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CVO Technical => Twin Cam => Topic started by: johnsachs on July 01, 2018, 06:23:14 PM
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2 sets of heads came in last week for mods.
Upon disassembly of 1 set this is what I found. Installed height within specs. Valve spring open and closed within 7 psi of specs.
I bet the owner never realized he had an issue with the springs. NO other damage. Put the shoe on the other foot, what do you think would have happened if it were a beehive spring ? >:(
John
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John you have just about convenienced me it time to get the beehives off the heads.
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Do you still get on airplanes?
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Yes, just so long you're not the pilot. ;D
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Lol
Good thing it was a double.
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Do you still get on airplanes?
Yep, but not built any of them lately either.
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Yes, the dual springs have that safety factor, if one breaks the other can reduce the chances of a catastrophic failure. But, as you can see by this example, the straight wound spring obviously can break just like the conical beehive spring. Looks to me like the quality of springs in general could use some improvement. Either that or there is something in the setup of the heads that's over-stressing the springs.
Perhaps we should go to desmodromic valve control?
Jerry ;)
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Yes, the dual springs have that safety factor, if one breaks the other can reduce the chances of a catastrophic failure. But, as you can see by this example, the straight wound spring obviously can break just like the conical beehive spring. Looks to me like the quality of springs in general could use some improvement. Either that or there is something in the setup of the heads that's over-stressing the springs.
Perhaps we should go to desmodromic valve control?
Jerry ;)
You trying to completely confuse the same HD engineers who couldn't properly design an oiling system, compensator, etc.? :huepfenlol2:
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You trying to completely confuse the same HD engineers who couldn't properly design an oiling system, compensator, etc.? :huepfenlol2:
Perhaps they should have bought Ducati after all. Learn from someone that uses them.
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Do you still get on airplanes?
not any that have valve springs
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Yes, just so long you're not the pilot. ;D
I have over 200 flight hours in my log book. So far, so good (I'm still here).
But I'd take a turbine over a piston engine every time given the choice.
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Fixed a set of heads a few nights ago with a broken beehive. Both valves bent and piston struck.
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Fixed a set of heads a few nights ago with a broken beehive. Both valves bent and piston struck.
Just imagine if you had been in an airplane
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Just imagine if you had been in an airplane
Commercial carriers don't let you run machine tools in coach.
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Fixed a set of heads a few nights ago with a broken beehive. Both valves bent and piston struck.
Factory beehives ?
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Yes
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Very rare
Far more broken retainers than springs
What do you suspect caused it?
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2 sets of heads came in last week for mods.
Upon disassembly of 1 set this is what I found. Installed height within specs. Valve spring open and closed within 7 psi of specs.
I bet the owner never realized he had an issue with the springs. NO other damage. Put the shoe on the other foot, what do you think would have happened if it were a beehive spring ? >:(
John
Looks like there's some reversion is going on too. btw...
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Very rare
Far more broken retainers than springs
What do you suspect caused it?
I had an LS Chevy head (similar spring/retainer) in recently where the retainer had
opened up (soft) and the keepers and valve had almost slipped through it. Another
pass and it would have dropped that valve.
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Very rare
Far more broken retainers than springs
What do you suspect caused it?
Just an oem part at the end of its life cycle. It had 40,000 miles on it, over 20k with a .590 lift cam. It is the third I can remember in 10 years of the heads I have worked on.
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Got this in today. Broken Beehive.
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Broke the guide too
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Another to add to the list. AV&V .650. Others use the same springs, there is no escaping this by brand changes.
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Cryogenic treating the springs and retainers will extend their life. It transforms the austenitic structures
into martensitic structures, which makes them stronger and more ductile (less prone to fatigue failure).
Food for thought...
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I know the spiel.
Not used on aerospace parts to the best of my knowledge because there is not consistant way to prove the material properties. I remember mondello. A proponent.
Or just use dual springs with TI retainers with the proper pressure.
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I know guys that cryo everything. Blocks, rods, head studs, pushrods, etc.
My mentor (Darin Morgan) is a big proponent as well. So I take what he tells
me at face value.
The metallurgical theory behind it is rock solid solid, and the results back it up.
Now, Weather it's worth the cost is an entirely different subject. But I can get cryo
treatment done for next to nothing (if I ship it off to N.Y. state)
going to look for a local source in the meantime.
After that last failure, I'm going to start treating the springs on my heads.
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The safest way to resolve the valve spring problem is simple. Use DUAL SPRINGS. May cost a tad more, may cost a few tenths of 1 horsepower , but it's like buying home owners, or auto insurance. :o
John
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The safest way to resolve the valve spring problem is simple. Use DUAL SPRINGS. May cost a tad more, may cost a few tenths of 1 horsepower , but it's like buying home owners, or auto insurance. :o
John
+1
That's an option too!
Although I'd like to point out that beehive spring failures are very rare in the grand scheme of things.
I've seen Two in the last 10 years. There's ALWAYS a chance of something breaking. That's the
nature of high performance. You have a better chance of dying in a crash if you really think about it.
Maybe I'm over-trivializing it, but I'm still going to use beehives because there's far more reasons to
use them than this one reason not to.
Disclaimer: This is JMO
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The safest way to resolve the valve spring problem is simple. Use DUAL SPRINGS. May cost a tad more, may cost a few tenths of 1 horsepower , but it's like buying home owners, or auto insurance. :o
John
Agreed and done
175# seat 390# rate, weight 111g, cam woods 9b
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WOW! nice micrometers, I'm impressed
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I've seen duel springs break and bend valves too. No getting around it. (Although they never fully dropped)
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Ran duel and triple springs on my BBC Drag boat. They broke every now and then, and the valve almost never
survived when it happened under full power. Frequent replacement of them helped, but never fully eliminated
the problem.
The aggressive cam lobes we ran had allot to do with it. When I switched to Blown gas, the cams were a little
more tame and we rarely had spring problems. .650 lift vs. .720+ had to have had something to do with it.
(I'm actually pleasantly surprised as to how long they last on these bikes however)
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Word I got is: Don't use bee hives on performance applications. (Over .500" ish)
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Word I got is: Don't use bee hives on performance applications. (Over .500" ish)
Got this and its mate back from machining several weeks ago. 625 cams. Have had beehives break before. Been a long time ago but it's happened. Had to pay a few bucks extra to get these. Never gave it a second thought.