Earlie A
Well-Known Member
You win.
Valvetrain Geometry
- Thread starter Earlie A
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I thought the compressive forces of drawing (or pushing I forget how it’s done…maybe it’s both ways) the bar stock through successive dies changed the grain structure or probably more correctly lets the grain flow bend and shape around the part, making it stronger than if rocker or whatever part was machined from a round or whatever shape of materiel you start with rather than just machining it.
Do I have that correct?
Also, there are times when you need the part to have some characteristics that absorb some shock loads like a main cap. I’d rather have the cap move and take some shock rather than have a stiffer cap on there and have that shock end up fracturing the block.
If the block was stronger to begin with then a billet steel cap would make the bottom of the block more rigid and stronger without causing the shock loads to fracture the block.
In the valve train, flexing always occurs but it’s generally a bad thing because that flexing can cause a part or multiple parts to excite and then you get the valve train out of control.
I forgot to mention earlier I’ve seen steel rocker stuff go crazy at a very low rpm (it started a 6k) and the engine would not get through it.
That was a 377 inch SBC Chevy that had stud mounted rockers and a stud girdle. So we took the girdle off and it went several hundred rpm higher and ran into the same issue. They dyno operator said I have a set of aluminum rockers. Let’s try those. I said WTF? That makes zero sense. And I’ll never forget what he said and that was then that’s why we should try it.
This guy was and still is a dyno operators dyno operator. At his age (today) I’d bet he has over a million pulls on his dyno. So we (the engine owner and I and ultimately it was his call even though it was my build) said go for it.
It ran well past 8k without an issue and we were stunned. My question was how did that even work? And his answer was that sometimes the resonance frequency of the multiple parts go into chaos at or very near the same rpm and when that happens you need to change something that has enough mass to affect a change.
It could have been a change in pushrod diameter or wall thickness or a spring change but we didn’t have those parts laying around.
Sometimes the behavior of these parts makes no sense. Im sure that that stud mounted rockers was affecting the situation.
You hit on some interesting things here.
One is the size of the OE shafts. They are IMO too big in diameter to allow for a needle bearing because the rocker gets thin in all the wrong places. You have built in stress points where the spring pocket is cut into the rocker.
Also, I had an engineer friend do some math and stuff for me in his free time about my oiling system and this rocker stuff.
IIRC he said that the smaller, solid shaft of rockers like T&D and Jesel is far stronger under load than the bigger hallow shaft does. And he said the bolt spacing is about as far apart as would be acceptable.
He also looked at the Chrysler OE mounting system verses the blocks the W2-5 heads used. He said the blocks provided a more stable platform for the shaft and the head and it was better than the saddles in any case. He also had me dowel pin the blocks to the head. And it stopped about 90% of the fretting is was seeing between the block and the cap.
He said if I could get 7/16 bolts in there it would stop another 5-6% of the fretting. Of course the stands would be weaker with the 7/16 bolt so I couldn’t do that, but the dowel pins were very effective is stabilizing the block to the head.
TT5.9mag
Two atmospheres are better than one
Lots of good info here. I’ll add something though, I bet I could count on one hand the number of guys here with more than .700 net lift. And I’d bet I could count on one hand the number of guys here that make power over 6500 rpm. And we have a crap ton of members. So that, in my mind at least begs the question, is all this theory worth putting to practice for the 90 percentile? I sure went through a lot of effort setting up my w2 stuff to make sure it was dead nuts and I’m not even sure that was necessary. But I definitely wont worry about spinning it 7500 with 20 pounds of boost. So maybe it was worth it just to give me the warm and fuzzy feelings inside.
Exactly. That’s why I want the valve off the seat as fast as it will tolerate the speed because these engines are under valved and port area deficient.
And that’s a 340 inches.
I’ve seen enough engines with bad geometry and broken parts to know that any aftermarket rocker needs a correction with the exception of TF heads and Mancini rockers.
Other than that, they need to be corrected. In fact I have to call Mike today.
Earlie A
Well-Known Member
What makes Mancini rockers correct? Do they have to be on a TF head?
I was told that TF used that rocket arm to place stands and the height of the stands when they made the heads.
So far, the geometry has been very very close when I’ve used them both. Even on the big block TF heads.
Yes. I refuse to use HS rockers because of the bearings. The Mancini rockers are the exact same rocker without the bearing. It’s far stronger.
That’s why I said the Mancini rockers.
Earlie A
Well-Known Member
The Mancini rockers for SBM list a max spring diameter of 1.65". The Harland Sharp roller bearing rockers have a maximum spring diameter of 1.50". This would mean the HS is 0.150" thicker in the spring relief area. The roller bearing thickness is 0.125". As can be seen in the first picture below, the HS rocker (for TF head) even has extra metal between the two roller bearings.
The second picture below is an old Mopar Performance (by Crane) rocker compared to a HS roller rocker. If ultimate strength is the criteria, my money would be on the orange one.
The second picture below is an old Mopar Performance (by Crane) rocker compared to a HS roller rocker. If ultimate strength is the criteria, my money would be on the orange one.
Can you take a picture of the scallop at the pushrod side and the valve pocket on both rockers?
The HS fail at the two points I just mentioned. I had a bunch of broken HS rockers that I just threw away.
I never failed a Crane rocker at over 8k and I think the least amount of spring I ran on them was 300 on the seat. By the time I went to the Norris rockers I was at 340 on the seat.
If you pop the bearing out of the HS rocker you can see how thin it gets right where the spring pocket intersects with the cut for the bearing.
That’s the biggest failure point.
I have seen some fail at the pushrod cup too.
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TT5.9mag
Two atmospheres are better than one
And oil pressure.
Earlie A
Well-Known Member
That's 0.125" per side.
By Joe I think you get/got it.
Yeah, my bad. It comes off just the inside so it’s .125. I was thinking half per side.
I always assumed the goal of basic valve geometry was to work to have the downward force of The rocker directly plum with the center of the valve stem decreasing side loading of any kind. And to be as stable as possible when achieving that, I know I'm probably dumbing that down but am I off on my hypothesis.
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gzig5
Well-Known Member
Lot of good info in this post.
You do have it correct, to a point. There is a skin effect when you push/draw the material through the die, with compression of material on the outside. But since the billet material goes though the same process, I don't' think there is a significant benefit for the drawn rocker, unless the center hole is drawn as well, which i doubt it is. I could be wrong. I just in general have a disdain for the whole "billet" part description because it infers superior strength that isn't present. Forged aluminum on the other hand is a whole different animal. Much stronger, and much more expensive.
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