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Old 04-26-2012, 02:01 AM   #16
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Originally Posted by Z'Stein View Post
Actually, I think you "are" wrong. The purpose of pinching the sleeve is to re-gain compression/tighten the sleeve as if is new, or better, to start the process of "fresh motor" over. Thanks for your comment though.
Would there not be a space between the head and the liner after pinching?
Not trying to create an argumentative debate, as in "theory" it shouldn't work. If the liner is malleable enough to pinch it should be malleable enough to expand and deform back into the pinch cavity against the block. But.. As many in the real world say, it works, so I am genuinely interested in what people have experienced.
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Old 04-26-2012, 03:59 AM   #17
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I had this done once, and it did work well in order to extend the lifetime of the engine. The pinched set probably did not last as long as a new set. I'm not a top-level driver, but I found the performance to be good -- I did not notice a loss of power compared to when it was still new. If you're trying to win the nationals, your may have a different opinion.

Hence, for most racers, a great way to extend the lifetime of your engine without breaking the bank.
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Old 04-26-2012, 04:02 AM   #18
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Indeed, you would say when pinching you do create space between sleeve and crankcase which can be filled up by expansion. But the expansion is not determed by the amount of space but only by the specification of the material.

Pinching is actually deforming the material by squeezing it together to a smaller diameter but the expansion rate will be the same.

Yes, there is a kind of memory that the material wants to go back to the original shape, when doing a small pinch just as much that the piston fits right can be easily pushed back. You must see it as a piece of piano wire, you can bend it a bit and it will return to its original shape. Bending it further there comes a moment it will stay on an angle but again you did have to bend it further to get this mall angle as end result and in use there is a chance that it will go back a tiny bit to the original shape.

With pinching you can see that, With a tight pinch some sleeves do not need a long running in to get rid of the tight pinch. That spring effect together with the force of the piston is shaping back the sleeve a bit.

It seems the harder the sleeve the less spring effect there is.
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Old 04-26-2012, 09:17 AM   #19
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Originally Posted by Roelof View Post
Indeed, you would say when pinching you do create space between sleeve and crankcase which can be filled up by expansion. But the expansion is not determed by the amount of space but only by the specification of the material.

Pinching is actually deforming the material by squeezing it together to a smaller diameter but the expansion rate will be the same.

Yes, there is a kind of memory that the material wants to go back to the original shape, when doing a small pinch just as much that the piston fits right can be easily pushed back. You must see it as a piece of piano wire, you can bend it a bit and it will return to its original shape. Bending it further there comes a moment it will stay on an angle but again you did have to bend it further to get this mall angle as end result and in use there is a chance that it will go back a tiny bit to the original shape.

With pinching you can see that, With a tight pinch some sleeves do not need a long running in to get rid of the tight pinch. That spring effect together with the force of the piston is shaping back the sleeve a bit.

It seems the harder the sleeve the less spring effect there is.
I like the piano wire analogy tls Roelof
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Old 05-05-2012, 07:24 AM   #20
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I have been pinching motors for a few years. Yes pinching would leave more of a gap between the sleeve and block. The sleeve is strong enough to hold its size without the block's support. I believe some engine manufacturers leave a slight gap on purpose so that when a motor gets hot it doesn't loose all it's pinch. That is why some motors can get over 300 deg and still keep good compression. Pinching is not just a band aid, most motors I have done hold there pinch as long as a new piston and sleeve did, without going through the hassle of a long break in. (I recommend 2 tanks with a re-pinch I have done)
I only charge $15.00 return shipping included, $38 if you send the whole motor. (Usa only for those prices)
www.rw-mods.com

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Old 05-05-2012, 08:46 AM   #21
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OS Rocket


Pass you soon...
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Old 05-24-2012, 11:42 AM   #22
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I had a worn out OS V-spec II pinched and it is still running strong. An inexpensive way to revive an otherwise dead motor.
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Old 07-17-2012, 10:18 AM   #23
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How is pinching done?
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Old 09-01-2012, 11:32 AM   #24
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How is pinching done?
The name pinching sounds a little crude, resizing just sounds better. There are different way to do it but only 2 people I know of that actually sell equipment to do this and it can cost over $1000.00 to buy equipment.
The same result is attained no matter who does it, of course some do a better more accurate job than others. The sleeve is squeezed smaller at the top to create metal pinch like when it was new. I do not pinch the sleeves nearly as tight as new as the piston and sleeve are already mated to each other. There are a couple people (myself included) that you can send the whole engine to and have the crank and rod measured, inspected and check the bearings etc. If the crank is worn it can get quite expensive to replace the crank, rod etc. and may not be worth rebuilding depending on the brand.

Rex
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Old 09-05-2012, 02:06 AM   #25
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Quote:
Originally Posted by 22Racer View Post
The name pinching sounds a little crude, resizing just sounds better. There are different way to do it but only 2 people I know of that actually sell equipment to do this and it can cost over $1000.00 to buy equipment.
The same result is attained no matter who does it, of course some do a better more accurate job than others. The sleeve is squeezed smaller at the top to create metal pinch like when it was new. I do not pinch the sleeves nearly as tight as new as the piston and sleeve are already mated to each other. There are a couple people (myself included) that you can send the whole engine to and have the crank and rod measured, inspected and check the bearings etc. If the crank is worn it can get quite expensive to replace the crank, rod etc. and may not be worth rebuilding depending on the brand.

Rex
Cool that's worth knowing, I've only ever had second hand engines which I've picked up cheap (Apart from my N12-3T).. I've found this is a cheaper way to race than rebuilding.

I've an old Orion CRF Wasp .12 which is absolutely ballistic! which is backup to my IDM Evo 4 .12, which i'm still to actually try out!

If I'd dropped the cash on a Keep-On I'd make sure I rebuilt it or pinched it when it was dead, but not worth it when you're buying engines for 60.
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Old 09-05-2012, 03:46 AM   #26
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Quote:
Originally Posted by 22Racer View Post
The name pinching sounds a little crude, resizing just sounds better. There are different way to do it but only 2 people I know of that actually sell equipment to do this and it can cost over $1000.00 to buy equipment.
The same result is attained no matter who does it, of course some do a better more accurate job than others. The sleeve is squeezed smaller at the top to create metal pinch like when it was new. I do not pinch the sleeves nearly as tight as new as the piston and sleeve are already mated to each other. There are a couple people (myself included) that you can send the whole engine to and have the crank and rod measured, inspected and check the bearings etc. If the crank is worn it can get quite expensive to replace the crank, rod etc. and may not be worth rebuilding depending on the brand.

Rex
Hmmm... I did not get any complains about the work with my 70 dollar tool....
Sometimes I have the feeling people on these forums are telling everything to keep the job at the right people.
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