File to fit rings on bone stock rebuild?

[AlanCasida]

I have the 390 out of my '67 F250 to rebuild. It will be basically a bone stock rebuild with cast pistons, small rv cam etc. Is it worth the trouble to get file-to-fit rings?  The only thing I may do with is convert it to a 410(416). I have a new in the box Scat 3.98 crank sitting in the shop that really needs a home.   

[FrozenMerc]

It is your time, do with it as you please. My $0.02, and that is all it is worth.  But with a stockish build, I always just by stockish rings and measure the gaps.  If filing is needed, then I file, but I would say that occurs less than 10% of the time.  I can't think of a single instance were the gap would have been considered too large out of the box. 

[thatdarncat]

Some years back I needed to do file to fit rings on one of my engines during a rebuild. A friend of mine loaned me his homemade electric ring filer, which had a foot pedal switch, that really made it a pretty quick process, wasn’t much trouble to do at all. I can see how filing them by hand could be a much more tedious job.

[My427stang]

If you have a common bore size, almost any ring does fine, moly top and a scraper style second (Napier, Mahle's THG), if you have a choice, but you still have to check gaps, and if required, fit them, but a good quality ring set has no idea if you filed it or the company did if they measure correctly in your bore.

However, if you have a nice engine, well machined, and it's planned to stay together, that preferred combo above is more limited in the cheaper rings and more choices if you set gaps, especially for odd bore sizes.  So, for those, usually file fit is best and deburr.

I have built MANY engines using pre-gapped and they do well, but you lose some freedom with the pre-gapped rings though, many of us have played with ring gaps and lots of info out there, my technique for a street motor is .0045 x bore top ring, .0055 x bore second, who knows what the pre filed will come out as but I'd suspect the second ring would be the same as the top.