Quote:
Originally Posted by PotvinV8
Modern engines and modern engine builds using modern components (IE roller cams, roller rockers, etc) don't suffer from the same issues as hydraulic or solid flat tappet cam setups. Incorrect break-in of a flat tappet cam is a notorious cause of flattened lobes. I've done it and have seen it done many, many times.
I worked in a machine shop with a cam grinder who had 50 years under his belt and he told every customer the same thing, break in the cam. Vary the rpm for 10-15 mins, don't let it idle. Keep the oil pressure up and the lifters spinning (flat tappet cam lobes are ground with a ramp to force the lifters to spin to prevent them from wearing a flat spot in them). The dyno shop we use does the same thing and they test motors day in and day out. They wouldn't waste 20 mins of dyno time if it wasn't necessary.
Now, how that concerns a Model A? If I was swapping in a new cam, I'd break it in. Rings, new pistons, etc. Probably not.
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Unfortunately you are leaving out several things in forming your opinion. When you factor in the quality of lubrication has changed immensely over time, the wear additives in modern engine oil alone allow for less chance of premature wear. We now have modern cam lubes that are meant to circumvent cam wear as it is very hard to wipe off this lube.
You also hit on one major thing that many Model-A rebuilders overlook. Tappet bores are often worn, and when a tappet is pressed against worn bore walls, it generally only has pressure contact in the extreme lower and opposite side upper. This generally causes a tappet to be unable to rotate. So when this machining step is omitted, the engine rebuilder is hoping that varying the RPMs will try to make the tappet rotate enough where the camshaft lobe will not be wiped out.
With all due respect to your camshaft grinding friend, there is MUCH in technology that has changed where his methods are obsolete. The engine machining tooling and supplies are different now. It isn't just engine machining that has changed in 50 years, ...look at paint & materials, battery technology, gasoline, fabrics, etc. and notice how much has changed.
I will also share with you that any performance Dyno shop that runs an engine for 15 minutes is doing that out of ignorance, -or you are mistaken. They have never done any of my engines that way, -and I have many close friends in the performance engine business and they don't dyno that way either. In the class we race in, a top quality engine is between $35-$40k, These engines are good for 1,000-1,200 laps. With lap times under 20 seconds, every 3-4 laps equals a minute. At an average cost of $35 per lap, I would not be interested in wasting $2,000.00 of run-time just sitting on a dyno listening to it run! Neither is anyone else!!
