Head Clearance discussion

[Norm Doerr]

View attachment 275774 View attachment 275775 View attachment 275777 View attachment 275776 The first pic is the stock heads. second is the moded heads. I used 2 different tools to make 2 different chamber with different cc but keeping every thing else the same. One tool is 1/4" and the other is 5/16". With the stock head only being 1/4" deep your hands are tied to how much you can do. Building one from scratch is a while different world.
When you can make the chamber as shallow as you want I use the 1/4" tool to make a 1/8 deep chamber.
But this is what I do with a stock head to gain cc's.
Stock heads are .32cc

Are those cutting tools over the counter or did you grind them? Asking for a friend who would prefer to buy.

 

[dwilfong]

The stock head has a small flat spot and a angled section. Not sure what the stock angle is . I always make a new strait angle so I know what I have. remember the squash clearance at .006 is only on the outer edge. It is much more where it enters the chamber with a 3 deg angle. I do not like the flat spot it makes a hot spot for detonation to start when you tighten it up to much.
If you are careful with the grease you can get the squash volume included in there.
This is not rocket science the numbers are just a reference to go back to after testing.
Remember it depends on what you want from the eng.....Two short runs or 6 +laps..........

 

[dwilfong]

Are those cutting tools over the counter or did you grind them? Asking for a friend who would prefer to buy.

MSC thy are in the book. Took me some time to look at EVERY THING and find them.......LOL Have fun looking......

 

[Timbo Whalen]

Are those cutting tools over the counter or did you grind them? Asking for a friend who would prefer to buy.

Norm-

In response to Dave's suggestion-

https://www.mscdirect.com

 

[Timbo Whalen]

The stock head has a small flat spot and a angled section. Not sure what the stock angle is . I always make a new strait angle so I know what I have. remember the squash clearance at .006 is only on the outer edge. It is much more where it enters the chamber with a 3 deg angle. I do not like the flat spot it makes a hot spot for detonation to start when you tighten it up to much.
Remember it depends on what you want from the eng.....Two short runs or 6 +laps..........

Exactly!...that's what my piston and button illustrated out at the edge.

 

[Norm Doerr]

MSC thy are in the book. Took me some time to look at EVERY THING and find them.......LOL Have fun looking......

I will grind them from blanks... IF I need to too...

 

[dwilfong]

I will grind them from blanks... IF I need to too...

I would look again but I cringe every time I have to try and find them in that book.

 

[dwilfong]

https://www.mscdirect.com/browse/tn...Matching+Categories#navid=12102066+4288235373
Here you go was not that hard after all

 

[Norm Doerr]

I would look again but I cringe every time I have to try and find them in that book.[/QUOT

https://www.mscdirect.com/browse/tn...Matching+Categories#navid=12102066+4288235373
Here you go was not that hard after all

Appreciate that... need to save your invoices man!

 

[Timbo Whalen]

Yeah, I'm guilty of that, too!

 

[dwilfong]

That is how I found it so quick this time, I have a on line account with them now and just look at the last few orders.

 

[Rick Doane]

My latest article discusses head design. I would love to hear criticisms from the members here.
namba.com/content/library/propwash/2019/october/4/

Lohring Miller

Lohring:

Thank you for sharing that information. It is always great to read how others are approaching this subject. I have always favored the old SuperTigre head style, your "flat toroidal" one. The reason is that the hemispherical shape is difficult to get the correct volume in the space/shape (hemisphere). However, I have always felt that volume is much more important than shape. Also, I remove the sharp edge from the squish band/bowl area. I have seen that sharp interface area frost before any other on the head. Another key point is I have read where others like a little frosting on the plug and head to indicate good burn patterns. That is NOT what I have found. The best runs have been with no frosting to the head or glow plug. No motor has run faster by turning the fuel down.

Before any changes are made to head volume, one should ensure that they can measure the volume accurately. I sometime have to make several measurements just to ensure consistency so I can be certain of the cut. I would also like to point out that accurate head clearance measurements are not made with a tool inserted into the glow plug hole. It depends if the motor has oil/fuel in it or not. As with anything else, the more heads you make or modify, it gets easier the more you do.

Comment on holed pistons..........too lean period.
Comment on piston hitting head.................... check engine assembly

Most of my latest engine work has been on the CMB brand. These motors have been most consistent when it comes to manufacturing each part. One still needs to measure all components/aspects of the motors to ensure nothing has changed. Question for all here: I would like to hear from others how they measure the port openings to determine time area calculations. Maybe a topic for another thread.

Thanks again for all your articles.

Rick

 

[LohringMiller]

Thanks for the complements. The holed piston pictured was probably too lean, but we melted pistons on several nitro engines on our dyno that were setup with the needle run in 1/8 scale boats. I believe our dyno put more load on the engines than the boat's propeller did. Maybe an even richer mixture would have helped, but it was getting expensive.

Lohring Miller

 

[Rick Doane]

Thanks for the complements. The holed piston pictured was probably too lean, but we melted pistons on several nitro engines on our dyno that were setup with the needle run in 1/8 scale boats. I believe our dyno put more load on the engines than the boat's propeller did. Maybe an even richer mixture would have helped, but it was getting expensive.

Lohring Miller

I agree with the dyno loading thought. Our props have unknown load efficiencies, until tested on the water, and the dyno directly measures total(?) ability. Learning how to burn nitro fuel is a lifelong experience.

 

[Rick Doane]

What are the benefits/consequences of raising or lowering head clearance? Lets assume I have a novarossi.21 motor and running 65% nitro. The consensus on this forum seems to be that I should run around.008” clearance. What benefits/consequences would I see if I ran at .010 or .006”? I seem to notice that I blow plugs easier at a lower clearance. I am just curious about the theories on this and what others have found through testing.

Hello Greg:

I have found that if you make say three head buttons of various increasing volumes, you can try each one on the same day with no problem. Use the same shims on each head and adjust the needle on the rich side (always). After each run, check the glow plug and make additional adjustments from there. You may find a whole different scenario than others have. You will have to know what your volume is to begin with and go up in approx. 0.2 cc increments. The better volume to run is the one that does not show signs of detonation or pre-ignition and providing nothing else runs through the engine during the test. Attached is an example of what I mean.

 

[timothy johnson]

Have to check...it fits the NR header perfectly, and the NR header fits some of the CMB engines.

Tim , were you able to see if the NR pipe fits the CMB headers?

 

[Timbo Whalen]

Tim , were you able to see if the NR pipe fits the CMB headers?

Sorry about that, haven't been around lately... I'll run and check it now...

 

[Timbo Whalen]

Tim , were you able to see if the NR pipe fits the CMB headers?

Yes, the CMB header is a virtual clone of the NovaRossi header, size wise-

 

[timothy johnson]

Thanks