Easy overview of rocker geometry

[Trevor Jessie]

https://flowspeed.com/rocker-tech.htm

 

[Hap Waldrop]

Yep, thats a good study on roller rocker arms, and what he says is dead on, most of the roller rocker set ups, have a stock shaft height, yet they take up more space than a standard rocker, so if you don't shim the pedestals, not only are you losing alot of lift, you rocker arm geomentry is all messed up as well. I did a thread here in the past where we used Titan 1.5 rocker arms on a 1380 engine, and ended up shimming them .125" and gained .030" lift back, I posted pictures of it. I have a pretty wild MGB race engine I just started on, we will be using Titan 1.65 roller rocker arms, I got Sean's shims for them, in both thickness to see what we get.

 

[Aggudabbu]

Hap,

You don't happen to have a quick link to that thread or a topic I can search for?

Thanks

 

[Hap Waldrop]

No I tried to search for it with no luck, best of my memory it was back in the summer, my and Gundy's buddy Alan was building his 1380, which I had help him with on some component work Anyway Alan wa doing final assembly and had the presence of mind to check lift at the valves, and was astonished at the loss of valve lift he was seeing, sent me a picture showing the rocker arm angle, it going up hill to valve. I told him Sean Brown had just did a study on MGB roller rocker arms, and them having too low of shaft height, and needing shimming at the pedestal to gain back lift, I suggested Alan find some flat washers that all measured the same, somewhere around .125", then put one under each of the rocker pedestals, retorque th head and check the lift again, he called me back and reported to me he had gotten back.030" of his lift, I also then posted his new picutre here with the washers in place, and just looking at it you could see the rocker arm geomentry had greatly improved, I suggested to him, perfecting the pushrod length, or even more shimming might result in yet more, but at that point he was satisfied with his findings. he then ordered some .125" precision ground steel and made himself a set of rocker pedestal shims, later I found out David Anton at APT offered them for sale, and since have stumbled across some in some of the spares I aquired over the years.

In the most simple of terms, most all roller rocker arms offered for our cars are designed at a stock shaft center height, but almost always the roller rocker arm is bigger in size than a stock rocker arm, so they tend take up more space and to go up hill to the valve tip, and this can be corrected by shimming the pedestal.

Theorectical lift, meaning cam lift x rocker arm ratio - valve lash, is just that, theorectical, you'll never get it in most cases, you may get close, but a rocker arm moves in arc, and as we ask it to move more (further downward) in that arc with higher lift cams the rocker ratio will decrease. David Anton and I have talked about this alot, he told me as delivered, that the Keith Dodds 1.5 forged non roller rocker arms come closer to actual advertised ratio than anything he has tested, but the good news is if you want roller rocker arms you can get back your lost lift with pedestal shims, and the Titan bushed shaft 1.5 ratio roller assembly are a good buy for the money.

 

[BlueMax]

Hap,
Found the photos depicting the rocker arm geometry. What I did to resolve the problem after a conversation with Hap. I had a few leftover flat ARP hardened washers that I used to put under the rocker stand, I believe they were about .110”to.115” thick, so I slide one under each rocker stand, they fit perfect between the head stud and rocker stud. I torque every thing back and re-adjusted all the valves with their correct valve lash. Then set up the dial indicator to see what I would get. I got an additional .030" lift and the pushrod was where it should be, you can see in the photos what I’m talking about. I knew that I should be some where in the .435 total with the SPVP-3 APT cam. I located some precision ground .125”flat bar stock, proceeded to make the shims out of that. I then set everything back up and check again, I was able to get .430” total lift which was good enough. Threw a photo of the combustion chamber! Thanks again Hap for advice!

 

[BlueMax]

Here’s a photo depicting the .125" shims installed, note the rocker geometry. It is now correct were by maximizing the proper rocker arm ratio.

 

[BlueMax]

This last photo is showing the modified combustion chamber with Rim Flow valves.

 

[jlaird]

Auhhh man, that is too preaty to run.

 

[Hap Waldrop]

Auhhh man, that is too preaty to run.

Gundy and I are hedging bets he may never anyway, he just make a coffee table out of that engine

Just ribbing my buddy a wee bit

 

[BlueMax]

Hey, don’t go on margin, someone could get burnt He-He!!

 

[Gundy]

Now ya'll done it. I want some rollers. Do they come in chrome?
I about laughed my head off when I saw those Titans installed
and covered by a perfectly sized clear casserole pan.
Looked just like a glass valve cover.

BlueMax looked like a kid at Christmas today with a pile-o-parts
from the Fatherland of the Frogeye.
I'm pushing our pal to make a Nov. deadline.
I ain't taking no bets. I only bet on a sure thing.
:banana:

Roller rockers...drool...

 

[Hap Waldrop]

David, those Titan roller rocker are 1.5 ratio, over the stock, 1.25 -1.3 ratio, so they offer additonal valve lift to whatever cam you are using which adds additonal performance, this can be easily done without pulling the engine or even removing the head, so if you want some I get you deal on them. You don't have to worry with vlave clearence issue at the compression ratio and piston to block deck heights street engine are built to, so easy enough to do. The Titan are well built assembly and with the addition of the pedestal shims, which we can now buy from APT (which I already have a set at the shop), we can dial this system in for your car if you decide to do it later on.