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Old 09-18-2019, 08:30 PM
v8volvo v8volvo is offline
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Join Date: Jun 2009
Location: Montana, USA
Vehicle: '86 745, '83 764
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If the timing belt broke then internal damage is guaranteed. No question about it, there is no chance of escaping piston and valve collision when this happens. The only question is how bad the damage is.

In these engines it is common for the camshaft to shatter when there is a timing belt failure. That's bad news since the cams are hard to find, but can be good news since the breakage of the cam helps limit impact damage to the bottom half of the engine, kind of like a safety valve effect. Damaged pistons, bent rods and cranks, and other theoretically possible consequences are quite rare. Often you can just repair or replace the cylinder head and get it going again without too much work. So in that sense, yes, you can put one back together after a broken belt and the engine can survive just fine in the long run. But there is no possibility that you'll just be able to put another belt on and have it motor on like nothing happened. Wish we could say otherwise.

If the motor was recently rebuilt and this happened after such a short mileage, that sometimes means the reason for the timing belt failure was not the belt itself, but instead was a slipped crankshaft dampener. This is always the result of an attempt to cut corners by the person who assembled the engine, trying to install it without the necessary locking tools to achieve the extreme high torque called for on the front crankshaft bolt. Unfortunately, if the dampener slips, it can mean worse problems since it sometimes eats up the front of the crankshaft and its keyway, and can make for more sustained piston to valve contact before it finally strips or snaps the timing belt, so the damage to the head and pistons in one of these cases is sometimes more severe.

The first thing to do would probably be to check on the timing belt and see what kind of damage it shows -- clean break or a lot of stripped teeth? Do all parts (water pump, idler, cam and crank) in the belt path turn freely or something seized?

Then see if the cam broke. You can usually tell this even without removing the valve cover by grabbing the front cam sprocket and seeing if it can move in and out axially. Or you can pull off the valve cover and look. If you do that, check for spider cracks in the tops of the lifters also. That will tell you how serious of an impact you're looking at. Finally, once you have the head off, you will measure the protrusion of the piston crowns above the block deck, which will determine if there was any damage to the rods or crank or pistons themselves and tell you whether you need to open up the bottom of the engine or can just fix the head.

Sorry for the bad news, broken timing belts on these engines are not much fun, as many folks here can attest. But the good news is that it's all repairable and the work is not difficult.

You have an LT40 here in the US? How did you get it? Photos?
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86 745 D24T/ZF 345k lifted 2.5"
83 764 D24T/M46 155k
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