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

[chilly460]

Digging up this old thread as I was searching for clearance info.  I’m working on rocker setup for my 352, it’s an old adjustable Ford setup. I’m getting .839 for the shafts which seem ok, but the rockers feel very loose and I’m getting .012” clearance using a small bore gauge.  Changed mics, measured with a decent caliper, all figures jive.  Has anyone seen one this loose?  This was supposed to be a cheap rebuild, I assume re-bushing the rockers would not be cheap with today’s labor rates

[67xr7cat]

Digging up this old thread as I was searching for clearance info.  I’m working on rocker setup for my 352, it’s an old adjustable Ford setup. I’m getting .839 for the shafts which seem ok, but the rockers feel very loose and I’m getting .012” clearance using a small bore gauge.  Changed mics, measured with a decent caliper, all figures jive.  Has anyone seen one this loose?  This was supposed to be a cheap rebuild, I assume re-bushing the rockers would not be cheap with today’s labor rates

Yeah is called worn out rocker arms. I'd avoid bushing them.  It has been done to stock rockers, but weakens them as they are not too thick to begin with. Just buy some new ones.  Problem is when there is too much clearance you get too much oil leakage. The .002" to .0025" spec is a good one to use.  The main thing is the shaft and rocker both have to be round. The problem with going tighter is not having enough clearance to get the oil out. On some shafts you will find they cut a groove across the oiling hole to help get the oil to where it needs to be.  If your shafts don't have this it is a good thing to ad. Also make sure the oiling holes are pointed down towards the head.

[pbf777]

    Since this thread was re-started, and previously "it seems we 'all' agree(d)" that of .002" (or so) was 'the' number, allow me to inject (muddy the water  ), so what connecting rod bushing to (piston) pin clearance to you run?   

    Oh, and to answer the recent inquiry and agree with: 

Yeah is called worn out rocker arms.  Just buy some new ones. 

   

    Scott.

[blykins]

    Since this thread was re-started, and previously "it seems we 'all' agree(d)" that of .002" (or so) was 'the' number, allow me to inject (muddy the water  ), so what connecting rod bushing to (piston) pin clearance to you run?   

    Oh, and to answer the recent inquiry and agree with: 

Yeah is called worn out rocker arms.  Just buy some new ones. 

   

    Scott.

Depends on the application.  On some applications, you'd be surprised....  I've ran .002" multiple times........

[pbf777]

Depends on the application.   I've ran .002" multiple times........

     Well yeah, intentionally sure, "in certain applications" or even just rationalized for reasons that have nothing to do with the mechanics of it!  But in general, and consider the similarities, and the dissimilarities, and think about it.  Why are we "wanting" to have .002" clearance? 

     It's just a question.   

     Scott.

[jayb]

If you are running a vacuum pump or a dry sump you need more pin to piston clearance.  You don't get the same oil splash in that case as you do with with a standard oiling system, and my understanding is that the additional clearance prevents galling of the piston/pin interface.  In my big SOHC with the dry sump I always run .0017" or so; never a problem in many miles of driving.

[pbf777]

     O.K.,  let's rephrase it this way:  If (generally) we determined that the wrist-pin to connecting rod bushing, or even that of the aluminum rod, clearance, is O.K. at something less than .002" (more often 'significantly' less) and this relationship is having to endure what is seemingly a significantly harsher environmental function, then why do we think the clearance for the rocker arms "needs" to be greater?   

     Still, just a question.

     Scott.