March 2011 Chevy High Performance Q&A - Performance Q&A

Under Pressure Round II

Kevin McClelland Feb 11, 2011 0 Comment(s)
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The engine has about 5-10 miles on it. Please let me know what you think before I rip it apart and start over.
David LeGrand
Arnold, MO

A: The first oil change on a fresh engine is always an aha moment. When you find the oil clean and the filter perfect you’re totally relieved. When you find material in the filter, or on a magnetic drain plug, your heart drops and you question where it came from. Sometimes it is quite easy; other times it’s like this couldn’t be inside this engine!

We highly doubt you have a ballooned torque converter after 5-10 miles of driving, unless those first few miles were repeated power brake launches. We don’t think your little 388 has enough torque to balloon the converter. You’ve listed the few sources your brass-type shavings in the oil could be from. The wristpin bushings are usually out, because if the bushing locks up, they rarely shed much debris, and the pin continues to rotate in the piston. Yes, over time it wouldn’t be happy because the rod couldn’t float from side to side with the pin locks retaining the wristpin. Some timing chain sets use a bronze thrust washer between the camshaft gear and the block, but the COMP Cams Magnum series timing set doesn’t. Finally, if you were running a roller camshaft, you’d be using a bronze distributor gear and they have to wear in from initial start-up. They are a service item, and you need to keep an eye on them over the lift of the engine. However, you’re using a standard cast camshaft and shouldn’t be running one.

This brings us back to the rear main thrust bearing, because it’s usually the culprit. We had a battle with our little 305 eating rear main thrust surfaces. After going through two bearings (slow learner) we finally figured out what it was doing. When the machine shop align-honed the mains, they cut the rear main cap on an angle. This caused the hone to cut a taper in the rear main that was slightly tighter in the rear of the main saddle. This, in conjunction with the cap being slightly cocked on the block, reduced the thrust clearance. We then sanded the rear main thrust surface to achieve 0.004-inch crankshaft endplay, assembled the engine, and thought we were good to go. Well, that slight taper in the rear main would allow the oil pressure to exit the front of the rear main and not lubricate the rear thrust surface of the rear main. Within about 20 dragstrip runs the endplay was about 0.020-inch and guess what we found in the oil filter?

The first thing we’d do is check your crankshaft endplay. If it’s still within spec, put a fresh filter and oil in the engine. Put some more time on the engine and give it a good break-in cycle. Service the engine and check the filter for debris. Check the endplay of the crankshaft to see if the clearance has moved. Sometimes on a fresh build things need to get happy with each other. You’ve identified where the material could come from. Good luck with your break-in.

Super Mixer

Q: I built a 372ci small-block with a B&M 420 Mega Blower and outfitted with two 750-cfm Edelbrock carbs. Out of all the Hot Rod and Chevy High Performance magazines I have read and I have read many I have never seen an article on tuning a 2-4 engine. What concerns me is, remember the old Torker manifold from Edelbrock for a big-block and how the carburetor was turned at an angle for fuel distribution? GM printed info on stagger jetting for this engine, but can you imagine all the mumbo jumbo it will take to get the plugs to read right? Dealing with eight carb holes! Could you please help me on this?
Charles Guarisco
Silverhill, AL

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