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Low end rattling - 100 motor

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healeynut

healeynut

Jedi Knight
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Hi -

Ok, this is really for my Atlantic but it's the same motor at the BN1/BN2 so here goes.

My Atlantic when at idle has a pretty distict bottom end rattle/metal banging noise. It sounds distinctly like a spun bearing of some sort.

My mechanic dropped the pan and I had a very good look at it... all the rod bearings are in good shape, so the noise isn't coming from that.

Haven't dropped the mains yet but I was wondering if I spun a main would it make the rattle noise I talk about? Can I drop the main caps without pulling the motor out? Sorry we are halfway through the job and I was hoping some of you may have sage advice.

If it turns out this rattling/clacking is not from the bearings, do you have any other suggestions of where I should look? Gudgeon pins? Rocker Arms? I'd prefer not to pull the head if I can avoid it.

Thanks!
 
Hi Alan,
I don't know what a "spun" main bearing sounds like. I would expect it to cause low oil pressure & definitely, crankshaft damage.

The main caps are a press fit in the block & would be very hard to remove with the engine in situ.

A couple of possibilities to check first are loose flywheel bolts & the front pulley. Also a very loose timing chain would make a rattling noise shortly before it broke & exited through the timing cover.
D
 
So many things inside of an engine can create a rattle
Not necessarily a "spun" bearing but loose worn rod bearings can deffinately cause it. I would plastiguage them for clearance,
Same with main bearings they can rattle if worn to excess.
The timing chain can cause a rattling sound if excessivly loose.
Worn Wrist pins {gudgeon pins} bushings can cause it {usualy on acceleration or deceleration} But not always.
A broken ring or piston will cause ratteling {usualy on acceleration or deceleration} But not always.
Worn Thrust washers Or bearing are another thing to check. {excessive crankshaft end play}
Pulleys loose on thier shafts can sound horrid.
Bad alternator/generator bearings can sound bad as well.
The rocker assembly, worn parts there can sound off too!
Flywheel and clutch parts {throwout bearing}.
What it amounts to is the sound can travel and seem as if it is coming from a specific area when it actually is not.
Typicaly a "Spun" bearing will affect the oil pressure {Not always}
One thing a "Spun" bearing will most deffinately do is eventualy sieze up, and possibly cause other majior damage.
What are your O.P readings HOT at idle? And at speed?
I rebuilt an engine and during teardown found a 1/4 nut inside the combustion chamber that had been "bouncing around" causing a horrid noise. It really did a number on the piston and valves in that cylinder too!
If your "Noise" goes away with slight acceleration {No load}
the timing chain MIGHT be worth taking a look at.

Just my HUMBLE opinion
 
Thanks guys, this is really helpful. On second thought I wonder if it's something else.

Yes, oil pressure while hot is still normal (25 psi ++) so spun bearing it probably isn't.

The rattling/clacking seems to occur during idle only, so - would this be the timing chain or possibly the water pump?

I should say the noise does seem to be coming low down and inside the motor, that's why we thought the bearings... but if a loose timing chain gives the same noise I will have a look there.
 
Used to get that death rattle in the old landrover slugging thru sand when the revs got down to about 5-600, just that a fuel motor doesnt like lugging that low like a diesel does
 
What is the condition of the oil. Any sparkleys in suspension?
 
The oil is old (I just got the car haven't driven it much) and dirty, but there are no sparkles in there. I guess that means no spun bearing.
 
ooops spoke too early. oil has silver in it... but not copper. Only can be from the main or rod bearings, everything else is copper. Also means wear hasn't been too much, so either a scored bearing or spun bearing likely.

/bcforum/images/%%GRAEMLIN_URL%%/wall.gif
 
BobHorvath said:
What is the condition of the oil. Any sparkleys in suspension?
Click to expand...


That sure be proof of the puddin huh ---Keoke-- /bcforum/images/%%GRAEMLIN_URL%%/lol.gif
 
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