Serious engine problem

[El Bandito]

Hola everubody El Bandito here and I have a big problem here. So 2 days ago I was riding and everything was going good until I heard this loud Snapping, cracking sound l
I decided to slow down a little bit and sound went away. When I sped up again the sound returned. When I went to go into idle, the motor died. I think it flooded and or the cdi died idk

 

[El Bandito]

Also after I stopped, and tried to start it up again, I heard the motor start up a little bit then I heard thia loud bang then it became silent. So I decided to wait an hour and every 20 minutes I tried to start again. It would start up and make thw wheezing sound like it has not beem used in a couple of hours. Today I tried to start it up and I got the motor to rumble alittle bit but I had to pedal if I wanted to keep it going. I have no idea whay happened ir what thay loud bang meant but I think it means that there was a backfire
Can anybody help?

 

[2door]

Bandit, the first place to check would be the cylinder head fasteners and the head gasket. The noises you describe are consistent with a loose head and possibly a blown/leaking head gasket.

Tom

 

[Davezilla]

I agree... sounds like air sneaking out from between the head and cylinder, tightening the nuts back up should have you up and running again. Sometimes these need to be re torqued once or twice before they stay put.

 

[El Bandito]

Update day 4, sorry I haven't responded sooner folks college started and lately I've been super busy with hw and today I discovered that the cylinder head is on super tight. I can barely even move one of the bolts half a rotation! Also, I believe that it is infact the gasket thay blew out as you people said l. Any ropsvor sugfesroons on hpw to loosen up the head?

 

[El Bandito]

By the way the bolts were super tight and not loose at all.

 

[Chaz]

Hey Bandito!

To loosen up the head bolts try some wd40 or any penetrating oil overnight. As to why the gasket blew and the bolts are still very tight it could be that the mating surfaces of the head and the top of the cylinder are a little off. Once you get the head off you can cure that issue by sandpaper milling those surfaces to get them nice and even. There's a number of threads regarding this procedure. Or maybe the gasket was faulty.

good luck

 

[2door]

Be careful. Overtightening those cylinder head fasteners will cause you big problems. You really should use a torque wrench when tightening them. 120 to 140 inch pounds is the recommended torque range. Some will recommend higher but 140 is safe and sufficient.

If you have the proper tools, a socket and ratchet handle, you should be able to loosen those nuts easily. If you have the kit supplied chrome acorn nuts there's a good chance that the stud will come out of the case before the nut loosens from it. The acorn nuts are notorious for causing problems because they bottom out on the stud and can damage the threads as well as bind on the stud.

If the head nuts are as tight as you say I doubt the gasket is blown or leaking bad enough to cause the issue you describe. You should be able to see physical evidence of a leak. There will be dark oily residue around the area where the head meets the top of the cylinder. However the acorn nuts can also be responsible for keeping the head from being held down tight enough if they bottom out before tightening against the head.

We're assuming the spark plug is tight. About 80 inch pounds is sufficient. I have seen some kit instructions, especially on older kits, that tell you to "finger tighten" the spark plug. This is WRONG! It has to be much tighter than 'finger tight'. A loose plug can also be the cause of compression loss.


Chaz is also correct when he recommends 'lapping' the cylinder head. Use the 'search' and look for information on how to 'lap' the head correctly.

Tom

 

[El Bandito]

Update. With help from a mechanic friend, I was able to get the head off and it appears that there are scratches on the gasket. It is not blown but, after doing a bike run test I noticed that there was oil dripping and my mechanic friend said that there was no spark going on. I replaced the cdi and took off the spark plug and that turns out to be fouled. So after another test, nothing changed but, the two of us determined the cause to be the carb and or the magneto.

 

[Agreen]

Since doing whatever work you already did, have you:

-Verified spark?
-Verified compression?
-Verified fuel?

-If it's not getting spark, check resistance of the magneto. Shouldn't be zero or open. Something in between. I don't recall the exact number of ohms, but if it's open or shorted, it won't work. If the magneto is good, it's probably the CDI. The spark plug, boot, and wire are notoriously bad. So are the CDI/kill switch connectors.
-If it's not spark, check that you have compression. This isn't hard to do. Is it really hard to spin the engine with the spark plug in? Is it easy to spin without the plug? Boom. You have compression.
-Carburetor. This one's tricky. If the bike ran but suddenly doesn't, it's probably not the carburetor. If it got clogged though, it's possible. There's not much to the NT carbs, so it's easy enough to pull apart and clean.

The snapping/cracking noise leads me to believe a backfire may have happened. Is the magnet still keyed in the shaft? It could be free spinning and getting a weird intermittent spark.

 

[El Bandito]

I checked spark, compression and fuel after I made the post. Everything worked except the spark.

 

[El Bandito]

I checked all of the above before I made the post and everything works except the spark. I forgot to mention it(my bad).

 

[El Bandito]

I checked spark, compression and fuel after I made the post. Everything worked except the spark.

Ignore this thread, it was incorrect.

 

[Kioshk]

My diagnosis is you blew the rings/cylinder. Perhaps one of the ring-retaining pins loosened up and got pinched between the piston and cylinder-wall. It would also allow the ring to revolve in the slot and start smacking the ports. That'd explain all the awful noises you heard...it'd also result in loss of compression. I suspect your fouled plug occurred AFTER the damage: unburnt fuel. Did your mechanic not remove the cylinder for inspection?

 

[El Bandito]

I took off the cylinder head myself and we both inspected it and the gasket, the gasket had scratches on it but no holes. I am unable to post the pictures online because the size image is too big.

 

[Agreen]

So no spark?

 

[Kioshk]

Just so we're on the same page...

This is a "head":

This is a "cylinder":

Did you remover the CYLINDER to inspect its walls as well as the piston and rings?

RE:

 

[El Bandito]

The head, yes. the Cylinder, no.

 

[maniac57]

Hate to say it, but I'm going to agree with Kioshk.
Sounds like a classic ring snagging a port and breaking stuff.

 

[Davezilla]

If you need a place to hold your images, you can set up an account with Imageshack.com and link the images into your posts in here... There are several other free image hosting sites you can use as well and most of them have an easy way to resize them for forum posting...

Back to the issue at hand... What does the inside of your cylinder look like with the head off and the piston all the way down at bottom dead center? Are there any scratches in the bore, any plating peeled off or missing? What kind of compression pressure readings were you guys getting when you checked the compression?

If you snagged a ring you'll have some nasty scratches inside the bore or some gouging at the ports etc, if it looks perfectly mirror smooth with some minor scratches it could be from dust and dirt making it passed the stock air filter, and if the bore looks perfectly mirror smooth with no scratches or plating damaged or missing it's possible the cylinder glazed before the rings seated which can cause some poor compression with no damage or gasket leaks etc...

Since you're saying you lost spark tho, let's look there first... Do you or any of your buddies have a multimeter? do an Ohm check from the black wire to the blue wire coming off your magneto with the CDI disconnected, look for a reading between 300 and 500 ohms, it can read higher or lower and still be good, but you don't want a really high or infinite reading meaning you got an open circuit or broken wire, and you don't want a really low reading like less than 100 ohms (give or take) or close to zero, or zero... this means the coil has a short somewhere in it and the mag coil is no good.
A good mag coil should read between 300 and 500 ohms (give or take up to about 100 ohms in either direction).
If the mag coil checks good, then check the CDI by plugging a known good one into your circuit and check for spark. If you got one of those plastic spark plug boots it's also possible that's the problem. You can un screw the boot off the wire and strip about 1/2" of the insulation off the wire then clip the bare wire to your plug and see if it sparks, if the plastic boot is the problem get a terminal and boot for an automotive spark plug and crimp it to your wire, slide a rubber boot over it, screw on one of those little snap adapters to your spark plug and clip the new end onto your plug... Lots of info on how to do just that.

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???