Thread: Discussion CLUB SAITO ON RC-Groups
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Old Jul 27, 2010, 06:20 PM
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Originally Posted by u2builder View Post
Talk to me about valves.
Does the valve gap get larger or smaller over time?Larger, mainly due to microscopic wear, however, the initial "gap" is to allow for heat expansion

What happens when it is too large (the valves don't open as much)Thats called "sloppy"

but what is a symptom?They get noisey and rattley (is that a word?) If you are also sensetive to your engine, then you will notice a lack of power (especially on something like uplines) or notice that it doesnt spool up as quickly. Mainly loss of performance. No horrible damages will ensue, within reason

What happens when they are too small (the valves don't close)Self answering...the valve(s) dont close.

but what is a symptom? If its any appreciable amount then your engine wont develop compression and it simply wont start. At that point it would also feel like it was "freewheeling" with no compression. I have had this happen in flight by breaking valve springs on an OS91 that I was aware I was over revving.

I bought a used Saito on Ebay and flew it for a while. It seemed like the engine would lose power after a few minutes of flying. I checked the valves today and the gap was quite a bit too large so I set them properly with the included gauge. Would too large a valve opening tend to cause a loss of power, presumably as the engine heated up.Possibly...let me run this scenario past you. Valve gap is too large. This means that when the cam lobe starts to open the valve that it really doesnt for a whlie because it is having to take up the slack in the valve train. Valve finally opens and motor gets to breathe, but a now limited amount of time. Fire stroke fires. Seems ok but we just started it and it still "cold". NOW its heated up. Same scenario and the valve FINALLY opens and the motor breathes in its now limited amount of air/fuel. With the engine HOT it now vaporizes and evaporates super quickly, so you not only got a limited "inhale" (charge) but part of that flashed off in the cylinder. Now you have limited the amount of fuel it has to make power by a drastic it doesnt (make power)

Tons of other reasoning here along these lines. Exhaust valve not opening proper....then your witholding exhaust within the cylinder and the engine is trying to run on it on the next compression stroke....that amount of exhaust is also displacing possible intake charge...

...and on and on and on.

Any "education" would be much appreciated. Thanks.

Edit 3-17-15 Some nice additional information by SrTelemaster HERE
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Last edited by Dad_Roman; Mar 17, 2015 at 06:37 PM.
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