Its hard to come by good rocker arms for some motors. The OEM design is often not compatible with todays cam grinds....especially roller cams. On another site, a fellow is doing some research/speculation about ways to cobble up roller rockers to suit an engine. He is a pretty knowledgeable fellow. We have been discussing some options and he is saying something that seems incorrect if not impossible. When pushing a valve open its best to impart as little side load on the valve stem as possible. This fellow has a 1.8 rocker arm and it makes a wide path across the top of the stem. It is also well centered on the stem. I'll use a shaft mounted rocker system as an example as its easier to explain. The pivot point of the rocker arm is the shaft. My understanding is that the centerline of the shaft should be the same as the top of the valve stem..........minus 1/2 of valve travel. This would seem to be the optimal location to insure there is minimal side load. (?) Anyway, I know you can raise or lower the rocker arm mount and change what happens, but that would seem to induce more side load and also change where the rocker roller makes contact......changing its ratio. I also understand that a much larger roller would make a smaller travel pattern on top of the stem, but would had weight to the rocker arm. OK, so this fellow is telling me that he can make the pattern narrower on the valve stem. I don't see how he can do it without changing(losing) some of the ratio and valve travel. What am I missing here ? Is there a way that works properly?
You are somewhat correct. The least amount of sweep will be achieved by having a rocker that the centerline of the roller axle and shaft centerline are 90° to the valve at 1/2 lift. Same goes for the pushrod side. Getting these aspects correct will accurately duplicate the action advertised by the cam manufacturer, and will be the least hard on parts. Roller size has no effect on sweep.
When the rocker arm is perpendicular to the valve stem at half lift, you will have absolute minimum sweep. Any change from this will widen the sweep and decrease total valve lift. The wider the sweep, the quicker your valve guides wear out.
Important to emphasize that the roller AXLE centerline is what should be considered, not the roller wheel contact point.
Are you looking for more power, or longer valve guide life? 1.8 rocker vs. 1.5, leans toward more lift and power, but will give a narrower pattern at a given lift.
So, yes you could reduce sweep even with proper set up as previously described. Sweep is determined by the arc created by the fulcrum point to the valve. If your fulcrum point is in some way movable, and pushrod placement has room to move, you could make a longer rocker arm. This would reduce the arc created by the longer arm, which is exactly what sweep comes from. Minimal gains for a whole lot of effort.
1.8 replacing a 1.5 with all other parts unchanged, and fulcrum point in the same location, will result in more sweep. The fact that lift is greater just makes the arm travel through more of the radius. In general, a manufacturer that sells different ratio rockers, only move the pushrod location to change ratio.
There are also some companies, like Jesel, that while they understand minimum sweep is with rocker pivot centerline and roller tip centerline perpendicular to the valve stem at 1/2 lift, they also consider what that sweep motion is imparting into the valvestem and pushing the stem sideloaded into the guide. Jesel uses something like perpendicular at 2/3 lift.....this way, the larger portion of the sweep is in the first part of the lift curve, when spring pressure is lower and the roller tip is better able to slip across the sweep pattern due to less spring pressure, and then have the lesser amount of remaining sweep when pressure is higher going to peak lift. This puts less thrust into the valve stem and valve guide when spring pressure is high, reducing wear. I'm not sure what their actual number is, but it isn't 50/50 mid-lift Yes, that roller tip doesn't roll, it slides. They are too small in diameter to create an effective couple to the valve stem tip enough to make it actually roll back and forth. Making it as a roller tip is just an easy to build solution...Crane used to make a aluminum roller rocker with a curved "shoe" tip insert, effectively just like current stock modern LS engine rocker arms are shaped...but it didn't catch on with buyers(hard to convince the typical non-tech customer that the roller tip doesn't roll) and was discontinued. Late 1980's time frame, same time they sold an aluminum roller rocker with a reversible pushrod cup insert, much like a uni-lug wheel washer....installed one direction makes 1.5 ratio, installed reversed, 1.6 ratio. It didn't catch on either. Here's the best mid-lift and stud rocker set up method, great video!
I designed my own roller rockers for my 302 GMC 6 30 years ago. I was wanting to help the side loads on the the valve guides I was replacing too often in my opinion. I’m not an engineer or pretend to be one but I knew that I wanted the roller tip to be at 1/2 lift and the rocker level. In my thoughts if the top of the rocker tilted up say 15 degree when the valve was closed and 15 degrees down when it was fully open I would easing the pressure either way on the guide. Designing the height of the rocker arm shaft thru the stand was my way of doing it. I felt that I could adjust this with shims under the stands I also wanted to improve the valve lift from the 1.45 to 1 stock to a ratio that would give my valve close to .600” lift because the head flow was not much help over that number. My cam lift was .380”. I did the best I could and found off setting the rocker shaft .100” closer to the push rod for me was going to be very close. I included Torrington bearings on the rocker to the shaft and Isky roller tips because I liked their axle clip of their bearing. I laid all this out in the deminsions I wanted on graph paper and made a deal with a machine shop I installed 3 phase 480 power panel and feeds to each machine he wanted. I supplied all my parts and he bought all the electrical part that I bought at discount from a supply warehouse. It was labor for labor. My calculations worked out my lift was .610” with gap of .025” and lash caps set the rocker at center when at 1/2 lift. I believe the lift ratio is a little over 1.6 to 1 and the witness marks on the top of the lash cap shows dead center at 1/2 lift. The system has been flawless for these past 30 years and I have not replaced a guide since and never needed a shim under one of the stands. Probably sheer good luck.
Getting overly nit picky here, but... At 1/2 valve lift, you should see 1/2 of your total sweep distance over center. Theoretical dead center sweep should occur at 1/4 lift and 3/4 lift. I do realize how overly precise Im being. Your arms obviously were a huge improvement over factory equipment, and I for one applaud you.
Beside measuring for pushrod length... Be prepared to either add shims to raise the shaft stand, or even machine/remove material from the stand to to lower the shaft height to get the rocker to the correct HEIGHT. I'll be going through this shortly on my own engine. Mike
Early hemi. Long valves, offset pushrod holes, big”ish” roller. Making new stands also. Everything shown is mock up.
Early hemi get oil once every revolution of the cam because the angle of the stem valve length is critical.
Yes. In this case, the arm will need to be drilled to the roller side. My particular set up will use pushrod oiling on the adjuster side. Lots of non standard stuff on mine , but great point to bring up for users of stock parts.
Yes, I understand that. He didn't say what motor he was working with, so I was giving him a clean page to put the fulcrum and pushrod hole any where he needed. Moving the fulcrum away from the valve would make less sweep for the same lift. Too much work and expense for what most of us do.
I had a cheap set of roller rockers in my SBF. Flat tappet Hyd Crane cam 242 @ .050.. .490 lift.. Some of the rollers wore into the sides of the slot they reside in effectively locking the roller from rotating.. You could defiantly tell that rolling was better than not rolling. The ones that would lock would wear flat spots on the roller diameter untill if/when they unlocked and locked again. The ones that did not lock had no wear issues.. Replaced with Harland Sharp 1.6 and during setting lash I noticed that the pushrods seemed short for the 90° at mid lift, in checking actual lift is .510. In hind site after reading in a previous post about where the Jesels became 90° maybe Harland-Sharp knew that. No problem for many years/miles.
Is it just me but it looks like Harland Sharp rockers cut down the amount of oil coming to the top end.
I want to Thank everyone for their insights and input. Lots to digest here and the videos were both excellent. The engine I'm working with presently is a 500 Cadillac and the rocker arms on them are notoriously junk with no high rpm (5500 rpm on a good day) capability. Actually most people shift before that. So upgrading the rocker system to compliment the roller cam I want to use is a "must" for this engine. There were some unknown shaft rockers out there. The specialty suppliers had some units they put together that probably work OK. I wanted adjustable rockers on whatever I used. I wanted to use Comp Cams stainless roller rockers with a 1.7 ratio and was looking into making my own setup. I ended up purchasing Harlan Sharpe shaft mount rockers. $$$$$$ Anyway I am looking for another Cad engine for another possible project. I have some ideas on how to do it, but the sweep question popped up. As I mentioned, a fellow on a Cad site showed a 1.8 ratio rocker sweeping across a valve and it had a wide footprint but was well centered. He showed it next to another one where he had a very narrow travel band. From what you guys have provided, I assume he is moving the location of his pivot point (up/down) if he is using the same 1.8 to get the narrower band. One thing I respectfully disagree with Trendz on is that the size of the roller on the tip does not change the width of the footprint. Its probably a minimal/moot amount, but I believe it will be different. Anyway guys, thanks for all the info and if you have any other thoughts or ideas or experience, please share......
What you wrote is exactly why I stayed away from the cheaper unknown roller rockers. I had some I bought for a smallblock Chevy many years ago and they seemed less than well made. I resold them at a loss rather than use them. Little things like roller bearing quality and type of material aren't obvious during internet purchases. Here is some info for anyone considering buying some roller rocker arms.......... You can see there is a little more to consider than the best internet price........
I went through the rocker arm alignment problem on a 428 FE with BBM heads and HS rockers. Ended up making some spacers for the rocker shaft stands. I worked with the spacer to have the rocker at a right angle at half valve lift.
I can appreciate your disagreement, but Im wondering what makes you think the roller size would change the footprint or sweep pattern? Not trying to be difficult, but either you or I need to change the thought practice on this. I may be missing something, but I don’t think so.
This is a comparative drawing of an exaggerated rocker. One side has a .500” roller, the opposite side has a 1.000” roller.(exaggeration for example) If the centerline of the roller is used as the set up point, the roller contact point with the valve remains constant regardless of the roller size.
The Jalopy Journal
