Plug reading.

[Samuel Hagan JR]

I know there is thread on it but I couldn’t find it. But I can read a plug pretty good but I don’t know what a certain issue is.

Ran out Sport 20 and runs great no issues. Brought the boat back in to check the plug to see if the plug looks good.

Plug looks new untouched but the middle of the element is gone.
What condition takes out the middle of the plug. No discoloring like it’s lean.

To me it seems like a vibration issue taking out the center of the plug.

 

[dave roach]

Head clearance to tight.

 

[Samuel Hagan JR]

I’ll remeasure it to be sure but I don’t think it is.

 

[FloridaScaleBoater]

What engine is it? how much time on the engine bearings & rod?

 

[Danny King]

One plug doesn’t tell you much. If it repeatedly does it that is a symptom. On a really good running boat a air pocket in the fuel line can pop a plug. Running it out of fuel can. A
Blast Of water can An extra hard u turn. A prop coming unloaded and reloaded can.
again. If it is really running good any of that can do it. Certainly
Head clearance crap in the needle.
different plugs are better then others. What plug and heat range you running. Lots of variables....

 

[Samuel Hagan JR]

I should’ve said the center of the element is gone. So when you look at the plug the element is there just not the center of it. Kinda weird.

 

[Samuel Hagan JR]

Motor is a DD Nova 21. Fuel is 50 percent. Bearings are good. It’s pickled after every race. Maybe got a Gallon of fuel in the motor.
I’ll see if it does it again. I’ve had the same issue happen on a VAC 45.
I had the crank balanced and it pretty much took care of the issue. But the crank looks already balanced.

 

[Terry Keeley]

What plug?

 

[Samuel Hagan JR]

ODO Blue

 

[Terry Keeley]

ODO Blue

That's strange. If I take a plug usually the whole element is gone with only about 1/2 a coil left.

You mean there's a few coils at the top where it's welded to the side then nothing deeper down?

 

[Samuel Hagan JR]

That's strange. If I take a plug usually the whole element is gone with only about 1/2 a coil left.

You mean there's a few coils at the top where it's welded to the side then nothing deeper down?

Yes. Exactly. I can see maybe a few coils at the bottom but nothing in the center. Plug looks brand new. No discolor.

 

[Samuel Hagan JR]

I have a bunch of dust flying around the shop from building a couple boats so I haven’t had time to measure head clearance. But I’m more then sure it’s not too tight. The pinch has loosened up quite well during break in.

 

[timothy johnson]

Like Danny says, nothing is conclusive until you have a repeated problem. Have you flowed your needle and run it again. If not you should since you have already concluded that your setup as it should be. Plugs can always go !!

 

[Samuel Hagan JR]

I can always see what happens again. But if it’s a continues issue what would be a good recommendation. I’m not trying to blow a plug every time we go out. That gets expensive real quick.

 

[David Murany]

The DD 21s vibrate a ton at high rpm. A loose engine mount helps. If it's rigid this will happen. Also if the compression ratio is too high I've had the same issue.

 

[Samuel Hagan JR]

The DD 21s vibrate a ton at high rpm. A loose engine mount helps. If it's rigid this will happen. Also if the compression ratio is too high I've had the same issue.

I’ll recheck the head clearance. Thanks

 

[Samuel Hagan JR]

Head clearance is at .017”

 

[Walt Barney]

Head clearance is at .017”

Try .006 or .007 head clearance. .017 is tooooooo much
Walt Barney

 

[Danny King]

Are you subtracting for the dish in the piston?

 

[Ron Zaker Jr]

what is the actual dimension of the dish recess on a DD .21 and do you find it consitant ? Thx.