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    Thread: Need advice on rod bearings

    1. Member Calimus's Avatar
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      05-31-2010 02:50 AM #1
      While I'm not positive that my rod bearings are bad just yet (visual inspection has not been done), they are suspect and I was doing some pricing. I see there are the OEM's avail all over the place and then some that are .25mm oversized. So, the question is, when is there a need for the .25mm oversized set? I'm guessing when there is a fair ammount of ware, but what are the limits and what is the best way to measure for the limit?

      I've never had to get this deep into a motor, so, sorry for the newb'ish questions.

      An if anyone wants to chew on the main issue with me, the problem is as follows.

      9a 2l 16v

      Engine knock at idle after a few min of engine warming up. Sounds like it's coming from the #1 cyl area of the block using the screwdriver to the ear method.

      When the engine is rev'd or is above idle, the knock is gone. Oil pressure is also suspect on the pump side, but alas, I need to check that as well. So, if anyone has any other ideas besides, spun rod bearing or crapped out oil pump, let me know.

      Thanks in advance.

    2. Member Rocco_crossing's Avatar
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      05-31-2010 03:30 AM #2
      There is a thing called "plastigage" for determining if you need oversized bearings. Basically you take one old bearing out, put this in the cap, torque down. I can't remember if you turn the motor over once or not. Then, remove cap and "measure" how much the stuff squished. Then you know if they need replacing or not.
      Quote Originally Posted by Ice Karl
      And let consequences fall where they may. Roll dice and accept
      outcome...

    3. 05-31-2010 03:56 AM #3
      The .25mm rod bearings are for cranks that have been ground .010" undersized. You want to replace std bearings with std & .25mm with .25mm etc. The bearing size will be stamped on the shell.

      Get a mechanical oil pressure gauge to see where you are at. If you have low pressure, then drop the oil pan. Check the oil pump, rod bearings & main bearings. If they all look good & are in spec, than you have a bad int. shaft bearing. If so use DuraBond, as they are the best & don't need to be reamed to size.

    4. Member Calimus's Avatar
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      06-01-2010 02:57 AM #4
      Thx guys. I did find that the .25mm are for re-ground cranks after some research. I have a mechanical oil pressure guage around somewhere, just need to locate it. Let the fun begin.

    5. Member Lord_Verminaard's Avatar
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      06-01-2010 09:52 AM #5
      Plastigauge it before you buy new bearings. You can get it at Advance auto, but you have to ask for it, since it's not usually out on the floor.

      You do not turn the engine over when using them, apply the strip, torque, then un-torque and measure.

      If the bearing clearance is all within spec, just re-use them. I could have saved myself $50 on bearings during the diesel rebuild since the old ones were in spec.

      I WOULD however check the crank thrust end-play- those thrust washers can get messed up with the clutch being the way it is on an 020 and from people holding in the clutch at a stoplight and/or pushing in the clutch to start the car. Don't use the integrated thrust bearings either, if you need a thrust clearance wider than those bearings are you are screwed, where the separate thrust washers can come in wider sizes.

      It takes a lot of abuse to mess up the bottom-end of a VW engine.

      Brendan
      '81 Scirocco 'S ...
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    6. Member Calimus's Avatar
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      06-01-2010 11:54 AM #6
      I'm fairly certain it's the rod bearings. A bit of background.

      I got the 9a a few years back, checked it out, all was well. Used it in my rocco when I did a digi-I conversion last year. Due to some wiring harness mishap, the system was dumping fuel like a mofo and thinned the oil down bad. When I heard the knock, I parked the car. Might have put 700 miles on the engine before I heard the knock.

      Got a new digi-I harness and rewired it myself. Changed the oil, fired it up, knock was gone untill the engine warmed up a bit, then it was back. It's only at idle which makes me think that the rod bearing might not be in horrible shape. Also, the reason I'm thinking rod bearing is that the knock isonly coming from #1 cyl area. Checked it several times to make sure it wasn't coming form the others. But then again, there are several things it can be.

      I'll definitely pick up the plastiguage and check that as well as check my oil pressure. Thanks for all the info folks.

    7. Member
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      06-01-2010 01:09 PM #7
      Non-invasive procedure for confirming/isolating rod knock:

      - loosen plug wires so that they're just resting on the spark plugs
      - start engine
      - lift/return plug wires until the knock noise changes/goes away
      - if the noise never changes or goes away you don't have a rod knock

    8. Member JPX's Avatar
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      06-01-2010 05:22 PM #8
      When I went after my headgasket change, I decided to change rings and rod bearings as well. Knowing that the crank had not been ground, I went with the 0.0 (STD) rod bearings. A measurement with Plastigauge would confirm this in your case.

      I had bearing wear, but more importantly I had some scoring.



      I did not grind the crank further since the journals were in good shape - a sign the bearings took one for the team.


      And my oil pressure is definitely higher on the gauge than before the rings/rod bearings change.

    9. Member Calimus's Avatar
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      06-01-2010 06:22 PM #9
      Quote Originally Posted by Anson86-8v View Post
      Non-invasive procedure for confirming/isolating rod knock:

      - loosen plug wires so that they're just resting on the spark plugs
      - start engine
      - lift/return plug wires until the knock noise changes/goes away
      - if the noise never changes or goes away you don't have a rod knock

      Didn't even think of that, Anson, thanks a bunch. Hows the Durocco these days sir?

      JPX - thanks for the visuals, gives me a much better idea what I'm looking for.

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      06-01-2010 11:01 PM #10
      Bearings are supposed to wear before the crank, it's when someone lets things go to long and the softer bearing metal wear completely away and then the crank rides on the steel backing then the crank goes away. I have replaced the rod bearings in a number of different engines with low oil pressure and that has always solved the problem.

    11. Member psykokid's Avatar
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      06-02-2010 12:07 PM #11
      PG (g60 motors) have a nasty tendency to be a bit more hard on rod bearings than most 1.8L motors due to the shorter stroke. That being said, when my bearings were due to be replaced i could only hear the rod noise on deceleration of the motor. At idle and on the throttle there was no noise.

      Since you have the noise at idle and not speed I would check the oil pressure first and foremost. If your oil pressure is out of whack from published specs then drop the pan and pastigauge the bearings to check for wear. While you are there you might as well check the mains for good measure. If the bearings are good then check the IM shaft as mentioned above, those bearings do wear and make some funky noises when they do. That would also throw off your knock sensor since the IM shaft is really close to the mounting boss for it. If all the bearings are ok then your oil pump would be suspect.

      If your oil pressure is kosher then I'd look at the lifters. They can get sticky or collapse and make a hell of alot of noise. Usually though, if a lifter is on its way out it will make a lot of noise at idle but when the revs go up so does the oil pressure and makes the lifters expand more..

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