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2002 Yamaha 70 2stroke bottom plug rusty

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  • 2002 Yamaha 70 2stroke bottom plug rusty

    I have a 2002 Yamaha 70 2stroke that I had to put a new head on last year due to corrosion eating through the head right at the spark plug. New head on and ever since the bottom cylinder hasn’t always acted right. Sometimes it will fire and sometimes it won’t. Pulled the spark plug out this evening and it is rusty on the inside. The other two look good. I’m guessing I’m getting water in the cylinder somehow. Any ideas? Head and head gaskets we’re both changed. Could it be on the cooling head side? Or do I need to redo the head gasket again. There was some metal loss on the power head around the bottom cylinder but it seemed like there was still enough to create a seal. Any ideas would be helpful.

  • #2
    Post pictures of this corrosion damage.

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    • #3
      This was the block prior to installing a brand new head

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      • #4

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        • #5
          I guess my question should be. What are the possible options for water to get into the cylinder?

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          • #6
            Water can get into any cylinder if both case and head mating surfaces were not immaculate cleaned to perfection, can use a medium grade sandpaper glued to a glass to polish/clean both sides evenly. Water can also get into any cylinder through the exhaust covers gaskets, the motor being 18 years old probably have them already dried, hardened, not sealing right or were never re torqued to specs since new.

            Both exhaust cover gaskets and cylinder head gaskets should be retorqued to factory specs soon after has been changed inmediately after say first 5 run hours...

            Happy Boating


            Sea Rider 320, 380 Sibs, 450 Rib, 2 Strokes Tohatsu 5,18 & 30 HP Proud Smokers

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            • #7
              I plan to regasket exhaust cover and retorque the head and see if it fixes. Thanks for the input.

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              • #8
                Originally posted by kevin11mic View Post
                I plan to regasket exhaust cover and retorque the head and see if it fixes. Thanks for the input.
                Much better to regasket both exhaust covers, clean both mating surfaces well. Did you changed both the upper and lower cylinder head gaskets or just the lower one ? Report if everything went well when all the work that needs to de done has finished.

                Happy Boating


                Sea Rider 320, 380 Sibs, 450 Rib, 2 Strokes Tohatsu 5,18 & 30 HP Proud Smokers

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                • #9
                  The engine was completely regasketed about 3 years ago and then both head Gaskets last year with new inner and outer head pieces. This engine was used in salt and put up wet by the prior owner. I got it super cheap and rebuilt it but I’ve been fighting corrosion from the start. I will report back after I make the repairs and let you know what I find.

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                  • #10
                    I pulled the exhaust cover and the head and there was no obvious Paths of water getting into the cylinder. All the gaskets looked fine. Is there anywhere else water could be getting in? Could the block be cracked? No obvious signs of cracking but the cylinder is obviously seeing water as it’s plenty rusty.

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                    • #11
                      Being a used motor could previous owner had a severe overheat and the cylinder head is warped ? check it with a metal ruler, head should be flat even on the entire extension. When you torqued previous cylinder and exhaust gaskets was with hand or with a torque wrench. Assume none were re torqued back to specs, right ? Are any of the mating surfaces pitted, uneven for gskets not to sit evenly Yep. plenty water intrusion for the lower plug to be so darn rusty...

                      Happy Boating


                      Sea Rider 320, 380 Sibs, 450 Rib, 2 Strokes Tohatsu 5,18 & 30 HP Proud Smokers

                      Comment


                      • #12
                        The cylinder head is brand new. Has one season on it. I never retorqued when I installed it last year. It was torqued with a torque wrench however. This go around I will retorque everything properly After the first use. Also changing the exhaust cover gaskets and cleaning/honing All gasket surfaces extensively. This was previously done however the exhaust cover gaskets are about 5 years old and were not Yamaha brand at the time. Going back with all oem gaskets and hoping for the best.

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                        • #13
                          Had water intrusion with exhaust and cylinder head non original gaskets, from that bad experience all are OEM now. Is not that have a fixation with retorquing gaskets, have retorqued several after first 5-10 hour use since replaced and all needed a small retorque. Heat compresses them a bit and lose the torque force previously torqued to so a retorque is mandatory. It's stated on most Service Manuals, but most boaters skips this recommendation.

                          Happy Boating


                          Sea Rider 320, 380 Sibs, 450 Rib, 2 Strokes Tohatsu 5,18 & 30 HP Proud Smokers

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                          • #14
                            OEM gaskets will be here today. Everything is cleaned and block is honed. I believe the OEM head gasket has a sticky adhesive on it already. However what is the opinion on applying a thin film of high temp copper RTV to the exhaust cover gaskets? I was thinking this could help seal off any little pitting/ irregularities. I've done this before on my old Toyota engines that can leak with new gaskets. On those engines I've got to where I coat all gaskets with RTV before assembly. I've even successfully used in on an exhaust manifold that was slightly warped and got it to seal. I also always use copper gasket spray on my head gaskets but with the Yamaha sticky on the gasket I don't feel that is necessary on the head gasket.

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                            • #15
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                              Also loctite, neversease, or dry?

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