HEMI Tech- Rockers, valves, pushrods, springs

If you're running any kind of stiffer springs, get the shafts hard chromed.

 

Found some REALLY good rocker rebuild info on this site:

http://www.hemihaines.com/Early-Hemi-Engines-6-146.html

 

I am collecting parts for a hot rod build 276 Desoto. I have to replace the original valves and guides, and install hardened ex seats. While I am at it I might as well put larger valves in and port the heads to match. I found a set of stainless SBC valves (1.940 X1.600) that are .033 longer than the Desoto valves. I am going to use a hyd roller cam with either adjustable pushrods or rockers. I am assuming that I will have to shim the rocker stands to restore the rocker tip geometry, Or will the adjustable stuff along with the hydraulic lifters absorb it? I am going to shoot for the same installed spring stack height as stock.
Are there any other glitches I have over looked from some one who has done this or somthing similar?

 

Larger valves not needed, just get stainless replacements
Port match with gaskets, the heads don't need that much help to flow..
Won't find adj. rockers, get pushrods from Smith Bros. (Oregon)
INTAKE???? Cam Size??? Ignition???
Ask 73RR (Gary) if you need some advice....

 

What SPOONS said..

 

Thanks for the feedback:
Intake, likely a Hamilton around 600CFM Holley
Cam size: Around .500 or so lift around 115 LSA (using a T5 and a 3.7 series gear in a coupe A) all subject to change but basically short duration high lift
Ignition pointless MSD
Shorty headers

 

Restoring "stock" geometry might be a good idea IF you had a stock cam!!!

I wouldn't rush to "stock geometry" with your high lift cam. Ideally you want the rocker arm to have a symmetrical travel (by symmetrical I mean when the rocker arm is perpendicular to the pivot - you are at MID lift. Another way to think about this is to picture a CLOCK HAND. Ideally you want your rocker arm (aka clock hand) to travel from 2 to 4. If you have a stock geometry set up that already dose that and then you switch to a high lift cam that now goes from 2 to 5 (more lift) you are no longer symetrical. In this high lift scenario you want to get the rocker arm HIGHER to begin with. So by installing a TALLER valve you can get it to start at 1:30 and move to 4:30 - again restoring symmetrical travel.

Make sense?

 

I've read through this guys website a dozen times, really good stuff. Wish I could just have him build mine, but I don't have that kind of cash and besides, I think it will be fun and an education for me to do it myself (other than the machining of course).

 

I am looking to set the rocker tip to move equally on either side of centre on the valve tip when I say restoring stock geometry which is what you are saying, I believe. Just a little tougher with shaft rockers vs Stud mounts. Typically I set the valves up with a light spring and blue the valve tips, then move the camshaft through a full cycle. Also check valve to valve and valve to piston clearance at the same time.

 

Mine is 450/450 @ 115 C/L, Yours is not much bigger than my stock re-grind From Clay Smith.
I'm running a ported cast iron intake w/ a 600 and she's a little fat. works ok..
Using stock dizzy w/ electronic conversion by GMC BUBBA. <----- Worth every penny.
Don't over think this thing....It worked good then and it will work now...

 

Earlier you mention shimming the stands to adjust the geometry. WhileI suppose that is a way it would be akward to do & you can do the same thing with the longer valves. Consider this just for the sake of conversation. Let's assume the factory geometry was symmetrical and the factory cam had .400" of lift at the valve and now you install a .500 lift cam. If you also installed a .050" longer valve the rocker arm would now be tilted UP an additional .050" - additionally at full lift it moves down another .050 past where the "stock" down limit used to be. So you have now restored "stock" (symmetrical?) geometry without mucking with the stand height. From here the only thing you now need to determine is the length of your pushrods.

I'm not sure if we are saying the same thing with different explanations or not. Forgive me if we are.

Now will it work ignoring all this - probably - you can always put your blinders on and take your chances. Or since these are a little bit expensive you might wanna dot your "I"s and cross your "T"s - which sounds like the plan you are already taking.


I've never fooled with a 276, but I know with the 392's the first thing we do is put better pushrods in them - & better means bigger in diameter. Without even getting radical on lift I have had to drill the heads to enlarge the push rods holes. You may want to double check that on your 276 as well.

 

Anyone know a source for adjustable pushrods with 1/4" ball ends? Seems the 5/16" are the only ones I can find.

 

Smith Bros. they will build you anything..

 

has anyone ever tried to convert non adjustable rockers to adjustable by spot facing drilling and tapping the non adjustables thanks bill

 

not enough meat in the rocker to put a meaningful thread into

 

73rr looks like nice work what do you charge . how about contact info. thanks bill

 

Rockerarms.com has been doing this conversion for years. Gary knows his stuff. This is a set done by them, along with my hard chrome shafts and rocker collar set.

 

Do you have to remov the bolts and heads to remove the rocker shafts?
Does it need to be done on an older engine been sitting for 10 years? Or should I just prime it?

 

You have to remove the bolts, heads might or might not stay in place. Might not be bad to see the chambers though!

 

I think they were talking about 351 cleveland because the stem was the right diameter

 

I've seen the Desoto guys using LA motor roller cam set ups and Donnie Johansen cams,as the lifters are the same diameter. And was planning on doing this in my 291, but now I just stumbled upon a Chrysler 354 I'm going to build first and put the desoto on the back burner. Does the Chrysler hemi (1956) have the same lifter bore and can you use this roller cam setup? any one know

 

Same lifters, the connecting bars have to be lenthened.

 

I got a couple valves out of my 270 last night and took some measurments. Intake 1.65 head, 4.80 length and .371 dia stem, Exhaust 1.40 head, 4.75 length and .371 stem. So then I did some digging in my melling valve book and found the 304 Jeep valves are intake .3715" Stem, 1.787" Head, and 4.898 length and the exhaust are .3720" Stem. 1.405" Head, and 4.892 length. I'm thinking I can make these work in my heads by just opening up the intake a little. You can get these valves in stainless on feebay for around $100. Also I plan to have my cam reground so the small amount of added length on the valve isn't a big deal. I do all my own head work so I'll take some pics along the way and post them.

 

I just got my cam back from the regringer. I ask how much he reduced the radius of the base circle I plan to mill the heads the same amount. Get a boost in compression and put the lifter preload back.

 

"Also I plan to have my cam reground so the small amount of added length on the valve isn't a big deal."

You are talking almost .100 additional stem length, which is actually quite a large amount, especially with the short rockers on a 270 Dodge. The cam being reground with a smaller base circle will have additional negative effect on the valve train geometry and will make the valve seem even longer.

 

While it seems like a good idea, remember that milling the heads will add lost preload at the base of the lobe, but will also increase the preload at the top of the lobe, which has only changed a few thousandths from original height.

 

300 Ford 6 cyl. valves work in a dodge if you go to 11/32 guides. Also Edelbrock 5822 springs are a nice up grade for high lift cams and at a little over $30 the price is right.

 

does anyone know where some of these are I need one ,M/t or donovan ?alum exaust rocker for a hemi 392 ,the ball seat seems to have failed ,or does someone know how or who would fix them?

 

I just reread these post, and thought I would add some comments. Several references have been made to valve stem lengths and geometry. Something that needs to be kept in mind. The way the hemi heads are designed....when you add a valve with a longer stem, the valve tip is moved away from the rocker tip. No amount of shimming the stands will correct this. The rocker shaft needs to be physically moved towards the valve, as well as being raised. This calls for custom rocker shaft stands. In the case of all hemi families, this is tough on the exhaust side due to the fact that the shaft is already close to the head bolts. The same goes for the Dodge and Desoto intake shaft. My $.02 for today.