Dismantle the Cox conrod from the piston. Help

Hi Guiseppe,

According to the artice on Sceptreflight about the MkII Special (see spécifications), the gudgeon pin is floating in the aluminium conrod and the cast iron piston. It is held in place by "pressed-on distance pieces" between conrod and piston skirt:

http://sceptreflight.net/Model%20Engine%20Tests/Cox%2015%20Special%20Mk%20II.html

When looking at the instruction sheet of this engine, the piston and conrod were sold together as 1 replacement part:

https://dbabd7f0-a-62cb3a1a-s-sites.googlegroups.com/site/nitroengine/15%20Tee%20Dee%20Special%20Mark%20II.pdf?attachauth=ANoY7cogtCzRnrZJf3mK6W-YatIOIar_5HeFE7tKFqVy3udj7pthdPJcugNMSV2Ktk90llhF2EzkyNJGiNZPtY7d7bwwRV36Aa95qwUD0HbOzAqO9TV7NqqHwdb2szkZPkn1jVKA0fHJjRluMAk_nbFAT-yUxfqy0TwxzxhG5k-hPDggLDUiGhiuhI6MHM62DcCfa80vkwFgudQwufPGk98gqXUqsu61X2zMTwNn3yRGO4CSyCg7-1g%3D&attredirects=0

That makes me think that piston and conrod were not assembled to take apart. But that does not mean that there is no way to do it.

Lieven

OVERLORD wrote:Hi Guiseppe,

According to the artice on Sceptreflight about the MkII Special (see spécifications), the gudgeon pin is floating in the aluminium conrod and the cast iron piston. It is held in place by "pressed-on distance pieces" between conrod and piston skirt:

http://sceptreflight.net/Model%20Engine%20Tests/Cox%2015%20Special%20Mk%20II.html

When looking at the instruction sheet of this engine, the piston and conrod were sold together as 1 replacement part:

https://dbabd7f0-a-62cb3a1a-s-sites.googlegroups.com/site/nitroengine/15%20Tee%20Dee%20Special%20Mark%20II.pdf?attachauth=ANoY7cogtCzRnrZJf3mK6W-YatIOIar_5HeFE7tKFqVy3udj7pthdPJcugNMSV2Ktk90llhF2EzkyNJGiNZPtY7d7bwwRV36Aa95qwUD0HbOzAqO9TV7NqqHwdb2szkZPkn1jVKA0fHJjRluMAk_nbFAT-yUxfqy0TwxzxhG5k-hPDggLDUiGhiuhI6MHM62DcCfa80vkwFgudQwufPGk98gqXUqsu61X2zMTwNn3yRGO4CSyCg7-1g%3D&attredirects=0

That makes me think that piston and conrod were not assembled to take apart. But that does not mean that there is no way to do it.

Lieven

Good evening Lieven,
thank you very much for this you reply with all the links, i understand very well and i agree fully with you, i think the same.

Thanks again and Best Regards
Giuseppe - Italy

Hello Giuseppe glad to hear from you hope you are OK , Man if there is no GOOD reason to take that apart Don't as Leiven said .. Eric

getback wrote:Hello Giuseppe  glad to hear from you hope you are OK , Man if there is no GOOD reason to take that apart Don't as Leiven said .. Eric

Hello Eric, i'm well and i hope that you also is well. Ok Eric i understand and thank you for the advice.
Please, let me know that is this model yellow that i to see in you logo ?

Thanks again and Best Regards - Giuseppe Italy

Lieven is correct, it's a press fit to the connecting rod. As long as it's rotating freely in the piston them it's not worth the risk.

While I have never done it to a .15, I have done it with automotive pistons. They are a one time press only.

Removal is done with a jig to avoid deforming the piston.

Cribbs74 wrote:Lieven is correct, it's a press fit to the connecting rod. As long as it's rotating freely in the piston them it's not worth the risk.

While I have never done it to a .15, I have done it with automotive pistons. They are a one time press only.

Removal is done with a jig to avoid deforming the piston.

Hello, thank you very much for the advise, i understand well.

Best Regards - Giuseppe Italy

Giuseppe , That yellow thing is my scratch built Baby Ringmaster    It stayed on the bench a long time to get straightened out ,, I have just been enjoying looking at It so far

This subject is 4 years old so hopefully you have worked it out before now.

The Cox TD 15 used a ball and socket small end with the copper plated piston swaged over the conrod's small end. The copper plating is a "stop off" to prevent the cyanide hardening salts hardening the skirt area during the hardening process.

The first Cox Special 15 used a bigger cylinder base thread than the TD 15, permitting bigger transfer ports. Cylinder was still mild steel but the piston was cast iron. Gudgeon pin was retained by two press fit steel spacers each side of the stamped al. alloy conrod. The Cox instructions refer to just one spacer fitted to the rear of the engine but if you remove the other one as I did the gudgeon(wrist) pin then moves into the cylinder wall whilst running and ruins both cylinder and piston.

The gold anodised crankcase, single exhaust port Special 15 Mk II used a gudgeon (wrist) pin with grooves at each end. The piston carried a skirt circlip groove located below the gudgeon (wrist) pin bore that broke into the gudgeon(wrist) pin bore at each end. The pin was retained by a wire circlip fitted up under the piston skirt and engaging with the gudgeon(wrist) pin grooves. The spacers were still fitted either side of the conrod but now slip fitted and I have found both steel and aluminium spacers. The end of the wire circlip was bent to loop over one spacer.

The piston, pin and conrod assembly in your picture is of the Mk II Special 15 type so disassembly is done by grasping the end of the circlip wire with forceps or very small snipe nosed pliers and moving it to the centre of the piston until it comes free of the piston's groove. The pin can then be pushed out by hand if the assembly is clean though a small mandrel press with aluminium V block to support the piston could be used if stuck with aged castor oil. Heating with a small butane torch will also reduce the push out force required.

Trust this helps - regards