Gudgeon pins

After removing my barrels I see some burring of the piston on the outside edge of the circlip that retains the Gudgeon pin (wrist pin). For this to happen the pin must be hammering against the circlip. What should I do? Thanks Dano.

Just check that the gudgeon will slide from side to side through the small end, I had a tight one in my race motor awhile back, it stopped the piston from centalising and caused a hot spot on one side of the piston.
It was generated by oil break down, turned out it was old stock and failed a few race sessions.
Honed the small end and solved the problem, used a different brand of oil, new stock
Just a thought for your issue
Regards Mike

Could you have had some detonation (pinking) going on?

The pin is not tight in the small end and the motor has never pinked

I'm interested.

I've seen it on pistons too.

Dano said:

After removing my barrels I see some burring of the piston on the outside edge of the circlip that retains the Gudgeon pin (wrist pin). For this to happen the pin must be hammering against the circlip. What should I do? Thanks Dano.

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Many light aircraft engines use buttons on the pin ends rather than clips. Metal smeared from these buttons onto the cylinder walls is pretty easy to identify during an oil analysis, and almost always points to a bent rod(s) brought about by over-revving. Propeller governor is prime suspect.

Nathan

wrong size circlips, if they are jcc pistons they came with clips to small, bent rod will cause pin to move sideways in piston

There could be a number of reasons including some already mentioned.

However gudgeon pins hammering on one side can also be caused by a non parallel crankshaft (to the deck of the barrel), the bore not at right angles to the crankshaft (sometimes not even parallel to the other bore) and/or the little end not being parallel to the big end and crank.

When you see this you need to get a good shop to "blueprint" the basic geometry of the engine. You would be surprised at the number of motors which are totally out of alignment. This is the basic first step in building any good motor.

You don't say where you are in the world. I can suggest a good guy in Wellington New Zealand but doubt that will help

Thanks for your input Johnm, I am in Aussie. This is the second norton motor that I have seen this on. Dano.

circlips around the wrong way doesn't help, one of the checks I used to do was with an engine up side down on a stand after fitting piston an crank was to wind over and watch small end and gudgeon pin and make sure its not moving around, movement indicates mis alignment, a bit hard to do with a bike engine