OEM Yamaha heads & cooling

[WAB]

I was putting my top end back together and notice the head gasket I had been using did not line up with the cooling passages at all. the 4 larger holes on the OEM gasket are completly blocked by the head's casting. It's been that way for a year, so maybe it's not a big deal.
Then I started looking at other heads I had. The left one is a 64x 760 head, middle is the one I took off, it's a 62t 701 head, and the one on the right is a 61x 701 head.

Why would the 61x head be so much more open for cooling?? I guess the 62t and 64x heads require a different head gasket?? :shrug:
Guess I will be using the 61x head from now on.



Freshness :biggthumpup:

 

[oxnard111]

I'm trippin out on how much larger the 61x 701 looks than the others. Why is the 64x head so much smaller than the 61x 701? Or is the picture reversed from your description above?

 

[WAB]

Think it may just be the angle.
Here's another in the same order

 

[Fathom]

Maybe the smaller holes are meant to keep the water in the jackets longer to remove more heat by slowing the rate of flow.

 

[WAB]

Maybe the smaller holes are meant to keep the water in the jackets longer to remove more heat by slowing the rate of flow.

Possibly, but I would think you want new, cooler water circulating through there, not the same hot water flowing slowly.
The water will get just as hot as the metal if it is not flowing.....

 

[Matt_E]

The pumps for the 62T and 64U platforms may very well have different cooling pressures and flows.
That has probably something to do with it.

 

[Fathom]

Possibly, but I would think you want new, cooler water circulating through there, not the same hot water flowing slowly.
The water will get just as hot as the metal if it is not flowing.....

There's a fine line when dealing with heat transfer. Cool water flowing fast will not always remove as much heat. There is still plenty of flow through those ports, even while smaller. Different pumps as Matt stated could be the answer. I'm curious to know too.

 

[Matt_E]

Also, the combustion chambers and squish bands in those heads might be different, and require different cooling (due to different load designs for those platforms) - much like the staggered jetting.