Engine turns over but no bang

[petrock]

Originally Posted by CHIPMAKER

Some one had chimed in that the ECM would read resistance to make a spark. As it took more energy to make a spark under higher compression, it would raise the spark level.

I think the guy in that thread was guessing. He is kind of correct, but for the wrong reasons. As compression increases the amount of voltage required to make the spark jump the spark plug gap increases. Ignition systems put out the same amount of voltage regardless of compression or RPM. So to compensate for higher compression a smaller spark plug gap is required.
The ECM couldn't read resistance at the spark plugs even if it wanted to. To read resistance at the spark plug, the ECM would need to be connected on the power & ground side of the spark plug. However, the ECM is on the primary winding side of the ignition coil. The spark plugs are on the secondary winding side of the ignition coil. The primary & secondary windings are not connected. So, therefor, the ECM and the spark plugs are not connected. Not to mention, the primary winding only has 12 volts flowing through it, and the secondary winding has hundreds of volts flowing through it. If the ECM was connected to the secondary winding, it would fry itself really really really quickly with that many volts flowing through it.

Hope that helps...

[papachop]

My local tool place doesnt sell a compression tool with a 10mm attachment so it will have to be a mail order deal. Found a shovel ryder to cme over with his volts meter and probe around for me. As great as petrocks direction is my mind just doesnt wrap around volts and ohms that well. shovel ryder also has a compression harley tool so the battle continues. Look for an update in weeks time for those following.

[petrock]

Most auto parts stores rent compression gauges/testers. They screw into the motor in place of the spark plugs. Just bring in a spark plug from your bike to make sure you get the correct adapter so it will fit in the spark plug whole. Good luck...

[papachop]

Un update the project. With the primary cover off and compression tester connected to the back cylinder throttle wide open I turned the engine over manually and through the start button and got no reading on the tester. Im also not any closer to figuring the spark issue. All in all im determined to get this thing going if it the last thing I do. Not sure if this means that there is no compression? Its pretty cold here in southern ontario this time of year so im hesitant to tear the top end down to see what it could be. Does anyome know any good shops in southern Ontario Canada or any handy Harley guys I could link with to get this done.

[papachop]

double post

[BVBOB]

I think you are chasing your tail here, first off you need to find out why you have no compression, do you have adjustable pushrods and are they adjusted properly, if not you may have a bent valve. Roller rockers? they can hang up on the covers and keep the valve open a bit. There must first be compression before you will get spark, the crank sensor needs to see the crank slowing down do to compression to fire the plugs, simple as that.
A simple test is to pull the pushrod tube and make sure the lifters are both down on a particular cylinder, then blow some air in the spark plug hole and listen to see if it is coming out the intake or the exhaust, or worse, the dipstick tube. If it has no leakage with the lifters down and blowing air in then your cams are out of time.

[CHIPMAKER]

before you will get spark, the crank sensor needs to see the crank slowing down do to compression to fire the plugs, simple as that.

Bob, I'm not following that.

[BVBOB]

Originally Posted by CHIPMAKER

before you will get spark, the crank sensor needs to see the crank slowing down do to compression to fire the plugs, simple as that.

Bob, I'm not following that.

As the crank spins it slows down as the piston is harder to push during compression stroke slowing it slightly, that coupled with the 2 tooth gap in the crank wheel tells it to fire. Check out a crank sometime, they are 32-2 meaning they have 32 teeth and two open spots.

[CHIPMAKER]

There must first be compression before you will get spark


Is this to say if the plugs are out of the cylinders, hence no compression, there will be no spark?

[BVBOB]

Originally Posted by CHIPMAKER

There must first be compression before you will get spark


Is this to say if the plugs are out of the cylinders, hence no compression, there will be no spark?

Yes, that is true

[CHIPMAKER]

Originally Posted by petrock

I think the guy in that thread was guessing. He is kind of correct, but for the wrong reasons. As compression increases the amount of voltage required to make the spark jump the spark plug gap increases. Ignition systems put out the same amount of voltage regardless of compression or RPM. So to compensate for higher compression a smaller spark plug gap is required.
The ECM couldn't read resistance at the spark plugs even if it wanted to. To read resistance at the spark plug, the ECM would need to be connected on the power & ground side of the spark plug. However, the ECM is on the primary winding side of the ignition coil. The spark plugs are on the secondary winding side of the ignition coil. The primary & secondary windings are not connected. So, therefor, the ECM and the spark plugs are not connected. Not to mention, the primary winding only has 12 volts flowing through it, and the secondary winding has hundreds of volts flowing through it. If the ECM was connected to the secondary winding, it would fry itself really really really quickly with that many volts flowing through it.

Hope that helps...

Sounds a little confusing.

[papachop]

Well if the valves are sticking or my pushroads aint in proper I wouldnt be surprised but on the other hand I followed the instructional videos on how to do this stuff to the last detail. In any event heres some FYI
Once the engine was assembled with the covers of I manually turned the engine 20 times or more so see if anything sticks or if it get stuck somewhere. I did not. The pushroads were installed as per speck front and back and bled down over 4 days to make sure they were seated proper. Im doing something wrong just not sure what may be.
Is it a fact that there will be no spark with no compression. It seems that the spark issue is seperate from compression.
As for the heads
The heads were assembled by me using used valves that came froma head shop. no reason to think they would have sent me bogus parts they are throw aways for them. Should I just tear the motor down to the bottom end and startover? Maybe the heads need to be bench testedor something
Im so close to putting this bike together myself that I really preffer not to take it to a shop if I dont have to.

[papachop]

Well this seems like sound advice going to spend my day off going through this exercise.
Let you know what gives


I think you are chasing your tail here, first off you need to find out why you have no compression, do you have adjustable pushrods and are they adjusted properly, if not you may have a bent valve. Roller rockers? they can hang up on the covers and keep the valve open a bit. There must first be compression before you will get spark, the crank sensor needs to see the crank slowing down do to compression to fire the plugs, simple as that.
A simple test is to pull the pushrod tube and make sure the lifters are both down on a particular cylinder, then blow some air in the spark plug hole and listen to see if it is coming out the intake or the exhaust, or worse, the dipstick tube. If it has no leakage with the lifters down and blowing air in then your cams are out of time.

[papachop]

Well for those interested. Dead of winter here in Canada decided to move the bike to a small shop. There going to run a full diagnostic on it and well find out at least what the hell is wrong with the thing. Im strongly considering selling her for a deposit on a 2013. Or a lightly used model form the dealers. Id really like to get some miles on her but these repairs can be costly and without end. Fingers crossed for the 06 SG makes it.

[CHIPMAKER]

Keep us posted, good luck.