Plug inside the cylinder head ??

When taking off the cylinder head I noticed the plug between the cam right in the middle of the head. I first tough I had to loosen it. After checking in the manual there was nothing on this plug. I checked on the yamaha site and found this info, part # 90340-12112-00 PLUG, STRAIGHT SCREW .

I already started to loosen it, just a bit. I retighten it to about 30 ft/lbs. What would be the proper torque ?

What is this plug for ? Is this plug part of the coolant system ?

Can this plug be unscrewed without damaging the head ?

Do I have to completely take it off to reapply some sort of sealant ?

I'm not sure what plug you are talking about, do you have a picture???

I see the plug you're talking about, but I'm not familiar with it. Located where it is, my guess is that it probably serves one of two purposes. It could be a plug that intersects the oil passage from the intake cam saddle to the exhaust, and was placed there to allow the passages a larger point at which to join as they approach in either direction to that point. Or, it could be drilled into the water jacket, but I can't think of a reason to do that on a 426 head inside the cam box. Something like that is sometimes done to aid in removal of casting sand from the head, but it doesn't seem that such a simple water jacket should need it.

What size is the thread/bolt head?

Does it have a copper washer under it?

What size is the thread/bolt head?

Does it have a copper washer under it?

Thanks for your reply.

It's a 14 mm bolt. I only started to loosen it, I didn't take it out of the cylinder head. So I don't know if there is a copper washer. From the part diagram of the yamaha site there is no washer.

I just hope that I didn't create a problem by playing with this "plug". I'd hate to see oil and coolant mix up. I retorqued it to 35 ft/lbs.

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!


Register a new account

Sign in

Already have an account? Sign in here.


Sign In Now