bebbetufs

What purpose does this ridge serve? Does it do anything like scoop oil onto the pin or is it for balancing and can be safely removed to lighten the piston?

rlm328

If you want to remove weight you may want to look at skirting the piston.

bebbetufs

I just need to remove a few grammes to balance the set. I need at most 2.5g gone from the heaviest piston/pin combo. I'm planning to use a Dremel tool.

rlm328

The usual practice is to take the weight off the rod.

Dave W.

If you have stock rods there's a flat section on top that can be ground down to remove weight.

bebbetufs

Thanks.
I thought the rods and the pistons were balanced separately? A few random hits from a google search:

Chris White

I prefer to balance the parts separately. that way you can mix and match rods and pistons. that can come in handy if you have to replace anything later.
Lightening the whole skirt has some risk - you should not take any material out of the thrust areas.
The tab you are pointing to is a good place to start - but do not take any more material off once it flush.

bebbetufs

Thanks Chris.

Unfortunately I am in too much of a hurry Today I balanced the set by taking material out of the trust areas because that's what they did to my other set when I sent them away for balancing (Opel tuner). I did however cover as much area as possible to minimize loss in one area. After grinding I hand sanded and polished as best as I could by hand to hopefully reduce the amount of stress risers.

Here are some photos.

What do you think? Hopefully I won't have to buy yet another set of pistons.

Chris White

You will be fine - the pistons have a very deep skirt so the small amount of weakening at the very bottom will no be a problem.

bebbetufs

Thanks. I think I've confused "thrust area" with "pin boss".

I've removed most of the material from the surface of the piston pin bosses. 1mm at the most. I had to re-chamfer the oiling holes to restore the original chamfer, but some of the chamfer was still left.

Chris White

When the piston is traveling down the bore there is a side load on the piston due to the geometry of the crank / rod and that forces the pistons against the cylinder wall. There is no thrust load on the front and back sides of the pistons and more loads on the right and left.

if you look at the pistons you should see where the skirt is lower that the rest of the piston - those are the thrust areas.

bebbetufs

That makes sense. That is where I see the most wear. Thank you.