Crankshafts

Your crankshaft goes from 0 to 3000 rpm in about two seconds. When the air fuel mixture expands in the cylinder head it forces the piston and connecting rod down into the crankshaft. At 8,000 rpm it does this 4,000 times a minute.

The crankshaft only appears to be rigid. It isn't. Anytime a load is applied to a part the part deflects. All parts ultimately act as a spring in response to a load. In the case of the crankshaft that movement will be very small but it will be intense. It will also happen very quickly.

When the engineers designed your engine they did a lot of calculations and they created a crankshaft that could withstand all of these forces. Now decades later you’re changing everything. You’re trying to get more horsepower out of your old engine, which blows up all those original calculations. You’re applying a lot more stress than the designer ever envisioned. And, you’re asking a fifty-year old part to do this.

Maintenance Schedule: Tom Lieb, founder of Scat Crankshafts, feels that the most important thing you can do is put your vintage engine on a regular maintenance schedule. Tom founded Scat Crankshafts in 1964 and they’ve become the premier supplier of racing crankshafts in the United States. Scat not only supplies most of the NASCAR crankshafts but they can also create a custom crankshaft for your vintage Bugatti, something they’ve done for several Bugatti owners.

Tom Lieb feels that your crankshaft should be magnafluxed and all the measurements verified on an annual basis. It’s not a bad idea to replace the main cap bolts and the connecting rod bolts at this time as well. You have too much at risk to keep using factory bolts that are decades old.

The crankshaft is part of a system. You need to monitor your oil pump, engine block oil passages and the crankshaft oil passages. Oil is critical to your crankshaft so you need to do everything necessary to ensure that oil is reaching your crankshaft.       

Preventative Replacement: If your crankshaft breaks it’s going to take a lot of components with it. You can almost certainly plan on a new engine block, not to mention any number of connecting rods. There’s always a lot of collateral damage when the crankshaft breaks.

You might consider replacing your crankshaft before it breaks.  Blocks are getting really expensive today. Even if you have a small block Chevy you’re going to spend a lot of money at the machine shop. You really don’t want to have to start all over again.

Bugatti

Some of you have rare engine blocks. Engine blocks generally won’t break unless the crankshaft breaks. Break a Bugatti crankshaft and you’ll need to check the limit on your Visa card. The good part it that you can still get a Bugatti crankshaft made for a reasonable price. At least reasonable if you operate on a Bugatti budget.

Porsche 914 

Modern race teams keep track of every single nut and bolt that’s used in the car. A NASCAR team can tell you have many minutes a valve spring has been in use. They can go to their computer and find out if they need to replace the main bearing studs. Most of us can’t do that. We tend to replace parts based on intuition and experience. 

Most of us need to start keeping better records. Do you have any clue as to how many hours are on your crankshaft? Do you have any clue as to how much it might cost you if that crankshaft breaks? 

New Crankshaft: You can gain a lot of security by purchasing a new crankshaft. The specialty companies are still making a lot of the crankshafts for our vintage cars.  A lot of us are still using cast iron small and big block Chevy engines in vintage racing. As vintage racers we can benefit from modern technology.

Crankshaft reliability is basically a function of material, heat-treating and the oiling system. Every one of these has changed a great deal since your car was originally built.  The material used in contemporary crankshafts today is far superior to anything that was used in the 1960’s and 1970’s.  Maybe it’s time to find out what a new crankshaft costs before you break the one in your car. At the very least you might consider have it checked at the end of the season.

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