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Old 01-23-2009, 05:09 AM   #1
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Default Motor Pinched??

Hi guys, im a knoob in this Nitro off road, ive seen alot of thread saying get the motor "pinched" and keep running, whats this??? Thanks!!

Mike
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Old 01-23-2009, 05:14 AM   #2
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Hi guys, im a knoob in this Nitro off road, ive seen alot of thread saying get the motor "pinched" and keep running, whats this??? Thanks!!

Mike
THis means that the sleeve where the piston move up and down is tighten and makes the engine faster. When you buy a new engine the sleeve comes pinched because it is new now when the sleeve does not have that pinch any more it is time to get it pinch or a new engine.. The life of an engine in the piston and sleeve.

Hope that helps a bit
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Old 01-23-2009, 06:18 AM   #3
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THis means that the sleeve where the piston move up and down is tighten and makes the engine faster. When you buy a new engine the sleeve comes pinched because it is new now when the sleeve does not have that pinch any more it is time to get it pinch or a new engine.. The life of an engine in the piston and sleeve.

Hope that helps a bit
.

are you talking about buying a new piston an sleeve??

Mike
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Old 01-23-2009, 06:27 AM   #4
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Triton: When an engine is new the engine sleeve is tapered to where it's smaller ID at the top than at the bottom. When you "break in" an engine you have to run the engine so where the extreme tightness at the top of sleeve gets worn in with the piston creating compession and a tight seal at the top of the cylinder.

When people refer to pinch they are referring to how much the piston grabs the top of the sleeve still. In other words the more you run a nitro engine the more the sleeve will wear and the less compression and power you will make and the less mechanical drag the piston will have at TDC. When the pinch is gone and the compression is lowered dramitacally people like to get their sleeves pinched.

Pinching is when you place the sleeve in a device which applies a slight uniform pressure to the sleeve at the top causing the piston and sleeve fit to be tight again similar to when new. Then you do a short breakin procedure and you have a good running engine for a few more gallons. Generally pinches won't last more than 2-3 gallons but that small cost helps offset the price of a new engine a while longer.

Hope this all makes sense......
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Old 01-23-2009, 06:30 AM   #5
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are you talking about buying a new piston an sleeve??

Mike
Buying a new sleeve which is not hard to installed. Once you buy a new sleeve you have a new engine again. There are people that can resize you old sleeve but I would just buy a new one..

Also check the top of the piston and it is not black or deform you may need to get a new piston can you take pic of the piston and post it here..
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Old 01-23-2009, 06:57 AM   #6
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Heys guys, a friend of mine has two OS 21RG motors in mint condition, i have a Losi 8eight buggy,i know that motor is old but would it be a good for racing??

Mike
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Old 01-23-2009, 10:41 AM   #7
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a caviot here...

Just because you don't FEEL a pinch at TDC on a seasoned engine does not mean the engine is loosing compression. Every method to check an engine's compression you will see posted is performed on a cold engine. Engines aren't cold when they are running. Low oil, a skirted piston & too low of a running temp will all cause the sleeve to wear faster.

Also, a pinch is ment to e-x-t-e-n-d the engine's life. Not revive a dead/dying engine. Pinching is best done at gradual intervals over an engines life.


...BTW, I don't subscribe to pinching on any of my engines.
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Old 01-23-2009, 11:40 AM   #8
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a caviot here...

Just because you don't FEEL a pinch at TDC on a seasoned engine does not mean the engine is loosing compression. Every method to check an engine's compression you will see posted is performed on a cold engine. Engines aren't cold when they are running. Low oil, a skirted piston & too low of a running temp will all cause the sleeve to wear faster.

Also, a pinch is ment to e-x-t-e-n-d the engine's life. Not revive a dead/dying engine. Pinching is best done at gradual intervals over an engines life.


...BTW, I don't subscribe to pinching on any of my engines.
"Pinching is best done at gradual intervals over an engines life."

The way you worded that is to make it sound like we should run our new engines for a couple gallons, get them pinched, continue to run them for a few more, get them pinched...and so on and so on. That is not right. You run your engine until you have lost all compression or almost lost it all and then pinch it to revive the piston and sleeve fit therefore reviving the engine.
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Old 01-23-2009, 12:35 PM   #9
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I had an HPI G3.0 engine lose compression, and I had it repinched then sold the truck. Apparently its running like new again
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Old 01-23-2009, 01:18 PM   #10
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Do i have to send the engine somewere?? if so, can i have a link??

Thanks
Mike
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Old 01-23-2009, 01:51 PM   #11
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certain companies will do it. in the UK there is a guy who charges about 10 a pop.
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Old 01-23-2009, 02:43 PM   #12
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Quote:
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The way you worded that is to make it sound like we should run our new engines for a couple gallons, get them pinched, continue to run them for a few more, get them pinched...and so on and so on...
you read me correctly. Pinching is not for resurecting the dead. If you've let the engine get to this point it's time for a new P/S.

Every time the sleeve is pinched is gets slightly distorted. Dont' believe me Run an engine until you wear through the nickle plate. On a non pinched sleeve a golden halo will appear around the pinch area as the plate is worn evenly. On pinched sleeve the wear will be uneven revealing "bars" of gold (brass) and bars of nickle in an unevenly distributed ware patern.
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Old 01-23-2009, 02:53 PM   #13
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Quote:
Originally Posted by HulkNT1 View Post
Buying a new sleeve which is not hard to installed. Once you buy a new sleeve you have a new engine again. There are people that can resize you old sleeve but I would just buy a new one..

Also check the top of the piston and it is not black or deform you may need to get a new piston can you take pic of the piston and post it here..
I disagree, putting a new piston and sleeve in a used motor does not make it new again. I rebuild lots of motors, the biggest thing I look at is crank wear. If the crank is worn it may be cheaper to just buy a new engine depending on the brand. You should have a mic to check the crank or have someone check it for you. Bearings are also very important, if a bearing goes out the metal particles can ruin a piston and sleeve.

The motors I pinch for people and my own get just as much life out of them as when it was new. The piston wears much more than the sleeve.
I actually prefer my pinched sleeve to a new p/s, a new one takes so long to break in. With mine I just run 2 tanks a couple hours richer. The trick is keeping the sleeve very round.

Triton, you can pm me, I rebuild motors and pinch sleeves. Here is a link to my thread.

http://www.rctech.net/forum/nitro-of...ebuilding.html


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Old 01-23-2009, 03:50 PM   #14
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Rex,

+1 on measuring the crank pin as a good indicator of the life left in the engine. I use +/- 10% deviation in the concentrisity of the pin as my wear indicator. Curious, what level of concentirsity do you accept up to?
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Old 01-23-2009, 07:58 PM   #15
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I usually just go by the size, although I measure in different spots around the pin. Most crank pins are 5mm, except for Rb's. I consider .002 inch wear to be done but will run if you need it, which would be pretty close to your 10%. Some crank pins wear all the way around more than others.

I have ground cranks and made smaller bushings in the rod but with not enough success to do it for customers.

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