Extreme Speed Prop Planes Discuss the need for speed with fast prop planes (Screamin Demon, Diamond Dust, Shrikes or any REAL sound breakin'''' plane)

does any one Lap their pistons and liners ??

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Old 07-14-2017, 08:12 PM
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the Wasp
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Default does any one Lap their pistons and liners ??

back when I ran RC boats a lot of guy would Lap there Piston/Liners on new racing engines, I was just wondering if people today do it for their plane engines

I understand what it is about, and I have my thoughts, but I was just wondering how people go about doing it to a piston and liner ??

thanks guys

Jim
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Old 07-14-2017, 09:03 PM
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GREG DOE
 
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Jim, There are several threads in the engine section that might be a better place to make this inquiry. Having said that, the proper way to lap a piston is in a "lap" tool. Many people assume that you would lap the piston to the liner, and you can do that if you like, but then you end up with a tapered piston. If you lap the piston in a lap tool, the piston retains it's straight sides. 40 years ago the typical ABC pistons weren't as round as they are today, so lapping helped. Most of today's engines ( the few that are still being made) are so well machined that they probably wouldn't benefit from lapping. The lap tools are specialty tools, and have to be close to the piston size. For example I have two "laps" just for 40 displacement engines. Another thing to consider is that after lapping, the piston must be thoroughly cleaned, or the lapping compound will get trapped in the porous aluminum, and continue to remove metal from the piston. I used an ultra-sonic cleaner. What I have mentioned is only part of the "story" regarding lapping, except to say that it is easy to remove too much material, but that is a whole other story. I wouldn't recommend it unless you have a good understanding of the "fit" you would like to achieve, or have lot's of pistons.
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Old 07-14-2017, 09:29 PM
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thank you GREG DOE, that's just what I wanted to hear, I am seriously thinking about buying an HP 120 Inline Twin (ABC), and I was wondering if it would benefit if I lap it, but I see no need for it now,

I have also learned> that not only do we have sonic cleaners today, we also have ultra-sonic cleaners today

thanks !!
Jim
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Old 07-15-2017, 06:18 AM
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I only do it if I have to. I use Brasso or Silvo. Lately all the motors have been fitted very well. The older CS and some Russian ones I had needed to be done. Some of the ABC ones that have a very tight pinch, I will do if they lock up too much, rather than heating the cylinder as most people do. I just leave the rod on and go up down and a figure eight motion without going past TDC, for less than a minute, clean well, check the fit, and do it again if needed. I have an old NIB Supertiger G .15 right now that has no taper in the cylinder that will need a lap made up. Maybe some day. I bought a new Picco .12 OFNA that came with what I thought was just a perfect fit, and most OS stuff seems pretty close to being right when new. The nickel plating goes on very even compared to the chrome which needs honing at the factory. That is a hand operation and the results are up to the operator.
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