I think Paul meant valve seat recession.  Without hardened seat inserts in the cylinder heads, the machined (ground for some of us, cut today by others) valve seats erode (wear) and the valve faces seat (wear) deeper into the combustion chambers.

My memory is fading, but I think it was '72 when FoMoCo began doing induction hardening of the valve seats in cast iron cylinder heads because of the shift to lead free gas.  This was in lieu of going to valve seat inserts.

Interference angles between valve faces and valve seats or the use of greater valve spring pressures can accelerate the wear of '50s period cast iron valve seats in our y-blocks.

Interference angles between valve faces and valve seats are often used to prevent carbon deposit build-ups in normal operation.  Increased valve spring pressures are used to prevent valve float with higher cam lobe lifts, longer camshaft valve open time durations, or to enable higher engine rpm operation.

Increasing an engine's output power or its range of operating rpm challenges its mechanical longevity between required service work intervals.  It's the old story.  Fooling around has consequences.  Everything is a compromise.  But, we're all only going this way once!     


NoShortcuts
a.k.a. Charlie Brown
near Syracuse, New York

That appears a little tight to me, I think the clearance is based more on the thermal expansion of components, block, push rods etc, not sure of the difference of expansion between chrome moly and conventional push rods but all come into effect. The purpose of rollers is it gives an infinate (so they call it) contact surface as the roller turns it is not contacting the valve stem in the same spot, However the valve stem is still getting pounded in the same spot and then you have bearings in the rollers that can wear.
Based on the fact that the conventional clearance for a Y is .018-.020 that spec still appears a little tight, and then as mentioned if the valve seats wear in a little clearance will tighten up and as the valve stem grows.I would try opening a little.

55 Vicky & customline

58 Rack Dump, 55 F350 yard truck, 57 F100

59 & 61 P 400's, 58 F100 custom cab, 69 F100, 79 F150, 82 F600 ramp truck, 90 mustang conv 7 up, 94 Mustang, Should I continue?

The sentence immediately following the phrase is a very clear explanation. Valve/seat 'reversion' was a less common issue back when the lead in most gasoline would accumulate and cushion the valve impact upon the soft iron integral-cast valve seats.

6 VOLTS/POS. GRD. NW INDIANA

Forgive my ignorance but what is valve reversion?

Durham Missouri

I had similar leaking problems with stainless lines. Had to really crank down and get them really tight so as to not leak. My guess is that the stainless lines are harder and require more pressure to compress and seal properly.

Your problem is similar to what I had with valve reversion.  The exhaust valves pound down into the head (non-hardened seats) and the clearances close up.  Rough idle when hot.

Try a little more clearance and see if that helps.


54 Victoria 312;  48 Ford Conv 302, 56 Bird 312
Forever Ford
Midland Park, NJ

YBLOCKEREDH, start a new thread for your fuel line issue.

The ratio of the rockers will not have any significant affect.  It's probably more complicated, but simple math and an assumption that Comp use a 1.5 ratio rocker in their specs indicates about .001" difference between 1.5 and 1.6 ratio for the same lobe lift.  The difference between low ratio 1.43s and 1.6 rollers is 5 ten thousandths of lobe lift for the same lash.  That shrinks to about 3 ten thousandths for 1.54s.  Again, this is an easy theory to put to the test, and well within reason for fine tuning..


Lawrenceville, GA

I have a question concerning the new stainless fuel lines from the pump through the glass filter bowl ending at the carb on my 57 stock bird. All fittings are original brass and appear to look fine at the flair. They all leak badly . I've tried snug and tight tight finally removed and used rubber line with clamps. Very frustrating...am I doing something wrong? The lines were purchased new from Concourse in Carson,NV.

Thanks guys for the response. So generally speaking, is the lash reduced for roller over standard rockers rockers because of the reduced friction or is it strictly dependent  on the cam grind?
Thanks, Rono

  Ron Lane,  Meridian, ID

Valve lash can be used to tune, so you can vary somewhat from the manufacturers specification.  However, if that is the clearance that Comp suggests for their own cam, then that is where you want to start and you don't want to deviate too far from it.

It's easy enough to test your theory.  Pull the valve covers when the problem exists and see if the lash has tightened up on any valves.


Lawrenceville, GA