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Old 03-08-2008, 12:34 PM   #1
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Hello everyone. Been awhile since I Have posted, but need some help. I have an engine noise that sounds like a rod knock, but...
At cold start up = no noise. (Oil Pressure 50 PSI) Accelerates fine. After reaching normal temp (195 degrees, Oil 25PSI) Noise starts, as if a rod knock. I can accelerate and the noise goes away. I can let up on the gas, no noise. It seems to show up at a certain range of constant RPM. I have noticed at Idle the oil pressure about 5 PSI. Anybody had similar problems , or know what my problem is?

Thanks,
Randy
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Old 03-08-2008, 12:34 PM   #2
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Hello everyone. Been awhile since I Have posted, but need some help. I have an engine noise that sounds like a rod knock, but...
At cold start up = no noise. (Oil Pressure 50 PSI) Accelerates fine. After reaching normal temp (195 degrees, Oil 25PSI) Noise starts, as if a rod knock. I can accelerate and the noise goes away. I can let up on the gas, no noise. It seems to show up at a certain range of constant RPM. I have noticed at Idle the oil pressure about 5 PSI. Anybody had similar problems , or know what my problem is?

Thanks,
Randy
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Old 03-08-2008, 04:29 PM   #3
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I'm surprised your oil pressure drops all the way from 50 to 25 as it warms up. And way low at idle. Wonder what are other folks seeing for warm oil pressures on a 454?

By the way, how old and how many miles on that beast?
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Old 03-08-2008, 05:42 PM   #4
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The speedometer has a reading of 110K, but the motor had been rebuilt by a previous owner at 60K. Apparently, the oil was drained but not replenished and driven dry. I assume that the owner did it himself, since I have the reciept for parts. I was a little concerned about the oil pressure myself, maybe some other folks might have some input. By doing a web search, some people have reported a knocking sound from the exhaustmanifold. I have replaced the exhaust manifold gasket, but not the donut. Could a blown donut gasket, from the manifold to the exhaust pipe give me the same symptoms?
BTW it is a 91 Coachmen, 454.
Thanks,
Randy
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Old 03-09-2008, 05:19 AM   #5
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<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by ROHawkins:
Hello everyone. Been awhile since I Have posted, but need some help. I have an engine noise that sounds like a rod knock, but...
At cold start up = no noise. (Oil Pressure 50 PSI) Accelerates fine. After reaching normal temp (195 degrees, Oil 25PSI) Noise starts, as if a rod knock. I can accelerate and the noise goes away. I can let up on the gas, no noise. It seems to show up at a certain range of constant RPM. I have noticed at Idle the oil pressure about 5 PSI. Anybody had similar problems , or know what my problem is? </div></BLOCKQUOTE>

I had a very similar problem in a late 80's Chevy V6. It turned out that the main bearings were shot and as the engine warmed up it would let the warmer and thinner oil just flow by, lowering the overall oil pressure. I'm not much of a mechanic... wish I could explain it better.
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Old 03-09-2008, 06:00 AM   #6
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How would one pull a motor out of a motorhome? This is a 1991 27'Coachmen, with the doghouse enclosure.

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Randy
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Old 03-09-2008, 10:02 AM   #7
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<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by ROHawkins:
How would one pull a motor out of a motorhome? This is a 1991 27'Coachmen, with the doghouse enclosure. </div></BLOCKQUOTE>
I would think you have to pull the grill and the radiator. Then out thru the front.
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Old 03-09-2008, 12:05 PM   #8
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<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Posted March 08, 2008 09:42 PM Hide Post
The speedometer has a reading of 110K, but the motor had been rebuilt by a previous owner at 60K. Apparently, the oil was drained but not replenished and driven dry </div></BLOCKQUOTE>


I'll bet your mains are gone if it was run dry. Next will be a rod going out , most likely when is is the least convenient
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Old 03-09-2008, 01:03 PM   #9
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It's possible too that when they put in the rebuilt motor, it was not properly lubed when it was first started. If the oil pump was not first primed, it could have been running on dry bearings when it first started, most professional builders use a grease on the bearings to help prevent this, but the installer has to also spin the oil pump to make sure everything is lubricated well and the oil pressure comes up quick. This is usually done with a drill and a old distributor used to turn the pump connected at the bottom. I have also seen the distributor left too loose at start up and pop out of the oil pump, causeing the oil pressure to go to 0, but the engine still run. (caught that one too late, ate the rod bearings in less than a minute)
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Old 03-09-2008, 02:46 PM   #10
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Everybody and those that still have more info, Thanks for your help. If I have to rebuild, was thinking about doing away with the ECM and keeping it simple. Anybody have any ideas on this thought.

Thanks again,
Randy
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Old 03-09-2008, 07:55 PM   #11
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Sorry Randy,

It's a main bearing gone (the others are probably out of tolerance too). That 454 should have at least 15 lbs at a hot idle even in the summertime. You shouldn't run it anymore. Even at idle speed it will cause all kinds of damage (especially unrepairable block damage) if it lets go. Even if the rod stays on the crank, there is usually solid and pulverized babbitt from the bad bearing(s) floating around the crankcase. It's great when it's used as a bearing material in the correct place; babbitt is is like sand when it gets where it isn't supposed to be. Best of luck.

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Old 03-09-2008, 08:00 PM   #12
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A guy on RV.net posted pics of pulling his engine and putting it back in. He did it thru the Doghouse.
He used an engine hoist on plywood in the coach.
Rv.net is DOWN now or I tell you who it was. Don't know if or when RV.net is coming back up. It's been very slow the past week.
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Old 03-10-2008, 05:34 AM   #13
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If it is a main bearing, wouldn't the noise get louder under a load? At about 55mph, I can accelerate and the noise goes away.

Thanks,
Randy
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Old 03-10-2008, 06:13 AM   #14
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Actually, from your description, (noise goes away under load), it sounds like a rod bearing to me. That can also cause a decrease in oil flow thru the crankshaft.

Ron
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