New timing belt or new mechanic? Maybe both.

Dear Car Talk | Oct 01, 1992
Dear Tom and Ray:
Phyllis
RAY: I think the problem is your mechanic, Phyllis. He may have installed the timing belts incorrectly.
TOM: When he installed the first belt, he may have either over-tightened it, or under-tightened it. That would explain why it broke again so soon.
RAY: It's possible that incorrect installation is causing the lousy performance, too. The timing belt is a notched, rubber belt which connects the crankshaft to the camshaft. The camshaft, in turn, controls the opening and closing of the valves. If these two shafts aren't lined up exactly right when the timing belt is installed, then the valves won't open and close at the right time.
TOM: That would cause the car to run lousy all the time. Of course, since this is an '86 Renault, you're probably accustomed to it running lousy all the time. So you wouldn't have noticed any difference, except under the most extreme conditions...like climbing steep hills.
RAY: But more likely, the lousy performance is the result of damage done to the cylinder head when the first belt broke. If the cylinder head was damaged in that incident, the valves could be sticking, and that would also cause the performance problems you describe.
TOM: In that case, your mechanic is also at fault for not noticing it. And if that's true, you need a new mechanic AND a new cylinder head. Good luck, Phyllis.
Phyllis
RAY: I think the problem is your mechanic, Phyllis. He may have installed the timing belts incorrectly.
TOM: When he installed the first belt, he may have either over-tightened it, or under-tightened it. That would explain why it broke again so soon.
RAY: It's possible that incorrect installation is causing the lousy performance, too. The timing belt is a notched, rubber belt which connects the crankshaft to the camshaft. The camshaft, in turn, controls the opening and closing of the valves. If these two shafts aren't lined up exactly right when the timing belt is installed, then the valves won't open and close at the right time.
TOM: That would cause the car to run lousy all the time. Of course, since this is an '86 Renault, you're probably accustomed to it running lousy all the time. So you wouldn't have noticed any difference, except under the most extreme conditions...like climbing steep hills.
RAY: But more likely, the lousy performance is the result of damage done to the cylinder head when the first belt broke. If the cylinder head was damaged in that incident, the valves could be sticking, and that would also cause the performance problems you describe.
TOM: In that case, your mechanic is also at fault for not noticing it. And if that's true, you need a new mechanic AND a new cylinder head. Good luck, Phyllis.
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