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360 Knock at Idle

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Midnight Rambler View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Midnight Rambler Quote  Post ReplyReply Direct Link To This Post Posted: Oct/19/2017 at 9:56am
Originally posted by Brynjaminjones Brynjaminjones wrote:

Thanks guys. What's the likelihood of it being a flex-plate? I figure I should check before doing anything else. Is it just a case of removing an inspection cover?

As for running on propane, it's actually reasonably common over here in the UK. Our 4.0 ZJ has been on it with no engine problems for the last 75,000 miles (now at ~145k).
Lots of guys in Aus seem to run these AMC V8s on it too.
I think you're right though, that it can cause issues on a lot of engines.
On those where it does cause mechanical problems, my research shows that it generally seems to be top end though, such as causing valve seat recession.

If my problem was caused by a bad main, would I have noticed a change in oil pressure?
A bad flexplate would probably cause a vibration.  I would think if it were compromised to the point of making a noise that the car wouldn't be driveable.

'66 American 440 Convertible 290/WC M-37/AMC 20 3.15
'97 Jeep Wrangler 4.0 5sp
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Brynjaminjones View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Brynjaminjones Quote  Post ReplyReply Direct Link To This Post Posted: Oct/19/2017 at 2:26pm
Cool, having listened to it again I don't think that is the cause.

I took the belts off tonight and started it cold - turns out the noise does seem to be there when cold after all.
Have a listen, it sounds a bit more ticky today:

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Post Options Post Options   Thanks (0) Thanks(0)   Quote vinny Quote  Post ReplyReply Direct Link To This Post Posted: Oct/19/2017 at 5:07pm
Sounds like valves to me.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote limachine Quote  Post ReplyReply Direct Link To This Post Posted: Oct/19/2017 at 7:49pm
Yeah I hear a valve tick. Maybe an exhaust leak. Hold your hand over the exhaust pipe and temporarily block it to see if the tick gets louder. Wear an insulated glove or use a rag, don't get burned. Try it cold, then warm. If its an exhaust leak, you'll force the air back up the pipe and out the leak. Just hold your hand over the pipe for a few seconds, let off, cover it again a few seconds, back and forth until you're sure it's not an exhaust leak.

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Post Options Post Options   Thanks (0) Thanks(0)   Quote Lyle Quote  Post ReplyReply Direct Link To This Post Posted: Oct/19/2017 at 11:21pm
So yes the knock changes frequency and pitch when you have taken forces off the front of the crankshaft.
If it is exhaust there should be no change, belts on or off.
That stated, now it does sound higher up and more like a valve noise but the video is just from one side and before the knock was just as loud at the bottom of the engine?
I would be pulling the heads in place and inspect valves/valve train and pistons. Still just guess work at this point.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Brynjaminjones Quote  Post ReplyReply Direct Link To This Post Posted: Oct/20/2017 at 3:42am
Thanks for the advice guys. I don't have time at the moment to look at this myself, so will be sending it to my local Jeep specialist as soon as possible.

Lyle, my thinking is that the change in pitch and frequency is probably more to do with the fact that this was a cold start rather than warm, although I've not ruled out the possibility that I have a knock when warm and a lifter issue when cold!
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Boris Badanov Quote  Post ReplyReply Direct Link To This Post Posted: Oct/21/2017 at 2:50pm
If it knocks only at half normal engine idle speed......
that's normal!

I still suspect a small engine exhaust leak.

Converter bolts are worth a look.

If loose, blue locktight them and torque them to spec.

I really like the no belt test, but not for too long.
Awesome idea there.

Piston slap, wrist pin slap, main bearing and or timing
chain slap can be potential causes.

Avoid an easter egg hunt, stay with the cheep stuff first.
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