Author Topic: Uh oh! Engine knocking?  (Read 10734 times)

Offline Bryan

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Uh oh! Engine knocking?
« on: February 08, 2014, 12:57:52 PM »
hey guys, I have a 8v71 engine. Today, it started making a loud knocking sound. Basically, when we start it, after about 3 to 5 seconds of idling, it starts knocking. Here is what we know, the water lines and heater lines are warm (not hot, not cold), and the oil pressure is at about 12lbs. What could this be?
Bryan
1996 Prevost XL
1967 PD4107-756
Toccoa, GA

Offline luvrbus

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Re: Uh oh! Engine knocking?
« Reply #1 on: February 08, 2014, 01:11:01 PM »
12 lbs at what rpm,any white smoke ?
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Offline Bryan

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Re: Uh oh! Engine knocking?
« Reply #2 on: February 08, 2014, 01:23:22 PM »
12 lbs at what rpm,any white smoke ?

basic idle so aprox 1,000 rpms, we haven't started it in about a month or 2, so there was some white smoke at the very beginning, but seemed to go away
Bryan
1996 Prevost XL
1967 PD4107-756
Toccoa, GA

Offline luvrbus

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Re: Uh oh! Engine knocking?
« Reply #3 on: February 08, 2014, 01:28:55 PM »
If it was only 12 lbs at 600 rpm which is the idle speed without the fast idle engaged on a cold engine you do have a problem any idea what the engine temp was ? 12 lbs is not bad for a hot engine at idle
Life is short drink the good wine first

Offline grantgoold

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Re: Uh oh! Engine knocking?
« Reply #4 on: February 08, 2014, 01:40:30 PM »
Have you gone back to the engine compartment and tried to take a video? This might help the experts on this board, watch the video and could perhaps be more specific in their help! 

Grant
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Offline Bryan

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Re: Uh oh! Engine knocking?
« Reply #5 on: February 08, 2014, 01:46:48 PM »
If it was only 12 lbs at 600 rpm which is the idle speed without the fast idle engaged on a cold engine you do have a problem any idea what the engine temp was ? 12 lbs is not bad for a hot engine at idle

I'm not sure what is considered a hot or cold engine. We had it running for about 10 minutes and then cut it off, Then we started it again to move it, it was during this time that the sound started.
Bryan
1996 Prevost XL
1967 PD4107-756
Toccoa, GA

Offline Bryan

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Re: Uh oh! Engine knocking?
« Reply #6 on: February 08, 2014, 01:47:46 PM »
Have you gone back to the engine compartment and tried to take a video? This might help the experts on this board, watch the video and could perhaps be more specific in their help! 

Grant

great idea! working on the video right now, will post it in 5 minutes.
Bryan
1996 Prevost XL
1967 PD4107-756
Toccoa, GA

Offline Ace

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Re: Uh oh! Engine knocking?
« Reply #7 on: February 08, 2014, 01:48:04 PM »
Sounds like a bad air compressor


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Lakeland, Fl. 33810
Prevost H3-40

Offline Len Silva

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Re: Uh oh! Engine knocking?
« Reply #8 on: February 08, 2014, 01:58:46 PM »
Is it a stick?  I had broken flywheel bolts sound just like an engine knock..

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Offline Bryan

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Re: Uh oh! Engine knocking?
« Reply #9 on: February 08, 2014, 02:01:57 PM »
Bryan
1996 Prevost XL
1967 PD4107-756
Toccoa, GA

Offline luvrbus

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Re: Uh oh! Engine knocking?
« Reply #10 on: February 08, 2014, 02:06:51 PM »
Sounds more like a clutch to me try depressing the clutch and see if it goes away
Life is short drink the good wine first

Offline Ace

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Re: Uh oh! Engine knocking?
« Reply #11 on: February 08, 2014, 02:12:43 PM »
Sounds louder on the fan side than on the clutch side


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Ace Rossi
Lakeland, Fl. 33810
Prevost H3-40

Offline luvrbus

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Re: Uh oh! Engine knocking?
« Reply #12 on: February 08, 2014, 02:18:02 PM »
Behind the fan there is a disk to drive the fan maybe the springs have broken and are rattling around in the housing check for slop on the fan
Life is short drink the good wine first

Offline TomC

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Re: Uh oh! Engine knocking?
« Reply #13 on: February 08, 2014, 03:57:42 PM »
Without a doubt-it is one of your Jake brakes firing off. Make sure the Jake brake is off. Good Luck, TomC
Tom & Donna Christman. '77 AMGeneral 10240B; 8V-71TATAIC V730.

Offline OneLapper

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Re: Uh oh! Engine knocking?
« Reply #14 on: February 08, 2014, 04:34:57 PM »
I agree with Tom, sounds like a Jake.  The oil pressure comes up and the Jake actuates. 
OneLapper
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