Don Terrill’s Speed-Talk

Have any of you who use 5/16" stemmed valves experienced lash closing up due to heat/growth on intake valves only? We have two sets of heads with 5/16" valve stems made by different manufacturers, and both experience lash closing up on intake, which is not normal. Manley and Ferrea valves. Valves are not cupping, nor is the engine overheating. 2.020/1.600" in one pair of heads, and 1.960/1.560" in the other heads. 10.4 cr, solid lifters, Iron heads, iron block, Harland Sharp roller rocker arms on shafts. Put a set of heads with 11/32 valve stems on, and lash doesn't change. Joe-JDC

Do you have good coolant flow in the jacket design around the guides, i did a static test once on a 2.02 and 1.6 valve, heated them up to 350-400* they grew in length .006-.008 and diameter by .0007 at the stem and .003 at the head, i know that may not be what exactly happens dynamically but something to look at, one combo i did i spend time making sure the internal guide bosses had room for coolant flow, steel and titanium stems, the titanium i ran at .0009 clearance and .010 lash @ 9700 never stuck one or had wear issues
Tom

Yes, good coolant flow, does not run hot. Both sets of heads have bronze guides installed in all 16 guides. However, the exhaust lash does not change, and the plugs look good. Joe-JDC

When are you finding this, after a race, cooldown, dose it return to normal at any point or are you constantly adjusting for the change
Tom

If the heads have recently been valve jobbed it’s probably just the valve settling.

Joe-71 , how much lash is missing ?

The intake valves will close up .006" from .012" down to 006". Have bent one intake push rod when trying to get the lash to .010" hot like suggested on card. Let the engine cool down, and lash returns to cold setting. This happens during dyno testing(40+pulls). Tried .018, .016, .012, ..010" and only the intake lash closes up hot. Joe-JDC

Joe-71 wrote: ↑Fri Nov 29, 2019 11:49 pm The intake valves will close up .006" from .012" down to 006". Have bent one intake push rod when trying to get the lash to .010" hot like suggested on card. Let the engine cool down, and lash returns to cold setting. This happens during dyno testing(40+pulls). Tried .018, .016, .012, ..010" and only the intake lash closes up hot. Joe-JDC

The only time I have seen an issue with Intake valve lash was , the carb had an air leak ( lean on fuel ) and the valves got overheated, the valves had tuliped in the couple of sets I had seen, it's strange your lash returns to the cold setting, I have two thoughts, 1st the fuel may be overheating the valves, I would try a different fuel , 2nd if the cam is in very early the intakes would have extra heat in them, I had a couple of new cams from a past member on here and he wanted the intake centerline in at 98* , we had a lot of temperature issues on the dyno , it made good power but had trouble controling the engine temp, it never overheated but it sure raised the temp about 15* , backed the cam up 4* and the issue went away, this was with 492 castings , 12.7cr , on Sunoco standard 110 oct with 36* ign timming. The only other thing I can think of is call the valve manufactuer and ask what he thinks and make sure you give him the spring pressures you are running. Keep us posted.

Are the valves 'stretching' when hot at the stem/head interface? Less support & rigidity there because of the thinner stem.

What are you using for locks and retainers?

Titanium retainers with machined locks. Three sets of heads with different valves, and only the 5/16" valves (both Manley and Ferrea) intake lash closes up when hot. The 11/32" valves do not affect intake lash. Three sets of springs/three sets of Titanium retainers/three sets of locks. Nothing interchanged between heads, simple R&R. Joe-JDC

Joe-71 , any info from the valve manufacturers, is the stretch normal ? Keep us posted , this is a serious issue, any info is appreciated.

Joe-71 wrote: ↑Fri Nov 29, 2019 11:49 pm Have bent one intake push rod when trying to get the lash to .010" hot like suggested on card. Joe-JDC

What caused this ^?

Apparently that lash was just .001" too tight and bent the pushrod. It was an intake, so it grew too much for the hot lash and bent. Backed off the lash, installed new pushrod, and no further problem with several dyno pulls. Lash still closing up on intake valves only. Joe-JDC

Let me interject some thoughts.

If the valve length is the same when cold (will call cold 68 deg) before and after the lash closed up, then the valve hasn't changed or stretched. If so the problem could be in the expansion ratio. Is the intake and exhaust valve material the same? If they are the same then the exhaust would lengthen more, as it should run hotter. The shape of the underside of the head, could make a difference. Exhaust are usually stiffer in that area.

Is there anything on the cam side of the assembly that is different on the ex vs in?