Plug reading.

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what is the actual dimension of the dish recess on a DD .21 and do you find it consitant ? Thx.
I have measured the depth in several pistons and found a variance of .003
average was .017 in depth, some were as deep as .020
Walt Barney
 
I’m not sure on the dish.
Don't worry about the center depth just buy some plastic gauge at the Napa auto parts and lay a small all across the top of the piston and turn it over 2 or 3 three times the take the head button off and compare the width at the widest point with the marking on the package ,that will tell you your head clearance. any questions call me 256-779-6472.
Walt Barney
forgot to tell you plastic gauge come in different colors that means different thickness. I use the red and yellow.
 
I’m not measuring the dish depth just where your suppose to measure. I’ll lower it down to .008” and see how it does. It loves fuel.
 
If youre using a dial indicator zero the button against the piston. I mark the head button and always install it the same direction as well. Zeroing against the piston is the only way to get an accurate measurement with a dome/dish style piston.
 
5C110749-4C17-4C82-9508-5470F6D7EE87.jpeg
Plug was still in the motor. I think I saved it for a reason. But here is the plug I was talking about.

You can see a coil maybe then where it’s broke.
 
View attachment 284160
Plug was still in the motor. I think I saved it for a reason. But here is the plug I was talking about.

You can see a coil maybe then where it’s broke.

Sam what does the piston look like? Does it look sand blasted at the edges? If it does you were on the lean side. Definitely check your engine mount setup though. The DDs vibrate a lot when you start getting the rpms way up. I had a lot of plugs that looked like that.
 
Sam what does the piston look like? Does it look sand blasted at the edges? If it does you were on the lean side. Definitely check your engine mount setup though. The DDs vibrate a lot when you start getting the rpms way up. I had a lot of plugs that looked like that.

Yes it does. It took forever to find a setting so it ran lean more then i liked to until I found a setting. My head clearance is way to low. Some I’m going to raise it up and retest.
 
Ok. If it continues to happen check the other things I mentioned. Strong engines once you get them figured out. Also change out the rod on a new one after a gallon and a half or two. Will save some headaches.
 
Ok. If it continues to happen check the other things I mentioned. Strong engines once you get them figured out. Also change out the rod on a new one after a gallon and a half or two. Will save some headaches.

No more rods available unfortunately. Out of stock on Rons site.
 
Anytime I have two or more identical plug failures I change brands and see if the problem goes away. If it does not then I look at my engine setup.
Head bu
Anytime I have two or more identical plug failures I change brands and see if the problem goes away. If it does not then I look at my engine setup.
Looks to me that the head button is toooooo close and it was running lean , I also would say you had a problem getting the higher RPMs
Walt Barney
 
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