I'm putting a 350 SBC back together that had flattened a cam lobe. (Keeping in mind that in spite of its 350+ hp and 4:11 rear gear and M4 transmission, this car is strictly a street driven car that my wife owns and drives on occasional weekends or to local car shows. (Not raced, in other words!)) I decided to put fresh bearings and rings in it along w/ new cam and lifters while I had it apart, when I ran into excessive ring gap. It should be .018 minimum gap (according to the Hastings - the maker of the moly rings), but I'm getting between .032 and .035. .018 is minimum, but what is "too much"???

According to the calculations, the bores are approx 4.005", confirmed with a dial caliper (bores are between 4.004" to 4.006" at the top of the cylinders. Ring gap is approx .001 to 002 less at the bottom of the bores than at the top.

I'd much, much rather stay with the (nice) TRW 11.25:1 forged aluminum pistons than have to spring for 10-overs (just now). What do you experts think about me buying "10-over" rings and re-gapping them? I know for sure I will want to go very lightly over the bores with the ball hone - the holes are big enough already . Aside from some piston slap (which will most likely be drown out by the side pipes anyway) do ya see any issues w/ what I have in mind??

BTW, the holes appear to be round (as in no gaps around the new ring inserted into the bore).

Bottom line Q: Use the 5-under pistons and re-gap some 10-over rings (save some bucks and live w/ the noise) or bite the bullet and bore 10-over and get new pistons

Thanks in advance, guys.

Paul.

 

Forged pistons get a .005 skirt to bore clearance. Cast pistons are .001 skirt to bore. On the rings, you might want to investigate a set of file fit rings at.005 over. I believe Hastings has them. {they make rings} they are not re-packagers like so many others with their name on the boxs.

they also make one of the best filters...

 

Not trying to hijack the thread, but can you elaborate on the filter comment? Thanks.

 

Plus the .005 wear that you have gives you .010 piston clearance. Have you measured the pistons across the skirt? With that much clearance they may have started to colapse already which will further increase the clearance.

 

You have to make the choice here. Either you bore it, put new slugs in and do the rest of the engine as new, or go with what you have. With the TRW pistons (which I like a lot), you've only got .0025 wear on each side (.005 total wear at the top, right?). In my book, I'd build it the way it is. A daily driver go-to-the-show engine doesn't care if it's a little loose, and they are very forgiving (think overheating or a sudden lean condition), and if you have any noticable piston noise, it's only going to be at start-up. I doubt you'll even notice. File fit rings are an option, but again, the replacements will be fine. Your building a street engine and want to save time and/or money from the sound of it. I'd say the only issue is extended higher than normal RPM's at freeway speeds due to the low rear gear. My two cents...

Hans

 

this ain't a motorcycle motor ... for sbc you'll have a tough time finding off-the-shelf 10-Over pistons or rings ... sbc typically +20,+30,+40,+60.

IMHO ... quik-checking bore w/ a typical dial caliper OK ... but you need to accurately measure bores & skirts ... & a caliper ain't good enough to confirm that.

You might "get by" having auto machine shop KNURL your pistons' skirts and file-fitting rings ... might be sugar ... might be sheet.
http://en.wikipedia.org/wiki/Knurling

I'd measure it correctly ... and if sloppy ... bore w/ new oversize pistons.