when are adjustable rocker arms required?

[sprecks]

At what point does it become necessary to use adjustable rocker arms. The hydraulic cam we are using has the following specs:
Intake duration: 268, 224@.050
Exhaust duration: 280, 230@.050
Intake lift: 0.477
Exhaust lift: 0.480

I have a set of 273 adjustable rocker arms but are they really necessary?

[Chryco Psycho]

the adjustable rockers are a more accurate ratio , non adjustable are closer to 1.4 ratio , + the extra spring pressure with newer fast ramp cams it is good insurance , if I had them I would use them

[sprecks]

Thanks for the reply CP. I'll go ahead and use the adjustables.

[crash520]

When you run out of beer and have to reach for the rum

[jimynick]

It sounds like the Comp XE268 cam you have. Being a hydraulic cam, you may want to call Comp and get their recommendation regarding setting the lash or lack thereof. Might be a wee bit trickier than you think, since not likely every rocker arm/adjuster will be exactly the same as all the others and you'll have to set the preload individually on every lifter. Not saying it can't be done, just not a "drop in the shaft/rockers and bolt 'er down" deal. Just my 

[73EStroker]

I would use them in any engine stock or not hydraulic or solid. Why you say? How can one determine if lifter preload is correct when you rely on fixed lengths for pushrods, valve height predetermined by engine rebuilder, are valves all exactly same height (answer no in most cases), no adjustment in rocker shaft, head gasket thickness is it the same as factory. Other way to ensure preload correct is custom length pushrods made for each valve. Then if you took the heads off you would need to recheck those lengths again! So adjustable rockers are the easiest way to ensure you have correct preload on the lifters. At least brand c has a locking nut that one turns for each individual valve to set preload. Not so Mopar.

[Aussie Challenger]

Up until the early '60's all motors had adjustable rockers or tappets so older mechanics know how to adjust them. When hydraulic lifters became standard at first they were adjustable so mechanics could set at the most desired "sweet spot" setting. But due to cost cutting non adjustable hydraulic lifters became the norm which means that sometimes after a head has had work done there can be too much lifter pre-load applied which can shorten valve life or lose performance. I always will go with an adjustable rocker over non adjustable, this is why 273 rockers are much sort after for the LA motor and you don't need to buy custom length push rods.

[73EStroker]

The Crane 273 rockers are being used in my B motor as well with lash caps on top of the valves. I have a solid cam though and am forced to have some adjustment method anyway.

[Mopar Mitch]

I agree with using adjustable rocker arms any time, regardless of lift, so to get the best/accurate pre-load on the hyd lifter.

A more critical concern, in my opinion and experience, is the final choice of pushrod.... the overall length is the issue.  I forget where I purchased my last set (maybe from Hughes?), but the length was correct at 7.25" (or a tad less... 7.23"?)... anything longer (for hyd lifters) makes the allowable remaining threads questionable, as well as the cup of the top of the pushrod possibly hitting the underside of the rocker arms.

I'm experienced only using the factory T/A rocker arms, and also the factory 273 rocker arms.   I know there are some companies advertising such pushrods, for adj rkrs and hyd lifters, at a length of ~7.3125 and longer at 7.375, and those are both too long which allows too little remaining threads and the cup hitting the underside of rocker arm.  It becomes worse if the heads have been cut, and/or using a thinner head gasket, as well as if the block deck has been cut (to square the block).   (Note: I've always used the Fel-Pro #1008 performance head gaskets, compressed to ~0.038-0.040... I was a past Fel-Pro engineer so I've always used only Fel-Pro.)

Also, I believe the original factory T/A hyd lifters were slightly different than the standard hyd lifters... the T/A lifters had a deeper recession for the pushrod to seat its into the lifter, therefore, a T/A pushrod lengths were slightly longer at ~7.3125 (or 7.375) and only functioned properly with the matching factory T/A hyd lifters.  However, those special-design T/A lifters have not been available for probably 30+ years.  The result of the other comopanies offering those longer pushrods (7.3125 or 7.375) for use with adj rkrs and hyd lifters becomes the issue I'm explaining.

Long story short... the length of the pushrods is critical.  Beware of trouble using pushrods of 7.3125 or 7.375 that are advertised to use with hyd lifters and mech rkr arms.

Happy holidays!     

[HP_Cuda]

P2V baby!

Thats why!!!