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    Thread: Cracked Valve Guides

    1. #1
      What's wrong with my car?
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      Cracked Valve Guides

      Ok, pulled the head off the son in laws 06 aveo, then pulled all the bent intake valves (it doesn't appear that any of the exhaust valves touched.....is that normal??). I had bought all the parts to repair the car.....except new valve guides. Every one of the guides is cracked.

      Do I have to replace them, or can I get by just breaking out the cracked parts & letting it go as is?
      thanks,
      Mike Sal



    2. #2
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      Ok so finally received the new valve guides. Can they be driven in & out with a mandrel & hammer, or should they be pressed in a shop press?
      thanks,
      Mike Sal

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      What's wrong with my car?
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      Seems I'm the only one on board that does engine work.......

      I dug thru an old thread by someone who also had to replace their guides & a big hammer was the trick. I made a couple of punches for removing & installing the guides on the lathe & it went really smooth. I cut the stem off of one of the bent valves to use as the small guide to ensure I didn't egg shape the guide on the way in.Name:  valve guide tools.jpg
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      I don't know why I have not seen this thread.

      you solved your problem, But I would test the head for the exhaust valves, I allowed my students to rebuild a daewoo 2.0 (save execII) and the exhaust valves looked ok, but we had four bent ones which was only evident out of the head.

      your lathe work looks nice


    5. #5
      What's wrong with my car?
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      I examined the pistons very carefully, before & after cleaning them, & could find no evidence of contact with the exhaust valves. Root cause of the failure was the tensioner (above the waterpump). The tab that bears against the spring broke, allowing the tensioner to unwind. The intake cam jumped time & crashed. The exhaust cam stayed in time & survived.

      I plan to install the head tomorrow. I may pull one exhaust valve from each cylinder just to double check.

      I put the cut off old stem into the mandrel so that the set screw goes into the groove for the keepers to ensure it stayed in place.
      Mike Sal

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      Quote Originally Posted by Mike Sal View Post
      I examined the pistons very carefully, before & after cleaning them, & could find no evidence of contact with the exhaust valves. Root cause of the failure was the tensioner (above the waterpump). The tab that bears against the spring broke, allowing the tensioner to unwind. The intake cam jumped time & crashed. The exhaust cam stayed in time & survived.

      I plan to install the head tomorrow. I may pull one exhaust valve from each cylinder just to double check.

      I put the cut off old stem into the mandrel so that the set screw goes into the groove for the keepers to ensure it stayed in place.
      Mike Sal
      Mike, you would be right at home in my Diesel Powered Equipment Class; if we can't borrow or Buy a tool we need, we MAKE IT! (for example, we cut down old Cylinder liners and tapered them to make Piston Installation tools, or turn pieces of Bar Stock on a Lathe to make Odd sized Clutch Installation Tools)

    7. #7
      Almost time to do my timing belt
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      Quote Originally Posted by Mike Sal View Post
      ...Root cause of the failure was the tensioner (above the waterpump). The tab that bears against the spring broke, allowing the tensioner to unwind. ....
      By "tab" do you mean the small piece of metal which has the outer pointer imprinted on it?

    8. #8
      What's wrong with my car?
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      Running like a top for the moment. Here's a pic of my son-in-law enjoying the sound of a dead car running again.

      Yes, it was the little section that once had the pointer on it. We made a discovery during the cleanup.....I found a small fragment of an exploded idler pulley laying in behind the battery box, and the old timing belt was a NAPA replacement......this car has been apart before. I wonder if the tensioner got compromised during the first failure & then failed after the belt change. Who ever did the work did a good job, as I didn't find any clues that it wasn't a virgin (like you normally can.....missing or scratched up fasteners, etc).

      Yes, as a blacksmith I've made a lot of tools over the years to do those odd jobs where nothing else will work.
      Mike SalName:  Joe On the Road Again.jpg
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    9. #9
      Almost time to do my timing belt
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      Quote Originally Posted by Mike Sal View Post
      ... Yes, it was the little section that once had the pointer on it. ...
      Glad you got it running again with no issues!

      If you still have the old part you'll see that tab is just an extension of the inner tensioner body. Although it does bear against the outer tensioner body, that's only before the tensioner is installed into the belt loop. Prior to installation it serves as the "stop" which prevents the spring from unwinding itself. But after the tensioner is installed into the belt loop and the WP is turned to tension the belt, this tab permanently moves away from the stop position. It essentially becomes a free-standing piece of metal just attached to the inner tensioner body, and doesn't bear on, or make contact with anything else. I can't imagine how this tab could break off without something else happening first, but also wouldn't expect a tension loss to occur if it did break off. However, if it did somehow break off with the timing cover in place, then the loose, pinballing tab would probably find a bad location fairly quick and destroy something else in the belt loop.

      I'm not saying all of this to nit-pick what you wrote, or argue about what happened to your Aveo. It's just that there have been a number of "mystery" timing belt failures posted here, and the waters are usually murky regarding what really happened to cause the problem. There was another failure just last week which was described as a tensioner "losing tension". But when I asked further, there was no reply confirmation that the tensioner spring broke.

      What's really going on with these belt problems is a concern to those of us who DIY this job, because if there's a defective part on the market, it would be great to identify it so that everyone could stay away from it. But OTOH, if it's something going wrong with the installations, that would be a big help to those who might avoid doing something incorrectly.

      When you opened up the timing cover for the first time, did you happen to attempt to turn the WP before loosening the 3 bolts? I'm asking because I believe the easiest installation mistake to make is leave one or more of those bolts loose, which then leads to the WP moving, tension being lost, and the belt jumping. So if you could move the pump without touching the bolts, that would point to a mistake on the install. Just trying to get more information about this chronic problem.

    10. #10
      What's wrong with my car?
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      The 3 w.p. bolts were tight when I removed them, I did look the pump over & saw no sign of fretting where it might have scooted. When I started on the car I assumed there would be a broken belt.....when I saw it was in one piece, I assumed I'd find an exploded idler/tensioner pulley....when they weren't broken, I was puzzled (I hadn't discovered that the car had been repaired before as yet). When I took the tensioner off and compared it to the new one, I found the piece broken off and the pulley was rotated to a different location than the new one.....this made me assume that I had found root cause. I didn't try to disect it to see why it was not in the same position as the new one.
      Mike Sal





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