I seem to have lsot my paperwork. I have Federal Mogul forged pistons (TRW), P/N L2143. NUmber 2143-97 is on inside of piston. Does anyone have the spec sheet that lists the piston clearance?

I seem to remember it was small.....0.0015" and add an extra 0.001" for performance applications...for a total of 0.0025"

Clearance right now measures about 0.0035, which seems tight, but still......more than the minimum spec...if I remember it right.

 

.0035 would be fine.

 

Well, I am just a bit worried. Right now I can slip a 0.003 feeler gauge in without trouble, but a 0.004" is very tight. Hence my figure of 0.0035" I came up with. Seems to me the last time I checked this type of arrangement I had closer to 0.005" and there was a tiny bit of piston scuffing....about the size of a dime, directly underneath the rings at the thrust sides. However, that engine did heat up quite a bit once from a pinhole in the rad, plus it was detonating a lot, which means extra heat. All this as it is a forged piston, not cast.

I did some Internet searching, but couldn't find anything on it, so I posted it here. Federal Mogul (TRW) paperwork that came with the pistons listed a lot of part numbers, so I was hoping that someone might have that sheet, even though it may have come with other part number pistons.

Basically, the piston is a Ford FE 390 piston with the top cut down for use with the longer stroke 428 crank. Can't rememebr the specs, but it is a Crane Fireball cam, am running 9.5:1 CR, have twin (progressive) Holley 600s and Crane's estimate for HP was 480Hp, although I think that's optomistic and would require perfect tuning. It's only used on the street, and in a car that weighs 2500lbs.

Anyway, I am hoping you are right. Those 0.007" clearances seem to be from 1960 vintage forged piston alloys and meant for very high HP cars used on the strip and/or track.

 

Overheating causes skirt scuffing - you answered your own question. You really need a set of mics and a dial bore gauge to accurately measure skirt clearances - but it sounds plenty close enough to be OK.

BTW - I wrote the Federal Mogul/Speed Pro Performance catalog you are using for data.

 

Thank-you. I did other measurements as well, but...er.....not the best. Used telescoping bore gauge with digital calipers. Double checked with another set of digital calipers. Also measured directly without the T-gauge. All seem to match up, but difficult to get consistent results with this type of gear on "round" items. I kind of liked the feeler gauge method as a 0.003" feeler gauge is very flexible.

I think I'll go with it. Clearance will probably be a bit more anyway once it runs a few minutes and knocks those piston skirts back as well as smoothing the cross-hatch. Might get another 0.0005" out of it......LOL!