Shaft rocker geometry

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70MC
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Shaft rocker geometry

Post by 70MC »

I am working on my sbc with standard 23deg. brodix T1s. I was setting the goemetry of my crower shaft rockers, and with .196 worth of shims i get a pattern on the valve that is .040 wide. That is the smallest pattern i could get, tried more and less shims and the pattern would get wider, and stay on the rocker side of the valve. The pattern starts from the rocker side and goes to the middle of the valve then back. So the pattern is a little off center towards the rocker about .025. I feel good about the pattern the way it is. But, when the lifter is on the base circle and you look at the pushrod in the rocker, if you would draw a straight line through the rocker adjusting screw and the push rod, they are perfectly lined up, give or take a few degrees. When i turn the motor over to max lift the pushrod is at a bad angle to the rocker, i could see the radius of the round end of the pushrod. It is a little scary looking, as though it could come out when running, although 80% of it is still in the rocker seat. When looking at my stud mounted rockers the pushrod seat is much deeper than my shaft rocker, so could this be considerd normal? The cam is a roller with a base circle of .900 and .650 net lift.
Last edited by 70MC on Sat May 21, 2005 9:31 pm, edited 1 time in total.
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bill jones
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Post by bill jones »

-how long are the valves in this set of heads (overall lengths)?
-How far do you have the adjustment screw out from being bottomed out?
-have you ever used Crower shaft rockers before or ran other shaft rockers where the pushrod screw angle is significantly better?
-Do you have the pushrods with the undercut ball ends that give you more movement in the socket?
-does the intake and the exhaust do the same exact thing?
---------------------------------
-I find it amazing that you can still buy so-called high class parts that just don't do all the tricks they should.
-I've used Crower stud mounted stuff for years with no problems but I never could bring myself to buy a set of their shaft mount because I had never seen a set in real life to investigate the geometries of both ends of the rockers.
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Post by 70MC »

how long are the valves in this set of heads (overall lengths)?
-How far do you have the adjustment screw out from being bottomed out?
-have you ever used Crower shaft rockers before or ran other shaft rockers where the pushrod screw angle is significantly better?
-Do you have the pushrods with the undercut ball ends that give you more movement in the socket?
-does the intake and the exhaust do the same exact thing?
Bill, the valves are Ferrea 6000 series part #F6115 int. & #F6100 exh., these valves are listed as being 4.960 stk/+.050, the Brodix valves that came with the heads are listed as being 4.965 long.
I have the adjustment screw turned out 1 turn from being bottomed out.
This is my 1st experiance with shaft rockers of any kind.
I have not bought pushrods yet, i am using Comps checking pushrod that gives you .050 with 1 turn.
Yes, the int. and exh. do the same thing.
Could these rockers be made for longer valves? That would seem to correct the pushrod angle and put my wear pattern closer to the middle of the valve.
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Post by bill jones »

-I'd consider two things.
-First is I'd try a pair of lash caps on top of the valve tips to see if that thickness or increase in tip length would help matters.
-you might have to work out a different shim package with the lash caps.
-if that appears to help then you could investigate longer valves.
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-Second is: if you have access to a mill, you could try slotting the stands/bedplates so that you can move the stands either towards the valve or maybe away from the valve something like .030".
-OR---if you didn't have a mill but had a lathe you could machine away most of the OD of the unused threads (if there is NO shank) that reside inside the stand (bedplate) holes, then you could slide the stands either direction just before you torque'm down.
-Just be careful about the edges of the cutter so that you don't leave a sharp line anywhere.
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-The thing about doing these modifications is you have to be pretty precise because the alignment of the bedplates depends on the accuracy of the bolt holes to the bolt threads
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-What does the Crower setup tool show you about the stand height?
-How does that relate to what you have done?
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-I must have done some Crower shafts that I forgot about because I have spare adjuster nuts, spare bedplate bolts & shims, and I have several of the setup gauges.
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-Make sure you mark the pushrod tip so that you can see if the rockers pushrod cup is marking up the side of the pushrod and trying to force the pushrod out of the socket at high lift.
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HMMMM

Post by Trev »

I have just spent a week getting mine set up correctly as well, mine are yella terra shafts but probably the same principle, did you read my post on contact patch, I spoke for an hour on the phone with the engineer from yella terra, longer valves will kill your contact patch width and the location due to the intersecting angles, but raising or lowering the pedastal height fixed mine, i ended up with a little over 2 mm patch near the centre. the engineer said it was much more important to get the narrowest patch as apposed to a central patch,
Also get the most movement of the roller across the valve at low lift where spring pressures are least.
Have a look at this sight, its from my manufacturer.
Trev

http://www.yellaterra.com.au/install.php
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Post by 70MC »

Bill, thanks for the info. The set up tool was very close, i am within .025 of what it said. There was many different rocker set ups for different heads, could i have gotten the wrong ones? The part number on the box is correct, or is that not possable since the set up tool was so close?
Even though it looks bad, i am still wondering if it realy is bad as it looks, could this possably be considerd good?


Trev, yes i read your post, and that is one reason i am not worried about the pattern on the valve. I am worried about my pushrod angle, when on the base circle it is almost a perect 90deg. angle to the rocker, then at full lift it is at such a bad angle it looks like it may want to come out. It seems to me that the pushrod angle should be close to 90deg. around mid lift? Trev what did your pushrod angles look like?
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Post by SchmidtMotorWorks »

Rocker geometry problems often look worse than they are.

I drew the geometry you decribed. I guessed on the distance from the rocker pivot to roller contact point to be a 1.8 radius (p1). With .600 lift (p6)

With these dimensions the change in angle is less than 20 degrees. (p8,)

Image

The way I see it changing the length of the valve won't make much difference if you then move the rocker pivot up to narrow the contact area on the valve again.

If you would take the shims out of the rocker stands that might help make a better compromise between contact on the valve and push-rod to socket angle but only a few degrees since the result would be in proport to the lift.

I think this drawing will help you visualize the cosequence of longer or shorter parts etc. but it seems to me that 20 degrees isn't too much to worry about and if it is, then the solution is in a rocket with a lower pushrod socket (Ii think?)
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Post by 70MC »

Rocker geometry problems often look worse than they are.

I drew the geometry you decribed. I guessed on the distance from the rocker pivot to roller contact point to be a 1.8 radius (p1). With .600 lift (p6)

With these dimensions the change in angle is less than 20 degrees. (p8,)



The way I see it changing the length of the valve won't make much difference if you then move the rocker pivot up to narrow the contact area on the valve again.

If you would take the shims out of the rocker stands that might help make a better compromise between contact on the valve and push-rod to socket angle but only a few degrees since the result would be in proport to the lift.

I think this drawing will help you visualize the cosequence of longer or shorter parts etc. but it seems to me that 20 degrees isn't too much to worry about and if it is, then the solution is in a rocket with a lower pushrod socket (Ii think?)
Thank you very much for for the info. The picture did not come up my computer. I was thinking too that maybe a lower pushrod seat, and or at a different angle would help.
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Post by bill jones »

-There isn't much you can do about the PUSHROD geometry as that is built into the rocker, except to make sure you keep spare adjuster screws and check the ball sockets for cracks or bad wear on a regular basis.
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-When I check roller tip travel above the valve tip I mount a dial indicator straight up and down and to the front and slightly off center to one side of the rollers crown.
-Then I take a dial caliper and measure 90 degrees from the dial indicator stem back in to the crown of the roller.
-I start at about .002" so that the valve train is loaded-get a number which would be something like about .300" or so, and call that my baseline and reference it as my zero point.
-Then I roll the crank over and open the valve in .100" lift increments and write down the numbers.
-What you see here is that the rocker rolls OUT towards the dial indicator, more so at low lift and the roll OUT slows down as the valve gets nearer to 50% open, and then there becomes a point where the roll OUT stops and begins to roll back IN.
--------------------------------------------
-I see a significant difference between stud mounted rockers and shaft mounted.
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-a stud mounted pattern may look like:
-.002" = .300" or zero as a baseline.
-.100" = .250" or rolled OUT .050"
-.200" = .218" or rolled out another .032"
-.300" = .194" rolled out another .024"
-.400" = .178" rolled out another .016"
-.500" = .178" quit rolling out
-.600" = .182" rolled back IN .004"
-.640" = .190" rolled back in another .008"
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-This shows the roller rolled out thru .400" worth of lift for a total of .122" and then rolled back in .012" thru the last .140" worth of lift.
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-This may not look perfect to you guys but this is what I have seen for 30 years as pretty typical on stud mounted stuff.
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-If you look at the numbers the rocker rolls out .106" in the first .300" worth of valve lift when the valve spring pressures are the lowest and looking at from .300" to .640" the roller tip is only moving a total of .016" OUT and .012" back IN.
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Post by bill jones »

-looking at the roll OUT and roll back IN results of a set of SBC 23 degree heads with 1.7 intake and 1.6 exhaust with backset shafts.
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-the intake lift was .729" at the valve raceready.
-the exhaust lift was .650".
-pushrod length was 8.000" intake and exhaust.
------------------------------------
-the intake rolled OUT only .029" and then back in .029" so total width of the pressure on the valve tip was .029".
-the exhaust rolled out .074" and then back in .020" and here the max width across the valve was .079".
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-Being that both rockers are connected to the same shaft height and the same valve lengths but different rocker ratios and maybe even had different lobe lifts the only way to get the both the intake and the exhaust roll OUT to the minimum is to change the valve length of the exhaust valve.
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-I tested this engine with light springs and again with raceready springs and the results with the light springs are NOT valid whatsoever.
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Post by SchmidtMotorWorks »

The picture did not come up my computer
I think I munged the link, try this

http://www.schmidtmotorworks.com/rocker_geo.jpg

or this

Image
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For Bill

Post by Trev »

One for you Bill

Do you do any checking of Piston to valve clearance or any other check for that matter with checking springs.

I have given up with that and do all my checking with the race gear already setup. I found clearances changed when going to the heavy stuff.

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Post by Trev »

70MC

Can you do a check for me.

Bolt on a set of rockers with out the pushrod then push the pushrod end of the rocker down towards the lifter until it stops do to bottoming on the stud.
Hope you get what i mean lol

How much clearance do u have between the top of the valve and the roller tip when you do this, you should have approx 3mm.

That 40 thou patch you have is brilliant, well under half what i have and im happy with mine. With the pushrod angle i havent even checked mine as ive never bothered about it, but I have been using ball end pushrods.

Trev
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Post by bill jones »

-Trev, I seldom ever use light springs except for maybe quick references for checking the circumference of the valve pockets.
-One of the very first race engines I built in the late 1960's I learned about the flexibilities of the rocker studs and the bendableness/flexibility of the cam itself so I have pretty well used race ready conditions to check everything ever since.
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-I experienced loss of lift at the valve when comparing the light spring method vs fully loaded valve train and that was just with solid flat tappet stuff that only had .500" lift at the time.
-So I went looking for where that lift went, and found the cam actually deflects like a worm and the pushrods shorten up and the rocker studs move in several directions etc.
-If you haven't yet used a rubber timing belt and 1000# open valve springs there is an eye opening situation.
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Hi

Post by Trev »

Thanks Bills

Same as what I found

Trev
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