Tech Question: SBC Cast Crankshaft Machining
 

Good Afternoon All. I have a tech question about a stock SBC Cast Crankshaft. In some of the "spec" lower hp sprint classes around the country I know some people still use stock cast crankshafts in their race engines. I am curious as to if every stock cast crankshaft needs the rear flange machined to fit inside the motorplate hole and torque ball housing (i know without the machining that sometimes the flange will rub on the inside of those)? I had measured from the rear of a stock cast 305 crankshaft that had been machined and the largest diameter of the flange was 4.9". I am also curious as to what the maximum diameter of that flange could be for it to still fit without any machining done to the motor plate and torque ball? Thank you.

I can't answer that but I had a motor with the rear flange large enough that we had to run a lightweight magnesium torque ball housing with Kevlar blanket because the steel housing wouldn't clear, for what it's worth.

Re: Tech Question: SBC Cast Crankshaft Machining
 

That brings me to another question then too. Is there a certain Torque Ball Housing/Torque Ball combo that has a larger ID where the flange would not be an issue?

Got me confused, I wasn't aware of the SBC had a flange that large, and the adapter for the yoke for the u joint took it thru far enough to not be an issue, what am I missing? Bob

Re: Tech Question: SBC Cast Crankshaft Machining
 

A cast crank has a larger flange than a forged crank. It extends far enough rearward to rub if it's o.d. isn't reduced.

Thanks, guess I never met a cast crank, I think the 396 had a counter balance bob weight on it, that required a spacer or the flywheel modified to make it usable, guess it doesn't come up enough to make the headlines. Bob

Re: Tech Question: SBC Cast Crankshaft Machining
 

Pretty sure you will have to have it turned, I had a stock steel crank it had a big flange, would not work. There are a lot of steel cranks out there floating around with a round flange, that you can pic up for 250 or 300. Probably cheaper than turning a cast one down unless you can do it yourself. We all learn that when we start racing sprinters. LoL

Re: Tech Question: SBC Cast Crankshaft Machining
 

Unfortunately, some sanctions mandate a cast crank.

Also remember that that flange that needs to be removed is a counter weight and will affect the balance of the crank. Most aftermarket crankshafts have a round flange and all of the shorter stroke cranks like a 283 or a small journal 327 also had a round flange. Longer the stroke or heavier the rotating assembley the more counter weight and or heavy metal needs to be added to the counterweight approximately 180 degrees from the rod throw. If you are lucky the crank has balance holes in the rear counter weight that can be filled with a steel slug and welded in, if not you will have to add heavy metal in the rear counter weight installed sideways in the counterweight.

Re: Tech Question: SBC Cast Crankshaft Machining
 

Sounds like a flaw in the rule department, why make a rule that totally goes against the rest of the reason for running the class, now he has to modify std parts to fit years old other off the shelf items, surly there are recon cranks out there with the proper flange end diameter to keep from having to modify at least 2 other pcs that are std. Turning the crank down wouldn't be a high dollar deal, just something else to get into your billfold. I'd look for something else I believe. JMHO Bob