'81 GS450 - No compression

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  • Waz
    • Feb 2026
    #1

    '81 GS450 - No compression

    Hey all - Thanks for this forum. I've been scouring it these past few days and learning a ton.

    This 81 GS450 had been running great. I recently replaced the o-ring in my cam chain tensioner. Unfortunately I set the spring on it incorrectly so that tensioner did not function properly. The bike idled for a minute, but then cut out with a clank. Initially, I was not able to advance the engine. Once I inspected the chain and reset the timing, I could again advance the engine manually.

    But all is not well. I don't have any compression. Intake valves C (.0025) and D (.005) are reasonably close to spec, but exhaust valves A (.014) and D (.020) are quite off.

    Any thoughts on what might be going on? What are some next steps I should take? Is it time to crack open cylinder head to get a better understanding of what's going on.

    Thanks!
    Tags: None
    • hillsy
      Forum Sage
      • May 2008
      • 1469
      • Brisbane, Queensland, Australia
      #2
      The clunk you heard was more than likely your pistons hitting your exhaust valves.

      You will need to either replace a lot of internal parts or try and find another engine.

      No harm in pulling it down to inspect though.
      Current:
      Z1300A5 Locomotive (swapped my Intruder for it), GS450 Cafe Project (might never finish it....), XT500 Commuter (I know - it's a Yamaha :eek:)

      Past:
      VL1500 Intruder (swapped for Z1300), ZX9R Streetfighter (lets face it - too fast....), 1984 GSX750EF, 1984 GSX1100EF (AKA GS1150)
      And a bunch of other crap Yamahas....

        Comment

        • Guest
          #3
          It seems as though cam chain tensioners are jinxed. Manual ones get adjusted wrong - too loose or too tight or set cold - and the auto ones leak and get reassembled wrong or left with the setscrew tight or whatever else can be diddled.

          I've never found the O ring to be the culprit but inevitably the seal on the knob shaft. Sure, while you're in there replace it, but the seal gets old and shrunken and the shaft vibrates and wobbles about. Add a bit of blowby crankcase pressure and it leaks.

          If the shaft is worn, clean it up as best you can with fine paper and use the Honda seal 91259-VMO-000 which is more flexible and tolerant of a funky shaft. Also available and cheap. Purists can whine, but it's a better thing, and has been sealing various bits of Hondas since the mid '70s.

          The exhaust valves have been the same since '77 and I think the GS500 ones are the same part#. If the pistons aren't hooped then it's just a matter of taking the valves out and lapping in new ones and resetting the clearances.

          'Just', he says?..

            Comment

            • hillsy
              Forum Sage
              • May 2008
              • 1469
              • Brisbane, Queensland, Australia
              #4
              Originally posted by John Park

              The exhaust valves have been the same since '77 and I think the GS500 ones are the same part#. If the pistons aren't hooped then it's just a matter of taking the valves out and lapping in new ones and resetting the clearances.

              'Just', he says…..
              The bike was running when the interference fit was tested - could be quite likely the valve guides have been cracked in the carnage as well. Which would make the whole exercise a bit more involved / $$$.

              Wont know until its apart though....
              Current:
              Z1300A5 Locomotive (swapped my Intruder for it), GS450 Cafe Project (might never finish it....), XT500 Commuter (I know - it's a Yamaha :eek:)

              Past:
              VL1500 Intruder (swapped for Z1300), ZX9R Streetfighter (lets face it - too fast....), 1984 GSX750EF, 1984 GSX1100EF (AKA GS1150)
              And a bunch of other crap Yamahas....

                Comment

                • Nessism
                  Forum LongTimer
                  GSResource Superstar
                  Past Site Supporter
                  Super Site Supporter
                  • Mar 2006
                  • 35790
                  • Torrance, CA
                  #5
                  Most likely just bent valves. Time to pull the head and see...
                  Ed

                  To measure is to know.

                  Mikuni O-ring Kits For Sale...https://www.thegsresources.com/_foru...ts#post1703182

                  Top Newbie Mistakes thread...http://www.thegsresources.com/_forum...d.php?t=171846

                  Carb rebuild tutorial...https://gsarchive.bwringer.com/mtsac...d_Tutorial.pdf

                  KZ750E Rebuild Thread...http://www.thegsresources.com/_forum...0-Resurrection

                    Comment

                    • Waz
                      #6
                      Thanks guys. I'll pull the head and take a look.

                        Comment

                        • herostar
                          #7
                          Take pictures and post them if you get a chance... It would be educational for others to see what this sort of damage looks like!

                            Comment

                            • Waz
                              #8
                              OK. I'll try to do that herostar.

                              I've got things disassembled, and confirmed that the exhaust valves are bent. Replacement should arrive this week or next. I just bought a 2007 V-Strom, so am not as motivated to get this GS back on the road. Since I have it half apart, I'm going to take my time and clean 'er up real nice over the next month or two as I put her back together.

                                Comment

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