Home » Public Forums » GMCnet » [GMCnet] Part II The Untimely Demise Of A Well Maintained 455
| [GMCnet] Part II The Untimely Demise Of A Well Maintained 455 [message #280958] |
Sun, 28 June 2015 20:29  |
BobDunahugh
Messages: 2465
Registered: October 2010
Location: Cedar Rapids, IA
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> Continued from Part 1
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> So what did happen to this well maintained (by it's owner) 455. It appears to have slowly started in the bearings selected, but mainly acerbated by contamination of the oil. Some of the source of the foreign material, may have been introduced while other work was done, or may have been introduced by the engine oil cooler.
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> You may think that the oil filter should have removed the contaminants. This is the situation. Oil comes out of the oil pump and goes directly to the oil cooler. If there is any trash in the oil, it then comes back to the oil filter to clean out the trash from the cooled oil. After leaving the oil filter, it goes directly to the bearings and lifters. So this oil should be clean for use, right? Not quite so. There is a oil filter bypass valve in the oil filter support housing. When the engine oil is cold, and thicker, the oil filter can't flow enough oil to lube the engine correctly. The oil filter bypass valves allows unfiltered oil to go to the engine bearings. In reality, the bypass valve is always bypassing unfiltered oil. And yes, GM planned it that way. I tested that oil filter bypass valve today. It opened at 6 oz of pressure.
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> The oil in the system is mostly clean all the time. The filter's job is to remove extremely tiny contaminants, mostly carbon from the combustion of gasoline in the combustion chambers. As a note, newer engines are made to not allow as much combustion contaminants to enter the crankcase. That's why synthetic blended oils are recommended and are are so good for so many miles in newer engines.
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> With the old design of the engines that we have, it's best to change your oil at shorter intervals. In this manner, you end up draining the contaminant of carbon that are too fine for the filer to hold. This carbon is very abrasive in our old technology engines. That's one of the reasons why engine oils get black. So it's best to use mineral based oils in our 403's, and 455's. For this reason, you will never see me put synthetic oils in any of my older tech engines. Plus, you should never leave any type of used oil in an engine for more than a year.
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> So if you drive less then 4,000 miles a year, what good is synthetic oil?
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> This engine had a High Volume oil pump which had nothing to do with this engine failure at this time. But the extra load of the HV pump was causing extra deterioration of the stock oil pump driveshaft. But the HV oil pump just may have been what got Glen, and BJ the last few miles home.
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> There is no doubt in my mind, and the minds of others, that GM did a great job in their design of the 403, and 455. There are lots of well maintained GMC's out there that have traveled a lot of miles over the years. The other day, Fred Hudspeth had a post that talked about the OEM engines that came in our GMC’s back in the day and his thoughts on why those OEM 403's, and 455's held up so well. He had a very good point. We use our engines in the way GM intended them to be used. Fred's point, and I totally agree, was to remanufacture them to the exact specifications that GM did when new. Don't go by the wide range of what might be shown as allowable clearances. Have it really built purestock as NEW. I'm not one of those old guys that think things must be kept purestock no matter what. That's not me.
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> If you want to put any engine in a service that the manufactures had no intention of it being used changes from stock are a must. As an example, I have several Yenko Stingers. (Corvairs) I take a Corvair engine that has a whopping 164 cubic inches, and a base HP of a huge 95 ponies. It is then modified so that when it's checked on a dyno, it can crank out 242 HP. The RPM redline is in the 8,000 range. No turbocharging, no nitrous, just pure engine. In this situation, mods are required. A friend once said that an engine like that is a hand grenade, with the pin half pulled. He has a point there.
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> My point here is that with our stock engines, OEM parts, and to new OEM specs will get that performance that GM designed into these engines to start with. (So here I go sounding like Wes at Cinnabar ) GM really knew what they were doing, and time has proved that. My OEM 403 has 154,000 miles on it. On the last long I trip got 10.122 MPG with a carb, pulling Linda's 5,000lb lift van. Our 403 GMC pulls loads that can reach 21,000 lbs GVW. I ran some tests on my 403 last year, and don't plan on doing any more tests till it gets to 180,000 miles. ( Go read Fred's e-mail to see his point. )
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> As to the High Volume engine oil pumps in freshly remanufactured engines, I fully understand why a HV oil pump is a good idea for some of the engine builders. The coach owner comes in to pick up their coach with its rebuilt engine. It had a stock oil pump installed. The engine reaches normal operating temps. Oil pressure on the road is at 35 to 40 PSI. They stop at a stop light and the gauge drops to 25 PSI. The owners thought is, that's not right, the pressure should stay at 35 PSI. But remember, on the road the pump is at 1,300 to 1,700 RPM. At idle it's at 300 RPM with no load on the engine. So to make the owner happy, the builder puts in a HV oil pump. The HV oil pump idea sounds like a great improvement, as more of anything is always better. Put in a HV pump so the gauge stays a 35 all the time. There is NO deception here to the customer in any way. It just puts the coach owner in an improved comfort zone, and the engine builder looks good. To demonstrate how little oil pressure these engines needed back then, most cars had a light that came on if the oil pressure was to low. The light came on at 7 PSI. That is ALL THE MOTOR NEEDS AT HOT IDLE! Folks who run a DigiPanel will hear their alarm screaming at them when the pressure drops below 20 and some of them have gone to a HV oil pump for that reason (Kerry Pinkerton for one).
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> Please remember that I'm NOT putting anyone down, or saying that I know more then anyone else. Just engage some common sense, and do what puts you in your comfort zone.
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> Just my 2 cents worth. Dialog Welcomed.
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> Bob Dunahugh Member GMCMI
> 78 Royale
> 4 Original Yenko Stingers
> 3 Corvair Convert
> 1 64 Chevelle Convert
> 1 96 LT1 Impala SS
> All Restored
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