Valve work - lapping vs. cutting/replacing
- ghostdive
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Valve work - lapping vs. cutting/replacing
11 Jul 2021 08:41
Hey there. I'm watching someone rebuild a GSX-R750 engine and he mentioned that, in the service manual, it instructs not to lap valves but instead cut them to a "velvety but not highly polished finish" which will then provide a surface for the valves to "seat" into. I believe he also mentioned that the bike has titanium valves; I'm wondering if, when I can and do rebuild my 750's engine (which is vastly different from this GSX-R engine) this is something that applies (as in, it's a development that would be good to retroactively apply to my engine) or if I'll be fine lapping with grinding compound.
1982 KZ750 Spectre - 6 speed swap, BS34s, 18" rear wheel
2001 ZX-6R
2001 ZX-6R
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Re: Valve work - lapping vs. cutting/replacing
11 Jul 2021 08:55
I think the first questions you may need to answer are after you tear down your motor and can inspect its condition .
Depending on what you find , then you can make a plan . Obvious , YES.
But I say this for the longevity of the motor into the future .
Point , Why cut into the seats if not needed . Sinking the valves which in turn causes more work
I agree to do all work needed , but why cut life out of the head.
I was able to just lap my valves on the last rebuild saving time , money and not reducing the life of the parts
Dave
Depending on what you find , then you can make a plan . Obvious , YES.
But I say this for the longevity of the motor into the future .
Point , Why cut into the seats if not needed . Sinking the valves which in turn causes more work
I agree to do all work needed , but why cut life out of the head.
I was able to just lap my valves on the last rebuild saving time , money and not reducing the life of the parts
Dave
Original owner 78 1000 LTD
Mr Turbo Race Kit, MTC 1075 Turbo pistons by PitStop Performance , Falicon Ultra Lite Super Crank, APE everything. Les Holt @ PDM's Billet Goodies . Frame by Chuck Kurzawa @ Logghe Chassis . Deep sump 5qt oil pan. RIP Bill Hahn
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- Nessism
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Re: Valve work - lapping vs. cutting/replacing
11 Jul 2021 10:02
When restoring my 750, which only had 10.8k miles on it, the valve to seat contact pattern was pretty crappy. The contact margin was okay on one side but really wide 180 degrees away. I used Neway cutters to dress the seats, removing the minimal material necessary to clean them up and create a proper contact pattern with the valve. The valves themselves needed a fair bit of clean up too. I took them to a machine shop that has a really nice centerless grinder for valves and the machinist guy had to take off more material than expected to get them all squared up. He tipped the valves at the same time to compensate for the expected sinking of the valves. Reason for mentioning this is because a simple lapping job wouldn't have renewed the head properly.
Ed
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1981 KZ750E2
www.kzrider.com/forum/11-projects/604901...z750e-project-thread
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www.kzrider.com/forum/faq-wiki/618026-new-owner-things-to-know
1981 KZ750E2
www.kzrider.com/forum/11-projects/604901...z750e-project-thread
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Re: Valve work - lapping vs. cutting/replacing
11 Jul 2021 12:11
Hopefuly I’ll be moving onto the head while the crank is out. I doubt I’ll take on valve work myself but I have a question. Is the trueness of the valve seat cutter dependent on the condition of the valve guide?
1976 KZ 900 A4
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1976 KZ 900 B1 LTD
1978 KZ 1000 B2 LTD
1980 KZ 750 E1
Kowledge Speaks, But Wisdom Listens.
Jimi Hendrix.
1976 KZ 900 B1 LTD
1978 KZ 1000 B2 LTD
1980 KZ 750 E1
Kowledge Speaks, But Wisdom Listens.
Jimi Hendrix.
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Re: Valve work - lapping vs. cutting/replacing
11 Jul 2021 13:24Hopefuly I’ll be moving onto the head while the crank is out. I doubt I’ll take on valve work myself but I have a question. Is the trueness of the valve seat cutter dependent on the condition of the valve guide?
There is a tapered arbor that wedges into the guide so even if there is some wear the arbor will center itself. That said, if the guides are sloppy it's best to replace them before moving to the seats. If you have a dial indicator it's pretty simple to perform the "wobble test" to judge guide condition.
Ed
Carb O-ring Kits : www.kzrider.com/forum/3-carburetor/61807...-o-ring-kits?start=0
www.kzrider.com/forum/faq-wiki/618026-new-owner-things-to-know
1981 KZ750E2
www.kzrider.com/forum/11-projects/604901...z750e-project-thread
Carb O-ring Kits : www.kzrider.com/forum/3-carburetor/61807...-o-ring-kits?start=0
www.kzrider.com/forum/faq-wiki/618026-new-owner-things-to-know
1981 KZ750E2
www.kzrider.com/forum/11-projects/604901...z750e-project-thread
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- bluej58
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Re: Valve work - lapping vs. cutting/replacing
11 Jul 2021 15:48
I had Larry replace my valves and springs 50,000 miles ago and last winter I decided to install new valve seals and clean and lap the valves.
The seals were hard and the valves were dirty but the job went well and I'm glad that is all I did to the head, working fine.
The seals were hard and the valves were dirty but the job went well and I'm glad that is all I did to the head, working fine.
78 KZ1000 A2A
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