What is causing me to go through motor mounts?
I have a '95 Jeep Cherokee 4 by 4 with 51,000 miles. It has the 4.0 liter
engine. The three motor mount bolts that go into the block sheared off on
the passenger side. They had to drill out the bolts. They put in a new
motor mount, too. The bolts on the driver's side were OK and tight. Six
days and 900 miles later, I went slowly over a railroad crossing and the
same three bolts sheared off again. What's going on? I don't drive hard,
and I don't go off-road. I've never hit a curb, stump or rock. This time,
it took a chunk out of the block, so it will need some welding. Why did it
take 50,000 miles for the first set of bolts to go and only a week for the
second set? What's going on? -- Neal
TOM: Neal, you poor schlemiel.
RAY: Here's what I think happened. For some reason, during that first
50,000 miles, those bolts started to come loose. Why? I don't know. Perhaps
they weren't tightened properly at the factory. Or maybe the holes were
never drilled and tapped correctly. The bolts should not have come loose on
your car, but they did.
TOM: The three bolts go through a bracket, and with one or more of the
bolts loose, that bracket slides up and down and has a shearing action --
acting like a knife against those bolts. Eventually, a bolt got sheared
off. That weakened the mount even further, making the shearing action even
more intense, and eventually the second and third bolts gave way, too. And
when the third one broke, the motor fell down and you noticed it.
RAY: And the reason it broke again a week later is because the repair was
not as good as the original. When you drill out broken bolts, you can't
always drill as deep as you'd like (especially when you're drilling into
somebody's engine block). So you often end up using shorter bolts, which,
in this case, weren't up to the job. Or maybe they neglected to use
"hardened" bolts. In any case, as you discovered, it didn't take much to
shear off those inferior bolts the second time.
TOM: It's possible that they can weld it all back together and make it
work. But it's also possible that the whole thing is going to be even
weaker still after another repair attempt. So if the next repair fails, the
next step would be a new engine block.
RAY: And in my opinion, DaimlerChrysler Corp. ought to pay for it. This
shouldn't happen on a 1995 car with only 50,000 miles on it, and they'll
probably agree with that. I'm not aware of any preventative maintenance
that Chrysler requires on the motor mount bolts. So it would seem as though
you're absolved of all responsibility. It seems to us clearly a
TOM: I'd make a case to your dealer and, if necessary, the company's zone
representative. Make a deal with them. Let them take a crack (no pun
intended) at welding it, but if it doesn't work, get them to agree to buy
you an engine block. Good luck, Neal.
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Copyright (c) 1999 by Tom and Ray Magliozzi and Doug Berman