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Post  11592_KW Tue Dec 27, 2011 2:48 am

I just found a little metal box with 2 drawers full of cox engines and parts at a estate sale. I remember these engines from when I was a kid. In the first drawer there is 2 Black Widows, 4 Baby Bees, 5 no tanked engines from out of the planes and 2 Pee Wees. In the bottom drawer there is 3 crankcases, 5 cylinders, 3 tank back plates, 1 red plastic back plate, 10 glow plugs, 1 plug clip and 8 pistons. As I remember these as a kid, i remember the pistons used to loosen up after several straight months of use. I dug out my reset tool to reset half of the pistons that were there buy they keep "mushrooming". I'm using the holder to hold the piston on my 1" solid steel workbench top and I'm tapping and rotating the piston. I was just tapping them but they were not resetting so I started to tap harder but now the socket is not resetting and the top of the piston is "mushrooming". What exactly am I doing wrong?

cheers, Ken
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Post  Admin Tue Dec 27, 2011 2:56 am

Are you pushing down, holding the holder still as possible when you are tapping? I have only had that happen when the holder is allowed to move around and slightly jump.
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Post  11592_KW Tue Dec 27, 2011 3:01 am

I was pushing down as hard as possible to avoid moving the holder when tapping on the tool.

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Post  Jaspur_x Tue Dec 27, 2011 3:01 am

I am not the resident expert here, however, mushrooming can come from not rotating the reset often enough as you are trying to keep the reset uniform, and could realy just be you are in too much a hurry and hit it too hard. I never mushroomed 1 yet(knock wood) but it is a relatively slow process.

1 stupid question I have for you, since these may be some old vintage engines mixed in there. Are you sure you aren`t trying to reset an early cox 3 piece piston?

Hopefully someone with more experience chimes in directly.
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Post  11592_KW Tue Dec 27, 2011 3:11 am

I know I have been turning it and spending at least 5-10 minutes on each piston. The pistons have the regular ball and socket, I have one old space jr or something like that that has a piston with a odd retainer in it, I'm guessing that is what you mean by the 3 piece pistons. I have been tapping and rotating for the last 5 minutes with no sign of tightening up or the mushrooming but after about 10 or so minutes it begins to get a slightly domed top and tightens up in the cylinder "mushrooming" with the socket still loose. I have reset pistons when I was younger so I know the tool works, I'm just having trouble now.

Ken
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Post  Paulgibeault Thu Dec 29, 2011 12:40 pm


DON'T use the piston holder! Some (not all) types caused the piston to mushroom.
Just use the reset tool & place the piston on a hard/dense flat surface, like a vice or similar.
Let us know how that works out. Good Luck!

Cheers, Paul
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Post  Cribbs74 Sun Jan 01, 2012 2:26 pm

Fill the holder up with some play dough and really pack it in. Peel it out to confirm the holder itself is not causing the problem. You could also use white glue and peel it out once it's set. It may be the metal was too soft and over time has become dome shaped.
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Post  microflitedude Sun Jan 01, 2012 3:00 pm

The top of the piston dome shaped? Some Wenmac pistons had dome shaped heads.
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Post  11592_KW Sun Jan 01, 2012 6:44 pm

Thank you for all of your replies. I was down at my LHS buying some more fuel last Friday, and I happened talk about the piston resetting. The older guy ringing me up said he has an employee who can do it and has been doing it for years. He offered to reset all of mine for free so I went home and grabbed them and brought them in. They said the holder likely got knocked out of shape and sometimes the holders are just machined wrong so they don't use the holders, they place the piston on a thick sheet of plate glass and then tap and spin. It took him 3-5 minutes to do each piston with small taps. They also repair model engines there and other model stuff, nice little place, its a shame these kinds of stores are disappearing.

This seems like a nice site, I would join but I don't work with these engines enough anymore and are only fixing them up to give to my 12 year old grandson who loves lawnmowers, weed whips and chainsaws just because they have engines.

Cheers, Ken
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Post  Jaspur_x Sun Jan 01, 2012 9:18 pm

11592_KW wrote:Thank you for all of your replies. I was down at my LHS buying some more fuel last Friday, and I happened talk about the piston resetting. The older guy ringing me up said he has an employee who can do it and has been doing it for years. He offered to reset all of mine for free so I went home and grabbed them and brought them in. They said the holder likely got knocked out of shape and sometimes the holders are just machined wrong so they don't use the holders, they place the piston on a thick sheet of plate glass and then tap and spin. It took him 3-5 minutes to do each piston with small taps. They also repair model engines there and other model stuff, nice little place, its a shame these kinds of stores are disappearing.

This seems like a nice site, I would join but I don't work with these engines enough anymore and are only fixing them up to give to my 12 year old grandson who loves lawnmowers, weed whips and chainsaws just because they have engines.

Cheers, Ken

Thats too bad,you would most likely enjoy being a member here,I sure do.
Thats my kind of LHS we need 1 of those around here Sad

It was nice hearing from you, Have a happy nre year Fireworks
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Post  Big Al Mon Jan 02, 2012 11:26 pm

Any one having problems using the reset tool should check the holder to see if it is made properly. There should be a raised ‘peg’ approx ¼ in dia in the center to support the piston directly under the ball socket only. Some holders have a flat bottom bore and worse yet have a small radius at the edge which will tend to deform the piston. Best not to use those.
al

piston reset tool Cimg0310
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Post  RknRusty Wed Jan 11, 2012 9:03 pm

I have yet to successfully reset a piston and have ruined several including both of my Black Widows. I'm very careful, patient and light handed on a hard stable surface (a Pontiac front brake rotor on a concrete floor), and rotate frequently. I wouldn't be able to use flat glass as some of mine have a nib in the center of the top of the piston. Maybe it's my tool. I'm about tired of trying, though some new ones have more slop than I like. I'll inspect it closer and maybe try one more time. It looks exactly like the picture above.

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Post  Ivanhoe Thu Jan 12, 2012 4:28 am

I've been using one of the cheap reset tools, worked great on a couple of pistons, then the other day the rod piece closed up on the conrod of the piston I was using it on, trying to remove it I managed to pull the conrod completely out of the piston! The moral? never buy cheap tools! Sad

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