Question about adjustable rockers on Big block

Orange71SE · Mar 14, 2018

Hi, ive started a build on a 440 engine I came across ( first time ive rebuilt an engine) and Ive been looking at comp cams products. Many of thier non-stock cams say that you need to run adjustable valvetrain. I wanted to know if this was true or not because aftermarket rocker s for mopars run around $1000, which id rather not spend.

Kern Dog · Mar 14, 2018

Some of the Jesel and Harland Sharp rocker arm sets are expensive, others can be bought for less than half of the $1000 you wrote.
Higher lift cams stress the rocker arms a lot more than a low lift stock cam. The aftermarket parts all seem to have roller tips...these maintain even contact on the valve stem through the whole rise and fall of the cam lobes. Stock rockers have a tendency to "scrub" the valve tip, sometimes to the point of causing early valve guide wear from pushing the top of the valve sideways a small amount.
All solid lifter camshafts need an adjustable rocker arm arrangement. Hydraulic cams can benefit too because the adjustability can make up for any slight machining errors. Stock engines with stock cams are so mild, they may not see any benefit.

moes · Mar 14, 2018

a certain amount of valve lash is necessary to compensate for thermal expansion in the cylinder heads, especially iron block engines with aluminum heads. Reducing valve lash effectively increases valve lift and duration, but also increases the risk of burning an exhaust valve or losing compression if there is insufficient lash and the valves can’t fully seat. With regards to cam design, lash affects the lower ends of the valve-lift profile. Those areas of the curve help “gently” open and close the valve. And if these areas of the lobe design are reduced or eliminated through excessive lash, then the lifter hits the more aggressive angle of the ramp too quickly and more stress is forced on the valvetrain. Plus, there’s a downside to overly tight valve lash. That's were an adjustable rocker comes into play.
With regards to cam design, lash affects the lower ends of the valve-lift profile. Those areas of the curve help “gently” open and close the valve. And if these areas of the lobe design are reduced or eliminated through excessive lash, then the lifter hits the more aggressive angle of the ramp too quickly and more stress is forced on the valvetrain. Plus, there’s a downside to overly tight valve lash.

dvw · Mar 15, 2018

The old Isky/Crane/Mopar steel adjustable rockers work well. I've run .650" solid roller cams with them w/o issue. I believe I have an old set.
PM me.
Doug

vintage chromoly · Mar 15, 2018

I agree on the old ductile iron Adjustable rockers.

I'm using a set on my RB. Solid flat tappet cam with just south of .600 lift.

I ordered a set of goodshafts, spacers and hold downs from RAS. The shafts are "banana grooved" for better oiling.

I didn't have the arms bushed or blueprinted for ratio, but I did have to have a friend put them in a lathe to narrow them for the use with the spacers and hold downs. I think we took .040 off each arm (.020 per side)

Also, all rocker arms "scrub" the valve stem tip.
Some have rollers and some do not. I'm a believer that the less little shafts and roller bearings you put in a street driven engine, the better.
Jesel sells a set of ultra high end arms that do not have roller tips.

The subject of setting the shaft location to achieve ideal geometry is another thing as well. Word on the interwebs is that Mike B is the man as far as that goes.

lewtot184 · Mar 15, 2018

the adjustable valve train recommendations probably have more to do with getting the plunger in the hydraulic tappet in the correct position. mechanical cams will have to have adjustable valve trains. how necessary all this is may depend more on the cam and use of the engine. the more radical the cam is from stock the more necessary the better parts will be, and the skills of the builder/installer to set up a valve train will come into play.

wyrmrider · Mar 15, 2018

I'd contact rocker arm rebuilders in Anderson CA
The can fix you up with industrial hard chrome shafts and bushed mechanical rockers, banana grooves etc
I may even have a spare set
what cam and valve lift- actually do not get a cam till compression, heads, pistons etc have been decided just estimate
if you change your base circle you will (likely) need custom pushrods
if you go to a really high lift cam lash caps makes adjustment and geometry easier (depending on decking, head gasket etc)

vintage chromoly · Mar 15, 2018

Heres the contact info for RAU. (Used to be RAS)
http://www.rockerarms.com/

wyrmrider · Mar 15, 2018

The stock stamped rockers work well for most hyd cams with the correct length pushrods
read up on rocker arm geometry
with high lift cams you may need to shim up your shafts, lash caps etc to get the center of the shaft to the rocker pad/ valve tip tangent to the valve stem at 1/2 valve lift
(non roller tip rockers stock or iron)

PurpleBeeper · Mar 15, 2018

Orange71SE said:
Hi, ive started a build on a 440 engine I came across ( first time ive rebuilt an engine) and Ive been looking at comp cams products. Many of thier non-stock cams say that you need to run adjustable valvetrain. I wanted to know if this was true or not because aftermarket rocker s for mopars run around $1000, which id rather not spend.

I've been going through this myself on my new "highway cruiser" motor. Some things I've heard are "you don't need them for cams under .500" lift" and a Hot Rod magazine article put that limit up around 0.530" lift or so. Are they better? YES Do you need to buy them? DEPENDS ON YOUR CAM & most streetable hydraulic cams won't require them.

Now, I will say that I'm running ductile iron Isky adjustable rockers on my current motor & they work great (except for valve cover baffle clearance). Even for the cam I first had in this motor (purple shaft 292/509) I didn't "need" these rocker arms.....ran the same cam with stock rockers too in a different motor.
Just my 2-cents

Bicylindrico · Mar 15, 2018

Not sure if you are looking into cylinder heads but mine came with larger diameter springs requiring me to factor this into my rocker setup. I ended up running Harland Sharps for this reason though my first choice was going to be the Comp Cams Magnums

IQ52 · Mar 15, 2018

Orange71SE said:
Hi, ive started a build on a 440 engine I came across ( first time ive rebuilt an engine) and Ive been looking at comp cams products. Many of thier non-stock cams say that you need to run adjustable valvetrain. I wanted to know if this was true or not because aftermarket rocker s for mopars run around $1000, which id rather not spend.

Let us see if we can just answer the question.

There may be a little confusion in reading the catalog. None of the hydraulic flat tappet cams in the Comp cams catalog (that I have) require adjustable rockers. The adjustable valve train is require when using the Comp Cams 867-16 Pro Magnum hydraulic lifters. This is because these lifters have a recommended preload setting of .002"-.004" hot.

https://static.summitracing.com/global/images/instructions/cca-867-16.pdf

Very difficult to achieve that .002"-.004" preload without an adjustable valve train. If you use the 822-16 lifters the adjustable valve train is not required as long as you have the correct length pushrods for the .030"-.040" preload.

http://www.compcams.com/Technical/Instructions/Files/COMP4-116.pdf

Now then, you guys make sure that everyone recommends a boat load of different adjustable rockers arms that aren't required, before you find out what cam he is running.

Bicylindrico · Mar 15, 2018

IQ52 said:
Let us see if we can just answer the question.

There may be a little confusion in reading the catalog. None of the hydraulic flat tappet cams in the Comp cams catalog (that I have) require adjustable rockers. The adjustable valve train is require when using the Comp Cams 867-16 Pro Magnum hydraulic lifters. This is because these lifters have a recommended preload setting of .002"-.004" hot.

https://static.summitracing.com/global/images/instructions/cca-867-16.pdf

Very difficult to achieve that .002"-.004" preload without an adjustable valve train. If you use the 822-16 lifters the adjustable valve train is not required as long as you have the correct length pushrods for the .030"-.040" preload.

http://www.compcams.com/Technical/Instructions/Files/COMP4-116.pdf

Wouldn't one have to factor if the block or heads have been surfaced on a 30+ year old engine? Maybe it's just a CYA for the camshaft manufacturer?

vintage chromoly · Mar 15, 2018

Bicylindrico said:
Wouldn't one have to factor if the block or heads have been surfaced on a 30+ year old engine? Maybe it's just a CYA for the camshaft manufacturer?

That's why you need to adjust the pushrod length

IQ52 · Mar 15, 2018

vintage chromoly said:
That's why you need to adjust the pushrod length

My point exactly! Thank you! A damn sight cheaper than rocker arms.

wyrmrider · Mar 15, 2018

Thanks for the update on Rocker Arm Rebuilders- that was their name when they where in Los Angeles
OP see my post in the 383 street thread- I think I meant it for here

IQ 52 has it right- and you may need new pushrods anyway

Question about adjustable rockers on Big block

Orange71SE

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Kern Dog

Life is full of turns. Build your car to handle.

moes

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dvw

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vintage chromoly

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lewtot184

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wyrmrider

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vintage chromoly

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wyrmrider

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PurpleBeeper

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Bicylindrico

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IQ52

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Bicylindrico

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vintage chromoly

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IQ52

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wyrmrider

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