Home » Public Forums » GMCnet » [GMCnet] Summary. Ultimate Demise Of A well maintained 455.
| [GMCnet] Summary. Ultimate Demise Of A well maintained 455. [message #283262] |
Mon, 27 July 2015 08:26  |
BobDunahugh
Messages: 2465
Registered: October 2010
Location: Cedar Rapids, IA
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> The discussion on this has been great over several subject lines.
> The information, and thought's bellow are intended to make GMC owner's a little more cognoscente of the effects of maintenance. Or the lack there of. And to shed some light of how vary important changing the oil. And even more impotently the oil filter in a timely manner. We must keep in mind that our engines are of an old tech design in comparison to the engines produced today. That change was brought on for the most part by the EPA regulations. The engines produced today put far fewer contaminates in the oil for the oil filter to remove. Thus oil filters are much smaller then in past years. The oil filter is designed to remove the larger abrasive contaminants that GM felt had to be remove during the recommended oil change cycle. And GM planned for the oil change to finish the job of removing the extremely fine abrasive contaminates that the filter is unable to capture. Synthetics are good oils. But leaving any oil in for extended miles. Still doesn't finish the task that an oil, and filter change does. Oil gets dark because it has abrasive carbon contaminates within. And even though these contaminates are extremely fine. They are still an abrasive that over the life of the engine. Take there toll no matter the oil type. At 120,000 miles I pulled the oil pan off of my 78- 403 to check the bearing clearance of the mains, and rods. The clearances were in the range of .0003 of new. That's extremely small over that many miles. According to the log book since new. The oil, and filter had almost always been changed under 3,000 miles. And no synthetic oils were used. It's at 154,000 now. And generally has a GVW from 17,000 to 21,000 lbs due to the enclosed trailer I pull. The general though is that engine bearings are in contact to the crankshaft. The two aren't to contact each other due to the oil film. And if you have too much abrasive contaminants in the oil due to long oil change enter voles. That's what wears the crankshaft bearing surfaces down.
As to the reason for the demise, it seems to come down to contamination that was either introduced during the re-manufacturing process, or possibly contamination that was overlooked during the cleaning of the engine components. I'm leaning toward contamination mostly. But both can't be totally overlooked. Maybe it's a case of too many people involved, and some details in cleaning are overlooked. Because one person thought that the previous person took care of the item that ended up being overlooked. The block looks perfectly new on the outside, it's got to be the same on the inside. RIGHT? Maybe that thought came up. Maybe someone had too many beers the night before. Who knows?>
> I'm purely, and completely anal over cleaning oil passages. And I think because of that, maybe that's why I've never had these types of failures that we've seen with 403's or 455's…. YET. An engine is an engine. All American engines are basically similar no matter the size or shape. There's nothing mysterious in any American V8. The problem has to be in the human end when it comes down to the details…and that's where the devil is.
>
> The engine appeared to have been well put together. The type of cam, lift, and duration was a good choice. There was a good name brand double roller chain for the cam. Water pump was the correct one. The distributor and carb had been well tuned. This was evident by the appearance of the valves and pistons. It had .060 oversize forged pistons with chrome moly rings. The pistons, rods, and crankshaft were balanced to a fairly closes tolerance with Clevite .020 undersized main, and rod bearings. A good choice. It had APR high load rod bolts. Very nice bolts,great for performance applications. But this is an engine that operates at low RPM's. I personally wouldn't have wanted to spend the $200 for the bolts installed. It had higher pressure valve springs…probably the springs that was recommended by the cam company. The thing is that the cam manufacturer expected that the cam would have ended up in a car. With a possible RPM range approaching double what our GMC's would ever see. Higher pressure springs are used to make sure that at higher RPM's. The lifter is able to stay in contact with the cam profile and not float. The cam was what is referred to as a towing profile cam. The intake lift was a little higher then stock. The exhaust was very close to stock. Profiles were slightly longer. Stock GM valve springs would have been perfectly fine in this application. You want a valve spring that will do the job that's required with as light a spring pressure as possible. Since we have the old, in reality, outdated flat tappet cam, any spring pressure over what's required just puts extra unwanted load on the cam. We’re all worried about with ZDDP and if we have enough of it in our oil. Heavier valve springs when not required it just exacerbates the problem. I very much like the stock valve spring that uses the GM positive valve rotators. Not the titanium valve spring retainers that are commonly used with the heavier valve springs.
>
> Now to the high volume oil pump, the HV pump had absolutely NOTHING to do with the demise of this 455. It too got destroyed in the process. GM designed the oil pump to supply the correct volume of oil to fulfill the engines needs. I truly believe GM knows more about our engines then anyone else. I've heard the comment that a high volume pump will put more oil into suspension to help cool the pistons. Again, if more oil was needed for cooling the pistons, GM would have addressed that issue then. A high volume pump can't deliver more oil for cooling except at idle. It's a problem that simply does not exist. If you really think that you need more oil for cooling your pistons, then put in a higher pressure oil pump.
>
> Next, let’s talk about the oil cooler. If you had an engine that was just tired, no parts chewed up, I would have it flushed out like the demo of Jay Leno. If it was chewed up, and was banging parts against parts. I would strongly suggest getting a new external cooler. I just don't see taking the risk.
>
> Now to the root of the demise. Glenn was using synthetic engine oil. It too had nothing to do to cause the failure. But how it was used in relationship to the oil filter, and oil filter bypass. I stated back at the beginning of all this weeks ago. That from what I had found, was that this deterioration had occurred over a long period of time. That comment still stands. It seems that some contamination had to have not been completely cleaned out of some oil passage. At some time this contamination started to slowly come loose. As the oil filter starts to get restricted just from normal contamination, this starts to have the oil filter bypass valve bypassing more and more unfiltered oil. This was all exacerbated by Glenn doing what most owners do when using synthetic oils. They leave their oil in for extended periods of time. A few years ago someone said that they change their synthetic oil every 12,000 miles. If Glenn would have changed his oil at every 3,000 miles. There would have been much less time that the oil filter bypass valve would have been open. This would have allowed more oil to be filtered and more contamination removed. That would have possibly saved the 455.
>
> In summary, GM chose an engine that has proven to have been up to the task. We use it as intended. Don't try to fix a design that doesn't need fixing. Re-manufacture it stock except install hardened valve seats. Balancing would be a good option. EFI will reduce crankcase contamination. As to synthetic oils, they're great for modern clean crankcase engines. Our engines are dirty, old tech engines. GM stated how many miles an oil filter should be changed, there never has been, or will be, an oil made that will extend the life of an oil filter. If you think synthetic oil is the best and leave it in for 10,000 miles fine. Just change the oil filter every 3,000 miles at most. Personally, I use a diesel blend. It has the ZDDP I need and handles higher heat and loads then standard oils. Diesel engines have a compression ratio of 20 to 1. We're at 8.5 to 1. They are blended to handle way more contamination of the oil then any other oil.
>
> So this is how I think things went bad. I'm building the replacement 455 stock to GM specs. I've never had one of my stock or competition engines fail. And I’m not starting with this one.
>
> Bob Dunahugh
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