motor doesn't run after new mods?

[mrfubs]

Hey everyone I'm currently running a punch head with arrows reed valve and I ground out the third transfer port and The Bike ran good. So I took the motor apart to rebalance the crank and is it possible I took too much material off and lost so much crank pressure that it won't start? It won't even fire with eather. Its got a lot of compression give or take 130 psi and has spark I tryed using the nt and my CNS carb with failure. Long story short the only thing I changed was the crank so I'm thinking if I stuff the crank there's hope?

 

[Ron344]

I don't think adding a third port would keep it from starting. Your compression is not that high I have one that's 150psi. and another one that's 180psi. I think it might be a timing issue our something else.

 

[Mike B]

Yup. I think you put the rotor on 180 off.

 

[mew905]

Hey everyone I'm currently running a punch head with arrows reed valve and I ground out the third transfer port and The Bike ran good. So I took the motor apart to rebalance the crank and is it possible I took too much material off and lost so much crank pressure that it won't start? It won't even fire with eather. Its got a lot of compression give or take 130 psi and has spark I tryed using the nt and my CNS carb with failure. Long story short the only thing I changed was the crank so I'm thinking if I stuff the crank there's hope?

When the magnet is pointing straight up and down (so the notches are on the left and right), the keyway notch will be at the 1:00 position. If it's in the 11:00 position, the magnets on the wrong way. I dont know why this makes such a difference, but it does. As for cranking pressures, potentially, but it should still fire, I drilled a buttload of material out of my crank and it still worked... barely, but it worked. did you stuff the crank again after doing that to regain pressure? IIRC the motors come stock at 1.2:1, you want 1.5:1 so a couple CC's of some kind of filler (JB weld, I used Permetex copper ) should bring it back up. temps in the crank arent very high, but you should fill the holes you drilled with something like aluminum or another lightweight material to keep your case pressure.

 

[mrfubs]

The magnet only Went on one way and I just checked it and it is getting spark at the correct time.

 

[mew905]

The magnet only Went on one way and I just checked it and it is getting spark at the correct time.

is the notch at the 11:00 position? It may appear the spark is firing at the right time because even if the magnet is on backwards (or upside down, whatever you want to call it) the spark timing will only vary by 60 degrees (at 1300 RPM, roughly the speed of a 12v drill, thats only a 7ms (0.007, 7 thousandths of a second) difference, which is ridiculously difficult for humans to pick up on. take the magnet off, flip it around, I dont mean turn it on its axis 180 degrees, I mean the side that faces the case should face away from it when you flip it. It takes 2 minutes to do if the half-moon key is cooperating.

a 60 degree difference doesnt seem like a big deal, I know, that confused me too, but when you think about it, thats 60 degrees of the piston compressing the gas, then decompressing it BEFORE it fires. I'm not sure how the key lines up with TDC, but assuming TDC is where the key is pointing straight up, then with the magnet with the notch at the 1:00 position will fire 30 degrees before the piston finishes compression (assuming the CDI aims to fire exactly when the magnet passes, which it doesnt, throwing timing off even more than this 30 degrees), giving the gases time to combust before thrusting the piston down. Setting the key at the 11:00 position will fire the spark LATER (because the magnet doesnt swing by until 30 degrees AFTER TDC). Meaning the piston's already compressed the mix, optimum firing compression is gone because the piston is already 1/6 through its cycle and decompressing the gas (the exhaust will be opening in another 60 degrees or so), and then your spark fires... burning some, if any, gas that happens to be near it, giving it pretty much no time at all to push the piston even slightly before being blown straight out the exhaust.

 

[Venice Motor Bikes]

I concur... Check that the magnet is in the correct way.

 

[mrfubs]

When the magnet is pointing straight up and down (so the notches are on the left and right), the keyway notch will be at the 1:00 position. If it's in the 11:00 position, the magnets on the wrong way. I dont know why this makes such a difference, but it does. As for cranking pressures, potentially, but it should still fire, I drilled a buttload of material out of my crank and it still worked... barely, but it worked. did you stuff the crank again after doing that to regain pressure? IIRC the motors come stock at 1.2:1, you want 1.5:1 so a couple CC's of some kind of filler (JB weld, I used Permetex copper ) should bring it back up. temps in the crank arent very high, but you should fill the holes you drilled with something like aluminum or another lightweight material to keep your case pressure.

Well that was it, noob mistake haha its running now. One more question are you happy with how your motor runs after attempting to balance the crank? I'm having trouble balancing mine and I think I took way too much off. Thanks!

 

[mew905]

I ended up replacing my crank as I drilled it on the wrong side and the motor barely moved on its own. The intense vibrations and the lack of case compression made it unridable, so I pulled the crank, threw in a spare one I have and all is good until I get some aluminum rods to fill the new holes with when I balance it properly. The more you take off though, the higher your 'sweet spot' RPM will be, some people have taken off ~33 grams from what I've read (off a 3-piece crank though), which is about 4 cubic centimeters (4ml) of material. If you remember what size hole you drilled, you can buy some aluminum rod and stick it in there (its gotta be a good fit though, not too tight though because aluminum expands at twice the size and rate as steel does, just enough that it wont want to move when the motor is still warming up), but it'll add approximately 1/3 of the weight you removed back into the crank. So if you ended up removing 33g, and replacing it with auminum, the total weight you took out would be roughly 22g, and you would retain your compression ratio.

PM me what procedure you used to balance it. I dont remember if it was you I "translated" the guides for into laymans terms. It is a long process, there's no shortcutting if you want to do it properly (very similar to extreme overclocking procedures: measure, modify, repeat. Measure is checking if the crank still rolls on its own on a level surface, modify is to remove weight from the heavy end to stop it from rolling, then check to see if it rolls again.) Being that the crank is very hard steel, its hard to do with a hand drill, a dremel could do it, I used a drill press and cutting lube.