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Post  F4D Phantom II on Wed May 01, 2019 12:54 pm

I read about piston lapping the cox engines to loosen the piston to cylinder fit and get better performance. I used a piece of clear vinyl tubing,3M white rubbing compound and CRC 6-56 oil. I placed the piston conrod inside the vinyl tubing and saw where the hole of the rod was. using an awl I punched a hole about 1/16 inch lower so the tubing would hold the piston firmly. Put a mixture of oil and rubbing compound in the cylinder and worked the piston back and forth giving it a small twist every so often. I did that for a while then I cleaned the piston and cylinder it was still tight so I did a little more,I cleaned and tried again. the idea is to go slowly and check often to avoid damaging your P/L set. here are some pics.
                                                                                                                            Juan







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F4D Phantom II
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Post  fredvon4 on Wed May 01, 2019 1:13 pm

Not seeing your technique...a HINT
Lap in the piston cylinder with the piston skirt UP.... checking often that the Piston Top stops at TDC and takes a slight tap to fall free into the bore

IOW never reduce the top of the cylinder or top of the piston
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Post  F4D Phantom II on Wed May 01, 2019 1:45 pm

Hello Fred
                    Thanks for the advice. I was doing it with the piston facing the top but I haven`t worn the P/L set. I`m experimenting and learning. Yesterday I had the engine running good and have been going up in rpm. it started at 19381 rpm and in the last run it hit 20,320rpm using an APC 4.75 x 4 and 25% nitro. I hope to get some more R`s from a timing change I`m doing. Thanks again.
                                                                                                                                           Juan
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Post  NEW222 on Wed May 01, 2019 7:48 pm

Good job. Sounds like you are on the right track. I cannot comment, as I tried doing this once, and ruined a piston/cylinder set. Before I knew how to do it properly, I assembled my engine, removed the head, put in some polish, then chucked the prop screw in my drill and ran it for a few minutes..... It was sort of like throwing a hotdog down a hallway when I was finished. Shocked It does run still, but very poorly. I am working on something to tighten it back up now, but it is still being looked into, so will not say how just yet.
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