Another valve train geometry question
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Another valve train geometry question

  1. #1
    Senior Member SoldHondaBoughtHondo's Avatar
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    Default Another valve train geometry question

    This one might be a little different. I work in a engine build shop and everything motor we do gets valve train geometry checked. The way the boss wants it done is by using the correct length pushrod to get the roller tip in the middle of the valve stem on the heel of the cam load claiming that if the roller runs off center it wears out the guides. Somehow I have it stuck in my head that because of the roller tip it can't push the valve off center. Part of the reason I think that was is because I had a set of heads with the most worn set of guides anybody has ever seen..I will post a video when I find it...had a machine shop do one head, replace the guides and touch up the valve job. I took the second head apart myself, its the one in the video..obviously the guides are way past junk (and it ran ok like that) couple things I did notice, the guides we're not worn out of round...like no it the geometry was off and the rocker was pushing the valve to one side, the wear was very even. The other thing I noticed was the top of the valve spring not being parallel to the bottom.. like maybe 15* when I put the motor back together I check the geometry using the mid lift method and the roller was right in the middle. I'm thinking that the cause of the wrecked guides I had and most other are caused by valve springs that don't compress evenly.. I asked the guy who did the first head about it, he said it didn't matter after they are installed. Anybody have thoughts on this? Thank mike
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    LP-25.com Infomaniac's Avatar
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    How much cam? Boost?
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    N/A. [email protected] 50. .700. 230/520 here is a set of slightly worn guides...and yes, it ran...no miss or back fire..
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    "A liberal paradise would be a place where everybody has
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    That almost looks like someone put 11/32 valves in a 3/8 guide.

    I can't give you specifics about a bbc with rocker geometry off from the mid lift theory. I can tell you this, I just ran a newly built SBC on the dyno and after pulling it off noticed that the guide plates looked a little funny. The rockers had just a tiny bit of tilt to them due to the guide plate position and upon tearing it down we found the brand new guides and valves almost ruined after 7 or 8 dyno pulls. And this was on a street style engine. I have never understood the theory of "the tip has to be on the center of the valve" concept. I do know that the wrong length valves or needing back-set rockers to compensate for the longer "needed" valves to keep the tip "on" the top of the valve. I have run into heads with the stud holes machined too close to the valves, but that was an odd one. I still follow the idea of mid lift as the best for preventing valve guide wear issues. Not being a regular engine builder I don't get to see enough stuff to really "know" one way or the other what causes this stuff though. I have to take the word of others for that.

    Paul

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    steelcomp was here
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    Here's a start;

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    Village Idiot fc-Pilot's Avatar
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    Gosh dang it Scott. I have been doing it for years by trial and error (lengthening or shortening the adjustable push-rod and measuring the results each time). The stupid part is I knew about this video and would even tell people to look it up to save me from explaining it. Now years later I finally watch it and see that I have been wasting time all these years. LOL

    Thanks for posting it up for us. I really appreciate the professionalism of the video. My brothers and I have been thinking about making videos in hopes of helping others from making mistakes (or to offset the bad info that is all over the internet and youtube) and you set the bar high as to how it should be done. For that we thank you.

    Paul

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    Quote Originally Posted by fc-Pilot View Post
    Gosh dang it Scott. I have been doing it for years by trial and error (lengthening or shortening the adjustable push-rod and measuring the results each time). The stupid part is I knew about this video and would even tell people to look it up to save me from explaining it. Now years later I finally watch it and see that I have been wasting time all these years. LOL

    Thanks for posting it up for us. I really appreciate the professionalism of the video. My brothers and I have been thinking about making videos in hopes of helping others from making mistakes (or to offset the bad info that is all over the internet and youtube) and you set the bar high as to how it should be done. For that we thank you.

    Paul
    Thanks for the compliment Paul. We did this mostly for our customers so that, when they bought pushrods, it was there to help them figure out how long they needed to be. It got real popular, real fast. I'm glad it's helped so many people.
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    That is why this site rocks! Thank you for the education, I am putting heads on this coming weekend and will be watching your video several more times!

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    Good info, thank. He mention something about roller to valve tip relationship..said get to that later...guess it's not all that critical or maybe when the pushrod length is established using this method to roller will be where it's supposed to be? What about with longer valves? Or heads with non stick valve and rocker stud angles?
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    I will step in for a minute, and Scott if I am off base please correct me, the roller tip does not need to be centered. I have had it both toward the exhaust side as well as the intake side on other engines. The brand of rocker, valve lengths etc. all play into it. I have one set of heads where we had to get creative as the rocker studs were machined too close to the valves, therefore the tip of the rockers were falling off the valve on the exhaust side.

    The main point is that with this geometry you are getting the most efficient straight down push as possible on the valve. Being just off center of the valve head does not induce a sideways push to cause guide ware.

    Paul

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    Minimum sweep trumps being centered. If your centered but the roller is moving .120" across the tip of the valve your going to wear out the guides. Minimum sweep of .060" or less will not work the valve. As long as your minimum sweep is within the center 1/3" of the valve tip your good to go.

    Aftermarket heads with longer valves have shortened the distance between stud and valve. This changes the geometry. Our BBC rockers that Scott designed are 8 intake rockers and 8 Exhaust rockers. When you think about that most aftermarket heads have a minimum of a .250" long intake valve and a .100" exhaust valve this makes sense. Also compounding the problem is some rocker mfg use the same part number to fit multiple engines.


    This engine had less than 1000 street miles on it and valve to guide clearance was over .007" with some...
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    What Paul said is pretty much where I am at. I took a BBC head with 3/8 guides, stuck a ,11/32 valve in it so it could flop around. Put spring/retainer/keepers and a roller rocker. Cobbled together a bolt with part of a pushrod welded on the end to simulate a lifter pushing up. Only had time to try it with the roller about 1/3 off center and half open the valve pretty much dangles in the hole... essentially no side load...I loosed up the rocker stud so I could move the guide plate around...that there could be a problem...looks like you might get away with a little misalignment but as soon the slop in the stud/trunion is gone it wants to drive the valve to one side. Get some time tomorrow I'm gonna heat up a spring to make it a little crooked to see what that does. If I understand the process correctly the mid lift method is also necessary to achieve max lift from the cam? And the farther away you get from that spec the more lift is lost in the angle of the dangle? And it also looks like it might load the rocker arm more than necessary? Thank guys!
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    steelcomp was here
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    Quote Originally Posted by fc-Pilot View Post
    I will step in for a minute, and Scott if I am off base please correct me, the roller tip does not need to be centered. I have had it both toward the exhaust side as well as the intake side on other engines. The brand of rocker, valve lengths etc. all play into it. I have one set of heads where we had to get creative as the rocker studs were machined too close to the valves, therefore the tip of the rockers were falling off the valve on the exhaust side.

    The main point is that with this geometry you are getting the most efficient straight down push as possible on the valve. Being just off center of the valve head does not induce a sideways push to cause guide ware.

    Paul
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