Serious engine problem

Davezilla said:

I don't get why people are telling you you got a broken or snagged ring if compression tested good and you have no spark???

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Because I believe, based on El Bandito's description, that his initial and most urgent problem is whatever caused the worrisome noises from his engine before it gave him grief.

According to him, the engine WOULD start after the incident, but exhibits the telltale behavior of an engine with a gouged cylinder-wall and probably snapped/skewed rings.

In fact, I'll bet you $0.10 it's exactly what I described: a loose ring index pin fouling up the works. (My condolences El Banditio; it'll probably run you $40 to fix).

Sounds logical to me, but I'm going off the no-spark condition (I think?). That would explain why it doesn't run at all. Rattling noise? If the magnet is free spinning, then that could be another reason it's not sparking and also rattling. Without being there and seeing it in person, it's just going to be a guessing game until I (we) can get some coherent responses from the troubleshooting guides laid out.

I have a feeling the language barrier isn't helping him much either.

Bummer on the stripped head, I'd say you could helicoil it but the helicoil kit costs more than the head... You can get a Fred head from his site for $39.99 tho once you get some funding built up.
For the no spark condition, take the multimeter and set it to read Ohms... Put the red lead in the volt/ohms socket in the meter, and the black to Common
Place the leads on the black and the blue wires coming out of the engine, you're looking for 300 to 500 ohms, give or take a few either way. If it reads really low it's shorted out and needs to be replaced, and if it reads really high, or just reads 1- this means it's an open circuit, if you're lucky it's just a poor ground connection at the other end of the black wire, if that's connected good and there's continuity to the engine from the black wire then the mag coil is bad. The mag coil is good if it reads anywhere in the 300 to 500 ohms range, it can read lower or higher tho and still be good... just nothing extremely out there...

Some say you can test the resistance on the cdi unit it's self but I wouldnt rely on this, if the mag coil checks good and the mag rotor is keyed properly on the crank shaft and there's no spark, just buy another new cdi, these things do go out from time to time and having a spare or 3 isnt a bad idea.

For the mag rotor, the magnet... if you can turn it independantly from the crank it's possible the key broke or is missing all together, the mag rotor's key slot should be in about the 1 o clock position with the piston all the way up at TDC, if it's not in that position we got a problem... either a broken or missing key. You have to remove the nut that holds the mag rotor on to check the key slot position, this thing can go on backward and it will not fire the plug at the right time if it does go on backward so mark it permanently somehow if you remove it for any reason. There are ways to tell if it's on right or backwards, but if you mark it before removing it, that's probably the safest way. You shouldn't have to remove the mag rotor anyway, just take off the nut and check the position and put the nut back on if it checks good.

Well, I guess I owe someone $0.10.

No problem, we all do our best with just the info given to us and not being able to see the engine up close and personal... which would make it a LOT easier to help diagnose accurately.

Bandito, just in case you weren't aware, you should be able to turn in the spark plug with your fingers and then torque down with the wrench. It's good insurance against crossing the threads. If the plug threads are sticky you can clean them with a wire brush.

hope you get back in the saddle soon

Chaz said:

Bandito, just in case you weren't aware, you should be able to turn in the spark plug with your fingers and then torque down with the wrench. It's good insurance against crossing the threads. If the plug threads are sticky you can clean them with a wire brush.

hope you get back in the saddle soon

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I agree here... and if using a head that makes it difficult to access the plug, you can use an old straight spark plug boot for an installation tool, just pop the plug into the boot and turn it like a screwdriver until the plug bottoms out before putting a wrench on it. What this does is prevent damage to the threads in the head from cross threading because if it gets really tight while putting it in the boot will flex and slip before the plug can damage the threads in the aluminum. This works great on cars where the spark plugs go deep into these socket tube where you definitely can't turn the plug by hand when installing.
On these engines where you can easily access the plug it's not such an issue but can still be used to prevent damage, but if using a head like the Fred head or puch hi hi, or any head with tall fins, using an old straight boot is an easy way to insert the plug safely without any worry of cross thread damaging the head.
Another thing I recommend for any aluminum head is to get some anti seize from the auto parts store and apply a Thin coat over the threads... it'll prevent the plug from seizing up inside the hole, especially if the plug is in there for a really long time. I just use a really small dab on all my plugs and use a small acid brush to apply it in a thin coat.

Yup... 3/8" fuel line hose works well for this... I sometimes use this and for those hard to reach ones, an old plug boot or section of 3/8" hose can be pushed over a socket extension or long screwdriver which will do the job quite well... Our engines have the plug right there but on most newer cars, they are recessed pretty deep so that's my trick... my other trick is to put a rare earth magnet inside a 16mm socket so when I pull the spark plugs out they stay with the socket, then they pull right off once out of the hole leaving the magnet inside the socket.

Very true.... a few tiny grains of that crud will do more damage to an engine than 20 years of hard use...

El Bandito said:

Hola everyone, sorry I haven't posted in a while(college and other things) but I have an update to tell. Turns out there were two problems that my mechanical friends(I got a hold of another one) helped me solve: The Spark Plug got fouled and surprisingly the magneto shorted out. Over the few month(es) that passed, I acquired the parts that I need: a new head(got stripped, re-threaded but leaves a slight gap), new magneto and 2 new NGK spark plugs. Hopefully today or tomorrow I can put everything together and test it out. P.S since I last posted on here, I left the gas and oil in the tank and occasionally gave it a good shake to keep it from corroding. Will there be any problems since I didn't remove the gas,oil mixture in the tank?

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I'm not sure if you say you got a new head or that it is renewed by taking the stripped head plug threads and used a thread chaser or tap to clean it as best it could be.

2nd I was wondering if not really a new head per say, but the 2nd choice as per above, what is meant by a gap. I would be concerned if the threads don't torque down proper without loosening. A gap if not a leak around the plug gasket, I wonder if you mean a bit of metal remove from thread chasing and it is now the spark plug is just a bit loose till it seats down.

The Heli-Coil are definitely a bit looser as the spark plug is hand threaded in, that is OK as long as it torques down and holds. They are much less prone to cross threading, and probably since they don't fit as tight, but they are stronger metal steel (kinda spring) they are more durable.

The gaskets built into most spark plugs today are good for a few times of removal and installation, but they compress and are at a point susceptible to not sealing well at the top of the head adjacent to the threads when worn out flat sometimes. The threads themselves are really not needed to seal the gases from leaking as it is not the threads, it is the gasket job to do that.

I had a leak from a spark plug gasket and eventually found it out after it was hard starting. The loss of pressure was bad, but I also suspect on in take stroke in dusty conditions a leak at the plug can suck in dust. Best for less than 5 dollars a new spark plug if you can't take a gasket from another plug that otherwise is broken, or you can't buy the gaskets separate to seal a leak.

I've bought Heli-coil for smaller threads from a distributor that sold individual part and the exact drill bit that are not common size and was told I could create a part to install the thread repair Heli-coil and use a sharp flat blade screw driver to break off the bottom of the coil to finish the job. The professional kits are not really a likely choice unless you're in business, so I have 1/4 - 20 repairs made a couple times successfully on the cheap.

I suspect you'll have it up running soon.

MT

Bandito, gas is fine, just drain the carb and add some fresh mix to your tank if you have it handy.

Good time now to lap the head and cyl mating surfaces. Lots of info on this if you search.

My simple understanding of the kill switch is that it does actually short out the magneto circuit to cut off the juice for ignition. I'm not sure what your friend is talking about so get him to do it for you.

you'll be up and running in no time

Frito Bandito, if you only hear the sound while pedaling then it's something in your pedal train that's making the noise.