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| Rocker Geometry after milling/decking/valves https://www.slantsix.org/forum/viewtopic.php?t=25158 |
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| Author: | sandy in BC [ Mon Oct 01, 2007 1:15 pm ] |
| Post subject: | Rocker Geometry after milling/decking/valves |
I have some questions about rocker geometry that may have been addressed somewhere individually but not as a "concept". I have decked my block, changed my cam, and installed longer SBC valves. I just purchased a new Erson cam and wonder about geometry. The old setup with Comp 264s was on the very edge of running out of rocker adjustment and I had installed jam nuts to keep the adjusters from backing out. I dont like more weight in the valve train. I would like to have the adjusters more in the middle of the range. I have had to dimple my valve cover baffle for clearance because the top of the adjusters can hit the baffle. I have had to grind a little on some rockers so they dont hit my valve retainers at certain lifts. I can solve the adjuster problem by shortening my valves or pushrods. I can solve both problems with a rocker stand solution. My questions: Was the factory geometry ideal? Are shorter pushrods a better fix than rocker stand shims or new stands? What are the implications of rockerarm massaging/trimming? Can I just file fit my valve tips to take up some slack like I did on my Flathead? |
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| Author: | Joshie225 [ Mon Oct 01, 2007 1:49 pm ] |
| Post subject: | |
Longer valves are a bad deal as they not only create rocker adjustment problems, but reduce the rocker ratio. The longer the valve the the closer to the rocker shaft the tip becomes reducing the ratio. In theory you need to move the rocker shaft upward and away from the valve stem to get the rocker to valve geometry correct. Then get pushrods to match. Decking the block doesn't hurt the valve train geometry only the needed pushrod length because the rocker pivot point is fixed unlike anything with a moveable fulcrum. The factory geometry is rarely ideal and usually falls short of the published 1.5:1. In your case you need either shorter valves or a higher rocker shaft placement. Simply moving the rocker shaft up will help you clear the reainer, but leave you with a lower rocker ratio. The implication of rocker arm trimming is strength. The valve tips need their hardened tip because the rocker arm wipes across the valve tip. The flathead didn't have rocker arms and no wiping action. Did I miss anything? |
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| Author: | sandy in BC [ Mon Oct 01, 2007 2:22 pm ] |
| Post subject: | |
Luckily I dont need to move the rocker away from the valve...its very good where it is....if I shim a little.... |
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| Author: | Charrlie_S [ Mon Oct 01, 2007 2:58 pm ] |
| Post subject: | |
Josh, are you looking at a slant head or a V-8 head? I am working on a long valve slant head, and my rocker shaft needs to be raised up and move toward the valve. On a slant head the valve stem tilts away fron the rocker shaft. On a Mopar V-8 the valve stem tilts toward the rocker shaft. On my head it looks like (eyeball) the shaft needs to be raised about .250 and moved toward the valve about .100. I still need to get acurate measurments. Then I will have to make longer pushrods (I think). |
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| Author: | mopardemon71 [ Mon Oct 01, 2007 3:08 pm ] |
| Post subject: | |
so I jumped in the other tread that took this subjuct up. Ill try again, if the head deck serface is not milled say past .050 would that creat a problem with the SBC valve useage? or is the lenght or the valves to much? Where can one find the shims to heighten the rockers to the correct lenght. Rocker ratio my be adjusted buy using 1.6:1 rockers. Also if they are roller type would that take off some of that "swipe stress". |
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| Author: | Joshie225 [ Mon Oct 01, 2007 3:14 pm ] |
| Post subject: | |
Quote: On a slant head the valve stem tilts away fron the rocker shaft.
Ahh, that's what I missed! So longer valves would help the rocker ratio on a slant!
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| Author: | terrylittlejohn [ Mon Oct 01, 2007 3:49 pm ] |
| Post subject: | rocker geometry |
the length that the ajustment screw is away from rocker also affects rocker geometry by lowering the pivot point witch lower rocker ratio, when i shorten my valves at the tip with all the milling on both surfaces,with lash done there was only 2 treads showing ,1 would have been closer as to clear push rod to rocker clearance at max lift.the valve tip show no wear although the mechanist did say the ex tip was harden at the tip. |
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| Author: | sandy in BC [ Mon Oct 01, 2007 3:50 pm ] |
| Post subject: | |
Looks like I need to go up about .250 to get to where I need to be with my setup as well. ... Then I would have correct geometry , stock pushrods .... Time to hand file some shims from an old shaft........? |
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| Author: | slantzilla [ Mon Oct 01, 2007 5:49 pm ] |
| Post subject: | |
Quote: Looks like I need to go up about .250 to get to where I need to be with my setup as well. ...
Be careful shimming the rocker shaft as it will split the sides off the stand. Then I would have correct geometry , stock pushrods .... Time to hand file some shims from an old shaft........? 
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| Author: | sandy in BC [ Mon Oct 01, 2007 6:50 pm ] |
| Post subject: | |
Quote: Be careful shimming the rocker shaft as it will split the sides off the stand
Hence my hand file remark. It definitely needs to be done correctly.A piece of thick wall tube same OD size as rocker shaft. Slice the top 1/2 off and hand file till the rocker shaft "nests" into the ID. Done correctly there should be no side loading on the stand...... Im good at making 2 items....the first is usually a mess..the 2nd pretty dialed....the rest are so/so cuz Im bored. "LUCY!....yoo bin filing loominum with my chainsaw files again!?" |
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| Author: | Charrlie_S [ Mon Oct 01, 2007 7:37 pm ] |
| Post subject: | |
Quote: Be careful shimming the rocker shaft as it will split the sides off the stand. I did that to a set of 440 heads, and used the 413 bolt on stands, to allow me to use some shaft mount Chevy roller rockers. Back then, I had access to a machine shop. Now I do not. |
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| Author: | Will [ Tue Oct 02, 2007 3:57 am ] |
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Add shots of rocker shaft, most will not need to go to this extream but it will give you some ideas. Got the truck back from body shop yesterday, I will add pictures of new paint. hope link works!!!??? http://slant6racer.mysite.com/?refcd=WSUOWS080630NE03 |
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| Author: | Charrlie_S [ Tue Oct 02, 2007 2:56 pm ] |
| Post subject: | |
Quote: Add shots of rocker shaft, most will not need to go to this extream but it will give you some ideas.
Will. The link works, but I don't see any shots of the valve train.
Got the truck back from body shop yesterday, I will add pictures of new paint. hope link works!!!??? http://slant6racer.mysite.com/?refcd=WSUOWS080630NE03 |
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| Author: | dakight [ Tue Oct 02, 2007 3:50 pm ] |
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Quote: Quote: Add shots of rocker shaft, most will not need to go to this extream but it will give you some ideas.
Will. The link works, but I don't see any shots of the valve train.Got the truck back from body shop yesterday, I will add pictures of new paint. hope link works!!!??? http://slant6racer.mysite.com/?refcd=WSUOWS080630NE03 |
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| Author: | Sam Powell [ Tue Oct 02, 2007 3:59 pm ] |
| Post subject: | |
Will, that looks really great. Let us know how it works. Sam |
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