so what exactly do too long pushrods do?
Thread Starter
Race Director
Joined: Jan 2008
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From: oregon
so what exactly do too long pushrods do?
A few months ago i swaped out a set of ported 113 castings for some nice pro action 180cc jobs. the problem i'm having is the pro's were shaved from 64cc to 58cc and the block has been decked .010 as well. the stock length 7.200" rods were not what i would call centered when they went back in. of course this has me thinking the motor should be using 7.150" to compinsate for the shaving. i just received a $30 off coupon the other day, this would put the comp magnum 7.150s at $89, doing sooner rather than later; but what's going on in the mean time?
Race Director
Joined: Sep 2000
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From: The Top of Utah
Too long a push rod will do the same thing as too short a push rod; mess up the valve train geometry. You don't know for a fact that you need shorter push rods until you check your valve train geometry. Just because of all the milling, you still don't know what you need unless you checked it and knew what you needed before hand. Most of the on-line cam catalogs, Comp, Crane, etc. have an article on how to check and adjust the geometry.
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Burning Brakes
Joined: Sep 2005
Posts: 993
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From: Iowa
With the valvetrain out of geometry there will be some additional loads imposed on several of the parts. These would not normally exist and are not taken into account when they are designed so try to make it sooner rather than later but at close to stock levels of pressure and RPM you shouldn't have too many problems with it.
Drifting
Joined: Mar 2008
Posts: 1,756
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From: Wichita KS
All the above are correct. Put simply, the roller tip of the rocker arm will be exactly centered on the valve stem tip at half valve lift.
Incorrect geometrey will wear valve guides and possibly seize a guide to the valve stem (worce case).
Incorrect geometrey will wear valve guides and possibly seize a guide to the valve stem (worce case).
Thread Starter
Race Director
Joined: Jan 2008
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From: oregon
Yep, the guides were my first thought as well, it would create a possible binding environment, probably cost HP as well. When i put the motor back togeather my concern grew when i noticed i wasn't centering on the valve stem. A local engine builder was with me and took a look, said "hmm..little long". At the time i needed to drive the car home since it was in my buddies driveway so we bolted it all back togeather. I probably should be calling summit in the next couple days and placing an order for those 7.150s. I could also see increased stem and rocker wear since the wheel on the rocker arm isn't centered on the stem like it should be. This motor constantly is spinning 6500rpm with 340lb of open spring pressure. Think it's 340, anyone remember what a comp 987 spring rate is?
Race Director
Joined: Jan 2002
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From: O'Fallon Missouri
Also, I'm with CFI-EFI that you need to measure for the correct pushrod length before you order.
Melting Slicks
Joined: Nov 2004
Posts: 2,799
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From: Cape Coral FL
Too long a push rod will do the same thing as too short a push rod; mess up the valve train geometry. You don't know for a fact that you need shorter push rods until you check your valve train geometry. Just because of all the milling, you still don't know what you need unless you checked it and knew what you needed before hand. Most of the on-line cam catalogs, Comp, Crane, etc. have an article on how to check and adjust the geometry.
RACE ON!!!
RACE ON!!!
You'll need an adjustable pushrod to do this... Once you've arrived at the proper length, measure the pushrod and order the corresponding length pushrod needed.
