Rocker Arm Change???????

OK all you camshaft guru's, here is a question for ya. I am currently using old Isky 1.5 rocker arms on my MEL engine. The Isky cam has a total of 505 lift at the valve. Due to possible NHRA rule changes which, if applied, will require a stronger updated rocker assembly (this is bullshit by-the-way, but may be mandatory). I have a new set of Harland Shart FE aluminum roller rockers which can be made fit my MEL. The issue is they are 1.76 ratio. This will up my lift to about 595. I will have valve spring clearance so that isn't the issue. My question is this:

If I switch to the higher ratio rockers, to keep good geometry should I:

1) Use lower rocker shaft stands
2) Use taller rocker shaft stands
3) Keep using the stock height MEL stands

Thanks for the help

 

IIRC,,, Taller by half the distance of the change in lift.

Should keep the tips closer to the centerline of the pushrod/valve through out the travel.

I think!

(Will need longer pushrods too)

 

I say shorter and here's why: Assuming you make no changes to the valves then the starting point is the same as before, but you are PUSHING the valve DOWN that much further. To keep the rocker arm centered as much as possible on teh tip of the valve you now need to lower the fulcrum. To check this you can measure the amount of travel the roller has ACROSS the valve stem. The LEAST amount of "wipe" across the valve stem equals the poin at which the rocker arm is moving in a "symetrical" path.

This is a confusing subject and even the valve manufacturers publish conflicting information, but the majority seem to agree having the rocker arm "perpendicular" to the valve at mid lift is the proper way. Makes sense to me as that means it is as close to the center at all times. Not sure if I made any sense there or not. I can draw a picture if that would help.

Edit: BTW running Taller valves is another way to "center" the rocker arm travel. Not that I'm sugesting that.

 

It may be easiest to simply use lash caps, along with different locks if ones are needed with the recess. It may be cheaper than using different pedestals & pushrods if needed, or longer valves. Bottom line is that you will need to mock things up....



Don't forget to check the retainer-to-guide clearance & piston-to-valve clearance, even if the springs are OK for coil bind.

Also, don't forget that you are slightly changing the effective duration "under the curve" with the increased ratio.

 

Nobody can tell you -- unless they have the EXACT same setup you have -- including valves, rocker stands, etc..

Here is what you should try to do:

1) Most people believe the best rocker arm geometry is to have the rocker arm as close to a right angle to the valve stem when you are at MID lift. Also, pay attention to the contact points at start, mid and full lift. Depending on the rocker setup, style, etc - it may not be centered at mid lift (probably on the outside of center) - though you'd prefer to keep it as close to the center of the stem as possible though the travel arc and min/max lift.

2) Mock up your head with one of those weak/tester valve springs.

3) Setup just one intake and exhaust rocker -- with the rest of the rocker assembly (shafts, stands, etc).

4) If you can setup the cam, then go ahead and use the cam - that way its easy to put a dial indicator on the valve (to test for the mid-point of lift) - as you slowly turn the engine over by hand.

5) Once you've done the above, you'll know how the rocker/valve geometry aligns. You'll be able to see where the rocker is at mid-lift. Obviously there are a range of ways to "fix" the geometry if it is off - usually changes involve some combination of the following:

a) Move the shafts (stands) to change the centerline location

b) Change valve lengths to change the centerline location -- If you need taller valves, you may be able to use lash caps. If you need shorter valves . . . well, you need shorter valves

c) Change the rockers themselves -- sometimes you end up with custom ones from somebody like RAS.

Hope this makes some sense . . . I'm going through the same things on some custom Hemi stuff.

 

I am with Bored and Stroked. Any time I tried to think something like this out, I went backwards somewhere. I always use the soft spring watch the rocker tip method. Try to keep the roller in the center of the valve stem. If it needs to go up, good deal. You can use shim stock. If it needs to go down ( I doubt it but don't forget. I am usually backwards) you will have to cut and try.

 

Assuming your origional setup was optimized the geometry can be compared to the big hand of a clock. Imagine the hand traveling from 2 to 4 with 3 of course being mid travel. This would represent an ideal (symetrical) geometry. Draw a verticle line upwards from 4 your clock (It's vertical because that represents the valve's travel direction). Now measure the horizontal distance from that line to 3. That represents the distance that the rocker arm roller tip has to travel across the valve. That distance is minimized because the travel is symetric - also note at the the mid travel the rocker arm is perpendicular to the valve.

Now imagine the same setup this time the travel from 3 to 5 (same valve lift). Draw a verticle line upwards from 5. Measure the horizontal distance from 5 to 3 - again this distance the rocker moves across the valve - it is now MUCH larger than before even though the valve lift is unchanged (well for the most part unchanged) - bad geometry - not symetrical.

So now add the extra lift from the increased rockers, bigger cam whatever. Say the travel goes from the old starting point of 3 and now goes to 5. That roller swipe across the end of the valve is no longer minimized. Adding length the the valve via lash caps or longer valves is one way to get that mid travel to be at the 3 position again. But if you don't do that then the only thing left is to change the rocker pivot point - THAT point has to be somewhere between 3 and 4 (mid travel) so it is THAT direction that suggest LOWERING your pivot point.

Edit: BTW - in response to the "change the pushrod suggestion" that is a great way to change the pivot height of the rocker IF you have stud mounted rockers - a little more involved if you have shaft mounted rockers.

Of course these are NOT real numbers - it needs to be verified (by measuring the roller horizontal travel and minimizing it.

 

I agree on the "most likely" that shorter stands is the answer. For sure though.....


1) There isn't going to be any changing the valves themselves. MEL valves are rare and I am not about to have special ones made. Lash caps???? Hmmm, maybe.

2) I have a set of stands that are 1/8th shorter than stock and a set that is 1/8th taller than stock.

3) I have already checked the retainer to guide clearance...no problem here with the additional lift. Ditto the piston to valve clearance...no problems there either.

4) I will take everyones advice and use light springs to set up one intake and one exhaust for trial and error.

5) Thanks...I love this site. Many freaking geniouses here

 

If you have the room on the stem, caps are the cheapest method, and the .090" you need makes the correction of .045" pretty close - there are caps in .050".
If the stem tip isn't long enough, the stand have to go down by 1/2 of the change - but 1/8" is far too much, you'd need the shorter stands plus shims.
However: this is only true if the geometry was already correct except for the extra lift.
IDK the stem angle or the pushrod angle of either the MEL or FE, but unless they're both the same (a degree or 2 is probably harmless) the FE rocker cannot be made to function as mid-lift. This is a design element, not an adjustment, the only question is "how bad is it?". If you have this problem, I would try to get the valve side correct and contain the angularity error to the pushrod side.
Attempting to correct the geo by watching the pad position. The exact position (centered or not) is far less important than the scrub path, and yes, you can have perfect mid-lift with the rocker at the edge of the stem.

 

There are absolutely no other valves with the same or similar dimensions as the MEL valves? From my experience (not with valves, but with similar setups used in injection molding) the dial indicator/mockup is the absolute best way to go...it might be possible that the 1.76 ratio could be a lucky coincidence to be optimized right out of the box, or with minimal shimming...

 

you should mock it up on the head,

and put some red felt tip color on the tip of the valve,
then rotate engine with the valvetrain/pushrods / rocker and make the rocker make a full motion up and down on the tip of valve.

this will give you a "witness mark" ( from the red colorant) that will show if the rocker needs to be moved closer or further away....or higher or lower.
stand height is only part of the equasion to get proper wear and lift that you want.

 

Your pushrod angle will change as well , so check clearance on head where rods go through .
I think you can buy longer adjusters for them rockers too if your pushrods come up only a little short, I know those are expensive

 

I my mind and past experiences with this the only thing you need to change is the push rod length. Most Cam grinders sell a push rod length checker. You can also buy one adjustable push rod or make one , then once the length is determined, buy a set the correct length. I believe in most cases the more the lift increases the shorter the pushrod needs to be.

 

Shaft-mounted rockers cannot use pushrod length as a method of correcting geometry, that's useful for stud-mounted rockers.
Pushrods should be replaced if too long (or the valve made taller), or if proper lash requires more than 1-2 threads exposed on the adjuster.
Using a longer adjuster not only changes the geometry and invites breakage, but also reduces the rocker ratio.

The position of the rocker's contact point (pad radius or roller tip) on the stem will change if the height of the stem or the stand change if the stem isn't vertical (almost always true), but you cannot correct the geometry by moving things around to put the rocker where you want it.
The "scrub path" length on the stem is far more important, and will be wrong if the geometry is not correct and the rocker's position on the stem is changed by moving the stand height.

The best path is the shortest, and begins (valve closed) with the pad closest to the rocker shaft, and to the stem's near edge (not the center).
The pad walks toward the stem center as the valve opens, and reaches its farthest point away from the rocker shaft, and closest to the stem's far edge at full lift.
As the valve closes, the pad walks back to its original position.

 

One of the reasons why this stuff is so annoying and complicated is that, in theory, the rocker arm should be constructed differently with significant changes in lobe height, unless the rocker arm ratio is very low (like 1:1), and the highest ratios (above 1.6:1) have the worst errors.
Since no car manufacturer ever does this, a rocker original designed for a low-perf motor (1958 332 FE) with .360" lift will never be spot-on when factory installed in a later engine (428) with a .480" lift cam.
No rocker arm manufacturer is going to actually tell you "this rocker is correct for engines with net lift between .600 to .650" only", because the customer simply hangs up the phone and buys the rockers from someone who doesn't confuse him.
Normally, what's considered safe (and the only practical thing to do) is to try to get the angle of the long (valve-side) lever corrected to mid-lift, and ignore whatever foolishness the short (pushrod-side) lever is doing (like breaking adjuster, popping out pushrods) unless it's really bad.

 

Panic, What you are describing is a method that I've seen SOME cam/rocker companies reccomend - however there are others who publish a DIFFERENT method. I can't say I understand the merrits of your description because it places the rocker arm travel in a non-symetrical path. Could you enlighten us on the benefits of this approach???

In simple terms (using a clock hand to help illustrate) you describe the rocker arm starting at a position let's say 1 o'clock - at mid lift it is at 2 o'clock and full lift 3 o'clock. That is the only way the arc travels and gets the rocker to start at one side of the valve and finish at the opposite side while wiping across the middle (unless there's a special contact profile of the rocker arm).

Using the same example, let's start at 2 o'clock, mid lift at 3 o'clock and full lift at 4 o'clock. In THIS example mid lift IS the farthest from the pivot point - and the beginning and ending points (2 & 4) end up being in the same place.

Am I missing something??? Please explain.

 

I apologize for the lack of clarity - we're describing the same thing (mid lift).
The path is also symmetrical: it begins and ends in the same place (valve closed and full lift both place the rocker pad at the same spot on the stem tip).

Please note: this is patented by Miller, partially due to his claims but also because not all original manufacturers use this method.
The other popular method opens the valve faster to match the point of highest vacuum (about 70-80° ATDC) to the point of maximum lift (ICL, usually 104-110° ATDC), which increases the curtain area earlier in the intake stroke, but also reduces the total window area somewhat. It's a compromise, like everything else.
This is done by raising the rocker shaft center, which angles the rocker down and gives most effective motion (in inches per degree of rotation) faster than mid lift, and decays later in the cycle.
There is no "best", "ideal" or "correct" - it depends on what you're doing, and the parts you have to work with.

 

Why not have custom rockers made to fit your existing set-up? Using what you have may be cheaper in the short run but not long-term.

 

This is all very technical stuff and I do not pretend that I can add any meaningful comments on how to correctly address the solution. However, I do have a question: If you use a higher ratio rocker, the valves will be pushed deeper into the combustion chamber. closer to the piston. If you reduce the pedestal height as some have suggested, shouldn't the piston to valve clearance be checked in addition to the already discussed relationships?

 

You're right on the valve lift being higher, but changing the pedestal height isn't the issue - it doesn't have any meaningful effect on the lift - it is more related to the geometry and mechanics of the valve train. If you're changing the ratio, then this is something that you need to worry about - should check the piston/valve clearance if you increased the ratio and corresponding lift.

 

Trust me, it's not that complicated if you remember trigonometry. If you can handle it at age 15 you can do it now.

The strength, weight, type of adjuster, ball vs cup, shaft diameter, material, spring rate, actual lobe dims, and the rocker ratio are not part of the input - they're part of the construction phase.

For analysis, all you need to know to see how well you're doing is:
1. valve stem angle to the bore axis (probably not vertical, but some are such as poly exhausts) of both the MEL and the FE, or any other 2 you're comparing. Common angles for wedge chamber are 10-20°.
2. pushrod angle to the bore axis (probably parallel, but many exceptions, and any engine with inclined tappets almost certainly has an angled pushrod such as Chrysler SB) of both the MEL and the FE, or any other 2 you're comparing.
3. new lift vs. old lift at the valve
4. what method you prefer (if not mid-lift)

"Get a custom rocker" sounds like a solution, but the problem is that (far too) many rockers for orphan motors are not designed for that specific engine - they're made from something they already have CAD/CAM or tooling for, with minor tweaks. You want something better than what you have now, but you won't get it unless they spend a lot of time on it - and have a MEL to inspect and measure.

Interchange with another engine is always possible (Old/Cadillac/Stude, etc.) but there are some dims that must be very close to even consider:
1. length from shaft to stem must be really close (like 1/16")
2. length from shaft to pushrod has more slack in it, but still important
3. offset (left/right)
4. shaft diameter
Others of the same brand are always candidates - have you examined Lincoln Y block?

 

I'd like to assemble a data base of rocker dimensions to help people to identify what they have ("I bought this as an Olds, but it's not"), and figure out possible donors ("I heard that you can use BBC rockers on a 292 L6"), but there is almost no information on line - even factory service literature only gives the ratio and shaft diameter, but nothing on the actual arm lengths and sometimes not even the stem angles.

This will be posted to my site on its own page (no charge) with a link here for public use. Anyone have any measurements please e-mail, and I'll list your name with the data (if you wish).

 

If you're considering different Rocker arms, you may want to talk to Gary at Rocker Arm Specialists . . . he is a super guy, sets up many custom rockers, makes CNC race rockers, etc.. For example, if you buy the Hot-Heads 392 alumiinum roller rocker setup - they're made by RAS. He made my 417 Donovan rockers -- took a long time to get them, but he had to customize his NC programs, we had to trial fit - make changes, etc.. Anyway - you might want to give him a call.

He also rebuilds stock rockers, converts non-adjustable to adjustables, etc..

Here is his number - he's in California:

(530) 378-1075

 

Panic, thanks for clarifying - when I read your origional post I misunderstood and thought you were STARTING at one side and finishing at the OPPOSITE side - (and I've seen major cam companies illustrate that THAT IS the "correct" method - to which I am not a believer- nor an understander(I am a fan of symmetry in this case). I misunderstood your post to be saying the same thing and was hoping for clarification. Thanks for clearing that up!

 

Holy sheeet batman,,,,,,,,,,,,my head hurts reading all of this,,,LOL. Not really, just kidding. I do appreciate the help from all of you. Not that I understand all of it, but i do appreciate it.

Hopefully NHRA WILL NOT change and demand "current style" after market rocker arms for the nostalgia cars. Mine are after market. They are Isky and are hard to find for the MEL engine. Back in the day we never broke one and I haven't broken one yet this time around. We will have to see. I am just trying to get ready JIC NHRA goes brain dead, but what are the chances of that??????????????