of grunt to bend the tube.



And here is he exhaust pipe after soldering the flange on.



Now that I know that the motor runs, I will finish off the fuel tank and stand, and decide how I'm going to mount the whole lot.

Paul.

 

[doubletop]

Hi Pete, surely the easiest thing to do is use 2 magnets on the camshaft, 180deg apart. That way the CDI will get the correct amount of pulses.

Paul.

Of course it is, and how simple would that be? Now you've got me thinking about the Bobcat timing as it has two magnets so that must be giving the CDI unit the correct timing.

After Brian’s experience's with the piston rings I'm begining to believe the the ring/valve seating is the most important aspect to get right, then the carb and then the ignition given some of the basic ignition set-ups that seem to work.

Pete

 

[Swifty]

Pete, I'm very happy with the ignition, I will certainly be using that brand in the future. As soon as I started to get more firing as I cranked the motor and eventually having it run, the valves sealed better. When I turn the flywheel now, I can certainly feel the better compression. I still have to fiddle with the carburettor, but will finish the fuel tank first.

I ran the engine in the garage, apart from the smoke, the smell of petrol has been hanging around all day. Next time I run it I may try shellite (white spirit) as a fuel.

Paul.

 

[Brian Rupnow]

Valves used to be my big Bugaboo with i.c. engines. After constructing a couple of the Geo Britnell valve seating tools, and following my strict regimen of 3 lapping sequences between the valves and seats, beginning with 350 grit, then with 400 grit, then 600 grit, before the engine is ever assembled seems to have sorted that problem out very well. I have built enough different kinds of carburetors now that even though the parts are minuscule, they don't frighten me. I gave piston rings my best shot with the engine I just finished, based on the Nemett Jaguar drawings. I did get it to run---you seen the video. But--at the end of the day, the engine still had rotten compression, and wouldn't idle worth a damn. I pulled the rings out, reinstalled the piston configured for Viton rings, and immediately restored a LOT of compression and great low speed idling. Close examination of the rings showed areas of very little wear pattern--which indicated low or no sealing in that area. This was after 4 hours of "running in to seat the rings" powered by an electric motor. I will not make rings the way that is advocated by Malcolm Stride again. There are other ring making instructions available which advocate making the ring blank oversize on the outer diameter, then spreading and heat treating, then compressing the rings, clamping them in a compressed state on an arbor, and then turning a finishing pass on the o.d. of the rings to guarantee concentricity. If I ever decide to try making rings again, I may use that method.---And yes Swifty--I normally run all of my engines on Coleman camp fuel, which is basically Naptha gas. I was told by Gail in New Mexico that automotive pump gas releases more energy when it burns than Naptha, so I went and bought some high test automotive gasoline to try and get my engine to run with the cast iron rings. It did make a difference, and I was able to get the engine running with cast iron rings. However, at the end of the day, my garage stunk. I stunk. Even after a shower and change of clothes, I smelled like a friggin gas pump. The Coleman fuel is marvelous, in that it seems to leave no smell at all in the garage nor on me.-----Brian
P.S.--Gail in New Mexico must be right about more energy in automotive gas than in Naptha. The engine with cast iron rings would not start on Naptha, but did start and run on the automotive gas. The only explanation I have for that is that the greater amount of energy released by the pump gas gave enough extra "oomph" to the engine to let it make two complete cycles and still have enough impetus to fire again, even though the compression was less than optimum.