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Old 02-22-2009, 06:21 AM   #1
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Default piston/sleeve resizing?

Has anyone had this done to there engine? I see it on ebay and figured i would ask the question. What do they do to the engine. im still pretty green in this sport so work with me. The pinch is the pressure you feel at TDC right? What is the pinch or i should say what causes it. I'm really familiar with combustion engines, nitros not so much? drop a line to help me and other newbies out. Thanks
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Old 02-22-2009, 07:57 AM   #2
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Get it done by Rayaracing, If you look at the Powerhouse thread and Mark can help you. He and Rayaracing help each other out.
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Old 02-22-2009, 08:35 AM   #3
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Pinch is the taper of the sleeve it gets smaller as the sleeve goes up.These little engines are all most like a Diesel they burn the flue off of comprising and if the Pinch gets Lose the engine wont run right are all. I use one of the guys off of Ebay Keith of 512 mods and he dose better work then most of the big guys i have been using him for about a year now and am HAPPY with his work.
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Old 02-22-2009, 09:20 AM   #4
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rayaracing.com
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Old 02-22-2009, 09:38 AM   #5
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i just gotone done from os rocket and i cant even turn it over with no glowplug in it. i have not ran it yet so we will see then.
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Old 02-22-2009, 10:49 AM   #6
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They mechanically squeeze the sleeve and compress it just slightly to restore the pinch zone at the top of the sleeve. When piston approaches top dead center, the piston to cylinder wall clearance is mechanically reduced by the taper of the sleeve (get smaller at top) so the piston develops a seal - this is when combustion takes place, and thanks to the seal, drives the piston back down through its stroke stroke, developing power.

Running wears the pinch out and one option is to have the sleeve re-pinched instead of just replacing sleeve and piston. Re-pinching is a lot cheaper and if doen correctly, can restore engine back to near new conditions.
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Old 02-22-2009, 11:09 AM   #7
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Repinch can give you up to 3 gallons more fuel through the engine, if done correctly. For $20 or so its usually well worth it..I would not recommend you do the same sleeve over and over again
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Old 02-22-2009, 06:34 PM   #8
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Nitro engines are designed with a tapered sleeve which narrows at the top. Though many believe this snug fit to be critical to maintaining compression... The real truth is that heat generated by the engine occures at the top of the sleeve, just under the head. This heat imbalance causes the sleeve to expand more at the top than at the bottom. The pinch is intended as compensation for this, so when an engine is "at temp" about 2 min after start-up, the I.D. of the sleeve is nearly the same from top to bottom.

As a practice, pinching should be treated as a mild correction & only be done in small doses (.001" - .0015"). IMO any pinch greater than .002" is damaging.

& BTW just because you may no longer feel the pistion being grabbed by the pinch when it's cold.. it doesn't mean it's time for a pinch job. I've seen too many sweet running engines get taken out of service because the head was lifted before it was necessary.
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Old 02-22-2009, 07:20 PM   #9
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Default resizing disasters

i have had two done by two differant people.both motors shatered the piston during breakin.im sure it doesnt happen to all but iv learnt mt leason.
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Old 02-22-2009, 08:15 PM   #10
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Quote:
Originally Posted by yeaklet4 View Post
i just gotone done from os rocket and i cant even turn it over with no glowplug in it. i have not ran it yet so we will see then.

I have heard Os Rocket does them pretty tight. I personally like to get the ones I resize about like a motor with a gallon on it. only 2 tanks slightly richer and go racing. Most guys get as many gallons out of a resized sleeve as they did before the pinch.


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Old 02-23-2009, 09:06 PM   #11
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Quote:
Originally Posted by yeaklet4 View Post
i just gotone done from os rocket and i cant even turn it over with no glowplug in it. i have not ran it yet so we will see then.
if you can't turn it over, send it to Ray A Racing. He can get it to the correct size. Ray is number one when it comes to resizing. He will set the pinch to however you want it.
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Old 02-24-2009, 03:24 PM   #12
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I've had to fix a couple sleeves for people also. I think they were ones guys tried to do themselves with the cheap tool off Ebay. They were out of round and with a mandrel made the right size they come out really round again.

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Old 02-27-2009, 03:51 PM   #13
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Please note that RayAracing pays very close attention first to the surface finish conditions of the sleeve liner along with piston surface finish, and first following initial inspection, make necessary improvements of surface finish. If the surface finish condition remains poor the seal will remain poor. After I am convinced the surfaces are clean and in good condition It is time for me to be very meticulous with the sleeves alloy reconstruction (resizing) resulting on an average 0.0003" ( 3 tenths of one-thousandth inch) thru 0.0005" ( 5 tenths. I do get aggressive with piston & sleeve sets that may have experienced dirt contamination and get up there in the the naborhood of 8 tents or better, but those are usually sets I find liner scratching and end up doing a very light honing on. Just thought I'd chime in and share some of my procedure with you all. RayAracing reconditions-resizes piston & sleeve sets. Kind regards,

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Old 02-27-2009, 05:28 PM   #14
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RayARacing is the way to go. I've had some done by others and have had some just pinched wrong mostly to tight and not the correct taper in the sleeve. Rays method and tooling is perfect for sleeve resizing.
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Old 02-27-2009, 05:39 PM   #15
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Default werks b3.21

just sent ya one ray,see what ya can do.it wasnt completly out but i was having to lean on the bottom to get it to idle so.this motor is suppose to be in a race on the 14th of march,hope you can hook me up..
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