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valvetrain geometry check - do I need shorter pushrods?

Old 05-12-2011, 09:49 PM
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Default valvetrain geometry check - do I need shorter pushrods?

Well crap - I did a quick mockup on the new engine to check valvetrain geometry. Installed one head and intake/exhaust lifters in #1. Spun engine over a few times with magic marker on the valve tips. Looks to me like I need a shorter pushrod. I am running stock length pushrods in it right now. Block had maybe .006 taken off to square things up - pistons ended up .008 in the hole. Heads were milled around .025 to help bring up compression. Head gasket compressed thickness should be .039 - this is actually an old gasket that I put on temporarily for the mockup. I was hoping things would even out because cam was reground for more lift and had about .050 taken off the base circle. I actually thought I might end up needing slightly LONGER pushrods, not shorter.

Someone who has been down this road a few times take a look at these pictures and let me know if I am OK, or if I need to dump another $300 on custom pushrods.









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Old 05-12-2011, 09:57 PM
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Default Fixx

yep! with shorter make sure the underside of the rocker dont scuff on the spring retainer..you may be able to get away with lash caps but you will have to change the valva keepers..lash caps will raise the valve tip some to center the rocker..
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Old 05-12-2011, 10:40 PM
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OK, so just for grins I went back out there and tried it again, this time I mocked the intake side up with an EXHAUST pushrod I had from a flat tappet motor. This pushrod is actually about .25 shorter than the stock pushrod.



The marks it left on the valve look pretty good to me!



I am doing these tests with the stock hydraulic lifters. They were pretty much pumped up all the way for the first few rotations. Now they have bled down, so tomorrow it's off to the hardware store to find a bunch of washers I can stack up inside a couple of lifters. Even if the plunger is going down a little bit, it further emphasizes my first test showing that the pushrod might be too long.

Stay tuned...
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Old 05-13-2011, 05:47 AM
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I worked with Bob Madara (Marine Kinetics) over the winter on this very issue. You can really hurt valve lift (full and mid) by not having correct valve train geometry and you will not take full advantage of the mods you have made to make hp. Bob has some articles that are very informative that he would be glad to share with you if you call him. His number is posted on here a million times. You need better geometry from the pics.
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Old 05-13-2011, 06:20 AM
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I'll give him a call and ask him. What do you think about the geometry shown in the last picture?
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Old 05-13-2011, 07:34 AM
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You might as well order in the test valve springs right NOW he is going to make you. then get a bottle of Crown reserve because he is going to shoot you about 10 pages of reading you will need to do. And it's all the right thing to do!
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Old 05-13-2011, 07:51 AM
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Originally Posted by Budman II View Post
I'll give him a call and ask him. What do you think about the geometry shown in the last picture?
When your valves are closed the roller will not be centered over the valve. Assuming your lifter is pumped up all the way your marks are very close to the center of the valve stem so I'd let it fly. However, if it's a hydrualic roller you should use test springs. If you milled the block and did a valve job theoretically your pushrod would need to be shorter but it looks as close as can be, again assuming the lifter was pumped up. You milled the block down but milled the cam down so you're probably netting close to the same installed heights.

Another thing to check is geometry from the top. Check to make sure the roller is centered over top of the valve. You can move the guide plates around a little bit and sometimes this can get everything close but if you can't get it close you have to modify the guide plate or buy the new Dart guide plates that have an adjustment in the center.

Last edited by Panther; 05-13-2011 at 07:56 AM.
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Old 05-13-2011, 07:54 AM
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oh yeah. I can't tell from the pictures. Do you have sealant on the rocker arm studs?
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Old 05-13-2011, 08:43 AM
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Check this site out www.mid-lift.com
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Old 05-13-2011, 01:40 PM
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Panther, it's just a mock up, so I don't have any sealer on anything yet. Going to check it again with a lifter that was made into a solid with some shims. Also have adjustible PR's to use.
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