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Rebuild - What to Replace and What Not?


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I have looked all over and cannot find a good accurate resource out there. I recently decided that it was time to tear into my 1990 DR350S. (suzuki) it would not run reliably or really at all anymore and I found that the compression was only about 80PSI. After tearing into the motor I found that overall it was in pretty good shape.. the Oil ring was stuck inside the piston so that it was not sealing well and it appeared that the valves may not have been seating well. Really I figure I can re-grind or re-seat the valves, replace the top end gaskets and piston rings and it should be good.. what I am wanting to know is how do you know if you should replace more (valves, timing chain, ect..) I do have a strong Mechanical background but have never liked or done much engine internals.. any advice would be greatly appreciated.  I do have pictures of the valves.. you can see them here https://goo.gl/NH76kw... let me know if that does not work and I can copy them to this post. 

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17 hours ago, plugeye said:

not sure about the valves but get a fresh cam chain while your in there

Thanks, I will have to look into that. I believe that the valves are in good shape. I really was not looking to go far enough into the engine to do the cam chain but, that is one way to get familiar with this motor... 

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  • 2 weeks later...

Get a factory service manual if you don't already have it, it'll have all the factory specs for tolerances so you can determine what needs replacing.

Assuming you're talking about the top end here and not splitting the case:

  1. New piston rings, check piston for damage
  2. Check cylinder for scratches/wear, hone the cylinder if needed
  3. Valve lapping (optional but not a bad idea, here's a video on my DR)
  4. Valve oil seals
  5. Check cam chain length/cam guides for wear
  6. Inspect cams for wear
  7. Valve adjustment

Those are the big ones off the top of my head!

If you're cracking the bottom end, check all the bearings for roughness or play and replace them.

Edited by Tekime
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On 2/27/2017 at 5:10 PM, Tekime said:

Get a factory service manual if you don't already have it, it'll have all the factory specs for tolerances so you can determine what needs replacing.

Assuming you're talking about the top end here and not splitting the case:

  1. New piston rings, check piston for damage
  2. Check cylinder for scratches/wear, hone the cylinder if needed
  3. Valve lapping (optional but not a bad idea, here's a video on my DR)
  4. Valve oil seals
  5. Check cam chain length/cam guides for wear
  6. Inspect cams for wear
  7. Valve adjustment

Those are the big ones off the top of my head!

If you're cracking the bottom end, check all the bearings for roughness or play and replace them.

Thank you, so far everything looks really good on the inside.. I have already ordered new piston rings, cam chain, and top end gaskets. I believe that the chain is find but thought I would do it while i was in there just to be sure. I am just waiting for the piston rings now so I can start going back together. Hoping this makes it reliable. looking forward to riding in the dirt again. 

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