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Discussion Starter · #1 ·
Hello all,

Can anyone tell me what these bolts are for? I've tried looking through the parts break downs but can't seem to find these.

253487
 

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Those screw plugs are in the lifter blocks. The lifter blocks are in this case designed seamlessly into the crank case. They receive the lifter cases which have O-Ring oil seals. So the hydraulic lifters sit inside the lifter cases which sit inside the lifter blocks.

As for those undocumented screws, a good look at the service manual and the parts manual seems to indicate the screws are plugs to cover a manufacturing method. The oil flow page shows the oil journals that run inside the lifter block (at the elevation of the groove in the hydraulic lifters) is apparently drilled from the outside then the case is plugged using a specific screw and a specific gasket which is not intended to be removed. There is seemingly one plug for the journal drilled for the front block, one between the blocks, and one for the rear block. You can see hints in the service manual oil flow pages. Im my opinion these three are just plugs due to a manufacturing method choice. I would not bother removing them. There is apparently no benefit.

There is no documentation on thread sealer or torque, and the undocumented stainless steel screws are threaded into the aluminum crank case. If you mess that up, your entire motor is at risk.

Obviously I could be wrong. But looking at the manuals and at the bike, it's the only reasonable explanation so far. And I've never had anyone offer a better explanation. Anyway, this is the best I can offer. One day we will know more.
 

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Discussion Starter · #3 ·
That is very good information. I was just curious about them because my bike developed a pretty good oil leak. It took me a while to track it down and I ended up having to look all around with the bike running. I eventually found the oil flowing out of that middle bolt. It surprised me to see oil coming from there. I knew there would be oil back there because of the lifters but didn't think those bolts would hold any in. I gave it a good snug with a wrench and ran the bike for a few. Didn't have any more coming out.
 

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Interesting. I used to work in an aerospace component machine shop and we did stuff like that all the time. If there was a component (blue part) that needed oil or other fluid to be routed throughout the body (arrows), sometimes the hole would have to be drilled from the outside (horizontal hole) in order to connect with the other two holes that were accessible (vertical holes) and then we'd plug the outside with a lee plug (green part). Usually, the lee plug would go into a counterbore hole to control how far in it was set, but apparently, Yamaha decided to just use bolts to plug the access holes.

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Learning something new every day. Good question @Charrisindy and response @arizonawarrior!
 
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