Messin with da plug

[Danno77]

Bored waiting on my new crank, cleaned up some parts, messed with the plug.

Here's the stock direction and depth of the plug

Take off the washers on the plug and you get the plug dropping down just a teensy bit and rotating to have the spark aimed downward into the cylinder.

Do you think the does anything for better combustion AND, do you think the slight reduction in the upper end of the cylinder would increase compression enough to do anything fun?

P.S. I cleaned that up a lot after these pictures were taken, so no comments on the carbon buildup around that plug and in the cylinder.

 

[pen]

That's not a taper fit plug, were those washers above the seal? If not, those are meant to seal the plug and create a "crush fit" for proper torque setting / seating. I wouldn't take them off if it were me.


pen

 

[Danno77]

That's not a taper fit plug, were those washers above the seal? If not, those are meant to seal the plug and create a "crush fit" for proper torque setting / seating. I wouldn't take them off if it were me.


pen

No, you are right, but I figured for this 170 it wouldn't be the end of the world and it would be just one more teensy mod to help them all add up. Mild porting, a muffler mod, and rejetting are all that I have in mind at this point. I guess I could jack with the piston and a grinder if I wanna take off .00001 grams of weight, lol.

 

[LLigetfa]

Reminds me of my hotrod youth when we had to index our plugs because of the close tolerances with shaved heads. The indexing was strictly for clearance, not to aim the spark. If we didn't index, the piston would close the gap on the plug.

 

[kettensäge]

Usually you don't want the threads exposed in the chambers because they can get carboned and make the spark plug difficult to remove.
Another reason is the thin metal of the thread will heat up and cause pre-ignition, not sure if this would be the case with a 2 stroke.
Also, the washer is there to seal the chamber, so if it's removed you may loose compression because the bottom of the spark plug body may not seal or the plug seat could be damaged.

And as LLigetfa said, you may also create plug to piston clearance issues, even in your saw.

You can buy several plugs and see which one will "index" more to your liking before you reassemble the saw.

I wouldn't run it without the washer but if you decide to go ahead with it be carefull.

 

[smokinj]

Do some polish work. Make sure you can clear the piston!

 

[Danno77]

Do some polish work. Make sure you can clear the piston!

I cleaned the carbon out really good. I still am doing some math and planning for the porting, so after I do that I'll clean it up again and maybe takes some pictures.

LL. definitely with ya on exposed threads and carbon buildup. I read that same suggestion on AS. I wondered if completely grinding of the last bit of threads would be a possibility. Otherwise, just knowing that it could be an issue I could just remove the plug more frequently and clean it before there are issue.

I've been looking at plug sizes to see if there is something a little longer that I can leave the compression washers on. Clearance to piston is not a problem at all with this small amount. When it was 180 in the other direction the ground strap's little bend stuck down just as far as this does even though it's screwed in a tad further.

 

[LLigetfa]

LL. definitely with ya on exposed threads and carbon buildup...

Actually, that was kettensäge but i fully agree with his advise.

 

[Danno77]

LL. definitely with ya on exposed threads and carbon buildup...

Actually, that was kettensäge but i fully agree with his advise.

LoL. oops. didn't pay attention well enough!

 

[BrotherBart]

Now if you could find a really tiny turbo...

 

[CTYank]

You might benefit more from some of the exotic alloy plugs, like gold-palladium or platinum, because of the shape of their electrode tips.
The very small O.D. of the metal of the tips, for a given ignition voltage, greatly increases the strength of the electrical field, making
misfiring very unlikely. (The way lightning rods work.) Just get the right heat range, obviously.
They work great in very high compression racing engines.

 

[MasterMech]

Danno, perhaps you can find some aluminum or copper washers to 'shim' the plug and set it's direction? Maybe just buying a few plugs and checking each one out for best direction? I don't see an advantage to lowering the plug, especially if it exposes threads or leaves the outer rim in the cylinder. If you have the clearance, you could swap it for a projected insulator type plug.

Edit: Second glance at the photos - Looks like you already have a proj. ins. plug? Would have a P in the part #. ie NGK BMR4A vs a BPM4A.

+1 on not running it w/o a plug gasket. If it leaks out it can leak inward as well robbing you of power (compression/cylinder pressure) in additon to creating an air leak, leaning out the mix. Would most definitely offset any gains from "indexing" the plug.

 

[Danno77]

The loose theory of having the plug into the cylinder is that it takes up some of that upper cylinder volume, thereby increasing the compression. You wouldn't think it amounts to much, but when we are talking about the tiny specs of this 170, it might be something...

 

[MasterMech]

The loose theory of having the plug into the cylinder is that it takes up some of that upper cylinder volume, thereby increasing the compression. You wouldn't think it amounts to much, but when we are talking about the tiny specs of this 170, it might be something...

Hmmm.... Maybe I should whip up a high comp piston for ya, lol. That'd be a fun project on the mini-lathe!

Seems to me that you would gain more from eliminating the cylinder base gasket. Are you going that route too?

 

[Danno77]

The loose theory of having the plug into the cylinder is that it takes up some of that upper cylinder volume, thereby increasing the compression. You wouldn't think it amounts to much, but when we are talking about the tiny specs of this 170, it might be something...

Hmmm.... Maybe I should whip up a high comp piston for ya, lol. That'd be a fun project on the mini-lathe!

Seems to me that you would gain more from eliminating the cylinder base gasket. Are you going that route too?

no can do. Cylinder is one whole piece with a little "lid" (on the bottom, lol) that locks the crank in.

I'll send you a piston and you can put a dome top on it, lol. This piston is so small I can hide it under the stamp on a postcard, so shipping would be negligible! lol.