273 adjustable rocker arms

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When do the 273 rockers need to be ground for clearance? I just purchased some Comp 901 springs and was wondering if the factory adjustabel rockers need to be ground for spring clearance (stock 340 cam).
It depends on the spring diameter. I used the wrong springs but the head shop made them work. I had to grind some clearance for the spring top and retainer.
100_5227.JPG
 
That's correct.
If the new springs have a larger OD than the stock pieces, and/or you're using aftermarket retainers, you will run into the rockers.
As you can see with toolmanmike's great photo, the stock retainers provide lots of clearance, but the Comp retainers (and others) run all of the way out to the edge of the spring. and they will hit.
 
Great info! Like you, I have checked them on several occasions and found them to be very close. They are better than they get credit for.

Well, the OP threw down the gauntlet and I foolishly picked it up.... at least for the 273 adjustable rockers. Set this all up and got better results than I expected, even up to .505" valve lift.

Here are data points using .010" valve lift as a baseline; first number is valve lift & 2nd number is ratio, computed as pushrod lift delta from baseline divided into valve lift delta from baseline. The ratio's listed in this tabulation do NOT include the loss of ratio caused by the pushrod to lifter angle. (More on that below)

0.028/1.64
0.061/1.50
0.100/1.55
0.141/1.56
0.174/1.56
0.204/1.55
0.230/1.53
0.256/1.53
0.283/1.53
0.309/1.54
0.340/1.53
0.383/1.53
0.447/1.56
0.505/1.55

I'd ignore out the 1st 2 numbers (as they are computed from very small deltas and so prone to error); the average of the rest of the numbers is 1.54 (excluding lifter-to-pushrod angle). This includes pushrod-to-rocker angles changes and rocker-to-valve tip changes.

If you want to factor in ratio loss for the the pushrod-to-lifter angle (for a 14 degree angle), that is .970. Multiply that by the average above and you get an overall lifter to valve ratio of 1.49-1.50 for lifts up through .500" or thereabouts.

What is really interesting IMHO is that the ratio stays steady up to high lifts. One would expect that ratio to drop as the rocker angles down more and more. But, the rocker contact point on the valve tip 'walks' further and further out as the lift increases; this outward movement in the rocker-to-valve contact point increases the ratio enough to compensate for the loss of ratio due to the increasing angle of the rocker. Pretty neato! Juuust maybe those Chrysler engineers back-in-the-day could do a lot more on paper than we might give them credit for LOL

You can see the rocker-to-contact point movement in the last 2 pix; the first is at .100" valve lift and the next is at .505" valve lift.

Below is a pix of the setup, which was worked on to make it repeatable and stable. The rockers' adjuster was put where there were about equal threads exposed above and below the rocker body, which seemed like a reasonable place to which to adjust it. The head is a 675 head with the stock. You can see the shims (feeler gages) used to change change the pushrod height; they would be set and measured separately for accuracy.

View attachment 1715253553

View attachment 1715253567

View attachment 1715253568
 
Great info! Like you, I have checked them on several occasions and found them to be very close. They are better than they get credit for.

I always check the rocker ratio on any engine I build. I keep a block close by for testing purposes only. The Mopar factory mechanical '273' rockers are very strong and durable, I find them in the 1.45 range. Best being 1.51 and worst 1.41 . Also with the pushrod and lifter not being 'in-plane' with each other loses .10 of lobe lift . Very easy to calculate actual lift at the valve with lash. Subtract .10 from the lobe lift from the cam card and multiply by rocker ratio and subtract lash puts actual lift within .001-.002 . Works for hyd. cams too, you have no lash to subtract .
 
63GT, can you elaborate on larger adjusters? How does a larger adjuster move the contact point?
I’m wanting to pair LA heads with a Magnum block/cam that are designed for 1.6 ratio.
I know I need to get oil to the shafts.
 
63GT, can you elaborate on larger adjusters? How does a larger adjuster move the contact point?

It is done during the machining process for the larger adjuster...
The OEM adjuster is 3/8-24NF thread, when boring for a 7/16-20NF thread (letter X drill, or .385) you simply offset the amount of the larger adjuster towards the fulcrum of the rocker. (I start with a 3/8 end mill, then follow-up with the X drill. it prevents 'walking' and makes a nicer hole)
When I do these, I don't 'clear' all of the old 3/8 threads when boring for the new larger 7/16 threads, so I get the full extra 1/16 (.062) worth of offset. This leaves only about 20° of old thread. not a problem considering you still have 340° of brand new thread for the larger adjuster that has much more inherent thread than the 3/8 did.
And, of coarse, I spot face the rocker for a nice flat surface for the jamb nut. Instant 1.6:1 + rocker !
 
Many thanks! I was hoping to hear the details of how you got to the desired offset with the thread size difference. Now if I only had a mill LOL

BTW, are you using the 7/16" adjusters with the cup, or sticking with a ball adjuster?
 
Many thanks! I was hoping to hear the details of how you got to the desired offset with the thread size difference. Now if I only had a mill LOL

BTW, are you using the 7/16" adjusters with the cup, or sticking with a ball adjuster?

For simplicity sake, I stuck with the ball end, so that I could use the same pushrods. It's the Crane 99680-2 (pair w/nuts)
 
It depends on the spring diameter. I used the wrong springs but the head shop made them work. I had to grind some clearance for the spring top and retainer.View attachment 1715254772
When my engine was rebuilt I put some 273 rockers on and had to Clarence them for the bigger Springs. I think I remember using a small piece of welding wire as my spacer to loop back there to make sure it would not touch.
 
That's funny, back in the '70's I ran Isky dual springs with damper in a .580 lift mechanical camshaft in my 273 and never even thought to look for clearance between the retainer/spring and rocker arms. Of course, I was also using aluminum retainers, which I don't see offered for sale any longer for some reason.
 
That's funny, back in the '70's I ran Isky dual springs with damper in a .580 lift mechanical camshaft in my 273 and never even thought to look for clearance between the retainer/spring and rocker arms. Of course, I was also using aluminum retainers, which I don't see offered for sale any longer for some reason.

Ooooh, I got cold shivers when you said aluminum retainers :) I've seen a few of those with the locks ready to pull through... They make cool keys chains tho :)
 
Of course, I was also using aluminum retainers, which I don't see offered for sale any longer for some reason.
I remember using those: I guess they were to lighten things up a bit. Mine did not survive being accidentally hot-tanked LOL. I'd guess the new, high spring rates made them useless.
 
Ooooh, I got cold shivers when you said aluminum retainers :) I've seen a few of those with the locks ready to pull through... They make cool keys chains tho :)
When they're making them out of titanium I don't know why someone would want aluminum.
 
For simplicity sake, I stuck with the ball end, so that I could use the same pushrods. It's the Crane 99680-2 (pair w/nuts)
Thanks. One more question: Did you retain the oversized, unthreaded area in the lower end of the adjuster hole to let the oil dribble down on the pushrod cup?
 
When they're making them out of titanium I don't know why someone would want aluminum.

Exactly right. I bought a set of 7° Titanium's from Doug Herbert back in '99 for $50. smokin deal!
 
Thanks. One more question: Did you retain the oversized, unthreaded area in the lower end of the adjuster hole to let the oil dribble down on the pushrod cup?

Yes, it's a quick cut with a small end mill. (half round, about .125 long)
Need some done?
 
For simplicity sake, I stuck with the ball end, so that I could use the same pushrods. It's the Crane 99680-2 (pair w/nuts)
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I noticed that on the 99680 the ball on these is a 3/8.

Where on the 66770as it uses a 5/16 ball. Did you go to a larger push rod in diameter.

66770as | JEGS
 
Yes, it's a quick cut with a small end mill. (half round, about .125 long)
Need some done?
Any pics? Sounds interesting. I wouldn't mind seeing a few pics of your 63 either. Love those 63 and 4 Darts. Especially with some tire underneath. You can PM me so we don't hijack this thread.
 
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I noticed that on the 99680 the ball on these is a 3/8.

Where on the 66770as it uses a 5/16 ball. Did you go to a larger push rod in diameter.

66770as | JEGS

You're right about that... I looked it up too fast, and gave the wrong number. my bad.
I did use the 5/16 ball adjusters.
Crane quit making the 5/16 ball 7/16-20 adjusters a few years back, (I was pissed) but I'm glad to see them in production again :)
 
Any pics? Sounds interesting. I wouldn't mind seeing a few pics of your 63 either. Love those 63 and 4 Darts. Especially with some tire underneath. You can PM me so we don't hijack this thread.

I scoured my phone.. couldn't find a single pic of a done rocker.. I suppose I could do one up, and send the pic..
It looks like I should do a build thread. I've been asked before. (sooo many pics to download!)
 
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