8mm vs 5/16" valve stem

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Perfect timing to read this. I have LS heads on one side of my bench (8mm I think) and Indy LAX heads on the other side (5/16 I think).
 
Hughes has 8mm, but not 5/16". They said 8mm and 5/16" are interchangeable. Really?

Hughes has 8mm, but not 5/16". They said 8mm and 5/16" are interchangeable. Really?
2.5 thousands clearance difference on a valve to valve guide measurement is a big deal. Guide needs to be sized properly for the valve stem. Guides and stems need to be measured sized properly to give adequate clearance period. As to Hughes you would think they would have learned their lesson with the first round of EQ's they sold that seized valves.
 
I had 8mm valves put in my magnum heads and my machinist had to size all the guides. He said it didnt take much, but they did have to be sized.
This ^^^
The same if you were putting a ls valves in some Magnum heads ..you would have to hone them just to get the valves in.
When you cut seals they have 1 pilot for the cutter to do both 5/16 & 8mm , but you do need to properly clearance/ size for the slight difference between the two.
 
2.5 thousands clearance difference on a valve to valve guide measurement is a big deal. Guide needs to be sized properly for the valve stem. Guides and stems need to be measured sized properly to give adequate clearance period. As to Hughes you would think they would have learned their lesson with the first round of EQ's they sold that seized valves.
Ive bought 3 sets of EQs for magnums, 1st set bare, 2nd and 3rd supposed " bolt on and go" right from EQ. the most recent was the only set of the 3 that I wanted with a magnum intake pattern. I put em in my wife's 360 Durango and didn't make 6 miles..... Seized stems. Needless to say I wasn't happy.
I sent em to the machine shop, and let them handle corrections. I never did hear why the stems and guides measured out to. #4 exhaust bent from contact, I do remember the machine shop saying they had never had a set of heads with such tight intakes and all that he had to do to fight with them to get them out....this set was bought Oct/Nov 2016 right off their dock in Chicago.
 
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