What shaft for ductile iron rockers?

[RemCharger]

stock shafts are not hard. they are far from being hardened.

the main reason i chase rocker geometry is to keep from tearing the valve guides up. the large scrub pattern of the ductile iron definitely can affect guide wear. there are some tutorials out on the web about setting geometry with a non-roller tip. the more lift the longer the scrub can be and geometry can become more critical. i think it's easier to check/set geometry with the heads on the bench than with the engine on a stand and virtually impossible with the engine in the car. i put checking springs on the heads, mount the rockers and shafts and then manually work the rockers with some typewriter carbon paper under the valve tip to show where the contact pattern is. if you try to set geometry with engine in the car about the only thing you can do is apply some layout dye on the valve tips, run the engine, then take the rockers off and look at the pattern. a lot less messy to just do it on the bench. there's a big difference in wear pattern on a non-roller vs roller tip. when that is solved then mount the heads on the short block and go after the push rod geometry.

So after you see a scrub pattern, what's your next step to changing it.

 

[lewtot184]

So after you see a scrub pattern, what's your next step to changing it.

if the pattern is more to the inside of the valve tip (inside being towards the cam/crank centerline) then add shim. to the outside you'll need longer valve tip. inside has always been the common problem for me. be careful with shim material. use something soft like alum or copper; no steel. rocker shaft stands can be cracked by not using an eccentric shim.

i have found thru the years that using the iron rockers on iron heads where the valve job and valves are correct, not sunk, little to no shim will work. naturally as lift is increased above stock there will be more travel at the valve tip and more of a chance correction will be needed.

another thing i've found on shafts when using adjustable rockers that it's easy to deform the shaft by over torquing the hold down bolts. stock shafts are very prone to this. even the heavy thick wall shafts will distort some above 30ftlbs of torque. the big problem is usually the ends of the shafts get distorted and it makes it very difficult to get the rockers off for service. if it were me to do again i'd do the heavier shafts and put a pipe plug in the ends to help them keep their shape.

something else to keep in mind is that induction hardened shafts are not hardened all the way thru. it's my understanding that induction hardening runs about .030" deep. maybe it should be treated as a surface hardening only. harland sharp may have a true hardened shaft to be compatible with the rockers fulcrum bearings; not for sure on this.

 

[lewtot184]

I meant each bank (each side) of the whole engine.... The shimming I'm referring to is side to side for each rocker.... The .015" clearance measurement will be found as a total in each pair between the rocker shaft hold-downs. This reduced clearance will allow for better stability and oil control. Some people call rocker geometry "shimming" because there is a way to use shims to lift the shafts up off the cast-in pedestals. I suspect this is what Lewtot184 is referring to in post #18, but he'll chime in I'm sure.
Try reading here for some info on geometry correction;

B3 Racing Engines LLC - Mopar Rocker Arm Geometry Tech

HTH, Lefty71

your correct that is what i was referring to. the ductile iron rockers don't come with side shims, just springs. i haven't tried using those .015" side shims with iron and springs but do with alum. i see no downside to using the shims even with springs and iron.

 

[RemCharger]

if the pattern is more to the inside of the valve tip (inside being towards the cam/crank centerline) then add shim. to the outside you'll need longer valve tip. inside has always been the common problem for me. be careful with shim material. use something soft like alum or copper; no steel. rocker shaft stands can be cracked by not using an eccentric shim.

i have found thru the years that using the iron rockers on iron heads where the valve job and valves are correct, not sunk, little to no shim will work. naturally as lift is increased above stock there will be more travel at the valve tip and more of a chance correction will be needed.

another thing i've found on shafts when using adjustable rockers that it's easy to deform the shaft by over torquing the hold down bolts. stock shafts are very prone to this. even the heavy thick wall shafts will distort some above 30ftlbs of torque. the big problem is usually the ends of the shafts get distorted and it makes it very difficult to get the rockers off for service. if it were me to do again i'd do the heavier shafts and put a pipe plug in the ends to help them keep their shape.

something else to keep in mind is that induction hardened shafts are not hardened all the way thru. it's my understanding that induction hardening runs about .030" deep. maybe it should be treated as a surface hardening only. harland sharp may have a true hardened shaft to be compatible with the rockers fulcrum bearings; not for sure on this.

Thanks for explaining your process.

 

[Jonas Nordstrom]

Thanks guys, this is golden info.

 

[Geoff 2]

Tens of thousands of Poly engines were in use from 1955 to 1966. They all had iron rockers & hard steel shafts [ shafts made from a hard grade of steel, not steel that was subsequently hardened ]. There was no problem with them.

 

[lewtot184]

Tens of thousands of Poly engines were in use from 1955 to 1966. They all had iron rockers & hard steel shafts [ shafts made from a hard grade of steel, not steel that was subsequently hardened ]. There was no problem with them.

we're not discussing polys and i do have some experience with polys.

 

[Geoff 2]

No, but Poly's used the same material for the shafts & rockers so it is veeeeeeeeeeeeeeeeeeeery relevant as to material reliability/compatibility.

 

[lewtot184]

No, but Poly's used the same material for the shafts & rockers so it is veeeeeeeeeeeeeeeeeeeery relevant as to material reliability/compatibility.

maybe, maybe not. have you ever looked at poly valve spring/camshaft specs vs big block; especially when using performance springs and cam lobes?

 

[RemCharger]

maybe, maybe not. have you ever looked at poly valve spring/camshaft specs vs big block; especially when using performance springs and cam lobes?

Yep. There's so little valve action, you can adjust them while running.

 

[Geoff 2]

Here are is an Isky Poly cam: 330 * adv duration, 0.540" lift. No mention or recommendation of upgrading shafts/rockers.
Here is an Isky 440 cam: 248* adv duration, 0.400: valve lift
.

 

[lewtot184]

Yep. There's so little valve action, you can adjust them while running.

looking at a 1965 service manual it shows 57lbs of seat pressure and 150lbs open pressure for the valve springs with a .397" lift cam; 244 degrees duration (probably about 180 degrees at .050"). that should be very easy on parts.

my first venture into mopar "hot rodding" was in 1966 with a '58 plymouth and a 318. there was very little aftermarket parts that i knew of at the time; i was 18yrs old. things never went well because it was the typical kids wrenching without much knowledge or tutoring. in 1968 i "graduated" to a '68 383 4spd road runner. i did beat on it! i broke so many rockers and bent so many push rods that i carried a bunch of spares in the trunk to change alongside the road. breaking all those rockers got me into the crane iron rockers (to my knowledge there wasn't any alum roller tip rockers for a mopar at that time) and i just had to learn the pros and cons the hard way. i had no idea how critical rocker geometry was or how to set it up. i just wrecked the valve guides not knowing why and would have the heads rebuilt. went thru that multiple times; now i'm paranoid of it,...lol! you can't enjoy your ride if you're working on it all the time and throwing money at it.

another thought; i've had 4 sets of the crane iron rockers, 1.5's, and they all checked right at or very close to a 1.6. a set of 1.6's i had checked to 1.65. keep this in mind when setting up retainer to seal clearance. always check aftermarket rockers no matter who makes them.

 

[RJRENTON]

never heard of or seen a factory "hard" shaft. i believe induction hardening was in its infancy for detroit cars and i sure don't remember seeing thick shafts; or at least i never had any. the smog engines that i've taken apart had those low pressure green springs on them. a magnum spring was only 230-240lbs open with a very gentle cam lobe.

In order to be accurate, the shafting matetial MUST BE specified AND the degree of hardness as well.....hardness is usually specified on a Rockwell Scale like Ra 40 0r Rb50 and can be achieved thermally or induction hardening or by the carbon content of the shafting matetial....with the highest percentage carbon yielding higher hardness. Realizing of course that lubricants at the shaft - rocker interface has EVERYTHING to do with the wear factor........just my thoughts.......
BOB RENTON

 

[fourgearsavoy]

I like the bronze bushed Isky rockers on a "hard" chrome shaft like a hydraulic cylinder rod. The RAS shafts are very thick and the hard chrome still looks like new after almost 10 years. I ran some pretty mild springs though, 170 on the seat and 380 on the nose with a small SFT cam.

Gus

 

[Jonas Nordstrom]

Ok, update.

My Rockers measure .875" so the nice Hughes 1620 shaft does not fit sadly....

So, where to find good .872 shafts?

 

[padam]

Ok, update.

My Rockers measure .875" so the nice Hughes 1620 shaft does not fit sadly....

So, where to find good .872 shafts?

View attachment 1512709

Probably easiest to have the rockers honed to fit.

 

[Jonas Nordstrom]

Probably easiest to have the rockers honed to fit.

I was thinking of that, though a .875" shaft is not close to getting in so that would be some honing to do.
...also, doesnt these have a hardened surface that would be removed with honing?

 

[padam]

I was thinking of that, though a .875" shaft is not close to getting in so that would be some honing to do.
...also, doesnt these have a hardened surface that would be removed with honing?

you are overthinking it. The bore would not be hardened, and removing a few thousands would not take long.

 

[padam]

you are overthinking it. The bore would not be hardened, and removing a few thousands would not take long.

But now that I think about it, with the cost of labor these days…

That’s why modifying an engine can turn into an expensive chain of events.

 

[Jonas Nordstrom]

you are overthinking it. The bore would not be hardened, and removing a few thousands would not take long.

Thanks. Im no expert on rocker shafts so Im double checking.
Then I will prolly go with the Hughes anyway and hone the rockers to fit.