Question about valve lash

[cudabob496]

Just set the valve lash on the solid roller in my big block. Almost all the intake valves were a little loose, and needed adjustment, but the exhaust valves were all fine. Wonder why only the intakes needed adjustment? Intakes are .600 inch lift, and exhaust are .625 inch. Intake lash is .020, and exhaust is .022.

[Cudadrag]

Originally Posted by cudabob496

Just set the valve lash on the solid roller in my big block. Almost all the intake valves were a little loose, and needed adjustment, but the exhaust valves were all fine. Wonder why only the intakes needed adjustment? Intakes are .600 inch lift, and exhaust are .625 inch. Intake lash is .020, and exhaust is .022.

Wow good question. I haven't seen this specific. But I have noticed that exhaust valve lifter is more likely to be tighter. I'm wondering if it's heat? Thus in your case the slightly higher heat expansion on the exhaust side rockers offset the normal loosening of all the rockers?

[cudabob496]

Originally Posted by Cudadrag

Wow good question. I haven't seen this specific. But I have noticed that exhaust valve lifter is more likely to be tighter. I'm wondering if it's heat? Thus in your case the slightly higher heat expansion on the exhaust side rockers offset the normal loosening of all the rockers?

Ya, since the exhaust valve is very hot, due to hot gas moving over it. Also, maybe the intake valve train sees more wear than the exhaust valve train due
to it having to work harder against spring pressure, while the exhaust valve opening is aided by the combustion process? Not sure, just throwing stuff out there!

At least the Crane roller rockers and rest of valve train seems to be performing well, as all valve lash
adjustments were almost identicle.

[Cudadrag]

Originally Posted by cudabob496

Ya, since the exhaust valve is very hot, due to hot gas moving over it. Also, maybe the intake valve train sees more wear than the exhaust valve train due
to it having to work harder against spring pressure, while the exhaust valve opening is aided by the combustion process? Not sure, just throwing stuff out there!

At least the Crane roller rockers and rest of valve train seems to be performing well, as all valve lash
adjustments were almost identicle.

I'm not sure which has a tougher job. I have noticed an exhaust valve itself won't last as long as intake. I'm sure that is because of heat. I know when my cam started going down lobe damage was indiscriminate. Both intake and exhaust were involved. In the hydraulic and solid flat range of lifters the spring strength is the same for intake and exhaust. Not sure if this is true in the roller ranges. Especially in high lift applications (1 inch +)

[JVMopar]

Are you setting your clearences hot or cold?

[cudabob496]

hot. pull into the garage, get the valve covers off, spill some oil on the headers, burn my fingers, and get to setting!

PS Pretty sure I used the right feeler guage as well.

One might think the exhaust valves, with more lift (thus higher spring pressure), would see more wear on the valve train, so the exhaust valves would be loser?

Suppose its not a big deal, as the intakes were only lose about .0005 to .001 inch.
Just strange.

Even with that small of an adjustment, the engine does seem a little crisper in the throttle response.

[JVMopar]

The exhaust valve would be tighter. The exhaust valve and seat get beat and as the valve sinks into the head the valve stem is allowed to come up and take some of that clearence away.

With a roller cam your gonna see almost no wear on the cam lobe or lifter roller. So you have the pushrod cup of the lifter, pushrod, and rocker arm assembly, and valve to wear. Since your running roller tipped rockers there should be virtually no wear on the tip of the valve either.

I bet most of the wear causing loose valves is in the rocker fulcrum.

Are you sure those lash setting are for hot valves? That seems like an awful lot of clearence. I'm used to setting valves 0.010-0.020" cold. Infact I just put headgaskets in a Duramax diesel and set the valves to 0.012" cold as there is no way to adjust them hot. It take about 3 hours just to get the valve covers off.

[cudabob496]

Makes sense.

So I assume with valve lash, it would normally loosen over time due to wear, but might tighten on the exhaust valves due to the valve sinking in the seat.

That would explain my situation.

[toad490]

Originally Posted by cudabob496

Wonder why only the intakes needed adjustment?.

Seeing as the valves live in completly different enviroments and are of different sizes with different lifts ect. ect. ect. ect. I would find it far more unusual if they required the same adjustment than that they required different adjustments. But I guess lifes mysteries are were you find them.

[djswwg]

the biggest problem with setting valve lash "hot" is that the last valve you adjust is a lot cooler than the first one you adjusted. try setting lash with the engine at room temp, (say 70 or so deg.) and take about .002" out of the specs. that way the lash will be very close to the hot spec when warmed up!.......cheers, djs

[cudabob496]

Originally Posted by djswwg

the biggest problem with setting valve lash "hot" is that the last valve you adjust is a lot cooler than the first one you adjusted. try setting lash with the engine at room temp, (say 70 or so deg.) and take about .002" out of the specs. that way the lash will be very close to the hot spec when warmed up!.......cheers, djs

good point, although I usually do one side at a time, instead of all at once.

[340_GTS]

If you are supposed to do them "hot" then adjust a couple correctly when it is hot. After it cools down to ambient temperature, check the same ones you adjusted "hot" in the now "cold" state. Those are your new numbers to adjust all the valves cold. Has always worked for me.

[sronan]

Seems so simple, but it makes sense (establish a baseline). Brilliant!