Author Topic: Nitrous on 50cc engine (Read 12665 times)

scottly · « **Reply #25 on:** August 27, 2016, 06:14:40 PM »

Ha ha!

Seriously, you are dumping a LOT of nitrous into that tiny motor, and from the looks of the video, much too soon. Rev the motor as high as it will go before hitting the button, instead of at a low RPM. You may also want to retard the ignition timing a few degrees, if that is possible. Thank you for sharing your experiments!

frodef2 · « **Reply #26 on:** August 27, 2016, 11:27:37 PM »

Yes, i would like to have it reving higher before i activate the nitrous, but the next size clutch springs i have are too tight. Atleast for na use.

I was not able to rev the engine to the point of clutch engagement.

Maybe it will engage with nitrous?

I have already backed the ignition 8ish degrees. So the static ignition is now about 15 degrees btdc.

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frodef2 · « **Reply #27 on:** August 29, 2016, 12:09:54 PM »

There were more damage than just the rings.

After assembling the engine with new rings, it refused to start. It would barely make a splutter. And only with full choke and no throttle.
I took out the sparkplug and it was almost completely dry. I knew the carb was getting gas and i have seen these symptoms before, so i took off the aircleaner cover and discovered a gas soaked filter.

The reeds have gone bust.

The engine on the healingbench. Please note the 15mm tall flangenuts on the 8mm 12.9 studs.
The same as on my cb750

I have never seen this kind of reed damage before. I was expecting a broken reed, not a dented one.

Anyone care to guess what happened?

Frode j

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simon#42 · « **Reply #28 on:** August 29, 2016, 02:09:44 PM »

the fuel mixture in the crankcase has ignited

Terry in Australia · « **Reply #29 on:** August 29, 2016, 03:01:57 PM »

Yep, it's exploded from within. Really, this thread could be re-titled, "How to kill a poor little bike". I do like that nitrous kit though, I think it'd be good fun on my XR500R.....

Lostboy Steve · « **Reply #30 on:** August 29, 2016, 05:45:55 PM »

There's your problem, it's a reed valve engine. I want to see you do this on a puch engine punched out to 70cc with a single ring non reed piston.

frodef2 · « **Reply #31 on:** August 29, 2016, 09:37:16 PM »

For the reed to get damaged like this, the detonation would have to be in the intake. I will have to watch the movie again to listen for intake popping. I thought about crankcase detonation too, but then i think the damage wouldn't be limited to the end of the reeds

Anyway, carbon reeds are getting installed today.

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scottly · « **Reply #32 on:** August 29, 2016, 09:49:20 PM »

Quote from: FrodeF2 on August 29, 2016, 09:37:16 PM

For the reed to get damaged like this, the detonation would have to be in the intake.

This is what I was thinking, too? You might want to check the crank-shaft seals; if there was an explosion in the case, they may have been blown out.

I don't understand why there is an issue with the clutch? You will need to let the bike accelerate to it's highest NA speed before feeding the nitrous.

frodef2 · « **Reply #33 on:** August 29, 2016, 11:06:48 PM »

The clutch is centrifugal. And with the stock springs it will engage at a measly 2000 rpm. With the "red springs" it engages at 5-6000 rpm. And with the blue springs i have in it now its in the 8000 range. The problem with these springs the last time i used them was that the engine dont have enough power at this rpm to make the clutch shoes engage. Its also almost out of rpm, in NA form

I have checked the seal at the gearbox side. And it was good. I will remove the flywheel and check the other side today.

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simon#42 · « **Reply #34 on:** August 30, 2016, 11:05:06 AM »

dont expect carbon reeds to be any stronger than the steel ones , if it blows back again they will just snap

frodef2 · « **Reply #35 on:** August 30, 2016, 11:13:53 AM »

I know, thats why i had the steel one installed in the first place. I do not have any more steel reeds , so carbon it is.

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simon#42 · « **Reply #36 on:** August 30, 2016, 03:58:04 PM »

its good you have used the steel reeds first at least you can see what has happened , the ignition has happened in the crankcase . the force has closed the reed and has tried to push it through the reed block , that is how it has become distorted . if the ignition had happened in the inlet the explosion would have mostly gone back out of the carb that i presume was wide open . some of the force would have opened the reeds against the stops and might have opened them up but would not have bent the reeds in this way . with carbon reeds it is hard to fault find as they are normally blown to bits

frodef2 · « **Reply #37 on:** September 02, 2016, 12:42:46 PM »

You called it, carbon is #$%* for backfires.

On the good side. The blue clutch springs did better than anticipated for the start rpm. They could in fact be even stiffer.

I managed to get 2 good passes with nitrous activated at high rpm in ~3 second bursts.

Stoked by this great success we made a 3rd pass with holding it in at high rpm. This worked amazingly until the auto changed to 2nd gear. Then the spluttering begun, and right as it passed me. Several very loud bangs with accompanying yellow flames from the exhaust.

This killed one of the reeds, blew the airbox lid, and almost melted the air filter.

So the next idea is stronger 2nd gear springs and new metal reeds

I was so stoked about the thing working, i dont have any good movies from the test.

I might get a short snapchat clip uploaded later tonight

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frodef2 · « **Reply #38 on:** September 02, 2016, 01:18:32 PM »

You can hear the splutter at the gearchange that destroys the reed.

simon#42 · « **Reply #39 on:** September 02, 2016, 02:43:36 PM »

well it sounded great until it stuttered , can you reduce the amount of nitrous by about 50% and try it again ?
how was the piston this time ?

frodef2 · « **Reply #40 on:** September 02, 2016, 02:50:43 PM »

I am using the smallest jet in the kit. And i run lower bottle pressure than recommended by NX (nx says 1050 psi in the manual), and i try to keep it at 950.

The nx jet size is 18 for the n2o and 16 for the fuel.

Is it advisable to let the n2o pressure go even lower? I assume the flow is related to pressure.

I am going to try and create some replica steel reeds by having spring steel shim stock, laser-cut.

I haven't taken off the cylinder yet. Im going to do that tomorrow.

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simon#42 · « **Reply #41 on:** September 02, 2016, 04:25:34 PM »

i dont know , i just thought if you started with a little and gradually increased the gas it would save you a lot of pistons and reeds .
do you have access to aviation fuel ? avgas is a much more stable fuel and burns slowly .it would not help with speed but it would help with reliability .

madmtnmotors · « **Reply #42 on:** September 02, 2016, 06:28:27 PM »

I hate to see you breaking parts, but I am thoroughly enjoying the effort. Hope you get it sorted before you give in to frustration!

frodef2 · « **Reply #43 on:** September 03, 2016, 05:25:11 AM »

Just came back from the garage. No visible wear on the rings or piston. The cylinder had some "stripes" but they could not be felt with the fingernail, so i think its no big deal. The cylinder is alu/nicasil, so its hard as nails.

I did a quck search for nx jet, and wouldn't you know. They have smaller jets in their store.

As i ordered the smallest kit i could find, i assumed the jets included where the smallest available.

Assumption is the mother of all #$%*ups.

And now its too late to order them online.

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scottly · « **Reply #44 on:** September 03, 2016, 08:56:30 PM »

Since you are under a deadline, consider soldering some jets closed, and then drilling them to an appropriate smaller size. Good luck with the race!

Terry in Australia · « **Reply #45 on:** September 05, 2016, 03:44:24 AM »

"Assumption is the mother of all #$%*ups." Words to live by!

frodef2 · « **Reply #46 on:** September 05, 2016, 11:01:06 AM »

The "black" primary clutch springs work like a charm. I can now engage the n2o at launch.

I have also sourced spare metal reeds. I have lowered the ignition even further, so i hope the reeds might last at least one trip. If not i will treat them as consumables.

Frode j

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simon#42 · « **Reply #47 on:** September 05, 2016, 01:29:42 PM »

scottly's idea about soldering the jet up and re drilling a hole is a good one , try it on one of the larger jets you are not going to use anyway .

and good luck !!!

frodef2 · « **Reply #48 on:** September 07, 2016, 09:19:46 AM »

I just remembered i work in electronics manufacturing, and have access to heaps of discarded solder paste stencils. They are made of some kind of stainless steel, and have almost the same feel as the stock reeds.

Just finished cutting one from 0,1mm and one from 0,12

Going on a testrun soon, and will report back.

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frodef2 · « **Reply #49 on:** September 07, 2016, 12:15:57 PM »

Some videos from this nights debacle

First video is with the old reed, reformed to be flat.

That's a fail. Blows the airfilter clean off the carb.

2nd video is with the 0,12mm homemade reed.

Not too bad, but still some hesitation and missfires
Video 3 is straight after the 2'nd video.You can hear that the moped is already slower than the first try. The reed has taken some damage.

Video 4 is the last cut from this test. We wanted to try and launch with nitrous.

The reed failed. with the same type of damage as the old reeds

I have a new theory as of why the reeds get damaged.

When the piston is on its way down, the exhaustport is the first to open, but only a few crank degrees later, the transfer channels open.
I think that the residual cylinder pressure, when the transfers open, is higher than the pressure in the crank. therefore slamming exhaust back down to in the crank and reeds.
This is less likely to happen at high RPM , since the crank pressure is rising faster due to the increased pistonspeed.

does this sound like it could be the cause?

News:

Author Topic: Nitrous on 50cc engine (Read 12665 times)