By Iron,you mean a cast crankshaft? I might be wrong but I'm thinking GM never used a cast crank before 1960,maybe later?
I'd start by looking at the radiuses. Use a 1/8 inch drill bit and a good light to help judge. If they have been ground small previously there is no way to grind a proper full size radius at the next two undersizes. Then I'd measure the length between the thrust flanges, and look at the condition of both thrust faces, especially the rear one (that would be loaded when the clutch is depressed and the cranks is pushed forward in the block). if its chewed up now, when it is ground smooth the end play will be excessive unless you can find a main bearing set with longer than standard thrust bearing, and those may have disappeared from earth for US cars. Then I'd get it magnafluxed (wet method). No sense spending another nickle on a cracked crank. Some will say "I've never seen a broken Chevy crank" or " I rang it, and it rang good." Smile, say thanks, and get your crank magnafluxed by a shop with a good reputation. I'd ask that shop to see the tester they use to check if the crank was successfully magnetized as the first step before starting the inspection. My preference would be a 30 under non-welded crank with good radiuses that still has acceptable rod side clearance and end play. Cranks >>can<< be successfully welded. They also can be compromised or even completely ruined in several different ways, and still have real nice looking fresh ground journals. One way is to use the wrong welding wire or technique, so the journal and especially the fillets/radiuses have cracks. Some grinders will say "oh those are just heat checks." If there is a crack in a radius it is a stress raiser or stress concentration right where it hurts the long term durability of the crank the most. It doesn't matter much whether the crack is a fatigue crack that started as an invisibly small microcrack last year and is patiently working and growing a little longer and a little deeper as the crank is subjected to additional torsional and bending cycles, or if it is an artifact of the welding process. Another way is by distorting the crank so the masses are displaced from when it was made. Grinding the main and rod journals true does not fix that. At the very least the balance is destroyed, and I've seen several where the crank snout, timing sprocket journal, and flywheel pilot had several thousandths runout relative to the gorgeous "new" main journals. The best weld ever made is a home made casting with filthy bastard alloy chemistry and subjected to largely uncontrolled cooling while passing from molten to solid as part of a large, cool hunk of steel. It is likely to have inferior mechanical properties (low yield and ultimate strength, large grain sizes) compared to the original forged low to medium alloy steel, and lots of locked in stresses to boot. And this weakest link material is put into service right where the stresses are highest, in the rod journal fillets.
I find this subject interesting. Back in the 70's I drove and built Hydroplane Race Boats, and Super Modified Race cars. After purchasing engines from both Grumpy Jenkins, and Smokey Yunick. I learned a lot dissembling these engines. I have an Automotive Design Degree from General Motors Institute, so anything different these guys did was always of interest to me. About this time I got hooked up with a machine shop in Massachusetts. I had five engines and needed someone that was local and reliable. He had a crank grinder and that machine ran two shifts six days a week. The big money was in welding, and grinding cranks out of the big diesel trucks. But they would grind a dozen car engine cranks a day. When the guys started running the 400 block with the 350 crank it took a main bearing set that cost $200 for the mains alone. At that time it was like $2,000 in today money. So we took the 350, and in some cases the 327 crank and welded the mains and reground them to fit the 400 block. This gave us different cubic inch displacements.We then played with the connecting rod length. If it was the 350 crank we used a 6" rod, and the 327 ran a 5.700" rod. This gave us around a 1.75 to 1 connecting rod to stroke ratio. When I had the yunick engine build it was a 327 and he used a stock length rod of 5.700". I got a lesson on connecting rod lengths. Earlier Smokey had found that the best stock rod length was in a 327 engine compared to all the others. They then started using the 6" rod in the 350 to get the same combination as the 327. It has to do with the first 22 degrees of connecting rod angularity on the power stroke. The Jenkins engine was a 302 and used a stock 5.700" rod. I ran the dog shit out of these engines. These where Hilborn injected methanol engines with roller cams and dry sump oil systems. I could twist these dam things 8,200 down the straightaways, and roll into the turns at 150 MPH on water. So what I'm getting at, I wasn't easy on these engine. When I built my own engines being guided by two of the best in the buisness. I used the same formula as far as dimensions as the engine that I had built for me with the exception of welded, and ground up crankshafts. I was never easy on my equipment and after laps, and laps of hard running these welded cranks never broke. Something that might be of interest to some of you guys. When talking Chevy engines always check rod bearing number 7. If it's good all others should be. I was told that around forty years ago. When I asked the big guys they just looked at me like didn't you know that. It's never mentioned in this time in history, but was known by anyone in the know back in the day. Being an Engineer I did some research around thirty five years ago. We dissembled right at 100 Chevy engines checking the bearings. In every case it was always number 7 rod bearing. So what the hell does all this mean. Well check number 7 and if it's good the engines should be good to go. The original post mentioned that one of the bearings on the crank was bad. Just wondering if it was number 7. We had a maintenance program where we would check number 7 every week. I had five engines and we ran different classes, so engine changes between heats was common. If he's only going to run the engine under 6500 RPM's. That's nothing. These little engines can have the snot run out of them, and never talk back. The other thing that was mentioned was a long skirted piston. I hope there not going to install a long 6" rod in a 327, and move the wrist pin up in around the ring lands. That's the wrong direction to go in. Well I hope I could help some of you young guys. The old timers probably already knew this stuff anyways. Thanks for reading, Johnny Sweet
Real life experience: I'm making over 700HP and turning over 7Krpm in the traps with a GM steel crank that is .030 under. We did have the crank nitrided after turning.
Thanks puddin. Your another gear banger that has stressed parts alot more than I will in this coupe. No wheels up expected. thanks V
As said it will be fine just make sure they get a nice radius on the fillet and tell them to turn it on index it makes for a much nicer motor,alot of shops are turning cranks out fast but are off index pretty far.When you get your crank back make sure to check the bearings so the dont rub the fillet when assembling.
vrod64, Take your crank up to Waco,,Crankshaft and Valve. I have used them since the mid 60's,, people in there have changed but the quality of work is still top notch. I have some .050 rod brgs for my next 288. Just saying. Earl
The Jalopy Journal
