New Four Stroke With Engine Knock
08-04-2011 | 04:23 AM
#51
RE: New Four Stroke With Engine Knock
Sounds like it is leaning out as the tank level drops. Using a uniflow tank set up could help here. You use two clunks, use your muffler vent line for fill vent only, plug the line before flight, do not attach to the muffler nipple. Use a clunk on another line and make it about a half inch shorter, some tie it to the pick up line, I do not think that is required. This works because the head on the muffler pressure is the same both upright and inverted. With this setup the tank should be centered with the needle valve, normal setups should be about 1/4 to 1/2 inch below when upright.
08-08-2011 | 06:22 AM
#54
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RE: New Four Stroke With Engine Knock
ORIGINAL: R-Duhb
<span style=''font-size: larger''>Well it's a year later and I've switched to 5% fuel. The engine will still knock if I lean it out too much, but I thought I had found a rich needle setting that eliminated the knock at full throttle and gave me decent RPM output (8400-9000). So far I've run about 3 tanks thru it. Thought I had it running pretty sweet. The low to high throttle transition (after it warms up) is extremely smooth with no hesitation. However, I'm still having a problem. As the run time increases (along with temp) the knock returns as I increase to full throttle. Of course I richen it up, but I sacrafice lots of power and frankly the engine sounds like crap. I really doubt it would fly well at this setting. Should I expect this to improve as I continue with break-in? Also, is there a rule of thumb for setting the air bleed screw? At one point when I thought I had it running great, I pointed the nose up which caused the RPMs to increase, and guess what....it started knocking. I'll have to adjust the air-bleed screw to fix this, but one problem at a time.
Thanks!!!</span>
<span style=''font-size: larger''>Well it's a year later and I've switched to 5% fuel. The engine will still knock if I lean it out too much, but I thought I had found a rich needle setting that eliminated the knock at full throttle and gave me decent RPM output (8400-9000). So far I've run about 3 tanks thru it. Thought I had it running pretty sweet. The low to high throttle transition (after it warms up) is extremely smooth with no hesitation. However, I'm still having a problem. As the run time increases (along with temp) the knock returns as I increase to full throttle. Of course I richen it up, but I sacrafice lots of power and frankly the engine sounds like crap. I really doubt it would fly well at this setting. Should I expect this to improve as I continue with break-in? Also, is there a rule of thumb for setting the air bleed screw? At one point when I thought I had it running great, I pointed the nose up which caused the RPMs to increase, and guess what....it started knocking. I'll have to adjust the air-bleed screw to fix this, but one problem at a time.
Thanks!!!</span>
Your engine is still in the break-in phase of operation. While OS is known for producing engines that break-in quickly most of the time, occasionally there may be one that slips through that needs additional TLC.
Your 11x7 prop is a bit too much load for a new FS-40. I would drop back to an 11x6, or less (11x5) for a gallon or two of fuel. When tuned appropriately rich during break-in it is not uncommon for an engine to run a bit raggedy and to produce less than optimum power. Be patient. Your OS FS-40 will run great when the fits all fall into place.
Ed Cregger
08-08-2011 | 06:46 AM
#55
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From: Bolingbrook, IL
RE: New Four Stroke With Engine Knock
<span style="font-size: medium">NM2K,
Thanks for the feedback! I've run a little over a half gallon thru it already. I'll have to pick up an 11x6 and/or an 11x5. What are your thoughts on a 10x6?
</span>
Thanks for the feedback! I've run a little over a half gallon thru it already. I'll have to pick up an 11x6 and/or an 11x5. What are your thoughts on a 10x6?
</span>
08-08-2011 | 06:51 AM
#56
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From: Kuala Lumpur| Malaysia, MALAYSIA
RE: New Four Stroke With Engine Knock
ORIGINAL: TimBle
how does a compression ignition engine ....knock?
I do understand the concept of knock, its just that in the absence of a spark to control the ignition point, in every power cycle there will always be knock.
Are you saying that its excessive?
how does a compression ignition engine ....knock?
I do understand the concept of knock, its just that in the absence of a spark to control the ignition point, in every power cycle there will always be knock.
Are you saying that its excessive?
Iskandar
08-08-2011 | 08:18 AM
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From: Athens, GREECE
RE: New Four Stroke With Engine Knock
ORIGINAL: iskandar taib
A compression ignition engine will, um, ignite the charge at some point of the compression stroke. With spark ignition, you control this by setting the point where the spark goes off. With glow engines, you have to do it some other way. It's a combination of compression ratio, fuel (mainly, how much nitro is in it), prop, and glowplug (and probably one or two other things I've forgotten). All other things being equal, a ''hot'' glowplug will set off the charge at lower compression than does a ''cold'' one, effectively ''advancing the spark''. When the charge goes off too early, it's the same as setting the spark timing too early - you get pre-ignition, or ''knock''.
Iskandar
ORIGINAL: TimBle
how does a compression ignition engine ....knock?
I do understand the concept of knock, its just that in the absence of a spark to control the ignition point, in every power cycle there will always be knock.
Are you saying that its excessive?
how does a compression ignition engine ....knock?
I do understand the concept of knock, its just that in the absence of a spark to control the ignition point, in every power cycle there will always be knock.
Are you saying that its excessive?
Iskandar
Exactly, in fact glow engines are compression-ignition, but we have flame propagation just like in spark ignition engines, because ignition happens at one point (on the glow plug). So, because there is ONE flame front, you must reassure that in no other place there is ignition (i.e. other flame fronts), otherwise you get "knock".
08-08-2011 | 09:28 AM
#58
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RE: New Four Stroke With Engine Knock
A 10x6 would be fine for break-in and even after break-in. The object is to keep the heat down by lowering the load placed upon the engine. Lowering the heat retards the engine's timing a bit, which should help reduce the chance of knock.
Ed Cregger
Ed Cregger
