Engine Mods

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Old 12-25-2005, 08:18 AM
  #196  
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Thanks guys, I'd been crashing my brain trying to make sure that was right.
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Old 01-23-2006, 06:50 PM
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Default How to modifiy intake and exhaust timing

Can anyone tell me step by step how to get degree of the intake and exhaust. I have a 360 protractor but trying to get the method down pack. Trying to modifiy my rb v12
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Old 01-23-2006, 08:44 PM
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Originally Posted by Quietroit
Can anyone tell me step by step how to get degree of the intake and exhaust. I have a 360 protractor but trying to get the method down pack. Trying to modifiy my rb v12

First, you need to attach the degree wheel to the engine. I take a broken prop, and cut both blades off. This allows you to use it as a spacer, and mount the degree wheel on the crankshaft. Tighten your prop nut tight enough that the wheel won't slip unless you want it to. You also need a reference pointer. I used a large metal paperclip--the kind with handles, sort of like a clothespin--and soldered a stiff wire to it. You can clip the paperclip to a cooling fin, and bend the pointer so it's pointing towards the center of the degree wheel. The whole idea is to be able to accurately and repeatable measure the rotational position of the engine. The more accurate your clip is, the better your numbers will be.

It's time to measure now! Take the glow plug out, so the engine turns easier. A flashlight will make measuring slightly easier--if you shine it in the spark plug hole, you'll be able to see the ports better.

Exhaust port first. Turn the engine counterclockwise until the piston top is going down, and just opens up at the top of the exhaust port. Write down or memorize the number on the degree wheel, or turn the degree wheel (but not the engine) so the pointer is at zero. You want this point to be the point at which the gases will just be able to flow through, with the piston top at the top of the port. Now, turn the engine to move the piston down, and keep turning until the piston has gone back up, and stop just as it reaches the top of the exhaust port. If you set your pointer at zero, you now have the exhaust port timing. Typically, lower timing numbers are for lower rpm. The higher numbers, are typically for higher rpm.

Repeat this step for the intake port (crankshaft window), which is in effect a rotary valve. You will measure from the instant the port opens until it's fully closed. Rotary valve engines have longer timing because they don't open until the piston is moving up at BDC--creating a vacuum in the crankcase--and they close just after the piston reaches TDC.

Now, do it again for the transfer ports. Usually, there are two mirror image ports, one on each side of the exhaust port, then there is a third transfer port that's opposite of the exhaust port. This third transfer port is called the boost port, and it's common to have different timing than the other two transfer ports.

Now you've measured the port timing on your two stroke model engine.

AFM
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Old 01-24-2006, 04:36 AM
  #199  
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Default counting the degree

Originally Posted by afm
First, you need to attach the degree wheel to the engine. I take a broken prop, and cut both blades off. This allows you to use it as a spacer, and mount the degree wheel on the crankshaft. Tighten your prop nut tight enough that the wheel won't slip unless you want it to. You also need a reference pointer. I used a large metal paperclip--the kind with handles, sort of like a clothespin--and soldered a stiff wire to it. You can clip the paperclip to a cooling fin, and bend the pointer so it's pointing towards the center of the degree wheel. The whole idea is to be able to accurately and repeatable measure the rotational position of the engine. The more accurate your clip is, the better your numbers will be.

It's time to measure now! Take the glow plug out, so the engine turns easier. A flashlight will make measuring slightly easier--if you shine it in the spark plug hole, you'll be able to see the ports better.

Exhaust port first. Turn the engine counterclockwise until the piston top is going down, and just opens up at the top of the exhaust port. Write down or memorize the number on the degree wheel, or turn the degree wheel (but not the engine) so the pointer is at zero. You want this point to be the point at which the gases will just be able to flow through, with the piston top at the top of the port. Now, turn the engine to move the piston down, and keep turning until the piston has gone back up, and stop just as it reaches the top of the exhaust port. If you set your pointer at zero, you now have the exhaust port timing. Typically, lower timing numbers are for lower rpm. The higher numbers, are typically for higher rpm.

Repeat this step for the intake port (crankshaft window), which is in effect a rotary valve. You will measure from the instant the port opens until it's fully closed. Rotary valve engines have longer timing because they don't open until the piston is moving up at BDC--creating a vacuum in the crankcase--and they close just after the piston reaches TDC.

Now, do it again for the transfer ports. Usually, there are two mirror image ports, one on each side of the exhaust port, then there is a third transfer port that's opposite of the exhaust port. This third transfer port is called the boost port, and it's common to have different timing than the other two transfer ports.

Now you've measured the port timing on your two stroke model engine.

AFM
How do you count the degree on the protractor when it goes over 90 degree is my setup:
Attached Thumbnails Engine Mods-dsc00376.jpg  
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Old 02-07-2007, 10:07 AM
  #200  
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Default Any Special Techniques for tightening the Flywheel

Do any of you employ anthing special for tightening the flywheel? The collet and flywheel will move towards the front bearing when the nut is tightened. This will pull the 2 insides of the crankshaft ballraces towards each other. This will surely tend to bind them up. The situation will get even worse under temperature, because aluminum expands faster than the steel crank.
This must rob power from the motor?
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Old 02-07-2007, 04:14 PM
  #201  
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Originally Posted by Team Duratrax
Never touch the sleeve.

I wouldn't go messing with port polishing either. The fuel/air needs to mix around together and if your ports are smooth surfaced then there is less chance of the fuel and air mixing together if you had rougher ports.

So basically, your engine would perform better without the port polish because of the fuel/air mixing together.

Sean
youre half right , The carb mixes the air and fuel before it enters the engine, what rought surfaces do is help break surface tension on the droplets of fuel and allows it to atomise more readily.
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Old 02-07-2007, 07:45 PM
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Originally Posted by Nosram
Do any of you employ anthing special for tightening the flywheel? The collet and flywheel will move towards the front bearing when the nut is tightened. This will pull the 2 insides of the crankshaft ballraces towards each other. This will surely tend to bind them up. The situation will get even worse under temperature, because aluminum expands faster than the steel crank.
This must rob power from the motor?
You don't have to worry about it-normal engine is designed the way that if you pull cranck forward to front bearing it still will have clearance on the main bearing to avoid binding
See attached pic- I tryed to make it visible with 2 arrows pointing on front bearing with no clearance and main bearing with clearance. This is way how all engines designed (unless.....)
BTW this pic is fragment from real nitro engine design work.
Attached Thumbnails Engine Mods-clearance.jpg  
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Old 02-07-2007, 08:13 PM
  #203  
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Thanks Edward, you are the man. I understand completely
Nick Marson
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Old 02-10-2007, 12:50 AM
  #204  
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anyone tried to sharpen the LSN? or even also the HSN?
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Old 02-10-2007, 03:18 PM
  #205  
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Yes you can change the tunability of the needle by changing its shape . Tapering the LSN is common ..
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Old 02-10-2007, 06:29 PM
  #206  
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oic, coz only recently some1 told me about it. but how can we sharpen it evenly?? do u use sandpaper or grinding stones?? to wat extend do we need to sharpen it to?
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Old 02-10-2007, 10:24 PM
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Ideally you would hold it to the side of a medium smooth grinding wheel and turn it evenly resting on an edge. Or with a dremmell you can use a pink stone flat turner, mount it and turn it onto the stone. As long as its even and smooth . You can finish it with some 800 wet and dry . Just bring the last 2 to 3 mm to a point then you can round the very end slightly.
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Old 02-11-2007, 01:16 AM
  #208  
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is there any bad with this sharpening, like higher temp?
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Old 02-11-2007, 03:06 PM
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Originally Posted by uniquexme
is there any bad with this sharpening, like higher temp?

No, just a different tuning feel, and maybe a slighly more linear trasition from idle to mid range ..
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