Head clearance. Nova DD 21

[RonShaw]

I am not measuring the dish part. I’m measuring top part of Piston.

Ok. That will work Sam utilizing a depth gauge to measure to piston top at TDC, and subtract the button reach and shim thickness, but in my experience, wont be as accurate as measuring with the button and shims mounted and tightened to the case.

 

[James Schmidt]

Sam I have the nova Rossi keep MP which is pretty much the same engine is a DD without the PTO. I run mine at 0.010 0.011 it's right between 10 and 11 since I don't have a shim thin enough to get exactly 11 or 10,000. in my experience this motor runs better with the engine loosened up a bit 8000 always work on my older engines but I get more RPMs when I go to 10 or 11,000.
The nice thing about running your engine at these clearances is that when you have days with lower air density you can switch to a hotter plug instead of lowering your head clearance.

Thanks Jim

 

[James Schmidt]

And don't forget about what Danny and Ron were talking about the dish on the top of your piston is .016 deep so you have to account for that as well

 

[John Seybold]

Thanks for the thread and info, because without it I may have messed up one of my new Nova’s. The dish pistons always give me trouble.

So, I opened up a brand new Nova 21DD for this test. The motor came with three shims measuring a total .028. I inserted my dial indicator and rotated my motor to TDC and zeroed the gauge. I then remove the head with the dial indicator attached and placed it one a piece of granite to read the gauge. The gauge had a difference from zero of .026”. So, IF the dish is .015” then the factory clearance would be .013? Does this sound right for a motor straight out of the box? Are most guys running two or three shims in their motors?

How can I measure the dish? Are all of them .015”?

If someone set the clearance to less than zero wouldn’t be able to rotate the engine right?


Thanks

 

[RonShaw]

Thanks for the thread and info, because without it I may have messed up one of my new Nova’s. The dish pistons always give me trouble.

So, I opened up a brand new Nova 21DD for this test. The motor came with three shims measuring a total .028. I inserted my dial indicator and rotated my motor to TDC and zeroed the gauge. I then remove the head with the dial indicator attached and placed it one a piece of granite to read the gauge. The gauge had a difference from zero of .026”. So, IF the dish is .015” then the factory clearance would be .013? Does this sound right for a motor straight out of the box? Are most guys running two or three shims in their motors?

How can I measure the dish? Are all of them .015”?

If someone set the clearance to less than zero wouldn’t be able to rotate the engine right?


Thanks

John,
The dish is easy to measure. Insert your gauge into the head button. Remove the piston/rod assy. Place the headbutton on top of the piston. Zero out your gauge. Place the headbutton/gauge onto a clean flat glass surface. The number you see will be the dish depth at center bore. It should be around .015. Now you can measure the engine the old fashioned flat top piston way and always remember to add this number to your measurements. If you measure .015 dish depth and want .008 clearance, you are aiming for .023 measurement. I hope this helps. When lowering head clearance below stock numbers, you need to develop an accurate technique with the right tools. Many have failed in these steps and ruined brand new engines. If you are not 100% sure, reach out to someone like Danny or Steve to walk you through it several times first. Good luck.

 

[Terry Keeley]

https://www.circuitspecialists.com/solder-wire-1.html

 

[David Murany]

Zero the head out against the top of the piston. It is the best fool proof way. I run my DDs at .0065. I was breaking the element from vibration so I loosened up the mount. I also brought the compression ratio down. We have 5 of the DDs between my dad, brother, and myself all set up this way.

 

[Terry Keeley]

Zero the head out against the top of the piston. It is the best fool proof way. I run my DDs at .0065. I was breaking the element from vibration so I loosened up the mount. I also brought the compression ratio down. We have 5 of the DDs between my dad, brother, and myself all set up this way.

 

[RonShaw]

https://www.circuitspecialists.com/solder-wire-1.html

No no no, not the solder again LOLOL

 

[Walt Barney]

Walt I appreciate the help. I’ll give you a call this weekend if your not busy. I also have a few tank I need to send you to check out.

Sam,
I'll be here all weekend send the tank to me asap, as I have several to build. Ph 256-779-6472
5929 Rosemary Ln.
Cedar Bluff, Al. 35959
Thanks
Walt Barney

 

[Samuel Hagan JR]

Thank you all for questioning my measurements. I rechecked everything and was way off. If I would’ve lowered it anymore I would have broke something. Glad I asked on here. Thanks again.

 

[James Schmidt]

Hey Sam, just curious. have you had a chance to try your Nova with your new head clearances.
If so, How dose it run now? And did you get a good noticeable improvement in performance?
What clearance measurement did you settle on for this time of year?