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Non-interference engine 86 300zx?
I have a 1986 300zx non-turbo 2+2. The timing belt just broke and my local mechanic is telling me that I have to replace the entire engine as it is not a non-interference engine. The timing belt is definitely broken but when the engine turns over there are no strange noises. I suspect that it is a non-interference engine and so just the belt needs replacing. Does anybody know anything about this? Thanks for any help.
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The belt drives the cams which open and shut the valves. When the belt broke, any valves that were open, remained so. The inertia of the engine's rotating mass would cause the crank to continue spinning a round or two, thus moving the pistons up and down. When the piston(s) went up on the cylinder(s) that had valves still open, the piston(s) hit the valve(s). Normally when that happens, something bends or breaks. You hope it's valves because they're not as difficult and expensive to fix. Sometimes, the valve pokes a hole in the piston. That's bad, real bad.
All of this is relative to the engine speed when the belt broke. Higher RPMs would, of course, make matters even worse because the engine would continue rotating longer, thus doing more damage. A compression check will tell you which cylinders, if any, are damaged. You may as well resign yourself to the fact, the heads (at the minimum) will have to be R&R'd unless you are the luckiest person in the world. |
Non-interference 86 300zx
Thanks for the reply. I was stopped in traffic when it happened so I'm keeping my fingers crossed and hoping there's no top end damage. Your comments are appreciated.
Originally Posted by johnZboy
The belt drives the cams which open and shut the valves. When the belt broke, any valves that were open, remained so. The inertia of the engine's rotating mass would cause the crank to continue spinning a round or two, thus moving the pistons up and down. When the piston(s) went up on the cylinder(s) that had valves still open, the piston(s) hit the valve(s). Normally when that happens, something bends or breaks. You hope it's valves because they're not as difficult and expensive to fix. Sometimes, the valve pokes a hole in the piston. That's bad, real bad.
All of this is relative to the engine speed when the belt broke. Higher RPMs would, of course, make matters even worse because the engine would continue rotating longer, thus doing more damage. A compression check will tell you which cylinders, if any, are damaged. You may as well resign yourself to the fact, the heads (at the minimum) will have to be R&R'd unless you are the luckiest person in the world. |
I had a belt break in my Eclipse 97 at idle, it was makin noises and I was gonna pull in a parking lot like 100 feet up the road and then pow, when I hit the gas it broke. Luckily, not a single valve was bent or anything. All I really had to do was change the belt and get goin again...but the dumbass mechanics messed something up...and to make a long story short, the next night I was goin home (after it got outta the shop) and at 80mph, the belt broke again...had to get a new head from a junkyard that time :)
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