I posted this on the C3 board too (since it is a C3 motor), but a SBC is a SBC, and I'm open to suggestions...

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.

 

You may find this worth reading.

http://kb-silvolite.com/feature.php?action=read&F_id=62

 

The easy fix is to gap new rings to the bore you have. I wouldn't use old rings. Lightly hone the bores to break-in the new rings. That should work on a street SBC. Good luck.

 

I wouldn't suggest using a ball hone. Cross-thatch is very important in order for ring break-in. A 45 degree cross-thatch is what the ring manufacturers suggest. Grit of stone is also critical. It's best to take the block to a machine shop to have it honed. If the machinist thinks there is too much taper in the bores, then it must be bored to an oversize to correct it. HOWEVER, there is another solution. Depending on what oversize the bores are now. You can sleeve the bores. I've had this done to a block I wanted to keep standard bore because of rules. This is a decision you can make. It may not be the cheapest or best way to go. It's just an option you have. Also, depending on how may miles these pistons have. The ring lands need to be checked. If the ring lands are worn, new rings will not correct that problem.

 

Well, alrighty then!!!

Thanks very much for that lil bit of info!

Stand by for heavy thunder (in a weekend or two!)

P.

 

However, the machinist said the block hone is best to finish up a new bore. But, in a slightly worn bore he told me the ball hone was the way to go. I'm aware of the 45º cross-hatching; type of hone not withstanding.

No sleeves for this babysan...She's a "Sunday driver" and only occasionally is allowed to get "frisky" (usually to blow off some buzzing ricer pest). Ami has owned the car for 4 years and in than time has put less than 3000 miles on it.

Thanks for your help!

P.