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Piston is locked 78 Rm400????


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Is this possible??? I rode my 78 Rm400 at the end of April and knowing it would sit until the Casey IL AHRMA race, I ran the carb out of fuel. I washed the bike and cleaned the air filter like always. I went to load the bike last week and the piston is locked??? When I took off the head it looked like moisture made its way into cylinder an that caused the sleeve to rust, locking the piston?? The position of the position was above the intake so I don't think the water came through the carb. Tell me if I am crazy. When I ran it out of fuel the cylinder is now dry, no 2-stoke oil, and from the heating and cooling of summer temps in my garage, can condensation form in the cylinder to cause rust?? Anyone ever heard of this??? Ideas?? The bike road amazing, as it usually does, before I put it away. Thanks

Also, anyone have leads on where to get piston kits for this bike?? Hard to locate for some reason. Thanks

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Sorry to hear that Keith! Have you tried alpha-sports.com? Their website shows a 0.50 piston set for our bikes for $115.18...definitely not cheap and I am not sure what it comes with but you could possibly give them a try. It doesn't look like they have standard or 0.25 pistons though. When rebuilding mine, the 0.50 ring was much harder to come by than the piston. I think I found mine on eBay though...

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Very strange. Most of my bikes sit for quite some time in the winter and being by the ocean, we have a lot of moisture, but I have had this issue, mine are 4 stroke engine 350 or 400cc. We have some 2 stroke that are barely run, but are 125cc.... and no problems in the last 10 years.

I guess the next preventive step is a tsp of oil in the park plug hole and keeping the piston at TDC.

The best derusting is 50% acetone with transmission oil

Michel

83XR350

80DR400

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Sorry to hear that Keith! Have you tried alpha-sports.com? Their website shows a 0.50 piston set for our bikes for $115.18...definitely not cheap and I am not sure what it comes with but you could possibly give them a try. It doesn't look like they have standard or 0.25 pistons though. When rebuilding mine, the 0.50 ring was much harder to come by than the piston. I think I found mine on eBay though...

Steve,

Good to hear from you again. I ordered the piston set from Babbits OEM and it shows the .50mm over is available as a set with the wristpin and ring. It listed it as parts 1-3, what are the chances the new OEM piston would come without a new ring??? That would never make sense. I can understand buying a new ring but running the old piston but not vice versa. I will let you know, it looks like it will come together, according to the fiche.

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