Hi All, I bought a set a set of Grant pistons from fellow hamber 'BostonCamaro' for my 283 and had the machine shop bore the block to the pistons that we thought were .060 over. Turns out they were .110 over according to the machine shop, but I noticed a marking under the piston says "100" --they have been coated though. I have not heard of a "299" sbc! Was this a normal sizing for these older forged aftermarket pistons?
Markings UNDER the piston are generally the slug or the blank number, as referred to by the manufacturer.
The other posters here have given you the correct advice. Only with a sonic check can anyone know what is the safe limit to bore any block, period. It doesn't matter how long you have been in business or have been machining engines. You are new here, and will soon learn the wealth of information and experience on this web site. I'd slow my roll defending a 40 year machine shop that didn't mic the pistons before boring the very first hole. Even to mic the pistons to determine whether or not you have a collapsed skirt on one that may have been damaged accidentally. I could go on in length regarding your expert machinists, but I won't. Best of luck.
I thought by Boston's description when he was selling them that there was a question as to the actual size and application. .110" over was obviously a special order. I thought about buying them and turning them down to .060" over for my motor. I have a Lathe and yes I know the ring lands would have to be turned down too... Anyway, I decided it was too much $ for not knowing what they were. My personal opinion is there is no good reason to go bigger than .060" over on a 283. Ok, one good reason, if the block was damaged and you had to go bigger to clean it up. If you want the cubes, go to a 327 block. Yea, yea, I know they bored 283's to 4.000". But why would you when 327 small journal blocks are available and even with sonic checking, the walls on a 283 bored to 4.00" are too thin. My 2 cents, Dan
"Back in the day" it was fairly common for rebuilders to bore early 283's .125 oversize. I got one of these shortblocks from Sears. It performed really well, didn't overheat and got 22 mph on the hwy in my 61 Vette.
If you chucked them in a lathe to turn them down, on the first light cut you might find yourself saying "why aren't these pistons round?" The answer is "because they aren't". Typically pistons are cam ground, which means the skirt is ground slightly egg-shaped or oval-shaped. The widest diameter of the skirt is at right angles to the piston-pin axis. When it is heated, it becomes round. The design allows for a closer fit in the cylinder so that there is a reduction of blowby gas, cylinder scuffing, and piston slap. It's pretty hard to duplicate the cam ground profile on a lathe.
Some of those old pistons ran .010-.015 clearance such as Jahns and that would mean bore it .110 and run .100 pistons. Grant owns Jahns now
Guess what ? Pistons can not be turned down in a lathe to end up with something useable. Rough them close but they need to be finished on a piston cam grinder machine.
Do the proper introduction Dan. Part of the deal here. And someone can bore these blocks +125 is ok. Too many were scrapped the last 10 years as it is.
you guys crack me up raggin on each other, hope its all in fun while getting your point across. as for 283s .125 over, I bored several to .125 over, was lucky I guess, had no problems except for one wanting to run a little warm probably due to the thinner walls.
I had a 327 with a set of those in it in the 70's and it sounded like the hammers of hell until it warmed up. I've got my wonderments about a "machinist" who doesn't put a mike on the pistons and if they are use thoroughly checked over before the block is set up to be bored. At least that is the way the guy I use does it.
George, We used to punch them .125 and called them a 301. GM didn't use a stock 283 block and punch it they used a stock 327 block (the large journal would have been 327/350) with a short stroke crank (283 if you will). The 301s that we built when we were young were throw away blocks. But we were building them when you could get complete strong running 283s all day long for 50 bucks. I ran a bored 301 inch 283 in a short bed '62 for about a year, then gave the truck to my mom. She kept complaining that it was running too hot so I snagged a good 327 block and moved the pieces over to it for her. It ran cooler which made her happy and she could still play when she wanted to. I believe there lies the kicker with a hawged out 283. If you have a block that will go .125 without needing to pour it full if concrete it will always want to run a little on the warm side because of the thin cylinder walls. You learn to live with it and now there are some modern ways to help it run cooler that we didn't have back then. But if you are not reasy for it you will end up on the HAMB saying, " My 283 runs hot." It isn't a 283 any more if it is a 301 and it is just going to run hotter than a stock engine. The older forged pistons required a lot of cylinder to wall clearance, they slap all to hell until the warm up and swell. If you think your engine sounded bad you should have heard one of my old race small blocks, we used to not only run forged pistons as loose as we could get away with but we turned then around and ran them backwards to loosen the lower end up a bit. On a well tuned small block the difference in rod angle was worth about 400 RPM. That difference can be make or break on the big end. A good machinist knows that no two pistons are alike, punching and finish hone with each piston in its perspective hole is the difference bewteen a blue printed engine and one that is just screwed together. That is why some factory engines really run and other just run, evey once in a while you get one that the guy got lucky and it wasn't just within tlerance but the tolerances are just right. The test engines were never assembly line engines and the advertised HP and torque was based on a blueprinted engine.
Well obviously they would make blocks with normal wall thickness. Just pointing out that that CID must have been a decent idea for them to start making them @ the factory.
Thanks for all the input. I should have mentioned that this motor build is for a project that will have limited street use and I am planning on running e85 with a tunnel ram, 327 rods, low gearing, L79 style cam, 4 speed and early 60s power pack heads. Just a retro build I guess, something I've been wanting to do for fun, though it may end up being a 'throw away' motor. I plan to get a build thread going on this once I make some reportable progress.
I have run many 301 inch 283's and would not worry about boring it again. You should probably have it sonic checked to check for any "core shift" that may lead to thin spots once done. If the shop is reputable they should make the work right and if not you should look elsewhere. To bore a cylinder without checking the pistons would be a red flag. Piston from different makers for given size are going to mic different anyhow so it should have been where they started. Your plans for the build sound like a very classic combination of the parts used in the day and should provide a fun little motor given that it is done right. Contrary to what some have said, those pistons are not going to provide ultra high compression ratios like 12.5:1. With a standard periond head and deck height you should be a point to point and half less depending on head gasket.
The only point is having pistons you want to use. In reality a 327 block anything other than standard bore does you no good because these pistons are made for a three inch stroke.
Thought I'd put out an update to this thread. Obviously I am not in a rush on this project. The Machine Shop confirmed they sonic checked the block and it was okay for the custom over-bore. I went ahead and had the Grant pistons milled to a 2mm dome height. I also picked up a .450 solid lifter cam. Here is the before and after on the pistons:
FWIW, a +.120" overbored 283 nets 301 cubic inches ........ a +.125" overbored 283 nets 302 cubic inches (the standard Z-28 engine, a 327 block running the 3" stoke crank). Many aftermarket piston companies sold the +.120 oversized pistons for the SBC 283 back in the sixties.
In the 1959 SAE paper about developing the 348 W motor GM talks about their inability to make a 4 inch bore SBC with the casting techniques they had at the time.
The Jalopy Journal
