Pushrod length and rocker arm setting - Team Camaro Tech
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post #1 of 20 (permalink) Old Apr 11th, 08, 04:12 PM Thread Starter
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Jon
 
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Pushrod length and rocker arm setting

Where should the rocker arm be set to start the pushrod length checking process? Seems like this would make a big difference in the final pushrod length. Have gen 1 383, AFR 195s, Harland Sharp roller rockers, and lunati 60104 (hyd. Also, it's my understanding that I want to end up with the narrowest pattern possible, that isn't too far off centerline. Is that right? Thanks for any help.
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post #2 of 20 (permalink) Old Apr 11th, 08, 04:39 PM
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Re: Pushrod length and rocker arm setting

Most guys say the rocker are should be at a middle of your max lift or half lift. I did this recently to determine p/r length on a small base circle cam. It really helps to use an adjustable ( $30) push rod checker . This way you can find the ideal length by checking roller pattern with a pushrod longer or shorter than ideal. I used a black marklot pen to color valve stem tip. The roller would roll over the center section of the stem and leave a mark pattern , telling you where you are at. If you wish to learn more here, do a search on the subject in the search above .

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post #3 of 20 (permalink) Old Apr 11th, 08, 06:09 PM
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Re: Pushrod length and rocker arm setting

I studied on this a lot, and spent some time doing the checker.

Where the rocker nut is is a function of the pushrod length, everytime you change the checking pushrod, you have to readjust the rocker to match.

Yes, you want the narrowest possible pattern. By definition, that pattern will be at the same place on the valvestem at base circle and at max lift, and it's widest point will be at midlift.





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post #4 of 20 (permalink) Old Apr 12th, 08, 06:55 AM Thread Starter
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Re: Pushrod length and rocker arm setting

Jim, I saw some of your previous threads, and I can see you put a lot of effort into this issue, but I didn't see anything on the rocker nut position. So, it sounds like there are two things to continually adjust, until it is optimized: the rocker nut, and the pushrod length. What would be a good starting point on the rocker nut and/or the pushrod length?
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post #5 of 20 (permalink) Old Apr 12th, 08, 07:18 AM
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Re: Pushrod length and rocker arm setting

The place to start would be the stock pushrod length, and go from there.





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post #6 of 20 (permalink) Old Apr 12th, 08, 07:19 AM
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Re: Pushrod length and rocker arm setting

Most of the cam manf. have extensive DIY diagrams for these subjects. Pushrod length is very important do it right

This link can explain http://www.compcams.com/Technical/FA...inGeometry.asp

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Ported 215 Pro1 Platinums
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post #7 of 20 (permalink) Old Apr 12th, 08, 07:51 AM
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Re: Pushrod length and rocker arm setting

I've played around with adjustable push rods and after hours I've come up with the conclusion that as long as the roller markings or foot print dissect the top of the valve stem or lash cap exactly in the middle you should be OK as the sweep will be the narrowest and exert the least side forces on the valve stem. Another thing to consider is to ensure you have a tight Push Rod guide to prevent the roller from sweeping sideways on the valve stem.

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post #8 of 20 (permalink) Old Apr 12th, 08, 08:56 AM
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Re: Pushrod length and rocker arm setting

At least according to certain people who should know, such as wolfplace on Team Chevelle, as well as bunches of people we've all heard of discussing this extensively on speedtalk, the above pic from compcams is grossly wrong.

The rocker should start at any point, let's say A, go to B at midlift, then return to A at full lift. Starting at B going to C and back to B would be just as correct, if that is what is achieveable in a particular valvetrain.

FYI, my pattern was toward the outside of the valve tip, but was MUCH narrower than comps example.





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post #9 of 20 (permalink) Old Apr 12th, 08, 09:58 AM
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Re: Pushrod length and rocker arm setting

Jim:

I didn't pay attention to that diagram but your right. There are only 2 points between the sweep in the tip of an efficient fulcrum ))

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post #10 of 20 (permalink) Old Apr 12th, 08, 10:39 AM
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Re: Pushrod length and rocker arm setting

I think the point is to get as close to center of the valve as possible thru the sweep and not at the edges. The diagram is exaggerated but correct in theory.

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TKO-600
400 4 bolt block .03 over
Ported 215 Pro1 Platinums
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286HR cam w/1.6 rckrs LS1 beehives
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post #11 of 20 (permalink) Old Apr 12th, 08, 11:12 AM
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Re: Pushrod length and rocker arm setting

Quote:
Originally Posted by quickboat View Post
I think the point is to get as close to center of the valve as possible thru the sweep and not at the edges. The diagram is exaggerated but correct in theory.
While that is what comp says, others have made some very convincing arguments as to why that is wrong.

What they have said is:
Push down nopt sideways on the valve.
If you are pushing (straight) down, it doesn't matter if you are on the center of the valve or the edge, down is down.
The narrower the pattern, the closer to straight down it is.

Bear in mind I really know nothing, other than the reading and talking I did prior to the one time I actually did this.

But, I have a tremendous respect for Mike Lewis as "someone who knows" and he talked to me on this subject on the phone, has written in a number of websites on this subject, and is backed up by some major "heavies." If you read threads on speedtalk about this, you will know the names.

Worth mentioning is the more lift, spring pressure, and rpm, the more important valvetrain geometry gets. Many of these guys are lifting the valves 3/4" or more, and doing it at ten thousand rpm!





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post #12 of 20 (permalink) Old Apr 12th, 08, 12:11 PM
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Re: Pushrod length and rocker arm setting

As Jim mentioned, the Comp Cams diagram is so wrong is almost criminal. If you really want correct pushrod length, you want set the length for proper mid-lift geometry. At 1/2 lift, you trunion centerline and roller tip centerlines are 90* to the valvestem tip...this gives you the tightest pattern. It most likely will be off the center of the stem. This is why its so wrong to just keep shortening the pushrod till its centered - that would be too easy:


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post #13 of 20 (permalink) Old Apr 13th, 08, 08:31 AM
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Re: Pushrod length and rocker arm setting

If you draw a circle from the fulcrum of the rocker and through the contact point of the valve, your radius will change as the valve goes from base circle to full open. The only item that can be changed is the center fulcrum of the rocker arm. Depending on rocker arm geometry, as you raise and lower the fulcrum the contact point moves across the valve tip. When the spring is depressed you will either have a lengthening or shortening of the contact radius, again dependent on valve train geometry. So the idea is to bring the valve tip sweep as close to center as possible by raising and lowering the rocker arm with the pushrod. The angle of rocker arm to pushrod and valve are secondary to this. The effect of side loading the valve stem is minimized with roller rockers of course but shouldn’t be overly discounted.
IMHO

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TKO-600
400 4 bolt block .03 over
Ported 215 Pro1 Platinums
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post #14 of 20 (permalink) Old Apr 13th, 08, 12:39 PM
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Re: Pushrod length and rocker arm setting

Here, if you want the source for mid lift technology...

Read throught the whole site if you can...

http://www.mid-lift.com/TECH/TECH-ML-ARC.htm
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post #15 of 20 (permalink) Old Apr 13th, 08, 12:59 PM
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Re: Pushrod length and rocker arm setting

I understand what Mid-lift is doing, but if you dont have their rockers your still stuck adjusting the way I explained. I'm not too sure we are that far apart when it comes down to it.

67 RS Deluxe Int. A/C car
TKO-600
400 4 bolt block .03 over
Ported 215 Pro1 Platinums
Forged/balanced 400 crank, pistons, 6" rods
286HR cam w/1.6 rckrs LS1 beehives
Forgelines, 18"f 19"r, 4 link w/ minitub
IROC s/gear, 4 wheel discs
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