TRW/SpeedPro Forged piston tolerance

[tminer]

Has anyone been checking the "improved tolerance" PowerForged (L2481F) pistons? I am curious as to the range of diameters that are being seen. FM shows .001 tolerance on their web site, but I am not sure if that is the new or old value.

Tyvm,
Tom

 

[QuickWrench]

FM shows .001 tolerance on their web site

I think the .001" is per inch of bore diameter, which is in line with the old value. I'd have a hard time believing that you could run a forging with only .001" - .002" of clearance...but it would be nice.

 

[tminer]

I am looking for tolerance, not clearance. Their clearance spec is .0035, so ideal diameter would be 3.7965 (std) or 3.7995 (.030 over). I am wanting to know how close they come to that spec. I believe that the .001 was the amount that they could be oversize, which would mean spec of 3.7995-3.8005 for .030 over.

I am really interested in std size, but I imagine that there is more experience with .030 overs.

Tom

 

[tminer]

Since the skirt coating may add .001", the size and clearance specs may be different than I listed.

I'm really trying to determine two things: the correct bore size and whether the pistons vary enough that the cylinders need to be honed to match the individual pistons.

Tyvm,
Tom

 

[QuickWrench]

Sorry 'bout that, I'm stupid. Not enough caffeine yet...

You are off on your calc's, though. A .030 over slug would most likely range from 3.82 - 3.83", not 3.7995". You're adding .003", not .030".

FYI...

I've never installed a set of forgings that didn't require per-cylinder setup for the final hones, regardless of the engine make/piston brand. I've used TRW, BME, JE, and KB's in Buicks, Chebbys, Ford, and Mopars, and they all had to be set up individually. I've rarely seen a complete set where all 6 or 8 weren't within .001" of each other, but they always vary enough to warrant a precision hone for each one, before pressing/Spiro-Locking them to the rods.

g'luck.

 

[tminer]

Thanks. That helps.

I think I'll get another cup myself, I hate them slipped digits!

Tom

 

[KendallF]

I did a set of TRWs about 3 months ago. They were all within .0005". My BRCs for my S2 had 5 that were within a couple of tenths, and one that was a full .001" bigger.

 

[Chuck Leeper]

Close??

I just finished checking 8 4.500" bore Wisecos for my HEMI
All were DEAD NUTS ON!!!
I guess it's a matter of how well the mfgr sorts his products as the sets are made up???

 

[tminer]

Originally posted by KendallF
I did a set of TRWs about 3 months ago. They were all within .0005".

Thanks, do you remember the actual range? Were the skirts coated? Is TRW's clearance spec still .0035?

Tom

 

[KendallF]

Originally posted by tminer
Thanks, do you remember the actual range? Were the skirts coated? Is TRW's clearance spec still .0035?

Tom

I don't remember the actual #s. The skirts were coated with whatever that black coating they're using is. Their spec is .0035" but I set the last two I did at .004"; they don't make noise when cold at .004" and the skirts weren't scuffed on one I had apart subsequently.

 

[tminer]

Thank you.

Tom