Plug inside the cylinder head ??

3 replies to this topic
  • Sylvain

Posted April 14, 2005 - 02:33 AM


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 ?

  • cowboyona426

Posted April 14, 2005 - 09:38 PM


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

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  • grayracer513

Posted April 14, 2005 - 11:31 PM


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?

  • Sylvain

Posted April 14, 2005 - 11:38 PM


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.

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