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Discussion Starter #1
have a set of iron n352 heads that were new and installed bronze liners after working on them.well i have put about 3500 miles on them and i pulled them off just recently to port them to match my new rpm2 intake and noticed guide wear is pretty noticable.looked at the top of a couple valves and it looks like rocker is riding correctly in the middle of the stem.very short pattern and IF any bias toword side it looks like the rocker arm might be riding closer to the exhaust side of the tip.

any other ideas on the problem,i normaly dont run into junk like this.:(

also i did use a custom length pushrod to get geometry close.like i said looks like valve is riding correctly with maybe slight bias toword exhaust side.
 

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Not real sure, could have had to much clearence to start with. Other than that, sounds kind of strange. Probably be better to drill them out, and put in bronze guides, instead of liners.

Good Luck, Greg(XSR)
 

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your pushrods are wrong. forcing the rocker arm to the center of the valve stem is not the correct way of determining pushrod length. (if this is not the method you used, then I may have overstepped with my assumption, sorry about that).

Continueing on, forcing the rocker to the center of the valve using pushrod length adjustment is simply all that does. It does not guarantee correct pushrod length.

There are all sorts of differeing angles and heights in the rocker arm geometry. forcing the rocker alignment to a particular portion of the valve stem is not necessarily the correct pushrod length.

The correct pushrod length (for durability) is the length that enables the line of action on the valve stem to be the most 'tangential' line of action possible from the rocker fulcrum. This will produce the narrowest wear pattern and will produce forces as close to the centerline of the valve as possible, and is rarely on the center of the valve stem.

If aligning the set-up in this fashion places the rocker too close to the edge of the valve stem, then some geometry changes have to be made. rocker arms brands switched, longer or shorter stem valves, etc.

This is the exact reason for all the TFS wear problems too.

Could be you have a bad batch of guides. never seen them before, but its possible. but my bet is the pushrod length is still not correct. I have seen guides trashed in a month on track cars. thats like 20 miles.

Buddy Rawls
 

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If your rockers are ridding on the out side edge of the center then that is not correct Kind of a basic way to look at is you want the rocker just slightly inside of center. As the valve is being pushed down the tip of the rocker should move towards the center of the valve stem and slightly cross over, at the midpoint of lift the rocker should start heading back towards the center again and be pretty much centered at max lift.
 

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hate to sound so weird on this, but the center of the valve has nothing to do with finding the correct length for the pushrod (period)

the center (or close as possible) of the valve is where you 'want' the alignment to occur. But forcing it to that position is not how to find the correct length.

the first iteration of determining the smallest wear pattern may be close to the edge of the valve stem. It may actually be off the valve stem all together.

This is where something that changes the angular relationship must be modified. The rocker tip to fulcrum length, or possibly a shorter stem valve, or maybe lengthening via a lash cap (by far the easiest).

Its not hard to see the relation.

draw the side view if a head assembly.

showing the valve and its tip height and line of action. then draw a stud and rocker arm and its pivot and valve contact tip or roller. draw it right with the angles of the stud and valve stem leaning toward each other.

draw a circle, with the center on the rocker fulcrum and the radius at the rocker tip.

now find a tangent line (orthogonal/90 deg to the radius of the circle).

what you really need is for the this tangent line to be dead on thru the valve line of action at close to mid lift. so you have to try several scenarios.

what you will see is that dependent on the length of the rocker arm (distance from the valve stem centerline to the rocker stud) or the height of the valve stem are very important. and that we have not even discussed pushrods yet!

as an example of what forcing to the center of the valve does:

take the same drawing and force the rocker arm contact point to the center of valve at mid lift, then draw the line from the radius of the circle thru the centerline of the valve. then from the same point, draw the true tangent line from the same point. this angle formed between the forced line and the true tangent line is the amount of off axis loading the valve centerline is seeing. this will result in heating of the wear path in the guide and eventually metal removal due to friction. this is guide wear.

I dont care what everything you read says, with regards to finding the center of the valve. but forcing it to that point does nothing in the equation to finding the correct geometry.

to find the correct alignment you have to find this tangency point. it is found pretty easily becasue it is the length that will give the shortest wear pattern on the valve stem.

I have seen alignments, by forcing the center of the rocker arm at the valve stem, that produced a wear pattern across half of the valve stem. by looking at the sketch described earlier, this is the pattern displayed when the tangent point is not close to the valve centerline.

granted finding the exact tangent point may not be practical, but if the pushrod length selected was close to this point you will be MILES ahead of the process than you would be by forcing it to the center.

Buddy Rawls
 

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and if all that is correct the rocker will line up and track just like I said LOL.
 

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buddy,

good info.
 

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Discussion Starter #8
thanks for the info,i do think the push rod is wrong.the way i came about a length was by finding the length for a flat tappet with these heads then subtracting the diffrence for the hydro roller and milling.after installing them the first time it looked like the pushrod was to long by looking at the relationship the rocker had to the rest of the valvetrain but after seeing ride in the center i convinced myself that it should work.

obviously i was wrong on this and when putting it back together i will try and set it up the correct way.
 
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