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TOPIC: Kz750 4cyl Head gasket bore size

Kz750 4cyl Head gasket bore size 10 Jan 2019 17:08 #796500

  • 750killacycle
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Does anyone know what diameter the factory head gasket is on kz750? I bought a vesrah gasket kit it's dead on 68mm my old gasket was 68.7mm I have a 68mm bore I'm a little concerned having the fire ring right up on the cylinder with the vesrah, anyone know the diameter of what comes with the 810 kit?

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Kz750 4cyl Head gasket bore size 10 Jan 2019 18:26 #796503

  • Irish Yobbo
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The 810cc kits have a 69mm piston, but I don't know about the head gasket size.

What you have sounds normal to me. The piston will never go higher than the deck, so having it flush won't be a problem. Your old gasket was probably the same size (68mm), but the spread a little once torqued down, hence the extra 0.7mm.
A mini is a bit like a motorbike, right?
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Kz750 4cyl Head gasket bore size 11 Jan 2019 10:40 #796534

  • Daftrusty
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I have both a compressed stock kz750 head gasket and a compressed 810 head gasket that I kept for some strange reason. But I guess it came in useful in this instance...

Stock gasket bore: 67mm
810 gasket bore: 72mm

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Kz750 4cyl Head gasket bore size 15 Jan 2019 13:45 #796835

  • gordone
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Daftrusty wrote: I have both a compressed stock kz750 head gasket and a compressed 810 head gasket that I kept for some strange reason. But I guess it came in useful in this instance...

Stock gasket bore: 67mm
810 gasket bore: 72mm


Maybe the 810 gasket compress more?
Don’t understand if not, why they want to have lower compression?
1981 KZ650-D4, with 1981 z750L engine (Wiensco 810 big bore).

Project:
www.kzrider.com/forum/11-projects/607213...sr-1981-z750l-engine

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Kz750 4cyl Head gasket bore size 16 Jan 2019 06:49 #796869

  • Daftrusty
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gordone wrote:

Daftrusty wrote: I have both a compressed stock kz750 head gasket and a compressed 810 head gasket that I kept for some strange reason. But I guess it came in useful in this instance...

Stock gasket bore: 67mm
810 gasket bore: 72mm


Maybe the 810 gasket compress more?
Don’t understand if not, why they want to have lower compression?


For the factory gasket I think they recess the fire ring so it stays cooler and does not create a hot spot that could cause pre-ignition.
On the 810 gasket, I'm not sure of why it has such an excessive gap, but I like that it expanded my quench/squish area in my combustion chamber. I am running ~10.25:1 compression and even with 87 US octane (91 RON) I never have detonation even on 100° F days.
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