What does a timing chain sound like when it breaks?

nrene

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Dec 16, 2006
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Lovettsville, VA
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So I was dropping a package @ UPS, and the truck died while idling. No fuss, just idling, felt a 'miss' and it died.

Tried to start, and the starter wouldn't even turn it over.

Towed it home on a flatbed, and tried to start it one more time, and it turns, but sounds VERY BAD inside... like a chain being ground up (or like a cement mixer in a way)...

122k on it...

Could it be anything else?
 

DarylJ

Well-known member
Apr 3, 2011
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Doylestown, PA
Sure it could be something else. You could have lost an oil pump and ate your bearings or any number of other bottom end kinds of things.

Drain your oil and see if its a liquid or a semi-solid sparkling mess, or if you have a moccachino in there.
 

thejaw77

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Mar 27, 2011
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loveland
You will notice a rattling noise underneath your vehicle's hood when you start it. If the chain is loose, you may hear a loud, knocking sound from the engine. It may backfire or misfire.
 

nrene

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Dec 16, 2006
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Lovettsville, VA
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thejaw77 said:
You will notice a rattling noise underneath your vehicle's hood when you start it. If the chain is loose, you may hear a loud, knocking sound from the engine. It may backfire or misfire.

I haven't let it turn over long enough to start, it sounded bad enough, I didn't want to grind it up more than it was...

I'm thinking about swapping with my other motor and then taking a peak inside this one and seeing if it's fixable within reason.
 

jafir

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May 4, 2011
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Northwest Arkansas
I'd try to confirm how bad it is broken first. And if it's just a chain, that shouldn't be too hard of a fix.

You won't have compression if the chain broke. I'd pull a spark plug or two and check compression. On some cars you can just look down through the oil filler cap and see if the rocker arms are moving, but I just check on my 99 and there is something blocking the view.
 

nrene

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Dec 16, 2006
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Lovettsville, VA
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I'm going to take a look at what I'm working with, likely on an engine stand, before I turn it over again...

I'm not sure checking the compression is going to help, it needed the heads done anyway, so I doubt that would tell me much.
 

robertf

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Jan 22, 2006
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354
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they always were running when the chain breaks.

Trying to start it again can make the difference in a few new valves or a complete set of valves and pistons
 

DarylJ

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Apr 3, 2011
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Doylestown, PA
robertf said:
don't try to start it. The valves are hitting the pistons

While I have not physically checked this, there is nothing in the overhaul manual or anywhere else that leads me to believe that a 4.0 or 4.6 is an interference motor. The original Buick 215 wasn't, and I don't believe that has changed.

Do you have a source that says otherwise?
 
DarylJ said:
While I have not physically checked this, there is nothing in the overhaul manual or anywhere else that leads me to believe that a 4.0 or 4.6 is an interference motor. The original Buick 215 wasn't, and I don't believe that has changed.

Do you have a source that says otherwise?


Darryl:
There are some here who have much experience with these engines. Sadly, some of that experience includes having put a timing chain on wrong and now there is a pile of broken rocker shafts, bent valves and badly bruised ego.

If you disbelieve everything else you read here, please believe me when I say that these are most definitely interference engines.

Robert, they don't always break when they are running. The highest torque is applied at start-up when everything is static. Freelander chains seem to break on stat-up far more often than while running.
 

jafir

Well-known member
May 4, 2011
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Northwest Arkansas
ptschram said:
If you disbelieve everything else you read here, please believe me when I say that these are most definitely interference engines.

Yeah, I'll take word of you and Robert on the interference of course, it's just always been my experience with OTHER interference engines that if it was running when the chain or belt broke, that the next step is pulling the heads off anyway.

So is the 4.6L interference also? I notice that is has nice dished pistons to keep the compression ratio close to the same as the 4.0L
 

DarylJ

Well-known member
Apr 3, 2011
440
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Doylestown, PA
ptschram said:
If you disbelieve everything else you read here, please believe me when I say that these are most definitely interference engines.

It's not that I have a problem believing a consensus of people here, but when I her something from one person that doesn't add up (why do the factory tear down procedures not indicate that it is interference like every other factory manual for an interference motor I've seen - it's kind of important information to know during a build) I like to be sure.
 
DarylJ said:
It's not that I have a problem believing a consensus of people here, but when I her something from one person that doesn't add up (why do the factory tear down procedures not indicate that it is interference like every other factory manual for an interference motor I've seen - it's kind of important information to know during a build) I like to be sure.

The 3.5 litre is also an interference engine. You might wanna go back and look at that Buick 215 because I suspect you'll find it was an interference engine.


As for why the FSM doesn't say anything, I don't know that I've seen it in other FSMs either.

I tend to assume an engine is interference as that's the safest assumption.