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Old 04-19-2010, 06:50 PM   #1
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Default what does pinch motor mean

i am looking at a used motar and the guy said it was a good pinch motor
i am still learning the nitro side of rc
and for some reason the seller wnt explain "pinch"
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Old 04-19-2010, 06:57 PM   #2
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I could mean two things like as backup motor, if your in a pinch and need something to get you through its a good motor.

Or it could be that he said that the motor still has good pinch, meaning that
the fit of the piston and sleeve are still tight.
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Old 04-19-2010, 07:03 PM   #3
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Originally Posted by RUNNINONMT View Post
I could mean two things like as backup motor, if your in a pinch and need something to get you through its a good motor.

Or it could be that he said that the motor still has good pinch, meaning that
the fit of the piston and sleeve are still tight.
he said the motor has break in and two tanks and a great pinch left
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Old 04-19-2010, 07:03 PM   #4
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Or, if it's already had several gallons of fuel through it, he could mean that it's a good motor to "pinch". In that case, it would mean having the sleeve pinched, which squeezes it in a special tool to make it undersized (allows a motor to re-gain lost compression by making the sleeve smaller).

There's nothing wrong with pinching a motor...you can do it a couple of times before needing a new piston/rod/sleeve.

Don't be afraid to ask the seller what he means...there's no such thing as a dumb question.
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Old 04-19-2010, 07:08 PM   #5
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Originally Posted by Stubbs View Post
Or, if it's already had several gallons of fuel through it, he could mean that it's a good motor to "pinch". In that case, it would mean having the sleeve pinched, which squeezes it in a special tool to make it undersized (allows a motor to re-gain lost compression by making the sleeve smaller).

There's nothing wrong with pinching a motor...you can do it a couple of times before needing a new piston/rod/sleeve.

Don't be afraid to ask the seller what he means...there's no such thing as a dumb question.
thanks he said he broke the motor in and took it out and upgraded his and said it has a great pinch left i asked him what he meant and told me to call him back when i figure it out .and no i am not buying it from that a hole
but i agree there is no dumb question u have to learn some where and this forum is helping alot thanks again
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Old 04-19-2010, 08:00 PM   #6
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Easier said when a nitro motor gets tired they loose compression the easiest way to tell is if ur flywheel turns over really easy and ur compression is refered to as a "pinch" when it gets ran alot it looses that pinch and dosnt run as good and some times will cause tune loss or it to blow up you can also get a motor re-pinched for longer life. So easy put if it has pinch it still has life some times buying used pinch can mean 1 gollon on it to 8 gallons depends on how well taken care of it was also just because it has pinch doesnt mean its strong which means it will last probley a few gallons at most me i learned the hard way and its just not worht buying used motors so if a guy says its used ask for piston pics, sleeve and block pics mainly look for nicks, blackining or wear. hope i helped!!!!
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Old 04-19-2010, 08:08 PM   #7
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Originally Posted by NitroXray80809 View Post
Easier said when a nitro motor gets tired they loose compression the easiest way to tell is if ur flywheel turns over really easy and ur compression is refered to as a "pinch" when it gets ran alot it looses that pinch and dosnt run as good and some times will cause tune loss or it to blow up you can also get a motor re-pinched for longer life. So easy put if it has pinch it still has life some times buying used pinch can mean 1 gollon on it to 8 gallons depends on how well taken care of it was also just because it has pinch doesnt mean its strong which means it will last probley a few gallons at most me i learned the hard way and its just not worht buying used motors so if a guy says its used ask for piston pics, sleeve and block pics mainly look for nicks, blackining or wear. hope i helped!!!!
Compression and pinch are 2 separate things. A motor can have 0 pinch left, but still have great compression.

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Pinch is the physical tolerance between the piston and sleeve. The sleeve tapers towards the top of the cylinder, and when an engine is new, the piston and sleeve are usually tight enough that the piston gets somewhat "stuck" at the top of the cylinder - some more so than others. That's pinch.

Compression is simply what it implies, the amount of compression the engine is able to produce during the compression stroke. A fresh engine will have a tight seal between the piston and sleeve, and therefore hold more compression, while a worn engine will have wear and more clearance between the piston and sleeve, and some of the compressed air/fuel mixture can leak past the piston. The amount of compression or pressure that stays above the piston is compression.

If you remove the glowplug and crank the engine, any resistance you feel is pinch. Re-install the glowplug, and even if there's no "pinch" left, the resistance you're feeling is compression.
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Old 04-19-2010, 08:28 PM   #8
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Compression and pinch are 2 separate things. A motor can have 0 pinch left, but still have great compression.
i stand corrected ur right but doesnt it have the same priciples ur pich is how tight ur sleeve is to the piston if its not tight u tend to loose compression right? Like my o.s. i have compression but very little along with my pinch is very lil but an off the wall question to you while im asking this my o.s. has low compression but i heard they get like that after a gallon or so but they really open up and you cant go by compression on those would you know if thats true?
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Old 04-19-2010, 08:34 PM   #9
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Originally Posted by NitroXray80809 View Post
i stand corrected ur right but doesnt it have the same priciples ur pich is how tight ur sleeve is to the piston if its not tight u tend to loose compression right? Like my o.s. i have compression but very little along with my pinch is very lil but an off the wall question to you while im asking this my o.s. has low compression but i heard they get like that after a gallon or so but they really open up and you cant go by compression on those would you know if thats true?
Yes, if your piston is not tight in your sleeve you'll probably have low compression. And yes, an O.S. is known to run on very low compression.
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Old 04-19-2010, 08:41 PM   #10
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doesnt the pinch mean on how tight, your piston feels when you go up and down with it? my used rb did have a kind, of tight feel to the piston but it went way now but still, has compression not tons of it though.
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Old 04-19-2010, 08:54 PM   #11
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doesnt the pinch mean on how tight, your piston feels when you go up and down with it? my used rb did have a kind, of tight feel to the piston but it went way now but still, has compression not tons of it though.
Pinch will feel like your piston is scratching the sleeve as it slides up, getting harder and harder to move. Unless of course you do have dirt in it.

Your piston gets stuck at TDC do to Pinch, not compression.
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Old 04-19-2010, 10:52 PM   #12
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Pinch, take the glow plug out and try and turn it over by hand. Can't get it past tdc.....its got pinch and is new or has been 'pinched'.
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Old 04-20-2010, 10:56 AM   #13
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it doesnt hurt the performance of an os engine to run on low compression like that?
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Old 04-20-2010, 11:59 AM   #14
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I have found that when a seller won't answer a question, it's typically because the seller himself has no idea what he is talking about. Good idea to steer clear of him.
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Old 04-20-2010, 04:10 PM   #15
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Default thanks to eveyone who responded

i want to say thank u to eveyone i have learned alot over thid thread thanks again
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