Harney's diatribe - rocker geometry to install & beyond

RoWaMe · Post by **RoWaMe** » Tue Oct 19, 2004 11:10 am

mharney- I recently encountered a similar situation when setting up the geo on my 1915 engine. I was "close" to perpendicular at half-lift (measured with a dial indicator) and no shims under the rocker shaft support blocks, so I tried using shims under the rocker blocks to improve. Had an adjustable pushrod and a light "test" spring. Still could not get it right at about 1/8" shims. So I took them off, took a spare set of rocker shaft support blocks, ground them down about 1/8" on a flat disc bench grinder, and not only was the geo still off (in the other direction), one of the rockers would touch the side or the corner of the rocker stand boss of the head when I rotated the engine off the cam lobe. So I undid everything, went back to stock support blocks, and saw that I was actually very close to "parallel" with the valve and the valve adjuster at half lift. No rocker block shims needed! Just had to cut down the pushrods about 1/16" shorter than stock, but that is determined by the amount of the case cylinder spigot face cut, and the desired CR (57cc chamber volume, 7.9:1 CR; no cylinder base shims needed either).

So the story is, sleep on it, take everything off the rockers and heads, do it again and maybe (along with the tips given by others here) it'll work out well.

boredandstroked · Post by **boredandstroked** » Tue Oct 19, 2004 11:17 am

Mark, while your at the lash cap thing you might be on to something. Berg sells super tall lash caps. they are .180 taller. I have a set that someone let me borrow, that were never used. I will check and see what he wants for them or I am sure you could buy a set. I can take measurements to see exactly how they may work for you if you like.

Tom Simon · Post by **Tom Simon** » Tue Oct 19, 2004 12:28 pm

boredandstroked wrote:... Berg sells super tall lash caps. they are .180 taller. ...

I was going to suggest the same.

Other possible solutions:

A) relocate the rocker stud holes .05" or so lower in the head (any competent machinist with a Timesert or Keenserts kit can tackle that job)

B) use +.100 valves, (the taller valve should improve things, and if you buy or borrow just 1 valve it would be easy to mock up)

C) try a different manufacture's rocker arm. For the life of me I couldn't get AutoCraft Pro rockers to set up on my AC 910 heads... JayCee suggested I try just one Pauter roller rocker to see if it helped. Not only did the problem go away (same problem you ae having, by the way) but I didn't need any shims at all.

D) if they aren't already, use .100" offset shafts and stands, which lower the centerline of the rocker arm. The shaft kits are sold with rockers a couple of ways, with all of the mix-n-match that goes on, even at the retailers level, it could be your rocker shafts are the "on center" type, and you need the ".100" downward-offset" type, which move the rocker assembly away from the valve stem.

dude, I know this stuff can be frustrating, but rmember that there are so many different combinations it is virtually impossible for someone to sell rockers that actually fit the first time. You are definately doing the right thing by questioning and getting it right the first time, you are saving a real big headache latter on... good luck and keep at it until you get it right! (which I know you will)

A_67vdub · Post by **A_67vdub** » Tue Oct 19, 2004 12:31 pm

This picture tells the story well. The red line needs to go through the center of the shaft. You can see that in order for that to happen the shaft needs to get closer to the head, or tip of valve closer to shaft. When I do mine I plan on using autocad so things will be to scale and I should be able to tell exactly the thickness of shims to use.

Steve

Post by **Marc** » Tue Oct 19, 2004 12:44 pm

Pre-`65 40HP rocker stands (the ones that look like cubes with no slit in them) will bring the shafts closer to the heads by a bit - there are two styles, the ones stamped "TOP" on one face will really move the shafts in if installed upside-down (of course the hole needs to be enlarged to fit over the fat part of the stud). You'll need to check for clearance between the head and the underside of the rockers as RoWaMe cautioned. Handy to have some of these around when sorting out geometry problems, pick some up at the next swap meet or boneyard trip.

mharney · Post by **mharney** » Tue Oct 19, 2004 3:08 pm

Thanks, y'all.

RoWaMe, I'd be interested to see what your situtation was visually. I know that I can do at least the 0.100" on the blocks, with POSSIBLE stud interference, but I have a lot of room to knock those down some. I'm not too worried about that. The rest will clear. You took 0.125" off if yours and I'd bet your rocker blocks weren't as thick as these on the head side. I've had it apart and back together several times now, and it's pretty consistent that I get this geometry.

boredandstroked, I didn't know anyone made caps taller than 0.080! That's an option too. I guess I might be a little skeered of a lash cap that is too thick though. Right now, I have about 0.260" with the stack on there like I had it in that latest picture, but I think I could get out with about 0.240" and have it right. I should try to find something that is about 0.100" thick to stick between the lash cap and the rocker and see what that gets me before I commit to those. I also know that Berg caps are tight fitting, so that sets me at ease on the whole "what if it falls off" thing. Still I get this feeling that taller caps could have a tendency to come off easier, since there is more moment about the valve tip. Maybe I am overthinking that one.

Tom, I think I'd buy new rockers before I'd let anyone relocate the holes. I'm skeered to sneeze on these heads much less have someone do anything to them right now.. It might turn out to be the best option though.. we'll see if I can do something easier that will work out. Taller valves sounds like a great idea, but I could settle for lash caps if that is the case. I am interested to see if the CB rockers align better. That's a $230 question though.

I had pauters but I traded them out for the Scats. As far as offset shafts, I am not sure what is available for these ProComp rockers. I know that the shafts are already offset. I am not sure how much but they are definitely not on center.

Marc, I'd have to have them machined to fit the 0.760 shafts, I'd guess, and I'd just as soon have these blocks milled. The shafts I have are offset too, so they wouldn't work with the stock type blocks.

A_67vdub, I think that getting the shafts back in or thick lash caps will center things up nicely. I appreciate your input.

Gonna think on it a little and decide which way to go here.. I may do a combination of things depending on what I decide.

RoWaMe · Post by **RoWaMe** » Wed Oct 20, 2004 5:56 am

Well, Mharney, my engine is now together, in the car, and running as of last Sunday! So I really can't make a clear photo of the geometry. I do have those cut-down blocks that I can photo, placing one next to an uncut one for comparison if you like. The blocks I used were the 1600 type, not the 1200 like Marc suggested (and I also considered in my experimentation!). With every variation of block thickness or shims, I had to lengthen/shorten the adj. pushrod. You're probably doing that too but I guess we should not assume anything. When I installed the pushrods, the rocker shafts and adjusted the valves after cranking the engine for oil pressure before first start-up, the valve adjuster locknuts had a few turns of thread to the outside of them at every valve, confirming to me that my pushrod length was correct.

mharney · Post by **mharney** » Wed Oct 20, 2004 7:25 am

RoWaMe, I have offset ratio rockers.. I am not sure what you had, but I can't use stock style blocks, the shafts are offset type. I would have to get another set of these blocks and mess with them if I wanted to experiment.

RoWaMe · Post by **RoWaMe** » Wed Oct 20, 2004 11:40 am

My rockers are 100% factory stock 1.1's.

mharney · Post by **mharney** » Thu Oct 21, 2004 4:06 pm

Well, after simulating a 0.180" lash cap, OR milling the blocks down 0.100", and using 0.080 lash caps, this picture shows the rocker at half lift. The axis is on, but the centering on the stem is not. AND I have determined that I would have to clearance the head bosses for the rockers to clear, since they are a little wider than the rocker blocks. I don't know what else to do to fix this other than relocating the studs on the heads, and I really don't want to have to do that. I shouldn't have to do that. I think the problem lies with the rocker design. I've seen others complaints of the same thing, and I can't see how others with similar setups could ever get them aligned right. I suppose lots of people have settled for something close. I'm not sure I think this is close enough. I either get centered on the stem, or proper axis. What else can a person do here??

A_67vdub · Post by **A_67vdub** » Thu Oct 21, 2004 4:43 pm

One thing to consider is that if it was perfectly in the center at half lift, then at both full lift and zero lift the rocker would be below centerline. Personally, I feel that you want the entire "path" that the rocker makes to be centered, which means it would be slightly under at zero lift, slightly above at half lift and slightly under again at full lift.

Do you have any side to side offset? If so, then the force will not be centered anyway. I've heard some smarter people than I say that on full race engines they don't have any offset because valve spin is not as important, but in my mind if it was offset (side to side) I think there would be less friction, because normally some of the friction force of the rocker sweeping across the valve is transferred to spinning the valve.

Steve

Michael Meyer · Post by **Michael Meyer** » Thu Oct 21, 2004 4:45 pm

Tom Simon wrote:
boredandstroked wrote:... Berg sells super tall lash caps. they are .180 taller. ...
D) if they aren't already, use .100" offset shafts and stands, which lower the centerline of the rocker arm. The shaft kits are sold with rockers a couple of ways, with all of the mix-n-match that goes on, even at the retailers level, it could be your rocker shafts are the "on center" type, and you need the ".100" downward-offset" type, which move the rocker assembly away from the valve stem.

I'd check into option D. I had the same problem last year... offset shafts solved it....

A_67vdub · Post by **A_67vdub** » Thu Oct 21, 2004 4:49 pm

Oh boy, my mind is going crazy again.

I think that shimming the rockers should affect where the rocker contacts the valve because the valve is not parallel to the pushrod. This means that the farther out you go the closer the tip of the valve gets to the tip of the pushrod. I don't know if there is any way to correct this without either relocating the studs or messing up the geometry.

Remember these are just my thoughts, I'm technically a valve geometry newbie, but I think I get it.

Steve

rcb78 · Post by **rcb78** » Thu Oct 21, 2004 5:49 pm

Have you tried contacting Scat to see if they have some offset rocker stands like they do for their 1.4s? Without these, the 1.4s/1.5s would have the problem you are experiencing. Here's a pic, they are both the offset type (notice location of hole for rocker stud), just different heights. --Ryan

mharney · Post by **mharney** » Thu Oct 21, 2004 5:50 pm

Michael,

My blocks and shafts are already offset, as in not centered in such a way that the hole is not through the middle of the shaft. If they make one that is 0.100" lower than what I have now, that might be an option.

I think I'm going to try some CB's and see what I get.