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You Guys Are Killing Me With This Shimmin RockersThing

Posted By: 71 FJ6 Charger

You Guys Are Killing Me With This Shimmin RockersThing - 07/17/09 06:26 PM

I have a stock 71 383 HP motor,the 346's on it are milled .030,and I'm using a .020 steel gasket.
I am using the factory cam(for now),and all the factory rockers,etc. After reading some posts on here,I am uncertain if I have to do this "shim the rockers" thing.
I did speak to Dave at Hughes,and from what I gathered(unless I'm a retard,still),unless the base circle of the cam is different than factory,he says,"why would you need to shim the rockers?". He says that there is a major common misconception for the reasons for doing this.
C'mon guys,my turn,enlighten me. I only want to do this once!
DO I NEED TO DO THIS?
Pleeeaaase,helpful and positve posts only if you could. I am sure youre all sick of hearing about it,just once more and I'll never speaks it's name again!
Posted By: JohnRR

Re: You Guys Are Killing Me With This Shimmin RockersThing - 07/17/09 06:45 PM

Shims go between the ROCKER SHAFT AND THE ROCKER STAND (head) , when you deck a block or heads are you CUTTING THE ROCKER STANDS ????

If the answer is NO then why would a person shim the rocker shafts to make up for decking the heads and block ? Why , because they are a

And I think you misunderstood Hughes or he misspoke , changing the base circle of the cam is NOT changing rocker to valve tip geometry , again , the base circle change does not change the height of your rocker stands so it will NOT effect rocker to valve tip contact. the fix there is a LONGER PUSHROD.

If your rocker to valve tip geometry were off and required a LOWER rocker stand postion to correct it the same line of thinking as ADDING shim under the shaft would be to just run a SHORTER pushrod ? NO , you would have to MACHINE the rocker stand shorter.

What you have done MAY require a SHORTER PUSHROD , PERIOD , END OF STORY .

MP sells ADJUSTABLE length pushrods , why , to FIX the above scenerios , except for lowering the shaft ....
Posted By: CJK440

Re: You Guys Are Killing Me With This Shimmin RockersThing - 07/17/09 06:46 PM

Bring the engine to TDC of #1.

Pull off the drivers valve cover and remove the rockershaft assembly. Strip off all the rockers except for #1 int and ex.

Reinstall shaft and finger tighten the adjacent hold down bolts until any pushrod lash is gone.

Lay a straightedge on the valve cover rail and lightly scribe a line on the 2 pushrods.

Tighten the bolts down completely and rescribe.

Remove the rocker shaft and measure the distance, thats your actual lifter preload.

That will tell you if your pushrods are the right length.
Posted By: mark7171

Re: You Guys Are Killing Me With This Shimmin RockersThing - 07/17/09 06:46 PM

appearently to change the rocker arm geometery. Side to side trying to keep it on the stem tip.

Agree with Dave, why would you?
Posted By: stumpy

Re: You Guys Are Killing Me With This Shimmin RockersThing - 07/17/09 06:47 PM

YOU DO NOT NEED SHIMS. Is that good enough for you?
Posted By: JohnRR

Re: You Guys Are Killing Me With This Shimmin RockersThing - 07/17/09 06:50 PM

Quote:

appearently to change the rocker arm geometery. Side to side trying to keep it on the stem tip.

Agree with Dave, why would you?



That's a different shim and they doesn't effect the rocker to valve tip geometry either , those center the tip on the stem .
Posted By: MoparforLife

Re: You Guys Are Killing Me With This Shimmin RockersThing - 07/17/09 06:53 PM

Quote:

YOU DO NOT NEED SHIMS. Is that good enough for you?

Short, sweet, and to the point. No you will not need a shim band aide.
Also listen to Dave and Kevin at Hughes, they have forgotten more than most here will ever know or learn.
Posted By: quick77rt

Re: You Guys Are Killing Me With This Shimmin RockersThing - 07/17/09 07:06 PM

Only dealing with small blocks Ive never had to shim anything, but then again why do they make shims if there is no real world use for them?

This is sorta like the lash cap issue it seems, some use them some dont...some say there is never a need but they still make them.

But isnt a lash cap also a shim of a sort?

Its pretty simple to know how and where your rocker tip needs to be on the valve so I say do what you got to do it make things correct.
Posted By: 71 FJ6 Charger

Re: You Guys Are Killing Me With This Shimmin RockersThing - 07/17/09 07:19 PM

Quote:

YOU DO NOT NEED SHIMS. Is that good enough for you?


Bring the engine to TDC of #1.

Pull off the drivers valve cover and remove the rockershaft assembly. Strip off all the rockers except for #1 int and ex.

Reinstall shaft and finger tighten the adjacent hold down bolts until any pushrod lash is gone.

Lay a straightedge on the valve cover rail and lightly scribe a line on the 2 pushrods.

Tighten the bolts down completely and rescribe.

Remove the rocker shaft and measure the distance, thats your actual lifter preload.

That will tell you if your pushrods are the right length.


THANK YOU
Posted By: buildanother

Re: You Guys Are Killing Me With This Shimmin RockersThing - 07/17/09 07:35 PM

Lotso fun. I would only point out that you should be sure to use TDC of #1 cyl FIRING stroke.
Posted By: patrick

Re: You Guys Are Killing Me With This Shimmin RockersThing - 07/17/09 07:56 PM

Quote:

Only dealing with small blocks Ive never had to shim anything, but then again why do they make shims if there is no real world use for them?

This is sorta like the lash cap issue it seems, some use them some dont...some say there is never a need but they still make them.

But isnt a lash cap also a shim of a sort?

Its pretty simple to know how and where your rocker tip needs to be on the valve so I say do what you got to do it make things correct.



yes, a lash cap effectively lengthens the valve stem, so does sunken valves, or running longer valves. if these instances occur, you may need to shim up the rocker arm shaft to correct the valvtrain geometry's relationship between the shaft and the end of the rocker to minimize side loading on the guide (which will cause excessive guide wear and valve stem wear).

if your problem is too much preload, you need shorter pushrods.
Posted By: MoparforLife

Re: You Guys Are Killing Me With This Shimmin RockersThing - 07/17/09 07:57 PM

Quote:

Bring the engine to TDC of #1.

Pull off the drivers valve cover and remove the rockershaft assembly. Strip off all the rockers except for #1 int and ex.

Reinstall shaft and finger tighten the adjacent hold down bolts until any pushrod lash is gone.

Lay a straightedge on the valve cover rail and lightly scribe a line on the 2 pushrods.

Tighten the bolts down completely and rescribe.

Remove the rocker shaft and measure the distance, thats your actual lifter preload.

That will tell you if your pushrods are the right length.


Just because there may or may not be exactly the preload you are looking for it can vary slightly as there is a H of alot of forgiveness built into the hydraulic valve lifter. Which in the case of street driven engines leaves a lot of room with out fear of damage. Personally I have taken up to .070 off heads and still had plenty of plunger travel. Granted that is pushing it but .030 - .040 will under most conditions be no problem.
Posted By: 64Post

Re: You Guys Are Killing Me With This Shimmin RockersTh - 07/17/09 09:22 PM

Again with this???
Posted By: 71 FJ6 Charger

Re: You Guys Are Killing Me With This Shimmin RockersTh - 07/17/09 10:26 PM

Alright guys,it ends here. I'll bother you no more about it. I'm boltin' 'em on,no shims. I will check pre-load,etc to make sure of things.
Thanks all!
Posted By: 64Post

Re: You Guys Are Killing Me With This Shimmin RockersTh - 07/17/09 11:35 PM

Quote:

Alright guys,it ends here. I'll bother you no more about it. I'm boltin' 'em on,no shims. I will check pre-load,etc to make sure of things.
Thanks all!



Don't stop on my account. We're all here to learn. Some things have to be in harder than others...

This internetS thing sure is entertaining though...

Here's my take on the geometry issue and, generally, just about everything else. If your stem-rocker contact is poor it usually means your valves are sunk from a crappy/incorrect/short-cutted valve job. You could have a bad rocker or two, but that is usually not the case. The seats ought to be replaced and recut to correct the issue. Shimming the shafts are a band aid. Yes, an incorrect contact pattern will wear the guides faster, but so what? The rest of the head is crap anyway. If you're not conscientious enough to do it correctly at the basic level, then why bother sweating other minor issues? Right...?
Posted By: Rug_Trucker

Re: You Guys Are Killing Me With This Shimmin RockersThing - 07/18/09 12:28 AM

This is one for my Yahoo Moparts file.



Posted By: BigTerry

Re: You Guys Are Killing Me With This Shimmin RockersThing - 07/18/09 01:05 AM

isn't the ideas to have the rocker tip center on the valve stem hence the needs for the shim when you shave the head too much?
Posted By: Sixpak

Re: You Guys Are Killing Me With This Shimmin RockersThing - 07/18/09 01:11 AM

If you are using stock rockers and something less than a .500" lift cam, shimming the shafts is a big waste of time, UNLESS you are encountering valve float from pumped up lifters.

I had a small block that after a rebuild with stock rockers and the block and deck milled, would not rev over 4500 rpm. Turned out the lifters were pumping up at that rpm and causing the valves to hang open. UNDER THOSE CIRCUMSTANCES, I would shim the rocker shafts, OR run adjustable rocker arms.

Shimming the shafts is an old NHRA Stocker racer trick back when they were forced to use stock rockers (mostly used on stamped steel, non adjustable rockers and pushrods.) It would help them get a few more RPM out of the motor by lessening the chance the lifters would pump up and cause valve float.
Posted By: 1_WILD_RT

Re: You Guys Are Killing Me With This Shimmin RockersThing - 07/18/09 01:17 AM

Quote:

isn't the ideas to have the rocker tip center on the valve stem hence the needs for the shim when you shave the head too much?



How does shaving the head effect valve to rocker relationship?... Valve stem height effects it & there is a specicfied height for them... The distance from the C/L of the rocker pivot to the point it contacts the valve effects it... But milling the head or deck surface doesn't... Again I'll post this picture which shows what shimming the rocker shaft effectively does...

Attached File
5359422-Rockergeometery.bmp  (63 downloads)
Posted By: 64Post

Re: You Guys Are Killing Me With This Shimmin RockersTh - 07/18/09 01:52 AM

Quote:

isn't the ideas to have the rocker tip center on the valve stem hence the needs for the shim when you shave the head too much?



Noooooo !!!
Posted By: stumpy

Re: You Guys Are Killing Me With This Shimmin RockersTh - 07/18/09 02:02 AM

If you don't change the rocker position or the valve position then you haven't changed the geometry. Shaving the heads do neither. You haven't changed where the rocker runs on the valve so shims aren't necessary. All you are doing is bring the head closer to the lifters meaning you possibly need shorter pushrods which is the only thing changed.
Posted By: MoparforLife

Re: You Guys Are Killing Me With This Shimmin RockersTh - 07/18/09 02:04 AM

Quote:

Quote:

isn't the ideas to have the rocker tip center on the valve stem hence the needs for the shim when you shave the head too much?



Noooooo !!!


Shaving the head will have 0 effect on the center line of the rocker to the center line opf the valve tip.
Posted By: 383man

Re: You Guys Are Killing Me With This Shimmin RockersTh - 07/18/09 04:11 AM

Shims can be a bandaid fix if the plunger in the lifters bottoms out on the cam base circle from decking the block and (or) milling the heads. It can cause the lifter plunger to bottom out and hold a valve slighty open. It happened on my friends car years ago when he started his fresh 383 and it was missing on 3 cylinders. The hydraulic lifter is made to have around .100 to .150 of plunger travel to keep the rocker right at the valve tip and adjusted at all times. If a valve job is done and the valves sink say .020 then the lifter plunger will bleed down or pump up to get the lash at zero. But if the plunger moves all the way down and bottoms out it can now hold the valve open. I like to set my lifter preload about .020. I actually watch and measure the plunger travel as I tighten the rocker shafts. I had to either get adjustable rockers or adjustable pushrods or shims on the 383 that was in my boys Dart. I had milled the heads and the lifter plungers were bottoming out. I was very short on cash so I used the rocker shaft shims. They were in the car for 7 years and worked fine. We raced the car many times and they did the job just fine.

Do you need rocker shims ???
Thats up to you. I would always check my lifter plunger travel and if they bottom out you need to fix it one way or another. The shims are a cheap fix as the best way is to get adjustable rockers and the right lenth pushrods. Just assemble your eng and check the lifter plunger travel. If it does not bottom out and you have some room for movement then you will be ok. Ron
Posted By: gregn96cuda

Re: You Guys Are Killing Me With This Shimmin RockersTh - 07/18/09 04:35 AM

I bought a 64 Fury with a rebuilt 361 (less than 50 miles on rebuild) about 8 years ago. With the car I got the receipts for the rebuild that totaled $1200.
The engine ran like crap, so I did a compression test and found 2 dead cylinders on opposite sides. I pulled one head expecting to find a burnt valve, but the head looked fine. I ended up installing shims, and it ran excellent after my bandaid fix.
Posted By: Junky

Re: You Guys Are Killing Me With This Shimmin RockersThing - 07/18/09 04:46 AM

Quote:

Quote:

YOU DO NOT NEED SHIMS. Is that good enough for you?

Short, sweet, and to the point. No you will not need a shim band aide.
Also listen to Dave and Kevin at Hughes, they have forgotten more than most here will ever know or learn.


The engine I run is a 383 out of a 1971 New Yorker, heads shaved 0.030 with 0.20 shims. Cam is a CompCam XE262H, stock stamped steel rockers. No need for shims. Buttoned the engine up and hammered down. Runs great.
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