No compression after timing belt replacement

Tiny
LADYRHONDA
  • MEMBER
  • 1998 LEXUS GS 400
  • 150,000 MILES
I replaced the timing belt in my GS 400 and the car won't start now. It turns over, it even started once, but it shuts right down every time. I was told that I could've bent the valves so I did a compression test and found that I have no compression on one whole side. So then I checked to see if all the valves were working and they are. How can I have no compression on one side and all the valves be working? And I've checked and rechecked timing marks but car still won't run. Help !
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Saturday, June 15th, 2013 AT 5:24 PM

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Tiny
CARADIODOC
  • EXPERT
Think of the valves as giant nails with big heads. It's the heads that are bent. You're just watching the stems go up and down. That's not the parts that seal. To see the damage you have to remove the head and flip it over.
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Saturday, June 15th, 2013 AT 9:21 PM
Tiny
LADYRHONDA
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Ok so say it's the valve heads that are bent, I still don't understand how all four on one side are dead (no compression). If they were bent by the pistohelprom the timing being off It would only damage two, right? Am I missing something here? What would cause all 4 to die? What do I need to do to get the car on the road again? Any help is greatly appreciated !
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Saturday, June 15th, 2013 AT 10:35 PM
Tiny
LADYRHONDA
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Ok so say it's the valve heads that are bent, I still don't understand how all four on one side are dead (no compression). If they were bent by the piston from the timing being off It would only damage two, right? Am I missing something here? What would cause all 4 to die? What do I need to do to get the car on the road again? Any help is greatly appreciated !
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Saturday, June 15th, 2013 AT 10:47 PM
Tiny
CARADIODOC
  • EXPERT
Your engine has four camshafts. Most likely just one is mistimed. That one will run all the intake valves or all the exhaust valves on one side of the engine. Each cylinder is identical in that which ever valve is open when the piston reaches top dead center will be the same for the other three cylinders too.

You'll usually be able to see the damage after the cylinder head is removed, but there's two tests that will identify which valves are bent. While the compression test tells you there's no compression, a cylinder leakage test will tell you why. You force compressed air through the tester into the spark plug hole while the piston is at top dead center. The tool will show the percent leakage but in this case we know it's 100 percent. The next step is to listen in four places for the escaping air. For a bent exhaust valve you'll hear it at the tail pipe. For the intake valve you'll hear it at the throttle body or air filter box. With worn piston rings you'll hear the air at the oil cap or dip stick tube, and with a leaking head gasket you'll see bubbles in the radiator or coolant reservoir.

The second method is useful when the valve leakage is too small to be seen easily. With the head removed and supported with the intake runners up you fill them with a liquid, then watch if the valves get wet. If they don't show signs of leakage within about five to ten seconds, flip the head over so the exhaust runners are up, then fill them the same way. We normally use parts cleaner but water can be used too. Brake parts cleaner and carburetor cleaner are not real good choices because they're too thin and they're designed to sneak into tight places. Those two chemicals will make acceptable valves look like they're leaking badly.
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Sunday, June 16th, 2013 AT 12:20 AM

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