| [GMCnet] Tid Bits: Why engines burn oil. [message #336538] |
Thu, 30 August 2018 15:38  |
BobDunahugh
Messages: 2465
Registered: October 2010
Location: Cedar Rapids, IA
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Short answer. Miles, and contamination in the oil. There are 3 ways oil gets into the combustion chamber. By the piston rings is the major way. Rings can last an extremely long time. Their life gets shortened in several ways. The choke on the carburetor isn't adjusted correctly. And stays on too long. choke pull off not working, carb float too high, enrichment valve open too long, metering rods not working correctly. This over rich fuel/oxygen fuel charge to the pistons. Gets way over the preferred 14 ppm ox to 1 ppm fuel. This slows down the flame front that travels across the combustion chamber from the spark plug. ( Indexing the spark plug to the chamber is preferred) All this allows some fuel to not get burned. Leaving raw unburned fuel to wash sway the tiny amount of oil on the cylinder walls. Plus producing excessive amounts of carbon in the chamber. Great if your making sandpaper. Luging the engine by not shifting down on hills. Puts excessive loads on rings. Engine overheating can take much of the tension out of the rings. Ignition timing way off. Valve stems/guide clearance is another expressway for oil to the chamber. Again here. An over rich fuel ratio is very damaging. The positive crankcase ventilation system is next. This system generally has few issue. Replace the PCV valve in the valve cover. And NEVER put on ANY pretty valve cover that doesn't have the stock baffle. Not having that stock type baffle. Makes a very nice express way for oil to the combustion chamber. The Howell EFI with spark control will solve all this except the PCV issues.
Now to the oil control piston ring. This lower ring on the piston. Is there to make sure that the cylinder walls, and the 2 upper rings get the proper amount of oil. That oil that this ring puts on the cylinder wall. Is a mind boggling tiny amount. And more bearing clearance with a HV pump doesn't help. There is absolutely no one on this earth that knows more about the 403, and 455. Then the hundreds of engineers at GM. And how these engines have held up for going on a half century proves that. There are 5 changes made on the 455 for the TZE units. 1-Water pump. 2- carburetor. 3- lowered intake manifold. 4- Distributor. 5 - higher Nickle content in the engine block. The 403 didn't have a lower intake manifold. Just the standard rear wheel drive car intake. A larger bearing clearance, and a HV oil pump aren't on that GM list. And for good reason.
So why do some engines fail at 75,000 miles. And some are running well at more the 200,000 miles. That's in the maintenance. And the carburetor issues above. It's the oil dilution by unburned fuel. The main/rod bearings should never come in contact with the crankshaft. There should always be an oil film between them. And cleaner oil will not have as much abrasive carbon floating in the oil. Frequent oil/filer changes have always been the salvation for you engine. By draining out the diluted oil by fuel, and the contamination contained in that used oil. I've known owners that changed the filter ever other oil change. That is pure dumb. In the microscopic world out there in our engines. Our oil filters. NO MATTER the brand. Are only filtering out the LARGE ROCKS that are traveling around the inside of our engines. And the ONLY way to remove the slightly smaller rocks, then the larger ones that got filtered out. Draining the contaminated oil out. The 403 that was in our 78 Royale. Had 152,000 miles on it. Was in pure excellent condition. The log book that came with it. Showed only a hand full of oil/filter changes that went over 3,000 miles. Synthetic oils are excellent for the modern clean engines of today. We need to change our oil to soon to take advantage of their longer mileage cycles. OK. I'll stop babbling, For now. GRIN Bob Dunahugh
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