Yoshimura Oil Filler Cap

There are various after market oil filler caps that one can use to replace the stock black plastic job, these fall into the category of bling and for the most part don't add any real function but just spiff up the look. I had a Yoshimura cap on my previous FZ1 and I liked the look.  It is a beautifully machined aluminum part and the one I had was anodized in a coppery bronze color, and for the five years I had it on the FZ1 it caused me no problems and it never faded which can be a problem with anodized parts in high temperature applications.  It also has holes in it so it can be safety wired for track use.  So when I sold the FZ1 and got the FZ-10 I figured it would be an easy swap over.  Eh, not really.  First, the design of the Yoshimura plug does not have a groove in it for an o-ring, for the older design stock caps that used a heavy o-ring it was an easy task to just transfer it to the Yoshimura plug and it sealed fine.  But the crossplane engine in the R1 and FZ-10 uses a different style plug that has a very thin o-ring that is larger in diameter than the old style.  When I swapped it over it did not seal well and I ended up with a mess on the engine case and muffler.  I went over to the dealer and got an old style o-ring but for some reason that didn't work either, I still had blowby.  The only thing I can figure is the internal case pressures are higher in the crossplane engine.  I just figured I'd have to use the stock plug.  I had the Yosh sitting on my desk and kept wanting to use it on the FZ-10.  I thought I would try one last thing so I ordered a piece of 1/32" gasket material for a couple of bucks on eBay and using a circle template and an X-Acto knife I cut my own gasket (35mm OD, 28.5mm ID).  Screwed the Yoshimura cap on and went for a 150 mile ride.  Hey, no leaks, tight as a drum, I'm back in business.

Revzilla sells these although now they come in black.  Everybody complains about the missing o-ring but at least there is a cheap work around.

www.revzilla.com/motorcycle/yoshimura-oil-filler-plug-Yamaha

Anyway, here is how it looks on the FZ-10.  Should be good for at least a 10 hp gain.