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More Valve Train Geo Questions...

  1. #1
    I'm No Expert Shaun's Avatar
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    Default More Valve Train Geo Questions...

    On my motor (both builds) i could never figure out the valve train geometry using the 'mid lift' method. I spent days on my first motor trying to figure it out. The problem i kept seeing was that i needed a push rod so long that it would push the rocker way up the rocker stud. It would push it so high up the stud that i needed at least a .5" longer stud (probably longer). The end result was me using the marker method and adjusting my adjustable push rod until i get the rocker tip centered and as small as possible. I can see the wear pattern on the exhaust valve tips and it's centered on the valve tip and probably 1/3 as wide as the tip.

    I decided that i'm going to order pushrods with oil restrictors built into them to see if that fixes my oil pressure issues on a hard pass. Since i'm going to be ordering new push rods i figured i might as well give the valve geo another try. I pulled the valve springs on #1 and put in dummys and away i went. With my current push rod length at midlift the angle of the rockers trunnions (sp?) to the valve is way off. I'm talking enough that i could fit my finger between the valve shaft and angle tool. The thing is though my max valve lift is only .002 off from what the card says. I then take my adjustable push rod and pull it out a bunch, i get the angle closer but the rocker is way up the stud and also my gross valve lift is now .040 higher than what the card reads. If i remember correctly from previous threads on this that shouldn't matter? the important part is the geometry right?

    My real question is, for a Mark4 BBC with 990 heads, morel solid lifters, and scorpion roller rockers how long of a push rod will i probably need (just to compare), and is it normal for the rocker to have to sit so high up the rocker stud to get the geometry right? It seams like i would be putting alot more stress on that rocker stud.

    ** note, i did the mid lift method on my buddys 468 with 048 heads, scorpion rockers, morel lifters and i was able to figure it out no problem. He did end up needing longer exhaust rocker studs through. I dont see how i could be messing this up, it's not that complicated, least so it seams.
    Last edited by Shaun; 11-17-2010 at 07:42 AM.

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  3. #2
    Village Idiot fc-Pilot's Avatar
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    One of the issues that some of us run into (like you are right now) is if the valves themselves are longer that stock (or what is recommended) it will often make the rocker sit very high on the stud and therefore have the rocker tip ride further toward the exhaust side of the tip of the valve. You will notice that if the geometry is right that you maximize your lift at the valve. That is why the really smart guys make the big bucks. They know how to get the valve length right so when the rocker makes the geometry right it will ride in the center of the valve tip. The rest of us (guys like you and me) are at their mercy as we try to do the best with what we have.

    Paul

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    www.highflowdynamics.com LakesOnly's Avatar
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    Shaun,

    Your terminology is confusing....you're using words in correctly and/or alluding to specific parts of the rocker arm dong things in your analysis that they have no business (or possibility of) doing.

    If everything is optimized, your lift at the valve should be as called out on the cam card. It is possible to get more lift at the valve than the cam card specifies, and this usually points to incorrect valve train geometry...specifically, over-arcing. Therefore, my guess is that you are not correctly applying mid-lift principles and theory while evaluating your valve train geometry.

    Shaun & FC-pilot,

    Where the roller tip rides on the valve has absolutely nothing to do with correct valve train geometry. Contrary to popular belief, the roller wheel on the tip of the valve stem is a simple contact point and does not affect geometry. Further, because of the roller tip placed at the end of the rocker arm, there is no concern in "guide wear" even if the contact point is way, way off center, because the forces applied by the roller tip roller rocker arm are always in-line with the valve stem throughout its radial sweep.

    We recently rebuilt a stroker Ford racing-only engine with a roller cammed, 2.200" installed height, valve train. It was run hard weekend-after-weekend for 7 straight years. Because of the +0.200" and +0.300" valves in these heads, the valve stems were effectively moved closer to the rocker studs and so the roller tips were on the very EDGE of the valve stems. Diagnosis? After 7 years of hard passes, all valve guides had clearances within spec and all clearances were identical guide-to-guide, and suitable for continued use. The valve train geometry was right on the mark....and so it was simply the long valves that moved the roller outboard of the stem centers. Adjusting the pushrod length so as to move the rollers to the center of the valve would have surely cost this engine horsepower due to the de-optimized valve timing events and increased frictional loads/losses.

    LO
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  6. #4
    I'm No Expert Shaun's Avatar
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    Lakes, what exactly am i saying that's confusing you and i will try to explain myself.

    The method I'm using is as follows. Install push rod & rocker, set lash, run through a full sweep to determine max valve lift (measured at the retainer, which was .612). Then rotate again until i get the valve lift to .306", i then take my square, align it with the center of the trunions on the rocker (center trunions and the center of the roller tip trunnion) and compare 90* to the valve stem.

    Am i doing this wrong, if the terminology is wrong please correct me so i at least sound like i know what I'm talking about in the future


    In my case, at midlift, the rocker is very high up the shaft.

    I cant remember what my install height was, i do know that the stem sticks out .050 higher from the retainer on the exhaust valves than it does on the intake.

    With the push rods i have now i get .612 max lift at the exhaust valve, the cam card says i should be at .610.

    If i adjust the pushrod to get the mid-lift angle correct, my max valve lift goes up into the .640's
    Last edited by Shaun; 11-17-2010 at 12:19 PM.

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    I'm No Expert Shaun's Avatar
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    Went and looked at a thread i had started about this from years ago and i said that it takes 15 turns on my adjustable pushrod to get mid-lift right. Well today i verified this to still be the case. My max lift with the correct mid-lift though is .642 when the cam card says it should be .610. Also checked and my rocker stud needs to be at least 1/2 longer.







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  8. #6
    I'm No Expert Shaun's Avatar
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    Just a note 15 turns is about 9.550

    also, Just checked my buddy's motor, the exhaust push rod after using the mid lift method is 9.500" long.

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    Village Idiot fc-Pilot's Avatar
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    Lakes, I understand that the roller tip does not need to be in the center of the valve, but I prefer (if possible) to have the geometry right AND have it near the center of the valves tip. Usually when it is then it means that the rocker is a little lower on the stud and has less chance for stud deflection (if not using a stud girdle) or will not have clearance issues with the stud girdle. It also ensures that the rocker will be located in the unthreaded area of the stud instead of slopping on the threads of the stud. All of this I am sure you know, I am just stating why I made the comments that I did earlier. It was not out of blind ignorance but from my own personal experience using the method you mentioned. Now, had a personal experience with having it setup near the edge of the valve tip. Due to harmonics the stem of the valve moved around enough that during high RPM runs the tip would actually come off the side of the valve tip (to the exhaust side). I know there were other factors involved, but this is why I prefer to try and get the tip to the center WHILE obtaining proper mid-lift geometry. It helps provide more piece of mind.

    Also, thanks for taking the time to post as I know many don't as they figure it will turn into a pissing match where someone tells them they are an idiot for doing things right.

    Paul

  10. #8
    gn7
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    Shaun, I think your jumping way ahead with the adjusting the pushrod length in the process.
    First, YOU DO NOT determine what max lift is with the valve, specially if you know or think your geo is off. You have to use mid LIFTER rise. Best method is to find at what crank degree this occures and then then you can rotate back to that point while determining the PR length.

    Then you start with a pr length you think is close, set the lash and see where your rocker geo is when you go back to the mid lift spot on your degree wheel. Then you make your PR adjustments, (while back a zero lift) and reset the lash and do it again. There are some short cuts, but seriouly do not recommend them to any body doing this the first few times. Its slow, and you cannot do it in one shot. Thats why I recommend knowing at what degree the crank is at when the lifter is at mid lift.

    You CAN NOT just find max lift from the retainer and then back it up to the bmid lift point.Your now at mid lift, but the geo isn't right. And you can't just make PR adjustments at that point until it is. Your not necessarly at mid lift on the cam shaft.

    PS I have looked at all your pics and for the life of me, cannot figure out what your trying to show. Which is just another reason I think you going about this wrong.

    You can not adjust the PR while the cam or the rocker is at midlift. This may account for you finding extra lift when you do this. When you have adjusted you way, have you gone back to zero lift, with out changing anything, the verify your lash is still correct.



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    Last edited by gn7; 11-17-2010 at 04:49 PM.

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    GN brings up a good point of making sure you re-set your lash every time you change the length of your checking pushrod. If you're not, this could account for your excess lift at supposed correct geometry.
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    gn7
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    Shaun, the easiest way I have found to do this as a novice, is to make all my pushrod adjustments while the lifter is on the base, and then go back to the midlift point on the timing wheel.

    There are short cuts to get close, but i would mess with them the first few times. Once you have done it a few times, you see whats happening, and you can figure out the quicker ways. In time, you can set the rockers pretty damn close with the heads on a bench if you know the cam lift. Then just measure for the push rod. But for now, determine weither the PR needs to shorter or longer with the lifter at mid lift, and make an adjustment on the base circle, rest the lash, and go back and check at the lifter mid rise point again. And again, and again, if necessary. Each time, on the base circle, and reseting the lash.



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    www.highflowdynamics.com LakesOnly's Avatar
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    Quote Originally Posted by fc-Pilot View Post
    Lakes, I understand that the roller tip does not need to be in the center of the valve, but I prefer (if possible) to have the geometry right AND have it near the center of the valves tip. Usually when it is then it means that the rocker is a little lower on the stud and has less chance for stud deflection (if not using a stud girdle) or will not have clearance issues with the stud girdle. It also ensures that the rocker will be located in the unthreaded area of the stud instead of slopping on the threads of the stud. All of this I am sure you know, I am just stating why I made the comments that I did earlier. It was not out of blind ignorance but from my own personal experience using the method you mentioned. Now, had a personal experience with having it setup near the edge of the valve tip. Due to harmonics the stem of the valve moved around enough that during high RPM runs the tip would actually come off the side of the valve tip (to the exhaust side). I know there were other factors involved, but this is why I prefer to try and get the tip to the center WHILE obtaining proper mid-lift geometry. It helps provide more piece of mind.

    Also, thanks for taking the time to post as I know many don't as they figure it will turn into a pissing match where someone tells them they are an idiot for doing things right.

    Paul
    I didn't mean to come across as condescending, and I apologize if I did. I instictively addressed both of you because of the "roller tip in the middle of the valve" clauses that were written, and that was my knee-jerk reaction to that statement wherever I see it. My post was intended for all to read even though I addressed those that said it.

    I think it's safe to say that we all would prefer to see the roller tip in the middle of the valve. And if all the design geometry is correct within a given valve train then the roller tip should fall in place right there indeed. But we are talking unique, custom engines and so when things don't have exacting design geometry when mid-lift theory is applied, the roller tip will not necessarily fall there. This does not mean the installed geometry is off. Errors in design geometry may include things such as a mis-located rocker stud, or a mal-designed rocker arm, or a longer than anticipated valve stem OAL, etc. And so, when applying mid-lift geometry, one must let the roller tip fall wherever it may in the interest of giving proper installed geometry the priority. Once we begin adjusting pushrod length just to bring a roller tip over the center of the valve, for example, we are also compromising the valve train geometry.

    Referring to my above engine example in post #3, the engine we went through: I gotta say that I sure didn't like seeing that roller tip on the outer-most edge of the stem tip, and I understad the risks involved should there be other matters affecting the system's operation. But in this particular case the individual components were intelligently selected and made for a very stable valve train setup and it worked just fine...and thereby serves as a good example of how things should work together when everything is just right. If we had been the original builders of that engine 7 years ago, I confess I might not have let it out of the shop that way; but because we were able to evaluate the results of this setup after 7 years of racing (it came in primarily for a new shortblock) I advised the customer of our observations and findings (favorable findings) and didn't attempt to upsell him on an additional $1000 of valve train upgrade/config that he did not come in for in the first place or necessarily need....unless he wanted it, and which he didn't since the system was functioning precisely as intended.

    Good geometry,

    LO
    Last edited by LakesOnly; 11-18-2010 at 09:56 AM.
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  14. #12
    I'm No Expert Shaun's Avatar
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    Bob, Ahhh so i need to be checking the lift at the lifter to determine mid-lift? The posts i've been reading from the old hotboat site were saying to check at the valve.

    Shaun...it's 90* at mid lift. You need to know what the lift is at the valve, and check the rocker at 1/2 of the net lift (at the valve).
    Also, i'm not adjusting the pushrod while at mid-lift, i was going back to base, makeing an adjustment, cycling back around to find max lift, dividing by 2, go back to mid-lift and check.

    I'll check at the lifter, and see what i get!

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    www.highflowdynamics.com LakesOnly's Avatar
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    Quote Originally Posted by Shaun View Post
    Bob, Ahhh so i need to be checking the lift at the lifter to determine mid-lift? The posts i've been reading from the old hotboat site were saying to check at the valve.



    Also, i'm not adjusting the pushrod while at mid-lift, i was going back to base, makeing an adjustment, cycling back around to find max lift, dividing by 2, go back to mid-lift and check.

    I'll check at the lifter, and see what i get!
    The above quote is checking the net results, not part of the preliminary setup / evaluation.
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  16. #14
    steelcomp was here
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    Quote Originally Posted by Shaun View Post
    Bob, Ahhh so i need to be checking the lift at the lifter to determine mid-lift? The posts i've been reading from the old hotboat site were saying to check at the valve.



    Also, i'm not adjusting the pushrod while at mid-lift, i was going back to base, makeing an adjustment, cycling back around to find max lift, dividing by 2, go back to mid-lift and check.

    I'll check at the lifter, and see what i get!
    Honestly, this is the first I've heard of checking at the lifter for mid lift. If you're adjusting on the base circle, re-setting lash, and then checking the geometry, there's nothing wrong with that. When it's right, it's right, no matter how you get there. Personally I think checking at the valve is more accurate.
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