Broken timing belt recovery question...
06-12-2008, 04:57 AM
#1
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Broken timing belt recovery question...
I am going to be looking at my wife's car (99 qtip, AHA, avant) soon. It appears that the timing belt broke. I am trying to understand what gets replaced and how, if the valves and pistons made contact. Assuming that *some* valves were bent, what do I need to replace? Obviously each bent valve, along with the stem seal and cam follower. What else do I need to replace for each valve that's damaged?
I'm not spending anything until I have surveyed the damage.
Also, should I pull the heads and have a machine shop evaluate them for things like distorted guides, or is that going overboard?
Thanks!
I'm not spending anything until I have surveyed the damage.
Also, should I pull the heads and have a machine shop evaluate them for things like distorted guides, or is that going overboard?
Thanks!
06-12-2008, 05:16 AM
#2
This is what I do:
Step one: Put a timing belt back on the engine and get it turning again.
Step two: Do a leak down test to find out which cylinders have problems and whether the bent valves are intake, exhaust or both. Most likely the bent valves will be exhaust valves. If you aren't equipped to do a leak down, do a compression test at the very least. Sometimes you get lucky and all the bent valves are in the same head.
Step three: Pull the head(s) and extract the suspected bent valves. Sometimes they are obviously bent, at other times it's hard to tell. An easy way to verify that the valves are sealing is to remove the cams, flip the head upside down and pour a thin liquid (gas, carb cleaner) on the cavity where all the valve faces sit. If the fluid drains, one of the valves is not seating. Figure out which one(s) it is.
Step four: Change the offending valves and their lifters. I would skip the valve seal. The seals are generally not a problem on these cars, they do not get damaged in piston/valve collisions, and they are not easy to replace. You may end up creating a problem rather than fixing one.
Step five: Put everything back together using new gaskets, head bolts, and timing belt parts.
Step six: Drive car.
BTW, when you reinstall the cams, sometimes the valves will not close properly because the lifters tend to hyperextend. Just slowly turn the cam by hand until all valves close completely when they are supposed to. You could verify that they are sealing with the liquid trick if you want to.
Step two: Do a leak down test to find out which cylinders have problems and whether the bent valves are intake, exhaust or both. Most likely the bent valves will be exhaust valves. If you aren't equipped to do a leak down, do a compression test at the very least. Sometimes you get lucky and all the bent valves are in the same head.
Step three: Pull the head(s) and extract the suspected bent valves. Sometimes they are obviously bent, at other times it's hard to tell. An easy way to verify that the valves are sealing is to remove the cams, flip the head upside down and pour a thin liquid (gas, carb cleaner) on the cavity where all the valve faces sit. If the fluid drains, one of the valves is not seating. Figure out which one(s) it is.
Step four: Change the offending valves and their lifters. I would skip the valve seal. The seals are generally not a problem on these cars, they do not get damaged in piston/valve collisions, and they are not easy to replace. You may end up creating a problem rather than fixing one.
Step five: Put everything back together using new gaskets, head bolts, and timing belt parts.
Step six: Drive car.
BTW, when you reinstall the cams, sometimes the valves will not close properly because the lifters tend to hyperextend. Just slowly turn the cam by hand until all valves close completely when they are supposed to. You could verify that they are sealing with the liquid trick if you want to.
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06-12-2008, 06:16 AM
#9
Best case scenerio, and generally pretty common is that the belt jumps...
...a bit on the bank one cam sprocket. It jumps enough to bend the six exhaust valves, which is enough to kill the engine.
06-12-2008, 07:44 AM
#10
AudiWorld Super User
All good advice. Sometimes it is easier to fill the inlet ports with fluid to find the bent valves..
this will show which are leaking although it will often be obvious by signs of contact between piston and valve.