3.3L V6 - What if I ignore timing chain rattle?

I have a 1990 Dodge Grand Caravan with the 3.3L V6 engine and 130,000
miles on it. I hear a a rattling noise at idle which goes away as the
engine speed is increased past the idling speed. Per another thread,
it was basically decided that it is likely the timing chain.
My question is what if I ignore it? I know at some future point it
will break (any thoughts as to how much further down the road?) but
aside from the rattling noise, is there any reason I can't just ignore
it? Does the rattling chain damage anything else (timing chain cover?)
When the chain finally does jump/break, will it damage anything else?
Is this an interference engine / will the valves be damaged?
Thanks,
Eric Kotz

 

Normally an 1/8 of an inch stretch of a timing chain is considered worn
out. If the chain is exsessively loose it may cause the cam sprocket teeth
to break and cause problems. However there are some on here that let there
customers wait untill the chain breaks before replacing em. I believe in
preventive maintenance.
Glenn Beasley
Chrysler Tech

 

Well, I know the chain is worn, I guess I'm asking what is the
potential damage to the engine when it finally does go?

 

Chain-timed engines are almost always interference types. If the chain
does jump or break, you'll at a minimum bend a few valves, at worst snap
off a few valve heads and maybe knock a hole in a piston or cylinder head.

130k is pretty short life for a timing chain assuming both cam and crank
sprokets are metal (most are nowdays, though back in the 70s a lot of
engines got nylon cam gears to reduce noise and they generally wore out
in less than 200,000 miles). But if its rattling, its probably best to
replace it.

 

AACUDA????

 

Chain or gear breaks. engine damage will occur

 

I've always wished there was some list somewhere for reference as to
which engines "bend valves" (interference engines).
You say that "almost all chain-timed engines are interference types."
I'm curious as to why that would be.
Are pretty much all belt-timed engines OHC? And if so, how would that
figure in to whether they're interference engines or not?

 

I can't imagine who told you this, but it must be one of the disreputable
types in my killfile. It's not so.

 

The comment about all chain timed engines being interference types was
from a poster just a few posts before mine.
And that would be nice if one could automatically know if it was an
interference engine just by determining if it used a timing chain vs.
belt.
I had never heard that either, but it piqued my curiosity in that so
many OHC engines are belt timed while pushrod engines are chain--two
distinctly different types of engines. Meanwhile, some engines are
interference types while certain others are not, but I was never sure
why that was or what made the difference.
So anyway this got me wondering if one of the main criteria for
whether or not an engine is an interference type is whether it's OHC or
pushrod.
Given the catastrophic damage an interference engine sustains from a
failed timing gear, why are these engines not deemed undesireable and
thus phased out or redesigned (since so many other engines are
non-interference & provide satisfactory performance)?

 

Because if all other things are equivalent, interference design engines can
generally produce higher power output. How many consumers actually know to
ask the salesperson if the engine is an interference or non-interference
design? (versus) How many ask about the engine's output in horse power?
If the consumer actually knew to ask and figured in the timing belt, water
pump, etc. replacement cost every few years then in my opinion there would
be much more demand for chain driven, non-interference engines.

Also, with regard to chains versus timing belts, about all you can really
say is that chains generally last longer and require less maintenance during
the engine's useful life. A belt is generally easier to change since it
does not require complete access to the internals of the engine, but can
still be very costly since you need to remove all the periphery, covers,
etc. to gain access

Bob

 

James Goforth wrote:

No. Many OHC engines ARE interference, and there are a number of pushrod
types that are not. I was commenting on the fact that *most* of the
60s-80s chain-timed Mopar pushrod V-type engines are interference
engines. Interference allows easier optimization of the combustion
chamber shape, keeping an engine non-interference puts a minimum
piston-to-open valve clearance constraint that either forces a lower
compression ratio or requires big valve reliefs in the piston, which can
affect combustion dynamics such as detonation. Thats why today you see
more and more interference engines of ALL types (OHC, pushrod,
belt-timed, and chain-timed) because of the requirements for better and
better combustion control to meet emissions requirements.

 

I don't completely buy it, and there are counterexamples. Subaru, for
instance, reworked their 2.2, 2.5 and 3.0 litre engines in 2000 to make
them NON-interference.

 

Perhaps their warranty costs were eating into whatever benefits they
realized from the interference design. My understanding is that valve
reliefs in the pistons provide places for hydrocarbons to "hide" from
the combustion process, resulting in higher emissions.

--Geoff

 

That's because its a general trend, not an absolute

And Chrysler gave up on keeping the 3.5 non-interference and made it
interference in '98 (or was it '99?) when they switched it to an
aluminum block and ooched the compression up again to give it 250
horsepower instead of 215. Counter-counterexample

 

Geoff wrote:

I also keep reading that the sharp edges around reliefs can become
detonation sources. I've also often wondered if valve reliefs are
always effective. I can imagine them filling up with carbon as an engine
ages, and then when the belt breaks and the valve suddenly tries to
occupy a carbon-filled relief that it hasn't occupied in the previous
100,000 miles, it bends in spite of the relief.

 

Thanks to the good folks at Gates, your wish has been granted (at least for
timing belts)

http://www.gates.com/downloads/download_common.cfm?file=GatesTBR.pdf&folder=brochure

Ken