Three Different Heads - Three Different Problems

[yuckfoo]

A couple of $h!# bombs in this one. NSFW.

 

[YetiWoodz]

I know for sure using a smaller spark plug for your blue head will work fine. I have a Fred Head with a small plug. Runs fine, electrically speaking its the same.

I have an Ngk c8hsa which is 10mm.

The ngk spark plug website is helpful with its specs. It'll tell you the heat rating, threads, size, all that stuff so you know what you need.

NGK 4629 C7HSA Nickel Spark Plug

$3.77 NGK 4629 C7HSA Spark Plug - Same Day Shipping. Free Returns. PayPal Accepted. Secure Online Ordering. Est. 1969.

www.ngk.com

 

[yuckfoo]

I know for sure using a smaller spark plug for your blue head will work fine. I have a Fred Head with a small plug. Runs fine, electrically speaking its the same.

I have an Ngk c8hsa which is 10mm.

The ngk spark plug website is helpful with its specs. It'll tell you the heat rating, threads, size, all that stuff so you know what you need.

NGK 4629 C7HSA Nickel Spark Plug

$3.77 NGK 4629 C7HSA Spark Plug - Same Day Shipping. Free Returns. PayPal Accepted. Secure Online Ordering. Est. 1969.

www.ngk.com

Thanks. I still think I may have a clearance issue with that head because of how the spark plug sits. I'll put that head on tomorrow and test fit it on the bike with the plug in. (If I can find it)

 

[yuckfoo]

I know for sure using a smaller spark plug for your blue head will work fine. I have a Fred Head with a small plug. Runs fine, electrically speaking its the same.

I have an Ngk c8hsa which is 10mm.

The ngk spark plug website is helpful with its specs. It'll tell you the heat rating, threads, size, all that stuff so you know what you need.

NGK 4629 C7HSA Nickel Spark Plug

$3.77 NGK 4629 C7HSA Spark Plug - Same Day Shipping. Free Returns. PayPal Accepted. Secure Online Ordering. Est. 1969.

www.ngk.com

I found the plug. I think it's Chinese. It's labeled "HD- XILIE / AC7TC" The width of the threaded part is about 9.8 mm

 

[yuckfoo]

I know for sure using a smaller spark plug for your blue head will work fine. I have a Fred Head with a small plug. Runs fine, electrically speaking its the same.

I have an Ngk c8hsa which is 10mm.

The ngk spark plug website is helpful with its specs. It'll tell you the heat rating, threads, size, all that stuff so you know what you need.

NGK 4629 C7HSA Nickel Spark Plug

$3.77 NGK 4629 C7HSA Spark Plug - Same Day Shipping. Free Returns. PayPal Accepted. Secure Online Ordering. Est. 1969.

www.ngk.com

Those plugs you linked are on back order. Everything is out of stock or on back order. We live in an age where you can buy anything you want from your living room but now the invisible enemy has everything slowly grinding to a halt.

 

[YetiWoodz]

I think the second angled head you got will work good too, maybe even the best. Even know that chamfer isn't centered, I think its just for an increased angle to theoretically "aid in getting more fuel in the combustion chamber."

And I think you're right about it with the swirl. But likely adds little to no power in the real world like you said .

The surface area of the cooling fins I'd say is more important than anything else since its an air cooled engine, and is why that head might be better. It at least looks like it has more surface area, I'd check.

 

[michael whiteman]

I think you have a real good understanding of what's going on between these 3 heads. First: don't even worry about the spark plug. If it sparks and ignites the fuel you're good. They will all do this. The flame front across the combustion chamber will be slightly unique but you will not be able to realize any performance difference because we're talking about a single cylinder engine here. The "swirl" of the fuel mix is determined by the ports in the cylinder and the piston dome shape. Not the shape of the combustion chamber. The only internal thing to consider here is the volume of the combustion chamber which is the determining factor of your compression ratio. The smaller the chamber, the greater the compression meaning more HP. Like you said, totally negligible on a small CC single cylinder engine. If you're interested, screw in a plug and fill the chamber with a hypodermic syringe and measure the CC's. You already know the bottom line. Use the head that will clear the frame with the largest fin area for cooling. Forget the blue one. It's a nice piece, but all show and that's not what you're after.

 

[YetiWoodz]

Note that cubic centimeters is the same as milliters.

Measuring the head surface area, you can just eye it up or use something like painters tape since it'll conform with the fins. Cut it off at the ends and take the tape off so its flat and measure it there.

 

[yuckfoo]

I think you have a real good understanding of what's going on between these 3 heads. First: don't even worry about the spark plug. If it sparks and ignites the fuel you're good. They will all do this. The flame front across the combustion chamber will be slightly unique but you will not be able to realize any performance difference because we're talking about a single cylinder engine here. The "swirl" of the fuel mix is determined by the ports in the cylinder and the piston dome shape. Not the shape of the combustion chamber. The only internal thing to consider here is the volume of the combustion chamber which is the determining factor of your compression ratio. The smaller the chamber, the greater the compression meaning more HP. Like you said, totally negligible on a small CC single cylinder engine. If you're interested, screw in a plug and fill the chamber with a hypodermic syringe and measure the CC's. You already know the bottom line. Use the head that will clear the frame with the largest fin area for cooling. Forget the blue one. It's a nice piece, but all show and that's not what you're after.

Thanks! Probably the most helpful response I've ever received. You are either the manager of a highly successful team, a trained therapist, or a CIA operative. Whatever the case I hope you are using your powers for good!

I know one thing now. If I had a build where I could remove the head without removing the entire engine from the bike I would just try each of these and see what happens. But there is not enough clearance to take the head off without removing the engine from the bike. To be clear this is my first build and the engine has never been run.

I have one other pressing question. Perhaps you can help. It's in regard to squish. When I measure squish, I tend to get a higher reading right up against the cylinder wall, then the numbers get smaller before getting larger again. According to Two Stroke Ports (YouTube channel) the optimal squish is 0.75 to 0.95 mm. On my original head I had a reading of 1.3 mm right up against the cylinder wall. Then the readings got smaller and smaller and bottomed out at .9 mm about 5 mm in towards the center before rising sharply. With the second angle head (with the off center squish band) I get a bend in the solder near the end. What part of the solder am concerned with? Is it the very, very tip, corresponding with the area right up against the cylinder? Because this area tends to be problematic. My readings seem weird. As I've said, with the second head I get a sharp bend in the solder when I put a piece through the spark plug hole. I've tried the methods where you put the solder in first then clamp down the head. My attempts at measuring squish have not resulted in any confidence with the readings whatsoever. This situation of larger readings against the cylinder wall is not mentioned by anyone in anything I've read or any video I've ever seen.

 

[YetiWoodz]

Well, like Chainlube said, the dome of the head must not be matched to the dome of your piston's crown. It would be a flatter angle.

I excluded the combustion chamber to see the angles better.