Anyone have experiance boring a 348? I am wanting to bore mine .125 over. While I see pistons available in this size, I wonder if this amount of overbore is safe? Is sonic testing a necessity at this amount of overbore?
General rule of thumb is: If they make pistons for it, it SHOULD be fine...I would have it sonic tested just to be sure. You do know it takes a special Bore to machine a 348/409 block right? This is because the deck is not square with the cylinder walls. Most machine shops will probably tell you they cannot do it.
Boring that far should be a last resort. You probably already know this, but the more a given block is bored, the more likely it will be to overheat. And once you've gone that far, if it ever needs to bored again, you'd have to sleeve it. Dave http://www.roadsters.com/
Greetings from Long Branch,NJ,Americas first seashore resort and 7 time U.S.summer capital....I have a few of those blocks around waiting to be refreshed....all you want to know at www.348-409.com Lee
Most of the machine shops around here use a boring bar that lines up off of the crank centerline and not the deck (like a Sunnen CK 10 or ???) now days. So they don't have to have the wedge plates that are used when you use a boring bar that lines up off of the deck. After you bore the engine .125 and it needs rebuilt, your block is junk or needs a full set of sleeves. If I was gonna bore one that far, I would check the cylinder wall thickness for sure. If it were me, I would go the smallest overbore possible to clean the cylinders up. Larry T
I'm thinking of just going .90 over based on what your saying. the pitting in one cylinder has got me nervous, but I think start at .90, if that doesnt do it, fuck it .125 over.
The reason for the bore plate is to preload the deck as if the heads are on and torqued. That way you get a perfectly round cylinder with the proper torque at the deck. Without it you end up distorting the block slightlly and that equates to loss in cylinder pressure. Look for a machine shop with a plate. Anything less and your not getting your moneys worth. I live in the mid-Michgan area and rebuilt my 348 back in 81. Only one guy in the area had a plate then. The motor is back in the shop as i write this and the same guy owns this shop. Doesn't need boring though. Just a refresh.. Had it out, valve springs got weak and started a miss.
Bad way to make Cubic Inches. I would start at .030 and go from there. If one bore is bad, go .030 over and sleeve the bad one.
I have to guess that you are not a machinist. Instead of wasting your cash the first time around why don't you take it to a competent machinist have him mic it and start there. It'll probably cost you way less than a second set of pistons and another bore job and you'll be done with it the first throw. As for .125 over, there is no rule of thumb that says if they make a piston that big you can bore it that far. Give me a fuckin' break. They make 4" pistons for 283s also but damned few blocks will go that far, well not without putting cement in the water jackets. 348s and 409s were prone to heating, mostly caused by trapped air in the heads, but heating none the less. I would try and get it done with as little meat removed from the cylinder as possible, and give it every chance in the world to survive. OPh yea maybe you can cruise on over to that resort and by a new block. Way to hijack a post with your damned spam buddy. Ok that was a little harsh, must be the codien, or not.
The old wedge deck plates were to set the deck mounted boring bar up at a 90 degree angle to the bore on the 348/409. The ones I've seen are not thick enough to be used as torque plates that are used to preload the cylinders for finish hone jobs. Are there plates to do both jobs? Maybe, but I've never seen them. Larry T
Bore plate. That's how it was explained to me....Does both. My 348 is +.060" and has Jahns slot top pistons and runs all day long and never had an over heating problem. A good radiator is pretty imporotant. If your running an old unit and two, three or four runners are pinched off and soldered because of leaks, you've lost a big percentage of your cooling capacity. However, I agree with doing the least over bore as possible to keep away from potential problems. Funny thing is my pistons were actually stamped .058" That's about what they averaged. One was even .055". A sharp machinst was watchng for this because going all the way to .060" would have been to much. The difference in going +.030" and lets say +.100" is never going to show a difference in a street engine. Next problem is how to get the new pistons with rings back into the cylinder bore.........hehe..... Check out the tech section on that. I sent a picture of the tool that I used to do it.
My job as a perfomance engine builder would be to not advise to bore all the life out of the block at once. We advise to bore the cylinders to clean up the bore and go on down the road. As many problems as you can have with core shift and thin ass cylinder walls I always advise the minimum on overbore>>>>.
Put a sleeve in the pitted cylinder to save it instead of trashing all eight by going to far overbore. And when sleeving the block sleeve the damaged cylinder first then bore all cylinders to size as not to fuck the bore up on the other cylinders by pressing the sleeve in last>>>>.
This months Hot Rod magazine has a good article about 348/409 engines, mostly dealing with the new Edelbrock heads for them. I can't remember if the listed their source, they usually do though, but I read the whole article and it gave you enough info to be slightly dangerous.
348's respond well to stroking.... Bore minimaly and use a 427 crank kit. Here's a site for more info: www.348-409.com
We ran one .125 over in a 61 Biscayne for 4 years before we sold the car. It ran good, never ran hot FYI
.125 is pretty keen for an overbore... unless it's about squeezing out every last 1/100th of a sec at the track, why bother? One bad bore can be fixed cheaper and result in a better motor than going all the way to .125, and that's IF there's been no core shift during casting... But that's just one guy's opinion...
I am not trying to be some sort of freak about cubic inches. The only reason I am going this far is cause I'm using a block that would have otherwise been considered junk by most of you. Yes I did mic the cylinder and yes its super rough. I could sleave it, but I did read the street rod mag and I did get the 427 crank. Why not make this one a hotrod motor? I think .90 will be close and what the hell, why not try to save the block? If it won't work, I'll sleave it and have a .90 over motor.
If the make pistons for it it is safe is very sound advice. In fact if they make pistons for it the pistons are usually pn the safe side. Some blocks can take a huge bore as theyw ere very thick to start with. A couple of examples are ford flatheads and slant 6 mopars. My slant 6 is .140 over and still runs about 187F even with a tiny race only rad on it. Very few if any reputable companies wil make pisotns for an engine that will cause them grief or warranty phone calls.
Just curious, has it been bored yet? If you can find a 409 crank (and that's a big if) stroke it. Otherwise I wouldn't go much over 0.090". -Lee Atomic Radio www.atomicpinup.com
409 cranks are not hard to find. Using a 396/427 crank with BBC rods is the better route to go; more cubic inches with better parts. Ross can build you pistons with whatever pin height and bore you need. If you have a later 348 block it may very well take the 0.125" overbore without issue and possibly have more left in it.
"why not try to save the block?" Why not? Now: you have a block that's worth a few dollars to someone. Then: you have $$$ invested in it, assemble it, start it, run it - and get 5 gallons of water in the pan. How much is the block worth now? How much did it cost to find this out? About $1,000 and 6 months of your time: replacement block, 8 more pistons, boring, gasket set. What does the maximum size piston you can buy tell you? That not every single engine bored to this size fails. That's the size they stopped making. How do they know when to stop? The pistons come back through the front window, they find 00 buckshot holes in their sign, etc. Then they make the next smaller size. When the window is still there in 6 months they have the right size. Did you think they built successful engines before selling you the pistons? No, they discovered that people used 324 pistons in 303s etc. (bore the engine to the size of the newest version), and made them. Back in the day, you could buy 3/16" over pistons for practically anything, and they failed 50% of the time (1 out of 8 cylinders cracked through to water on 1/2 the engines bored). 1/8" over: 25%. .090" over: 10%. 1/16" over: 0%. How can you tell in advance? Have the engine sonic tested is a start. Yes, I cracked a 409 at 1/8" over. My nerves don't stand odds like this very well - I prefer to accept the smaller damage in advance rather than wait to see if I have to pay a lot more. Find another block.
How bout 0.060 over, I need to bore mine, and try making some power. Needs some pistons. Where are the good cam selections.
I'm quite sure +.060" is quite safe. Mine is that size. Actually it was a trifel under that. The shop is going to rehone the block to match a new set of +.060" pistons. I ordered a set of cast slugs with the valve reliefs from Egge for $318.00 The ones from Showcars on ebay and in their catalog don't have the relief in them and will only accept a cam with valve lift limited to .458" I bought my cam which is a Comp unit from a guy named Aubrey Breneau out of Canada. He specializes in the 348-409 stuff. He was very helpful also.
My old 348 was 60 over. Nice size. I have never had any of the local shops say they could not work on a W motor.
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