Shovelhead rocker arms

[nifty]

-66 1966-70 OE rocker arms were copper plated as part of case hardening process. Purported widely to be 1.43:1 rocker ratio. (or similar sub 1.5:1 number)
17360-66A ROCKER ARM, rear exhaust and front intake 71-78 retrofit to 66 will fit to 84
17375-66A ROCKER ARM, front exhaust and rear intake 71-78 retrofit to 66 will fit to 84
71-up, OE raw steel arms have improved hardening (-66A arms, forging numbers B19 & Z, possibly all 1.5:1 rocker ratio) At least one set of -66A OE arms from unmolested 73 actually measure up at 1.5:1 rocker ratio.

1979 rockers had raised pad on underside with forging numbers 12382-66
82’-84, radiussed rocker pad at valve end purportedly ground 1 degree out of true to offset for negative angle of 82 up rockerbox. Intent supposedly valve rotation.
82-84 arms purportedly 1.5:1 rocker ratio,

41-84 PARTS BOOK LISTS ONLY THE -66A ARMS 66-84.

S&S once stated categorically, that all shovel arms were 1.43:1, they have subsequently revised that to: “Our experience has shown that the actual rocker ratio of stock and aftermarket Shovelhead style rocker arms can vary widely. Some are less than the nominal stock 1.43:1 ratio and some are more”.

Probable worst case scenario is 2 wildly different ratio intake rockers in same motor.

Bottom line is the only way to be sure of what you have is to measure the actual lift at valve, and that requires a pair of test solid lifters and a spare rockerbox cut-away/modified into a tool.

Or a tool whereby the assembled head & rockerbox can have measured cam lift applied to rocker arm and valve lift measured.

Does help to explain why some superficially identical engines, out-perform others.

Nifty

[Mongrel505558]

That's interesting. Wouldn't the ratio be a function of the distance between an arbitrary contact point on the rocker arm pad and its axis centerline? Either there or the center of the pushrod cup (or both)? Seems a simple measuring fixture could be made with a shaft, sliding marker for the pad or pushrod cup or both, and a digital caliper. Seems a lot easier than installing into the rocker box, then box onto the head, head on the motor, pushrods, etc., and measuring at that point.

I guess the tricky part is identifying a point on radius of the pad or center of pushrod cup that can be used as a consistent reference point for all rocker arms.

Actually, as I think this through, it should be a lot easier than that: put the rocker arm on a pivot and press one end a known distance. Measure the lift of the other end. This may not give the absolute lift, but would be useful for matching rocker arms for a build or rebuild.

[RooDog]

Thanks, Nifty, for clarifying this info on SH rocker ratios, I never suspected anything like that existed.
I have Crane roller rockers in my Shovel, and $&$ in my Evo, both have cams advertised @ over 1/2" lift.....
I just checked with Donny Petersen, and he said nothing about an yof this in his Vol V, Part I, SH book, or I didn't look deep enough. I don't have Part II, perhaps this info is there?

PS: I had a set of rockers & blocks from Tedd's V-Twin that I couldn't shorten the Colony* early Pan style PRs (OE -48 adjustable lifters) enough to install. I removed the Tedd's and reinstalled the OE rockers, PRs went right in, adjusted properly, and everything fit as it should on that old motor that has been in my family since 1967....
....RooDog....

* Colony aluminum push rods for 74, FL, length jugs, EL" PRs from Colony are shorter and probably would have fit, but what else would have been amiss?

[nifty]

That's interesting. Wouldn't the ratio be a function of the distance between an arbitrary contact point on the rocker arm pad and its axis centerline? Either there or the center of the pushrod cup (or both)? Seems a simple measuring fixture could be made with a shaft, sliding marker for the pad or pushrod cup or both, and a digital caliper. Seems a lot easier than installing into the rocker box, then box onto the head, head on the motor, pushrods, etc., and measuring at that point.

I guess the tricky part is identifying a point on radius of the pad or center of pushrod cup that can be used as a consistent reference point for all rocker arms.

Actually, as I think this through, it should be a lot easier than that: put the rocker arm on a pivot and press one end a known distance. Measure the lift of the other end. This may not give the absolute lift, but would be useful for matching rocker arms for a build or rebuild.

Jim,
Absolutely, what you suggest in your last paragraph would suffice as a comparator to ensure reasonably equal rocker ratios go into an engine.
But to know the effect of the radiused pad requires measurement at the valve, and the pads drag us into the world of rocker to valve geometry, which is another can of worms.
Nifty

[kitabel]

Thanks for the info.
By using only 2 shapes (each serves as intake for one cylinder and exhaust for the other), the rocker geometry is somewhat off being a compromise to align all pushrods with a single cam base circle. Panhead same problem.
Very annoying and delicate to correct, IMHO pointless in a street engine.

[RooDog]

Thanks for the info.
By using only 2 shapes (each serves as intake for one cylinder and exhaust for the other), the rocker geometry is somewhat off being a compromise to align all pushrods with a single cam base circle. Panhead same problem.
Very annoying and delicate to correct, IMHO pointless in a street engine.

Exactly. This is racer tech. Don't mean shit on s stock'ish motor.....

[Mongrel505558]

So if they didn't use rocker box gaskets on the early shovels So I guess the valve geometry changed some more when they started using them. Not much, and the effect was probably made moot anyway by the manufacturing tolerance of the rocker arms.

[nifty]

So if they didn't use rocker box gaskets on the early shovels So I guess the valve geometry changed some more when they started using them. Not much, and the effect was probably made moot anyway by the manufacturing tolerance of the rocker arms.

Yep,
And every cam change alters geometry and earlier gaskets were only around .010", whereas at least some modern gaskets are around .020".
To put Roodog's summary another way: So long as arms approximately match and rockers aren't thrusting valves too much in guides, a street Shovel is what it is.

Any thoughts on why MoCo initially didn't spec rocker gaskets?
And why the special waisted studs? Intended to stretch with intent to maintain constant pressure on mating face? Repops inc S&S just use commercial SHCS.
Maybe MoCo knew the boxes squirmed around due to stud stretch?
If so, what made them think aluminum paint alone would maintain a seal?

I suspect that careful prep and not too runny aluminum paint, carefully applied and very careful assembly might actually seal, but due to the work involved in re-doing the job, I have never been brave/foolish enough to actually try it.
I have an original, early Shovel rocker box, still messily slathered with aluminum paint by a long ago, careless "mechanic".
Was the original intent to use rocker box as a heat sink, to pull temp out of head?
If so, perhaps designers thought aluminum paint would be less of a heat break than a gasket?

Nifty

[Mongrel505558]

Why not use a copper gasket if you want heat conduction? Too thick? As for the waisted studs - I never thought about it, but maybe it's to make assembly easier. You have to push the box and head together as squarely as possible. If cocked in any way you're going to have a very hard time. You have 9 studs on some random head that have to line up with 9 holes in some other random rocker box, and there are manufacturing tolerances. Perhaps the studs are waisted to give them some flexibility.

[RooDog]

I assemble my $&$ heads & rocker boxes with ARP hi-strength stainless steel 12pt cap screws. Never gave it any thought, but then I'm often thoughtless on many things. I wonder if they make for a more rigid assembly than the OE studs. I would think rigid is better than flexible. Both Pans and Knuckles featured hard mounted rockers. Rigidity is an important factor in valve train design & function, no?
....RooDog....

[nifty]

Gasket TSB
Nifty

tsb 593 69 rocker gasket.jpg

[Mongrel505558]

I assemble my $&$ heads & rocker boxes with ARP hi-strength stainless steel 12pt cap screws. Never gave it any thought, but then I'm often thoughtless on many things. I wonder if they make for a more rigid assembly than the OE studs. I would think rigid is better than flexible. Both Pans and Knuckles featured hard mounted rockers. Rigidity is an important factor in valve train design & function, no?
....RooDog....

Good point.

[nifty]

I assemble my $&$ heads & rocker boxes with ARP hi-strength stainless steel 12pt cap screws. Never gave it any thought, but then I'm often thoughtless on many things. I wonder if they make for a more rigid assembly than the OE studs. I would think rigid is better than flexible. Both Pans and Knuckles featured hard mounted rockers. Rigidity is an important factor in valve train design & function, no?
....RooDog....

IMO, provided the shafts aren't loose, the Shovel rockerbox is a very rigid structure, more so than Knuckle and Pan. Until clowns saw them in half for the sake of fashion.
Nifty

[RUBONE]

I assemble my $&$ heads & rocker boxes with ARP hi-strength stainless steel 12pt cap screws. Never gave it any thought, but then I'm often thoughtless on many things. I wonder if they make for a more rigid assembly than the OE studs. I would think rigid is better than flexible. Both Pans and Knuckles featured hard mounted rockers. Rigidity is an important factor in valve train design & function, no?
....RooDog....

IMO, provided the shafts aren't loose, the Shovel rockerbox is a very rigid structure, more so than Knuckle and Pan. Until clowns saw them in half for the sake of fashion.
Nifty

I don't think I'd claim more rigid than Knuckle, which were carried in the actual head casting.

[nifty]

I assemble my $&$ heads & rocker boxes with ARP hi-strength stainless steel 12pt cap screws. Never gave it any thought, but then I'm often thoughtless on many things. I wonder if they make for a more rigid assembly than the OE studs. I would think rigid is better than flexible. Both Pans and Knuckles featured hard mounted rockers. Rigidity is an important factor in valve train design & function, no?
....RooDog....

IMO, provided the shafts aren't loose, the Shovel rockerbox is a very rigid structure, more so than Knuckle and Pan. Until clowns saw them in half for the sake of fashion.
Nifty

I don't think I'd claim more rigid than Knuckle, which were carried in the actual head casting.

Rubone, I base my opinion on the fact that Knuckle rocker shafts are only rigidly attached on one side, to vertical ears of head, other side of rocker shaft attaches into aluminum "knuckle" casting, which is bolted to over-hung horizontal ears of head. I agree the Knuckle and Pan rocker installations are adequate, my primary point was that, possibly apart from their waisted studs, the Shovel rockerbox is very rigid.

Nifty