KZ750 valve seat.

Greetings all. New member, longtime reader. I own a 1977 KZ650 (B1) with an old 720 kit, Kerker header, and filtered velocity stacks, runs great. Bought 750 jugs & head for an 810 winter project. I found a crack on the hardened intake seat #3 by the plug hole on the project 750 head. Is this common? The crack is not on the valve contact area. Should I get another head? JB weld it (says it's good for 600 degrees)? I have not torn my bike down yet, just getting ready. Thanks for any advice.

Cracked seats are not normal. I don't think JB weld will work there because it gets too hot.

The steel seat itself is cracked, or the aluminum by it?

Jay

Just the steel seat, just on the lip at the cumbustion chamber edge. The small crack starts, runs a small arc, and returns to the edge. I checked the APE site and you show bronze seats, but not steel. This was a $20 E-Bay head, but I've cleaned it and tapped the emission holes, and started to pocket port the valve pockets. If it's not worth it I'll search for another. I am using an early 80's 750 head before the Hy-Vo chain.

If your lap mark doesn't go thru it, I would say you are OK.

Jay

Dallas 650 wrote:

I am using an early 80's 750 head before the Hy-Vo chain.

Hmmmmmmmmm. Mine has a H-Vo cam chain. I thought all the 750/4s were Hy-Vo???

JR wrote:

Dallas 650 wrote:

I am using an early 80's 750 head before the Hy-Vo chain.

Hmmmmmmmmm. Mine has a H-Vo cam chain. I thought all the 750/4s were Hy-Vo???

They are

I suspect people get confused because the KZ750 heads (but not the GPz750) still have provisions for the roller cam chain parts.

Thank you Jay, the crack is not close the the lap/contact area.

Dallas, valve seats are similar to cyl sleeves in that they are generally top-hat shaped affairs which are interfearance fits within their respective homes. both rely to some extent to difference in expansion rates to keep them in place. your' cracked seat may stay in place for-ever,the cracked bit could drop out and be washed out w/ exhaust and never be missed. it could also either nick a valve, or allow seat to drop. seats can be replaced, tho it would probly be cheeper to find another head. if you plan on playing porting games, I'd carve away, leaving bit in -sittu, a $20.00 head & some gaskets could yeild excellent gains, even if it's w/another head. luck G. PS, It's been my exeriance that straightening intake flow renders better results than just opening ports.