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stock valve train geometry

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Invectivus
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Joined: Tue Nov 27, 2007 11:41 am
Location: Morgan Hill, CA

stock valve train geometry

Post #1 by Invectivus » Tue Dec 03, 2019 12:58 am

Does anyone know the valve stem angle, and is it measured from vertical? Could I find that by measuring the angle of the spring seat, since stem and seat should be perpendicular?

Also, it would be handy to know what the stock push rod angle is as well.

I'm assuming these numbers are the same for all small sixes but if not, I'm wondering primarily about the 200.
1967 mustang coupe - 200ci, 69 dizzy, adjustable rockers, headers and dual exhaust, T5.

1964 convertible falcon - Gutted.

1973 EB Bronco - 302ci (sorry!) DUI ignition, C4/D20, Dana 44, 33's

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wsa111
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Re: stock valve train geometry

Post #2 by wsa111 » Tue Dec 03, 2019 7:30 pm

I don't know what you are after, but the ideal contact of the rocker arm on the valve stem is as follows.
At maximum lift the contact should be in the center of the valve stem.
The sweep of the rocker arm should start at the first 1/3rd, full lift center & after full lift the last would be the last 1/3rd.
67 mustang,C-4, with mod. 80 hd, custom 500 cfm carb with annular boosters, hooker headers, dual exh.-X pipe, flowmaster mufflers, DSII dist. MSD-6al & MSD-Blaster 8252 Coil. Engine 205" .030" over with offset ground crank & 1.65 roller rockers. 9.5 comp., Isky 262 cam.
2003 Ford Lightning daily driver. Recurving Distributors. billythedistributorman@live.com
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Invectivus
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Posts: 384
Joined: Tue Nov 27, 2007 11:41 am
Location: Morgan Hill, CA

Re: stock valve train geometry

Post #3 by Invectivus » Wed Dec 04, 2019 12:10 am

So what I'm after is trying to calculate some varying geometries off different bits.

So the order of planning looks to be:
1 - document cam lift
2 - multiply by rocker ratio
3 - take that valve lift to discover mid lift for rocker pivot to tip 90 degree angle (this is why I want the valve stem angle, though I can consider the valve stem as 0 degrees as the absolute reference angle)
4 - take the pivot length (?) to calculate where the pivot goes in relation to the pedestal mounting surface. This would be to build either custom shaft pedestals or rocker shaft bedding.
5 - take the push rod angle to see what the optimal mid lift point is along the curve of the rocker. For scavenged rockers, we're almost assured to be off the optimal by varying amounts. My understanding is that the angle of the push rod from vertical at rest is the same angle up from horizontal along the rocker's rotation.
6 - once the most optimal adjusted pivot point for that rocker is determined, either measure and order push rods, throw those rockers out, or start massaging the number to see if changing the rocker shaft axis or adding lash caps or getting longer valves will help. I recognize sub optimal push rod to rocker geometry hurts actual lift ratio and stresses assemblies.

In the simplest terms, I want to make some garbage on my mill to put rockers on my engine that were made for something else. It might work, or might blow it up. Smarter and more educated people than me have messed in this arena and not really come up with anything, but I'm bored and like spending money.
1967 mustang coupe - 200ci, 69 dizzy, adjustable rockers, headers and dual exhaust, T5.

1964 convertible falcon - Gutted.

1973 EB Bronco - 302ci (sorry!) DUI ignition, C4/D20, Dana 44, 33's

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