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Discussion Starter #1
Guys, I need some help quick so I can get the top end back on my crippled TW. I'm the one with the "Metal in my oil, crap!" thread here in the tech section. Cases have been split, cleaned out, and bottom end is finished up and back on the bike. I'm ready to put the top end back on and have a question.



I have all of the Orings and gaskets to do the top end. While I was cleaning the top of the crankcase from residual cylinder base gasket, I noticed a small Oring down in the hole at the right rear hole. I know an Oring goes in the recess between the cylinder and the crankcase, but this small Oring was down in the hole. I haven't found it on any of the OEM fiche pictures. The previous owner has less than stellar mechanical skills and ethics, so I don't trust anything he has done. Like I said, I'm ready to finish the bike and get it running but I don't want to screw it up by omitting or leaving the Oring before buttoning this thing up.



The OEM parts diagram at stadiumyamaha, ronayers, rockymountainatv, etc don't show the small oring as far as I've seen. Does anyone know if there is a small oring down in the right rear hole in the case? I've included a photo showing the small oring and the hole that it is in.











I honestly don't think an oring goes down in that hole. It doesn't fit well. However, it is obviously not the oring that goes on top of the crankcase in that recess. The oring that goes in that recess larger.



So who knows?
 

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I can't answer your question unfortunately as I had an engine builder put mine back together. He just finished it last week and he may remember. You could email him your pictures and ask him. His website is www.dwmsracing.com



That is where oil is pumped up into the head though so a o-ring may indeed go there.



I'm sure someone else here will have the right info soon enough, its a great bunch on this forum.
 

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Discussion Starter #5
Thanks for the quick replies. If all else fails I'll email your mechanic nitrodiver. Rainman, I have the oring in post #26 of Bdubs post. I need to know if there is a smaller oring down in the hole below that oring that fits in the top recess. I'm going to go back and read Bdubs excellent sticky on base gasket replacement but I really think that oring down in the hole doesn't belong there. Anyone know for sure?
 

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Discussion Starter #8
Rainman, thanks for that parts diagram. I wanted to post it here but couldn't figure out how. Part #4 is the one I have and it fits perfectly in the recess in the top of the crankcase. I have no idea why there was an oring down in that hole. Of course, the PO may have dropped an oring down in there or in the crankcase and just left it. I have no idea how it got there but I don't think it belongs there.
 

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Discussion Starter #9
Top end is on and I've set the cam timing. I know there is not supposed to be an oring in that hole. I watched bdubs base gasket tutorial and there was no mention of it. There are no parts diagrams with that oring in the hole and the service manual doesn't mention it. Of course, now the question is where did it come from in the first place. Like I said, if someone will leave a shattered piston in the bottom end along with 3 wrist pin circlips, I wouldn't put anything past them. At any rate, I'm gaining on this project. Hopefully in the next couple of days I'll get the carb installed, valves adjusted, clutch adjusted, and start the little beast. Here are the 2 orings side by side. The bigger one is the one in the parts diagram above that sits between the crankcase and the cylinder. The smaller one is still a mystery.



 
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