Circlip coming loose During Run

Happened to me once in a tanked engine. Didn't do any damage, but I fitted a new clip and threw the old one away, figuring it must have just been weak. That engine went on to win its class in my last Tach Race, pulling 24,100 rpm without clip failure.

Happy to say that I have never seen a Cox clip failure or any other Cox engine mechanical failures, but having said that - I will no doubt wish I had not!

Bill

Will I've had a few failures. Snapped cranks glow plug dieing and broken needles. But the Reed valve circlup or retainer sucked up in the motor during run that is a very first. Hope last!!
Ice

I did not include plug failure as that is a normal maintenance item on most engines we use. Still had very few plug failures and none at all since switching to Nelson plugs!

Bill

Perhaps the clip was in a bad position, I have often wondered why the conrod isn't catching the circlip all the time...

On other engines (non cox) the conrod can wander a little along the crankpin but is held in place by the flat face of the backplate. On a cox engine it would instead rub against the end of the circlip (if it is well open), so why doesn't it simply catch and break more often?

Had a few copper reeds get sucked in but not the G clip.Small props and lots of nitro. We doubled up the reeds sometimes back in the day. Cranks broken on the older TDs with the thinner web going through the case. Holes in the top of the piston. Wear, or too much or not enough resetting?

I think the groove cut around the crankcase holds the big end of the rod on the pin and the rod cannot rub against the backplate, only the pin if the axial play of the shaft is excessive after numerous abuses with electric starters..there is no groove near the TDC but then the rod is in a higher position than the circlip open center therefore the two cannot interfere even there..I think even this detail was very thoroughly thought over by COX engineers.


Apart from a broken hollow crankpin in a TeeDee 050 (RC), I only had one mechanical failure in my hundreds of hours runs with COX engines when the swaged balljoint cup in a TeeDee 049 piston broke and the schrapnel killed even the cylinder. (I may have put a crack in the cup with a prior joint setting so even this cannot be blamed on the engine)

The holes punched into piston tops IMHO are results of bad balljoint setting with no gap left hence the varnish and metal are rubbed until a hole is punched in lack of proper lubrication. (Learnt that from my own failure committed with the very first balljoint settings)

Iceberg wrote:Had a first today anyone else had this?

Running a postage stamp back .049 with exterior tank. Running 17-18k rpm. Running quite good. Then stopped and seized. Thought broken crankshaft or piston rod.

Teared down and the circlip had come loose and come forward sucked in and jammed tight with piston rod and crankshaft. Bent the circlip up real bad too. Had hard time to remove it. The copper reed was sucked up into the motor and ruined as well. Got it replaced with another back plate and circlip. Didn't damage the piston assembly.

I have never had this. Once a reed was sucked out of the new style into motor but never the circlip. Any ideas? Obviously the plastic backplate groove is softer than the aluminum ones.

Very strange.
Ice

Back when I was buying a lot of Cox engines I found this exact same condition in three or four.  I took some pretty impressive pictures at the time but they all went away when my computer crashed.  My guess the cause is previous owners didn't secure the clip properly.  I always roll them in with my thumb while twisting until I hear a snap then ensure the reed is free to move.

Bob

balogh wrote:I think the groove cut around the crankcase holds the big end of the rod on the pin and the rod cannot rub against the backplate, only the pin if the axial play of the shaft is excessive after numerous abuses with electric starters..there is no groove near the TDC but then the rod is in a higher position than the circlip open center therefore the two cannot interfere even there..I think even this detail was very thoroughly thought over by COX engineers.

I have seen wear on both the backplate rim and the circlip itself, but perhaps that is more excessive on the Queen Bee engine. Here is a picture of a Golden Bee engine, it will not take much for the conrod to hit the end of the circlip...

Yes Kris I see that. Maybe we should check that the free end of the circlip should not protrude into the rotation plane of the pin and rod. Simply placing the backplate on a flat surface with the circlip side down and see if the rim touches the flat surface in its full circumference?

Yes, putting a ruler across the backplate will be a good way to check the position of the circlip. Something to remember for the next time a circlip is mounted.

and don't forget there are two different thicknesses and style of Cir. clips ,more the thickness to fit correctly in the groove . https://www.coxengineforum.com/t8552-mylar-stainless-steel-reeds-with-circlip-type-reed-retainer?highlight=circlip