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Old 09-11-2010, 09:10 PM   #1
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Default checking compression

is there a tool for checking the compression on these nitro motor's and if so where can i get one and what is a good compression and what would be considered the a bad one or is there a range for this
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Old 09-11-2010, 09:29 PM   #2
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i dont think there is a tool (if there is its not necessary)but here is how i determine weak compression..
with the engine at normal operating temp you can easily roll the flywheel over with light finger pressure with glow plug installed.
Looking at exhaust port and rolling the flywheel over and the piston rolls past the porting windows before any compression is felt.
With the piston & sleeve removed, the piston pushes well past tdc or just below the head button.
if you encounter this just send the piston and sleeve to rayaracing for a reconditioning service or 'pinch'.
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Old 09-11-2010, 09:36 PM   #3
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Default compression

ok ! i was not sure if there was a gauge for this or not . im new to nitro and im wanting to learn alot about these motors and how to adjust the clutch properly
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Old 09-12-2010, 08:47 AM   #4
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Dynamite makes one. Part #DYN2514. www.dynamiterc.com
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Old 09-12-2010, 09:20 AM   #5
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Hobbico used to make a compression tester also cause thats the one I have, but apparently been discontinued.
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Old 09-12-2010, 09:28 AM   #6
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Default compression checker

thanks Calvin yep i thought there had to be some out there and how good does your's work ( Duster 360 )
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Old 09-12-2010, 10:45 AM   #7
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The problem with the compression testers is that I have yet to see one that will work in a turbo plug motor.

Plus, it's not really needed. When these things have good compression, they run great. The moment something happens, they become a nightmare to tune. They will flame out, not want to idle and the tune will change throughout a run. When that happens, time for a new motor or a rebuild.
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Old 09-12-2010, 10:52 AM   #8
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why will the tester not work with a turbo motor , because that is what i run and therefor im very interested in that
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Old 09-12-2010, 10:55 AM   #9
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All the ones I have seen thread into the glowplug hole and all of them are threaded for standard plugs.
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Old 09-12-2010, 11:04 AM   #10
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As was mentioned, an engine that has lost compression will be a nightmare to deal with. If the engine is in good shape it will run and you can get a tune on it. An engine all over the place that seems rich, then too lean and you didn't do much...plus flameout randomly with no real warning...that's an engine past it's prime.

Basically I turn the motor with my finger, if it's hard to turn when the piston hits TDC then it's still got good compression. If it just spins freely then it's time to service that engine or get a new one.
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Old 09-12-2010, 11:04 AM   #11
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Default gauge

ok thanks wingracer i will not spend the money on that then, wow getting some good info thanks guys
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Old 09-18-2010, 07:10 AM   #12
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Quote:
Originally Posted by wingracer View Post
The problem with the compression testers is that I have yet to see one that will work in a turbo plug motor.

Plus, it's not really needed. When these things have good compression, they run great. The moment something happens, they become a nightmare to tune. They will flame out, not want to idle and the tune will change throughout a run. When that happens, time for a new motor or a rebuild.
+100%.

Plus, those testers really do not test compression, they test blow by which is a totally different thing, compression is the rate between the total BDC and TDC chamber volumes. You can really have an engine with all the blow by in the world, super soft with 20 gallons and not have idle, flameou and tune problems if the piston and sleeve fit(more like "shape" this one) is still a good one.

Right know I have an engine with about 8 gallons and it has absolutely no pinch at all, when hot you can turn it with your pincky if you want, but it still makes a perfect tune from top to bottom and has all the power it ever had.

Remember that for blow by to affect compression it needs to be very bad and by that I mean VERY, like having a piston with a different shape than the sleeve (which technically speaking IS what happens) but if there are no abnormal things like that just think of this:

If you turned your fly wheel when the motor is hot and it is soft but you can still feel the cycle, you can still feel the stroke with your flywheel spin at what 15 RPMS? how fast can you really go and at that rpm you CAN actually feel the pulse of the cycle.

well if at 15 rpm, and hot the motor gets to the point where blow by is not enough for you to NOT feel the compression stroke, then divide 15/idle speed lets say: 15/3500 = 0.43%, thats what you loose, AT IDLE!!! if you do it 30,000 rpm its virtually nothing.

xe
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Old 09-21-2010, 04:35 PM   #13
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Quote:
Originally Posted by 2056dennis View Post
is there a tool for checking the compression on these nitro motor's and if so where can i get one and what is a good compression and what would be considered the a bad one or is there a range for this
Dont confuse compression with pinch; Sleeve Pinch is not that important contrary to popular belief. The question is how well it seals as soon as the piston starts to close the exhaust port and if it holds compression after you roll it to top dead center.
Place a few drops of after run oil trough the top (removing plug), then place plug in place, then roll piston to top dead center and listen and look for air bubbles through exhaust port. If theres none, then your engine still has compression, even if it has no pinch.
The fastest motors I use, have zero pinch. I even had them run to over140C and they have survived well. Though I certainly don't recommend it.

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