Rocker arm to shaft clearance spec ???

[427Fastback]

I have to hone out my Dove/Comp rocker arms for clearance.Most of them are tight at .0005 to .001 clearance.I am fitting them to a nice set of H/S heavy duty shafts.They measure identical to each other....I would imagine the rockers will expand some what on the thick shafts....

I was thinking around .002 clearance but am interested in thoughts and opinions..
Engine is solid lifter 270S and no crazy valve spring pressures..

They will be honed on a machine for trueness and I have a ($$$$)Bower 3 finger measureing device that will read to 5 decimal points...

Cory

[rockhouse66]

I wish I had all that fancy stuff to do this job - or maybe I am better off without it    I just went through this, fitting a set of new HS rockers to a POP shaft.  They would go on, but very tight and I measured maybe .001" clearance or less.  Oddly, they were free on the shaft in some locations and not in others.  I still don't understand how this can be unless maybe the two halves of the bushing in the rocker aren't "square" with each other....

Anyway, I just used a regular wheel cylinder hone and honed them a little at a time until they moved smoothly on the shaft by feel.  Pretty low tech, but they still feel very snug clearance-wise (no rocking on the shaft) but don't "stick" anywhere.

I am curious how these materials expand relative to each other with temp.  In my case, steel shaft, bronze bushing.

[jayb]

I have seen Ford specs for this clearance in service manuals from .002" to .005".  On steel rockers I usually have them honed on a pin fitting machine if they are too tight, and go to .0025" clearance.  Since aluminum rockers will expand more with temperature, you can probably get away with running less, but I think if it were me I'd hone them to .002".

[427Fastback]

I did some measuring today on all the shafts I have.(stock,FPP,H/S and replacements)There is quite a bit of variance between them all.Even the two H/S shafts measure different....839 and .840...The rockers are plus or minus as well..By putting the big rockers on the big shaft the measurements work out .I have a couple rockers at 1 1/2 thou but I think they will be fine when warm...Most are at 2 to 2 1/2 thou..I don't have any with to much clearance which is good...

It has been 2 months since my truck accident and I finally have some energy to do something.....even if its just measuring parts....

Cory

[cjshaker]

And to think I just used some fine emery cloth....and my fingers....on my HS rockers and shafts

[Ted]

I'm with Jay in that I hone the aluminum rockers so that the rocker to shaft clearance is a minimum of 0.002".

[427Fastback]

It seems we all agree that .002 is the target..I will recheck the clearances when I do the final assembly on them.For now I am happy to know that they are close...I will polish up any of the tight ones...

Thanks...Cory

[MaSnaka]

I did this a few months ago and it was recommended to hone the bushings to 2 thousandths clearance.  We used an adjustable reamer.  That was from the POP valvetrain instructions.

John