DIY rocker arms

[jimmy six]

Mine were stock width both the stands and the rockers and flat on top. The adjuster side was offset to side of the stock one; if you look at a stock ones both right and left from the top down you will see what I mean. Width was about .850" to hold the nut.

The roller tip side was .750" width  3/4's of its length just to remove some weight. And it's offset just matched the stock one too.

The lower side looks like a stock one with the thickness around the bearing at .250". If you didn't use a bearing it should be thicker in my opinion. The Arias ones are .275" and they seem to work for the guys that use them. However the shaft is much smaller in diameter at .750"

After the gentleman who made them for me finished the basic rocker (1 left and 1 right) and one stand he had me mount them on the shaft and put on a head to see where center the roller tip should be placed. The .750" width came from the width of the Isky pin and room for the clip and they are not in the center but in the center of the valve end.

That's about it. I'm no engineer I just wanted roller tips and a little more lift and the offset of the shaft stands gave me that. You need to measure that for yourself. Since I used the stock shaft all the oiling remained the same altho I didn't continue with the overflow or have squirters for the top of the push rods cause I didn't know shaft systems like the T & D had them.

As a side note the gentleman running the machine shop told this job was worth about how $2000 not including my parts which was everything but the rockers and stands. I had this done in the late 80's. Good Luck

[jimmy six]

Panic, interesting comments. When I was designing mine I didn't think about the clearance for the spring but was lucky as nothing touched. That part of the fulcrum is pretty long (and your going to make it longer) when you consider the original measurement from the center of the valve to the center of the hole for the push rod which is what I started from. It was said the stock ratio was 1.5 to 1 but it was closer to 1.4. Today 1.70 or 1.75 seems to be what is wanted. This and the correct geometry so the roller moves correctly over the valve tip. Luckily today you have long stem valves, lash caps, stand shims, and beehive springs to make "errors" correctable. One good thing is I don't need to do it again and as long as my rocker cover is on no one knows what I did or what I'm doing under it and that's way it will stay.....JD

[Interested Observer]

“the remaining contours are entirely for weight reduction and clearance.”

Nice to know that the stress levels and structural integrity can be disregarded.

[panic]

Fixed it.

Happy now?

[Jack Gifford]

Spin-test result doesn't speak well for my design skills...

[rebelce]

Dang, get up in the morning and the entire thread is shorter.  You know JD, we've known each other for many years and what happens under my cover will remain a mystery too, despite what is said on this forum. There's so much more to building an engine than this, it's in the process of building, the details, that's the devil of it.   I have a set of Jesel Sportsman rockers here and was thinking of emulating their general shape out of 7075 T6 along with their bearings and roller tips. I have a good friend who is an engineer at Boca here in CT and he's in on this. At least his mill is DRO equipped. The Jesel's are apx. .895 wide and because of the extra length involved 1" seems a better way to go. I can see why the Arias rockers would be .275 around the bearing area at the bottom. With a length of apx 4" from the pushrod to the valve contact point there's a lot of stress. I don't have a set of stock rockers. Head, block and crank was all I picked up, figuring I'd have to build or buy all the rest anyway.

[Peter Jack]

Spin-test result doesn't speak well for my design skills...

Jack, I'm sure that fertile mind will come up with a solution. You've just offered proof that it pays large dividends to test rather than completeing everything and then having a series of linked failures. Well done. Keep up the great work.

Pete

[jimmy six]

Reb, funny these questions seem to have a mind of their own after the first few statements. When I was designing mine on a sheet of graph paper (that's all the machine shop got too) I don't remember why I arrived at the lower demension on the underside. I was using Torrington bearings an new there strength there too. The machinist may have made that .desision. The Arias set is rocker on shaft and the bottom needs to be strong. On my sons 1/2 mile Super Stock engine we are moving to T&D's as I really don't like guide plates and stud mounts; one of the many things we changed since starting 5 yrs ago.

Many years ago I considered moving the valves around but $$'s got in the way plus (a big one) I felt I had not met the full potential of the head as manufactured and maybe I still haven't. I've continued to improve speeds as the records show at Bonneville and I am going to concentrate on El Mirage until I'm too old to drive. We will see this weekend if I've still got it. We've not run there much and I'm looking forward to getting into the seat with the car actually set up for there.

When I ran 171 at Bonneville I had reached the goal I wanted with a stock head on gas and now I would like to reach the number in my mind at El Mirage. I'm smart enough to know it will not be easy as nothing ever is and there is always disappointments thrown in. And....there is the reason I own 2 different 12 ports after all these years of stock heads......Good Luck on your project.

[wobblywalrus]

That might be a good application for titanium.

[rouse]

If you go with Titanium, I'd suggest G5 which is 90-6-4 alloy. Has around 120,000 tensile as opposed to 65,000 for commercially pure.

The fatigue strength of G5 - Ti 6-4 is Plenty for rockers, just get rid of sharp corners. Shot peenning or tumbling will make them look better, I'm not sure just how much it really helps longevity, but can't hurt, and dues soften sharp edges.

Rouse   

[jacksoni]

There is a long thread on Speedtalk about what alloy might be best as well as other thoughts on making your own rockers here:

http://speedtalk.com/forum/viewtopic.php?f=15&t=40559&hilit=rocker+arm+material

[jimmy six]

I think we need to go the original question about making rocker arms for an obsolete engine that hasn't been made since 1959 to actuate valves with a push rod that makes a SBC look like a tooth pick. There always will be an expense that some thru friendship can get made reasonable. They will never be a viable sale item so you do what you can do. I for one will not spend my retirement making unobtainium rockers for 5 horsepower on an engine with shared intake and combo exhaust. I made roller tip rockers to quit wearing out valve guides which is what you get when you go from .300" lift to over .500 with a cam. I feel the same about having 7 main bearings instead of the stock 4. I'm not looking to spin my engine some pie in the sky RPM, I look to get out of it what I can with the restrictions of the engine and under the SCTA rules.

I am not against innovation and using new thoughts and ideas and probably have used many of them to get my engine where is today of which I am very proud. Many things I have done came from other forms of racing and also worked in LSR. I applaud my competitors and others using other obsolete engines for their achievements. Good Luck.

[wobblywalrus]

Jimmy, obsolete is not a bad thing.  As an example, this four valve Triumph engine I am working on as compared to an old style two valve one.  The old engine has cams with gear drives that can be indexed to set the cam timing exactly where needed and also to make track side adjustments.  The new engine has cams with the sprockets press fit on and no way to adjust them.  What I use for cam timing is what they have when I unwrap them after the UPS guy brings them.

The valves and ports in the old two valve heads could be opened up without much of an issue with shrouding and removing metal from the combustion chamber to keep good flow.  The four valve head has the seats at the corners of the chamber and putting in bigger valves requires lots of metal removal.

The bridge between the intake valves on the new 4 valve motor is sorta like an intake charge heater.  Exactly what I do not need.  There is a lot of surface area in the split ports with accompanying heat transfer and friction.

The dual cam towers reduce cooling air flow to the top of the combustion chamber compared to the old pushrod one.  The new motor weighs over 200 pounds and that's 1.5 times as much as the old one.

I could rattle on, like the parasitic oil drag in the new wet sump design compared to the old dry sump, lubing the tranny with engine oil rather than proper gearbox oil, etc.

Old can be a good thing.

       

[rebelce]

jacksoni, that was one heck of a read! Very informative, thank you, it gives much to consider. I know the Jesel rockers are 2024 and for general availability and machinability the T351 temper might be the way to go.  Jimmy6, I love racing the old iron, there's something about taking that engine out of an old car or truck, designing and building your own parts or digging through a ton of parts manuals to find something that might work, that is satisfying to me. Yes, cost does come into play but doing as much as I can helps on that end.  Ray wants to do this and I'm all for giving him my best shot.

[rebelce]

Does anyone know where I can find a program to help with the strength calculations for rockers? I'd rather go into this with some idea of what's happening rather than guess by what looks good and no, I can't use a slide rule.