vettenuts

iTrader: (4)

The only way to change the wipe pattern on a fixed pivot point rocker (assuming the same cam is used) is to raise and lower the pivot point. To raise it you need to shim. To lower you need to remove material (or in your case the shims). If you are unsure of the situation you are in, you can install the rockers with a check spring (no pushrod) and use a dial indicator to measure lift at the valve. Mark the top of the valve tip with a Sharpie and rotate the rocker with your hand through the lift provided by your setup. This will allow you to verify the wipe pattern and adjust it without a lot of work. It will also verify that the installed shims are required and correct.

Not to say your shop didn't do this, but it is time consuming and most shops don't bother. Also, if you provided the pushrods and they were required to use them, they may have shimmed to adjust the lifter preload.

jdoyle

iTrader: (27)

a quick question, how much does a decent dial indicator usually cost? i am going to be taking one of the heads off very soon and would like to compare the cost of doing this myself versus having the machinist check the wipe for me while the head is at his shop.

i cant check the wipe/swipe by putting some sharpie ink on the valve tip and turning the engine over by hand, can i?

Duffster

iTrader: (103)

By milling the the head, you physically drop the fulcrum point of the rockers by how ever much you mill. Is it significant? You would have to do the math. Does it change the required length of the pushrods? Again, I say yes. If you shave 0.050" off the face, and keep the same 7.400 pushrods, once you torque the rockers back into place, the preload of the lifters is stressed by that extra 0.050". Will the lifters correct this? Probably, but you can do one of two things... change pushrods to some ~ 7.350" OR shim your rockers UP by that same 0.050". If you do neither, it's like using 7.450" pushrods. Will this be significant with regards to the wipe of the rocker on the valve? I doubt significant, but it will no longer be perfectly centered. Deny this and you're probably a racist-homophobe commie who's afraid of trigonometry . . .

jdoyle

iTrader: (27)

i would agree with you that it changes the required length of the pushrods as well.

i just need to figure out if it changes my wipe/swipe or not.

Oh by the way, I measured the shims at .035"/shim. I had two shims under each pedestal so I was shimmed up 70 thousandths. When i was shimmed up, a 7.4" pushrod gave me ~60 thousandths preload.

so does anyone know if dropping the pedestal down .070" and using a 7.325" pushrod (ill sacrifice the 5 thousandths in preload) will change my wipe/swipe?

vettenuts

iTrader: (4)

I guess that's me except the trigonimetry part. Milling the heads won't affect the rocker wipe pattern with a shaft rocker if rocker movement begins at zero lash. Many methods of verifying the geometry of a shaft mounted rocker are done on the work bench where head milling doesn't come into play. I have even done stud mounted rockers on the work bench, and pushrod length will effect wipe on a stud mounted setup.

vettenuts

iTrader: (4)

Yes it will, however I am willing to bet the wipe is not correct to start with. By eliminating the shims, you are moving the pivot point of the rocker and by doing so you are changing the wipe pattern. However, based on your numbers I think they installed the shims to adjust preload so they could use the 7.400" pushrods.

I don't see anything in your profile, are you running a cam or aftermarket heads?

vettenuts

iTrader: (4)

You can get one from Comp Cams or you can get one from McMaster-Carr. Can't remember the cost of the Comp unit.

If you are pulling the head, the wipe pattern can easily be bench checked with check springs. You can't do it on the car because if you turn the motor over by hand the lifter will bleed down and the lift will not be correct. You would need a solid lifter. This is very easy to bench check.

KCS

iTrader: (20)

I found a dial indicator at Harbor Freight for about $15 IIRC.

KCS

iTrader: (20)

I wasn't arguing anything to the contrary of what you just said. I agreed that you would need different length pushrods for milled heads, and that shimming the rockers will not fix a "geometry problem" associated with milling the heads.

However, I do not think milling heads requires shimming the rockers unless the geometry was already bunk or you're too cheap to buy new pushrods and don't mind the added side loading of the valve.

KCS

iTrader: (20)

I'm getting the same impression.

With the stock rockers, I'd probably try to change the rocker based on the changes made, and not the wipe pattern. For example, if the cam was .100" bigger, I'd lower the rocker by half of that (.050") or add a lash cap on the valve. If the valvejob sunk the valve, I'd shim the rocker that same amount. That way, the geometry would be at what the GM engineers intended from the factory. I personally like using raw data, rather than trusting my eyeball and a sharpie.

vettenuts

iTrader: (4)

At this point not sure what the OP's setup is. That is sort of where I was going, if he is running GM heads with the harder guides the shimmed rockers may actually be make things worse even with a cam. Last time I corresponded with Erik at HKE he stated he found the stock rockers provided better geometry with an aftermarket cam by lowering them so if the OP has a cam and the rockers are raised by 0.070" I wouldn't be surprised if the rocker tip is near the outside edge of the valve stem at full lift.

KCS

iTrader: (20)

Exactly, plus without a roller, if it's bad enough the tip of that rocker will dig into the valve and really cause issues.

jdoyle

iTrader: (27)

ya guys i should have posted my setup.

ill post everything from the cam to the valve.

tr224 cam on a 112 (224/.563/112)
Comp 850-16 lifters
7.4" pushrods
stock rockers
Ferrea intake valves (either a 2.02 or a 2.055)(are these taller than stock intake valves?)
patriot gold springs
853 casting head milled .030 at one point, then they were true'd after my first "tuner" popped either one or both head gaskets, so id say that they have been milled another 2 - 5 thousandths to clean them up.

please let me know if you need any other information. BTW, the car has been running like this for about 20K miles. the valve stem/tips don't look rounded or anything to me.

does anyone have a write up on how to bench test the valve/ rocker wipe/swipe? i found one on corvette forum a couple days ago, but i didnt bookmark it and now i cant find it.

i think so as well.

something that Erik posted on hardcorels1.com is what got me thinking about the shims and stuff. Erik is very hard to get a hold of.

vettenuts

iTrader: (4)

That post on Corvetteforum may have been mine. Here is the link. Link

Stock rockers can be done the same way. If you have an old aluminum rocker support (they are cheap anyhow) you can break off the end two rocker supports and thin it out to lower the rockers to see if that helps. If it does, you can get a set of steel rocker supports and get them machined to the required height. I think Erik has some information on that over on hardcorels1.

Based on your cam, I believe your rocker height is way too high.

jdoyle

iTrader: (27)

yup it was your post.

couldnt the rocker pedestals be shimmed up because i have a really tall intake valve (taller than stock)? not trying to prove you wrong, im just trying to visualize/understand this.

could you tell me why the rocker wouldnt need to be torqued down all the way to check the wipe properly? actually, i imagine that you mean use a ratchet, just not a torque wrench when you say, "Hand snug is fine and will eliminate thread wear as the bolts are taken in and out several times during the process."

jdoyle

iTrader: (27)

could you elaborate on this please?
i know that these heads have had a minimum of 2 valve jobs done to them.
in my head, i could see how 2 valve jobs and using a taller valve (i dn if my valves are taller than stock valves) could make shimming the rocker pedestal necessary. do you think that this could be the case?

vettenuts

iTrader: (4)

Yes, if the valve stems are taller then that will have an impact on the rocker setup and could result in the need for shims.

Also, as far as the bolts, when you tighten the rocker it will first bottom then the bolt will tighten up to the torque value. All you really need to do is make sure the rocker is fully bottomed to make the measurements so there is no need to load the aluminum threads with each measurement.

chrisfrost

iTrader: (8)

Yes the lifters will absorb some , but probably not all because the spring inside the lifter is gaining pressure the more it is compressed . So ultimately , the valve will probably open a few thous. more than before the mill . So , it can and probably will change the swipe a little , and in some cases the valve may not close solidly .

KCS

iTrader: (20)

Raising the valve with a lash cap or by cutting a valvejob has similar effect as lowering the rocker from a geometry standpoint. You need to understand that most of rocker geometry that a builder will deal with is getting the height of the rocker and valve tip correct in relation to eachother.

Depending on how much was cut when the valvejobs were done, the shims could have been necessary. However, if new seats were installed for the larger valves, it's likely that the valve was actually lowered, so there's now I could give you a straight answer without knowing more.

I think it's about time you talk to the guy who did your cylinder heads for more info about your particular head. It sounds like a lot of work has been done to it to the point that we can only give you "what if's" and "maybes".

KCS

iTrader: (20)

No, the lifter is going to absorb it all until it bottoms out. The spring in the lifter is not going to overpower the valvespring. You will just end up with more preload.