valve spec and fix

24 replies to this topic
  • Yzflier977

Posted March 25, 2016 - 01:46 PM


Interesting. Thanks man. I'm really leaning to stainless and lapping them myself. Would like to go back Ti but that's $700 to do that with new seats. I could do stainless with new springs for a fraction of that.

  • Yzflier977

Posted March 27, 2016 - 07:33 AM


Still no difinitive answer on can lap new stainless valves to old seats and be okay......

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  • grayracer513

Posted March 27, 2016 - 07:42 AM


Faction MX is the brand. If I remember right they weren't all that expensive.

 They aren't all that good, either.



So valve replacement always involves sending your cylinder head off to have the seats refinished? Even if replacing wih steel valves? Can steel valves be lapped to old seats?


The correctly configured valve seat is perfectly round and concentric with the valve guide.  It will have a 30 degree cut below the seat surface, a 60 degree cut above it in the port, and a perfectly conical 45 degree surface for the valve to seat against.  In a worn seat, the seat surface will have begun to round over.  When you lap a new, perfectly conical 45 degree valve against that rounded surface, part of what happens is the valve tends to grind the seat flatter, but the rounded seat also tends to grind a round groove into your brand new valve.


The seats ALWAYS need to be correctly refinished with the right tooling.  Lapping, if done at all, should only be done after that.

  • WYO522

Posted March 27, 2016 - 07:58 AM


 They aren't all that good, either.


100+ hours of practice and hillclimb events, dirty an dusty conditions, lots of rev limiter, with 30hp shot of NOS installed for the last 40hrs, and the FactionMX valves and springs haven't worn at all. The clearances at the end of last season were same as the day I installed them. They aren't all that bad in my opinion.

Edited by WYO522, March 27, 2016 - 07:58 AM.

  • grayracer513

Posted March 27, 2016 - 08:26 AM


They're serviceable enough most of the time. They aren't as durable as the OEM stainless valves in the 400 and early 426 were, and I've heard of a failure at fairly low hours, but overall, I think you get a reasonable value from them.

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