CP Piston - Oil Ring Gap Question - Do Not File

[mikedsilva]

This might be an easy answer for some:
I'm gapping the rings for a set of CP Pistons in my 3.0.
Top and 2 rings are coming out well with a little filing on the gapping tool.

The specs call for a minimum 0.015" on the oil rings... and states "do not file". Problem is, in my cylinders, I am getting a gap of 7-8 thou... approx half what it calls for as a minimum.

If I am not supposed to file them, then what do I do? Just run them?
Mike

[brighton911]

Perhaps contact CP and get their opinion. They were very helpful for questions I had about a custom piston set I had acquired.

[RedCoupe]

I think the reason for the do not file message is that the oil ring rails can distort when worked too much and can also make nasty burrs. I have filed oil ring rails and haven't had a problem by supporting them in a small flat jawed vice and the dressing the edges afterward with a small jeweler's file. Question - are you sure that the rings are absolutely straight and square in the bores when you are measuring the gap? Many 911 Pistons aren't very good for squaring up the rings. I turn a fake piston out of wood for this. Besides squaring up the rings, it prevents scratching of the cylinders.

[mikedsilva]

Originally Posted by RedCoupe

I think the reason for the do not file message is that the oil ring rails can distort when worked too much and can also make nasty burrs. I have filed oil ring rails and haven't had a problem by supporting them in a small flat jawed vice and the dressing the edges afterward with a small jeweler's file. Question - are you sure that the rings are absolutely straight and square in the bores when you are measuring the gap? Many 911 Pistons aren't very good for squaring up the rings. I turn a fake piston out of wood for this. Besides squaring up the rings, it prevents scratching of the cylinders.

Hi, yes, I am fairly certain.
My cylinders had all been freshly nikasilled and honed. Plus i allocated a set of rings to each cylinder and checked the gaps for each oil ring in its respective cylinder. Mine were all reading .007 inch.

A rep from CP emailed me back, saying it was ok to file the rails, but not the expander ring. I ended up using a precision honing stone to take off material and debur. They are all reading .015 now so I am happy.