Valvetrain geometry

[TurboBuRick]

Damn Earl. Thats some good info! We need to stick that in it's own thread.

 

[jpwalt1987]

Earl, here is what I measured this morning. How does this look to you? I have a 7.95 length pushrod checker installed and the lifters are pressurized with oil. What would you do with this?

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[jpwalt1987]

This is at .250 lift

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[earlbrown]

Don't worry so much about getting everything perfectly square. since the 3 main datum points on the rocker are fixed, you just can't do much. The main thing to look for is is all the errors are on one side, or any binding, and how the shoe sits on the valve as it goes through the motion.

Look at the last pic you posted... it's a .250 lift (Is this a .500 lift cam?) See how close to 'centered' on the shoe tip the contact patch is. That's tells you, the contact patch is probably utilized correctly. If it was out at the tip at mid-lift, you'd be on the very edge of the rocker wiping the valve at full lift (and pushing more sideways than down) If it was close to the shaft side, you'd be rocked up on the edge of the valve tip at 0 lift and bad things would happen.

Spin the crank a couple times and watch how the rocker contact plays with the valve tip. Paint the polished part with a sharpie and you see where the actual contact is made. Then while you're there, watch the pushrod side and notice how it moves closer and further to the shaft as the rocker rotates about it's pivot point. Then imagine that lateral motion causing the pushrod to sing like a tuning fork at 6000 RPMs.


Also, if that seal is one of those hard plastic parts, throw that thing as far into the woods as you can. Walk out there, pick it up and throw it again.

 

[PSID6]

Wow, I was thinking that I knew a little bit about this. After reading Earls post , I have decided I don't know shit. Great write up Earl

I probably would thank Jim Miller. The guy that wrote the book lol.

 

[earlbrown]

Earl did in his first post. He actually corrected the book.

 

[PSID6]

Don't tell me you got a letter from Crower too.

 

[jpwalt1987]

http://www.circletrack.com/techarticles/ctrp_0611_rocker_arm_valvetrain_geometry/


Here is some more good info I found about rocker geometry.

Earl, if you look at the pictures on the first page you will see what looks like the rocker sitting on the corner of the valve stem. That is what I am really concerned about. The pattern looks good as far as the way the rocker goes across the valve. Still not sure if I should just run with what I've got.......

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[earlbrown]

That article made me no longer know how valvetrain components work together. The author also made a few overly simplistic statements that weren't exactly true.

Are you talking about the picture where the guy is holding the valve and rocker with his hands?


You've got a dial gauge. How does your actual valve lift compare to your published lift? (it is possible to lift even more than the card says with overarcing)

 

[jpwalt1987]

I was talking about the picture on the first page of this thread. I will check the lift in the morning. Thanks for all the help.

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[earlbrown]

Oh, your pictures. It's hard to tell if how it looks on my screen is the same as how it looks in real life. Without lowering the shaft on a mill, the only way to rock up on the edge is by sinking the hell out of the valves.

If you got a valve job and they didn't tip your valves correctly I guess it could rock up on the edge. Measure the tip height from the seat. I believe spec is 1.697" to 1.757". If they're taller than that, it might be time to take a look at the valve seats.

 

[jpwalt1987]

Funny thing is, these are brand new Champion CNC heads. To me it looks like these valves are taller overall compared to a stock set of heads I have. It looks like the rocker arm shaft needs to be raised.

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[jpwalt1987]

Well after some more measuring I think I found what is going on. I layed a straight edge across the top of the valve stems on the champion heads and then on two different stock untouched heads. I then measured down to the seat of the rocker pedestals. I made damn sure to keep everything squared up. Subtract the thickness of the straightedge and you have the height of the valve relative to the rocker pedestal. The stock heads valves where .590 above the pedestal. The Champion heads valves where .680 above the pedestals for a difference of .090. Thats huge. I then loosened the hold down bolts .090 to simulate a taller installed position thus changing the geometry of the rocker arms. I held the rocker shaft in the up position with a pry bar and a block. I then adjusted my pushrod checker to the new length @zero lash for now. I made a few rotations of the engine to observe the rocker arm placement and movement. Everything looked much better. So basically the valves are taller and the rocker shaft needs to be raised up approximately .090.
How the hell am I going to do that????

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[jpwalt1987]

New pushrod length comes out to 8.093+0.50= 8.143

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[earlbrown]

Is there enough room to tip the valves enough to square them up? I kinda doubt it since you have to tip "1.55ish" thou for every 1thou in 'drop'

Lay a straightedge across the valve tips and measure down to the spring seat. What does that read?

 

[jpwalt1987]

The spring seat on the champion heads stacks up like this.
2.190-.170 (straightedge)-.093(shims)=2.027
There is about .160 of valve stem above the keepers.
The stock heads I have, have a spring seat of 2.10-.170 (straightedge)= 1.930

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[jpwalt1987]

I have new measurements and talked to Tom@ Champion. I was thinking that the valves could possibly be longer so I pulled off one head and pulled the valves out. The valves are the same length as the stock valves just as Tom said they would be. However the Champion heads valve tips are still about .090 higher than the stock heads valves when measured in relation to everything else on the top side of the head. Tom doesn't understand why and neither do I. ?????????

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[PSID6]

So what was his solution to your problem?

 

[RmvBfrFlght]

The valve seats sunk.

RemoveBeforeFlight

 

[jpwalt1987]

The heads are brand new Champion CNC heads. Never ran.

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