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Old 08-14-2004, 10:07 PM   #1
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Default Engine "pinch"

I keep hearing people talk about their engines still having good "pinch". What does "pinch" mean or refer to?
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Old 08-14-2004, 10:26 PM   #2
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It is a reference to how tight the piston/sleeve is.
A tight motor still has good pinch.
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Old 08-14-2004, 10:34 PM   #3
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How do you test for pinch?
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Old 08-15-2004, 11:17 AM   #4
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Pinch is a useless measurement. A square piston whose corners fit tightly into the sleeve will have "pinch". Picco motors, for example, never have tight "pinch", but they seal well when hot.

Pinch is the fit of the piston in the sleeve when the motor is cold and there is no glow plug in the head. This has absolutely no bearing on how the engine will run. To check how well the engine seals, run the engine until it's hot, then shut it off, and try to turn the engine over by hand. If there is no resistance, then it's time for a rebuild.
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Old 08-15-2004, 12:24 PM   #5
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When you say turn the motor over do you mean rotating the flywheel by hand?
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Old 08-15-2004, 12:31 PM   #6
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Yup.
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Old 08-15-2004, 01:09 PM   #7
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Is that the same test that you use to test compression?
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Old 08-15-2004, 01:47 PM   #8
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As far as I know, there isn't a tool to measure the exact compression of an engine this small yet.

An engine that seals well will have good compression.
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Old 08-15-2004, 03:29 PM   #9
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Be careful since OS engines like the VZ-B does not hold compression like other brands but it will still run real well even when it does not pass the test that Aaron suggested.

On other brands of engines I totally agree with Aaron.
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Old 08-15-2004, 03:37 PM   #10
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ok so on my Picco G1 XP-21 I should heat it up first, then kill the engine and try to turn the flywheel correct? If I turn it to a point where then it gets real tight and impossible to turn anymore with my hands, then my engine has good pinch correct? All this with the glow plug installed?
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Old 08-15-2004, 04:27 PM   #11
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If your engine is tight when it's hot, when it seals very well and will have good compression. "Pinch" is usually what is referred to when the engine is cold, which doesn't mean anything.

eltorito - VSpec or not, an engine has to have compression to run at all, it just might not feel as tight as other motors.
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Old 08-15-2004, 08:59 PM   #12
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agreed. i just dont want anyone to feel their OS needs a rebuild just cause it is very easy to turn both hot or cold ;-)
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Old 08-15-2004, 11:12 PM   #13
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im pretty sure the term "pinch" came from the fact that the sleeve is tapered, but i agree w/aaron and elitro, theres no true way to test pinch/compression. each motor is different, run it till the needles are seated!!!!!! only kiddin, u should get around three gallons+ or so on average
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Old 08-18-2004, 01:23 AM   #14
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its one of those things that is a completely useless and subjective charactoristic (sp?). its kind of like how guitarists talk about how good their guitars sound unplugged, even though they will NEVER ever play them unplugged.

when people talk about it the usual response is "cool! .....i want a hot dog." dont fall into that pit! just chuckle when youre in that situation knowing that they have too much free time on their hands
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Old 08-18-2004, 02:13 AM   #15
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Would it be better to just put an OS .15 CVRX(S) In my Rustler or just to rebuild the existing Pro.15? It's WAY overdue for one. The second I saw that test Aaron Posted, I went out and did it... Pathetic! I guess non stop running for 4 years will do that...
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