oil plug

On right front side of the head there is a drilled

oil passage.It is about 10mm in dia.It is blocked by a metal softplug.

When I was riding I noticed the right radiator was

covered with oil.Pulled tank off and started bike to see if I could find oil leak,saw that plug was gone.Slight spray

comming from hole.I am hoping that this is the oil return side of that route.

1)Has anyone else ever had this happen?

(I would think 426 would have same hole.)

2)What could have caused That plug to pop out?

(To much oil ?.Plugged breather vent?)

I had my breather tube rerouted to air box.

I might of had it pinched creating to much crankcase

pressure.Back to stock for now.

It was a easy fix,10mm soft plug from auto store.

Tap it in . About 75 cents

Yamaha did not even show it in part book.

I hope I did not do any damage to the head.

Bike seems to run just as good as before

Hmm...I'm guessing that this plug you are refering to is where the decomp lever would go in a 426. There is no oil pressure behind there, but it would spit out a bit of oil if it was left open. As I don't have a 450 I'm guessing, but is there a bolt on the side of the head that holds the plug in place?


the tt store sells a plug and seal for the hole. the stock plug is a press fit. go to shop tt, engine, .....plugs, quasi moto racing. the new one uses the small screw near the hole to hold the plug in place. you will need the seal also.

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