I've got a 350 L46 with the stock domed pistons. As far as I know, it's never been bored or even rebuilt.

I bought a new set of .000" standard size moly rings at AutoZone (Hastings, I believe).

I pushed a new top ring down the cylinder with a piston and checked the gap. It was .024. I did the same with the original top ring and it was also at about .024. My Haynes manual says the top ring should be at .010 to .020.

First question: Is there anything wrong with the off-the-shelf moly rings I got at AutoZone, or are there much better brands?

Second: Is the .004 larger gap too much and should I take the standard set back and get the .010 oversized set?

Third: Should I take back the rings and get gapless ones?

Thanks in advance,
Rick

 

Rick, How much ring wear is evident in the bore? (You will want to remove this to make the bore square.) If your gap is .024 & the book calls for .010-.020, then yes I would get .010 over rings. Otherwise you'll still be getting the same amount of blow-by. For a no-mod engine those moly rings should be fine. I have no opinion on the gapless question.

 

I don't see much if any evident ring wear. The bores don't seem tapered and there is almost no ridge whatsoever (kinda makes me think I shouldn't have started rebuilding it, but it had 90k+ on it and it was out for the frame-off, so...). The bores show no signs of scoring anywhere either. If it weren't for the fact that the original timing chain sprocket nylon teeth were busted up, I'd think this motor was recently rebuilt.

Anyway, I ran across these pages on the web...I knew about rings moving around, but I thought the gap was more important than they said it was for controlling blowby:

http://www.diagnosticengineers.org/Page%20B5-37.htm

http://www.dol.net/~dave.reed/tips.htm

Maybe I shouldn't even bother getting the 0.010" oversized rings and grinding them down to fit exactly? Maybe the 0.024" gap is OK?

 

I don't know how many miles your engine has on it but if it were me
I would check
cyls with a dial bore gauge to se how round they were and how
much wear but I may be paranoid, as long as the rings you have are
made out of nodular iron go with them, I doubt they even bother
to coat standard iron rings with moly. I can't see where gapless rings
are any big deal.

 

Sounds to me that your block needs to be bored. I wouldn't go using .010 rings unless I bored the block .010 too.

 

Why not spend a few bucks more and get file fits? They should put you right where you want to be. It's doubltful that they'll seat very well, though, without a fresh hone.

 

My guess is if you check it down low in the bores your going to find out of round, moly rings seat well but they only use moly on the top ring.

 

SanDiegoPaul: If there was cylinder wear enough for a fresh re-bore, wouldn't I see a noticeable ridge at the top? I don't really see much of one at all. I really don't want to take my numbers-matching block in to a machine shop if I don't have to, but I might if I do.

L88Plus: That's a thought. Would doing that be different than getting .010 oversized rings and just filing them to spec? Also, I'm planning on honing the cylinders too.

 

the thrust down at the bottom is what does cyls. in.

 

.010" wear would qualify for almost no ridge. You need to take measurements with micrometers to make the proper determination, eyeballing it won't work very well.

 

You need to at least hone the cylinders or the new rings won't seat. Pull the motor and take it to a professional, you can't see squat unless you have the proper dial bore gauge and mics. You are wasting your time if you don't pull it, eventually you will, do it right the first time.

 

You can't eyeball such things. Boring the block if needed does nothing to the numbers on the block. Decking it does that. Now that the engine is apart, if it were mine I would spend a few bucks to ensure its done right. If the car is not driven much, it may be the last time you'll have to yank it out. Take the parts down to a local engine shop and have them make the necessary measurements. Piston to cylinder clearance can be as low as .001" for hypereutictic pistions. That requires a good set of tools. Have them check the crank, rods,etc. If the machine shop is honest, they should inform you of things out of spec, things in spec, and things that may be marginal. With any luck you may walk away spending a couple of hundred bucks with little to no machining work needed.
I am not an engine builder but base my opinions on common sense. A roughed up cylinder bore is needed to seal (wear) the rings. To rough up the cylinders they needs to be honed. The rings may not seal properly with smooth walls and the engine will have to be torn apart sooner than later.

 

Well, I didn't simply look down the cylinder to check for taper...that obviously wouldn't tell me anything. What I did was measure the ring gap at several points up the length of the cyl and they all measured identical. Yeah, I know, that's no substitute for a dial gauge/mic, but it was a quick check. And yes, a honing was intended before I put the pistons in (I already borrowed a honing tool, maybe a bit prematurely).

I think what I'll do is take the block, crank, pistons, etc. to the same shop that is going to do my heads, since I need to have those done anyway. Like I said, I'm in the middle of a frame-off, so everything is pulled already

Maybe they can check if everything is in spec using the proper equipment and re-bore/re-grind if needed. Maybe they can balance everything too? I'm just hesitant to do anything with the block based on some of the horror stories I've heard (they take block in for re-bore and the machinist decks it too, just because).

Next question: can anyone recommend a good machine shop to do these things here in Austin, TX?

 

Just make sure they don't deck your block, if you really want to do it right
plan on bore an hone, keep your cyl walls thick as possible and see
if you can go with .020 pistons and rings the thicker a cyl is the
better the ring seal another 010 in bore size wont do squat for extra power, factory small block chevy blocks are not that great when it comes to thick cyl walls.

 

For the top ring, you're looking for .004 gap per inch of bore size. In your case....016" gap. .010 is in my opinion too tight. A little looser is better. The engine will be fine at .024, but file-fit rings would be better. Of course this assumes a perfect 4.000 bore, which without a bore gauge, is all you can do -assume.

 

Just to chime in here....the first motor that I ever rebuilt was a 350 Chevy that I pulled out of a '74 Camaro that was sunk up to its axles in mud forever. I had a machine shop hot tank the block and change the cam bearings after I cut the (rather noticeable) ridges with a cheap chinese ridge reamer and ran a ball hone through the bores. I polished the crank with 500 grit strips of emery cloth, cleaned the ring grooves with a cheap chinese ring groove cleaner, scrubbed the piston and rod assemblies with scotch-brite and carb cleaner then cleaned them off finally with gunk and water. I rebuilt the short block using a $39.00 Summit ring, bearing, and gasket set (file-fit cast iron rings of course) along with an RV-grind cam and lifter set that I got from a local speed shop for about a hundred bucks and reinstalled the heads after a $200.00 hot tank and valve job, topped it off with a $75.00 Weiand aluminum intake and a $118.00 Holley 600. It lit off on the first crank, pulled my '72 Chevy truck around with my race car attached to the back up and down the west coast as well as to work and back for some 50,000 miles without using a drop of oil, whereafter I pulled it out and sold it to a friend for $400.00. To the best of my knowledge it's still running today and I built it 16 years ago. Of course it's not really advisable to cheap out to THAT degree (especially with a numbers-matching Vette) and I would not advise that you go to that extreme, but if you're just looking to do a low-buck rebuild I would suggest just cleaning up the bottom end (by that I mean go to a reputable machine shop and have it properly hot tanked or jet-cleaned), get the cam bearings replaced, have the crank polished and then balance the rotating assembly. Have the heads freshened up (get them hot tanked, grind the valves and have the guides replaced if necessary) then put it all back together with file-fit iron rings, a new cam and lifters, timing set, etc.- as long as you don't try to blow it up it'll give another 100,000 miles of reliable service for minimal dough. Also, if you haven't yey got your copy of "How to Rebuild Your Small-Block Chevy" by David Vizard get it and read it through before you go any further. Enjoy!!