Maistrelli
Well-Known Member
Hughes has 8mm, but not 5/16". They said 8mm and 5/16" are interchangeable. Really?
8mm vs 5/16" valve stem
- Thread starter Maistrelli
- Start date
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Pretty darned close.
5/16" + 7.937mm
5/16" + 7.937mm
Maistrelli
Well-Known Member
Seems to me, 5/16" stem in guide reamed for 8mm is gonna have excessive clearance. 8mm valve in 5/16 guide, too tight.
Beat me to it, great minds think alike
If your 5/16 guide was a little worn/loose wouldn't a 8mm stem tighten things up?
Along those same lines, I wonder how many guides get hit with a 8mm. reamer and new valves installed.
Maistrelli
Well-Known Member
New head casting. Appears to be 5/16". Have a ball gauge coming and I'll know for sure.
No way they are interchangeable if you want correct clearance. Maybe why I hear of stuck valves.
Krooser
Building Chinese Free Engines since 1959...
They are interchangable as long as the guides are properly reamed or replaced like they should be done when rebuilding a head.
Now if you're doing a regrind only no they are not interchangable.
Now if you're doing a regrind only no they are not interchangable.
Oh sure. And 3/8" stemmed valves are interchangeable with 8mm and 5/16 if you wanna dance the dance.
PRH
Well-Known Member
Not interchangeable.
If you’re doing it right.
If you’re doing it right.
moper
Well-Known Member
PRH
Well-Known Member
It’s pretty basic really......
A lot of 5/16 valves have a stem diameter of .3110.
Which would provide .0015 clearance if used in a .3125 guide.
The typical 8mm valve stem diameter is .3130, which won’t even fit in 5/16” guide that’s sized for .0015 clearance with a .3110 valve.
How is that “interchangeable”?
It’s really more of a case of “some modification required”.
A lot of 5/16 valves have a stem diameter of .3110.
Which would provide .0015 clearance if used in a .3125 guide.
The typical 8mm valve stem diameter is .3130, which won’t even fit in 5/16” guide that’s sized for .0015 clearance with a .3110 valve.
How is that “interchangeable”?
It’s really more of a case of “some modification required”.
Krooser
Building Chinese Free Engines since 1959...
PRH
Well-Known Member
It’s actually almost comical that people are arguing over this.
5/16 is not the same as 8mm.
I can hear the conversation now.......
“I ran out of 5/16” guides for your head, so I used 8mm instead.
Yeh, there’s an extra .0025 clearance....... but I read on the internet that 5/16 and 8mm are interchangeable, and I didn’t bother fitting the guides to the valves because you don’t have a race motor”.
5/16 is not the same as 8mm.
I can hear the conversation now.......
“I ran out of 5/16” guides for your head, so I used 8mm instead.
Yeh, there’s an extra .0025 clearance....... but I read on the internet that 5/16 and 8mm are interchangeable, and I didn’t bother fitting the guides to the valves because you don’t have a race motor”.
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yellow rose
Overnight Sensation
I agree. Another reason Jimmy Carter screwed the country with his shift to the metric system. We are so ignorant we can't do fractions so we decided to dumb ourselves down with the metric system.
8mm and 5/16 are NOT the same. That's why we have the decimal system. That's why zero has a value.
Just because Dave Hughes said it don't make it right.
RAMM
Well-Known Member
It is basic but it can get confusing which is why I like to have all parts in front of me to measure and do the math. For example Ferrea doesn't know what a 5/16" stem is supposed to measure --every valve I ever got from them measured .308"-.3085" and that is not even close to 5/16". So if a guy never saw that before he would assume the aftermarket calls a .308" stem a 5/16" stem valve size. J.Rob
PRH
Well-Known Member
Of course, thats still not interchangeable with 8mm stuff.
turboking15
Well-Known Member
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.
Close but no cigar. Not without modifications.
"Magnum engines and A-engines do not use the same valves. Because the diameters are slightly different, the Magnum uses a slightly shorter valve by about .060 inch. It also uses a thinner valvestem. They are not interchangeable."
Maistrelli
Well-Known Member
From Hughes, 8mm intake valve #1038a =.311" OD, 8mm exhaust valve #1048 =.312" O.D.
From me, new EQ head casting guide 3115" I.D.
Need a reamer or maybe two. My valves are back ordered. Have to wait and see what diameters I get.
From me, new EQ head casting guide 3115" I.D.
Need a reamer or maybe two. My valves are back ordered. Have to wait and see what diameters I get.
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Rcuda2
Well-Known Member
Thanks for this about Ferrea valves, I just ordered 4 replacment valves for a Magnum head with 5/16" stems that didn't fit. Measured valve stems installed at 0.308". Now I know where those valves came from.
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