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Old 02-19-2011, 04:34 PM   #1
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Default ninja MR 21-R01 question

does anyone know why does this engine have so many head shims...theres two .02mm and two .01mm head shims?
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Old 02-19-2011, 04:46 PM   #2
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does anyone know why does this engine have so many head shims...theres two .02mm and two .01mm head shims?
same with mine,i keep those shims when im using 25% fuel..
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Old 02-19-2011, 04:53 PM   #3
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well i run 20% ...could i take one out...like a .02mm shim
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Old 02-19-2011, 05:01 PM   #4
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well i run 20% ...could i take one out...like a .02mm shim
I'm no ninja expert but you probably could pull a .1. I wouldn't pull a .2
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Old 02-20-2011, 06:56 PM   #5
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does anyone know why does this engine have so many head shims...theres two .02mm and two .01mm head shims?
That would equal 0.6mm, but Novarossi/RB .21s have 0.8mm shims - instead of changing the clearance naturally between the sleeve and head button to use less shims, it's probably better to use more shims instead of changing the machine that makes them.

In my POV, I know what I'm saying and thinking, but I have no idea if somebody reading this could make any sense out of this!!
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Old 02-22-2011, 06:58 PM   #6
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Originally Posted by DJ_Shakespear View Post
That would equal 0.6mm, but Novarossi/RB .21s have 0.8mm shims - instead of changing the clearance naturally between the sleeve and head button to use less shims, it's probably better to use more shims instead of changing the machine that makes them.

In my POV, I know what I'm saying and thinking, but I have no idea if somebody reading this could make any sense out of this!!
Ok, now explain that in english
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Old 02-22-2011, 11:36 PM   #7
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Ok, now explain that in english
I wish I could - it makes sense in my head!! But I'll try anyway:

**important to the people that might crap on me for this: this is just how I see engines today, and its only my opinion**

The bit of the head button that sits inside the sleeve has it's own length (i've never measured it, but Im guessing between .12's they would be very close to each other from different manufacturers, and the same for .21's)
Say for example, universally they can all sit 6mm inside the sleeve, for example. The shims change the depth/how far it sits inside the sleeve. Not entirely true for this next bit, but the exhaust port - being the last port closed/first port open, more or less determines how much collected air/fuel mix can be compressed.
*thinks about what to explain next*
Because of crank/port timing and new technology and whatnot, more and more engines today can cram more air/fuel mix into a single stroke and make more power, but then there comes a limit to how much you can compress before you start having problems (undershimming for example).
So to be able to control the amount of compression made, and to be able to adjust the ignition timing, shims are there so you can advance timing or retard it - almost like how you change the spark timing through the dizzy on a full scale car (12-8 deg BTDC)

Something like that!
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Old 02-23-2011, 12:51 AM   #8
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Those are simple words?

You want a real headclearance? Just use a piece of solder 1mm thick, bend it in a L-shape and put it through the plug hole and be sure the end tip is touching the cilinder and you can hold the other end. Turn over the crankshaft, squeeze the solder between piston and buttonhead, take out the solder and messure the flat spot. With most .21 engines a distance of 0.6 to 0.7 is needed at 25% nitro but it is no standard! I do have a later model Novarossi which has a much deeper combustion chamber and the headclearance is set to 0.55mm....

If your engine comes standard shimmed then it is normally set to 25% of use. Running 20% does not need a change buit you can take out an 0.1mm shim or use a hotter plug.

What is the story....
As mentioned all is based on ignition timing.
- less nitro gives a later ignition
- more compression gives aa early ignition

Both changes gives the same ignition.

The same but with less influence goes with glow plugs:
- a colder glowplug gives a later ignition
- hot weather gives more temp in the engine so it gives an early ignition

See here the relation between plugs and weather.

You can also play with the ignition timing:
- an early ignition gives more bottom power but prevensts going high rpm
- a later ignition looses botom power but makes the engine going to high rpm.

It is just a matter of what is needed on the track.... Be aware a to soon iignition does give detonation which shows quick broken plugs and with a extreeme high compression a rough surface on piston and head.

But what about the space between piston and head?
It is called the squish band, if you want to know more just use google to find some detailed information, it is all about power. In theory you want to have the space to zero but you have to deal with flex in the crankshaft and play on bearings and rod which becomes bigger at higher rpm and with more use at the time. At zero rpm it is 0.6mm but at 44.000 rpm it can be 0.3mm, with F1 engines with very small tolerances they know how far to go and makes it possible to squeeze a hair between piston and head at high rpm (19.000) without touching each other.

And why that much shims? Beats me but with the explenation you can imagine with 0% nitro you do need to take away some shims, for sure when running on high altitudes, it does give some space to setup the engine for all situations.
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Old 02-23-2011, 01:00 AM   #9
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Good call, much better explanation than mine - like I said, makes sense in my head.
I wasn't after the name of the squish band, but the name of the section of the head button that sits inside the sleeve. Inner headbutton??
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Old 02-23-2011, 02:05 AM   #10
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Quote:
Originally Posted by DJ_Shakespear View Post
I wish I could - it makes sense in my head!! But I'll try anyway:

**important to the people that might crap on me for this: this is just how I see engines today, and its only my opinion**

The bit of the head button that sits inside the sleeve has it's own length (i've never measured it, but Im guessing between .12's they would be very close to each other from different manufacturers, and the same for .21's)
Say for example, universally they can all sit 6mm inside the sleeve, for example. The shims change the depth/how far it sits inside the sleeve. Not entirely true for this next bit, but the exhaust port - being the last port closed/first port open, more or less determines how much collected air/fuel mix can be compressed.
*thinks about what to explain next*
Because of crank/port timing and new technology and whatnot, more and more engines today can cram more air/fuel mix into a single stroke and make more power, but then there comes a limit to how much you can compress before you start having problems (undershimming for example).
So to be able to control the amount of compression made, and to be able to adjust the ignition timing, shims are there so you can advance timing or retard it - almost like how you change the spark timing through the dizzy on a full scale car (12-8 deg BTDC)

Something like that!
Thanks for clearing that up.
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Old 02-23-2011, 06:34 PM   #11
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Roelof did it better
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