Piston Skirts Scuffing

[65TripleBlack]

I removed the oil pan on my 327 after about 100 miles of driving on a rebuild, just to check. I can see some vertical lines on 6 of the bores. Looks like the skirts are contacting the bores because the vertical lines disappear about 1/3 the way up the stroke. Should I be worried about this? Will it go away after further use. If I have to tear down, are there any shortcuts I can take. What could possibly be causing this.

Thanks in advance.

 

[Ken Anderson]

How much piston clearance are you running? Forged or cast pistons? Sounds like too much clearance. You could have knurled the skirts and that would have helped a lot. Do you hear "piston slap" on a cold start?

 

[65TripleBlack]

Ken:

They are forged pistons, and I don't hear any piston slap. I recieved my block back from the machine shop, who also ordered all the internal parts needed. Rotating assembly was balanced and blueprinted by shop. I assembled engine and checked ALL clearances. The entire assembly was done under "surgically clean" conditions. ALL measured clearances were right on the money. The only thing I didn't measure was the piston clearance. It is logical that since the shop machined my block, and supplied the pistons, that they would be properly sized and clearanced. Also, if ALL other clearances (bearings, journal end play, ring end gaps, etc.) were within spec, then why suspect ill fitting pistons.
I have been told that slight scoring is normal. I don't think that I have severe scoring, but I will check it more thoroughly now.If I can take some clear pictures, I will try to post them.
Knurling the skirts?? What is that? That doesn't sound right to me.

 

[66427-450]

.......
Knurling the skirts?? What is that? That doesn't sound right to me.

it's done in an attempt to decrease piston-wall clearance, I wouldn't recommend it........ bore to the next size if your too loose.

 

[Ken Anderson]

NEVER assume the machine shop did it right! I'm assuming you rebuilt your stock 327. You should have bored it .030 over and honed the block to spec with a deck plate and used a TRW or equiv forged 11:1 pistons. If you reused your old pistons a light hone and knurling the pistons would be in order, IF the piston clearance was in spec. Since you don't hear any "slap" on start up (kinda sounds like a diesel), I wouldn't worry. I can't even believe you pulled the pan on a fresh motor. Why did you pull it? Put it together and forget about it, just run it HARD!

 

[65TripleBlack]

Ken:

Yes, they are brand new Federal Mogul Forged Domed pistons, L2166NF-30, as original. My calculated C/R is 10.65:1 plus or minus .15. I would never, ever reuse old pistons with a .030 over bore. I still refuse to believe that knurling skirts of old pistons is wise, at all. Seems to me, that knurling will concentrate friction points and absolutely insure excess scoring.

I pulled the pan to replace a broken dipstick tube. Yes, I could have replaced the tube without removing the pan, but this was an "excuse" to go inside for the following reasons. While I was in there, I decided to install a missing windage tray, and install all new main cap bolts. Also figured, "let's take a look around" while I'm in here.