Technical Zero valve lash for solid lifters?

I'm thinking about valve lash settings a lot in the last time. Given that on a 261 with solid lifters the lash gets wider when hot, I was questioning my self - why would you want anything more than zero lash (when cold)?

From what I know, hydraulic lifters always try to keep it zero lash, when the engine is running - right?

"A hydraulic tappet, also known as a hydraulic valve lifter or hydraulic lash adjuster, is a device for maintaining zero valve clearance in an internal combustion engine. "

So with solid lifters, the next best thing would be to set the lash to zero (cold) and live with whatever gap they end up when hot.

Did I miss something? Would there be any adverse effects?
Why is there a spec for anything more than zero anyway, when the gap widens at operation temperature?

Frank

 

On any engine I'm familiar with as the engine heats up all the valve train components expand and the lash gets tighter approaching 0 lash at operating temperature.
What engine are we talking about.

Phil

 

Chevy 261 all iron.

 

I know that this is going to sound crazy to most everyone out there, but here goes anyway. I have a '54
3100 with a stock 235", solid lifter motor. 30yrs ago when I bought it, I was always trying to get the valve
lash just right......warm motor, feeler gauge and setting the lash with the motor running at the lowest possible
idle. I was having coffee with a very, very good long-time mechanic who only worked on Chevy 6's, and
he told me to throw away the feeler gauge, warm up the motor, lowest idle possible, and tighten down each
rocker arm by ear. Tighten it until it JUST stops clicking, and set it. It worked great. That was over
40k miles ago, perfect idle, great power and NO lifter noise. It's almost like it has hydraulic lifters. The
only way I do it now.

 

I wonder if the ramps on the lobes of a solid lifter cam, are designed any differently from the ramps on a hydraulic lifter cam? Perhaps the answer to this question might help my decision of what clearance to run?

Since the guys who made the cam know the answer, I guess I'll just stick to their recommended clearance.

 

Yes, they are more aggressive and lash is needed to soften the opening of the valves.

 

What happens when you zero lash a solid cam and the exhaust valve stem expands when it gets to operating temperature? The valve is held off of its seat, the engine develops a misfire and more importantly, you burn a valve. When is the only time a valve gets to cool itself? When it’s on its seat. My next question for you is this: Why do exhaust valves usually have larger clearances than intakes? Hint- the answer is above.

It’s because the exhaust valve runs hotter than the intake and expands more. The engineers who designed these engines know far more than we do, I would stick to the recommended specifications.

 

I agree with @Truckdoctor Andy and @squirrel

set it to spec . There’s a reason there is a spec .

I’m sure there are some performance gains in playing with lash , but my guess is this is only realized in upper high end performance engines .

I’ve set valve lash by “eye” or “ ear” over the years simply because I could not get it within factory spec .
In these instances it has always worked for me , but I’m sure I was only compensating and masking another issue that I could not be bothered looking for .

 

I don't get it. IMHO a gap would do exactly the opposite. When I have a ramp already built into my cam, then what is the gap for (other than crating a sharp impact on my valve train at every valve event)?

Wouldn't that soft ramp work best with zero lash, so the lifter and everything else up to the valve would work like one solid piece and could closely follow that ramp, instead of the valve just sitting there and waiting to get a smack over the head with the rocker?

Frank

 

I guess you don't understand what the term "ramp" means. It's the opposite of a smack, it's a gradual lifting.

 

I know, but with a gap in the system you break that gradual lifting.

 

You should have been around when they were inventing these things, and showed them the right way to do it.

 

At the very least you need clearance for an oil film between all the mating surfaces from the cam bearing to the top of the valve stem. These change from static to running condition and oil viscosity. These add up. Hydraulic lifters compensate for this dynamicaly.

 

Zero lash....
As in many things, it depends. I've run an OT air-cooled, horizontally opposed, flat four engine for a long time in my drag racer. I run zero lash (cold). Adjust it so the push-rod still spins, cinch 'er down.
Once the motor get any heat in it, it grows, and the lash at 160° oil temp is close to .010" and keeps growing from there. Aluminum crankcase, iron cylinders, aluminum heads, steel pushrods.
How much does your engine grow?

 

That gap goes away in about the first .010 of lift.

 

Frank, not matter if we were talking Chevies, Fords ,BMWs, Porsches anything with a solid lifter cam, there needs to be a specific valve lash that´s closing up as the engine heats up. Even hydraulic lifters have that adjustable lash built into them. If you bottom them out, the valve wont close once hot. I´ve done it by mistake and it didn´t work.
I´d suggest you to just go and give it a try. I bet your zero lash 261 will idle very poorly once hot , if at all, and lack power. If you are going to try it, I´d suggest not to drive very far or long, you´ll most likely end up with a burnt exhaust valve or seat.

 

Back in the day the common knowledge on stovebolts was that happy valves made a little ticky sound. If they didn't they would burn the exhaust valves early. Because they wouldn't remain on their seat long enough to transfer enough heat to the head. Valve jobs at low mileage were common with those that insisted on a quiet idle..

 

And to make things even more interesting, we need to account for the head/block materials…

Here’s an excerpt from the article below:

“For an engine with cast-iron heads and steel valves, you can expect the lash to tighten up a couple of thousandths of an inch as it heats up-so for the cold lash you would set the valve lash a couple thousandths larger than the cam manufacturer's recommended hot lash setting.

If the engine has aluminum heads with a cast-iron block and standard steel valves you can expect lash to loosen up approximately 0.006. If you are running aluminum heads with an iron block and valves with narrow 6mm stems you can expect the lash to loosen up 0.010 to 0.012. And finally, if you are running an all aluminum race engine, the lash can loosen up by as much as 0.015.”

https://www.motortrend.com/how-to/ctrp-1012-setting-valve-lash/

On my iron head/iron block 348 Chevy I add 0.004 to the hot lash setting, set the lash cold, and they are spot on when hot.

EDIT: maybe I add 0.002. I’m not home and can’t see my sheet. Either way, the lash decreases with heat.

John

 

I use a fairly radical flat tappet steel Howard cam. (Johanson) I was told by Don to set the clearance at .020” hot. I set them cold at .025”, check after a hard run and find them at .019- .021”. Iron block and iron head. aluminum roller rockers. Been doing this since 1976 and then have always been the same.

 

Maybe another way to say it that might cut through any of the OP's foggy thinking is, with the "heat", the "oil film", the "ramps", and all the other factors thrown in, the lash specs are to make sure that the valves close completely when you need them to.
In my limited, inexpert experience, I've played some "less-squash" games with hydraulic lifters to gain a few RPM and eliminate possible valve float because they can pump up. I lack experience with solid lifters but it just seems like going to "0" with the solid valve train is the opposite direction and you would get the opposite result causing the valves to lift.

 

This isn't rocket science, many cam companies explain this on their websites why these types of cams are designed this way. Also, a flat tappet solid cam requires more valve spring pressure than a flat tappet hydraulic of the same lift because of the quicker opening ramps, or you have lifter bounce on the lobes because of their design. Isky used to have a tutorial section on their website that was one of the best ones. They also explain why flat tappet cam lobes have taper ground into them as well and are off center from the lifter bores and other trivial facts about cam design and function.

 

Proper lash on the proper spot on the cam is essential to quality performance and longevity. Inline engines can be set 5 and 7 or 6 and 6 and be on the Proper Spot of the cam base circle. I'm real familiar with inline 8s which start at 1 TDC then go 360 deg for the next round. On my big Packard 8 services I set em cold at the hot spec. We're rewarded with silky smooth idle quality and power delivery, zero tappet noise at operating temp. Done it that way for decades, never an issue. And as said above, oil film is critical too and likely responsible for the lack of noise. Never do inline cylinders 1 at a time, do the 180 (360) thing. Again, not as hip to 6s.

 

My dad was a mechanic early in life. He adjusted the valves by ear as others have said. The cars ran great until they were too rusty to be roadworthy. He saved my bacon with cars a couple times. My friends 66 Plymouth was running rough so he asked dad to look at it. He stared at the engine for a minute then swapped 2 wires on the distributor to make it run right. My friend had changed his plug wires and had the 2 crossed.

 

If that is indeed a given, I'm inclined to agree with your logic and be similarly curious. But I'm unsure about the given. The increasing lash when hot seems illogical.

Chris

 

Pete

 

L-head dodge/Chrysler/Plymouth engines have a spec of around .006 and .008(intake/exhaust) when hot. I’d have to look in my Motors manual to verify those numbers. The cold/initial setting is .014/.014 as I recall.
Might be a difference between valves in the head v the block?
But I only adjusted the 235’s and 216’s I had while running and a warmed up engine. Plays hell on feeler gauges. But those were the only solid lifter engines I’ve had.
Never rechecked the 216/235s I had when cold though.

 

That’s not been my experience. There are 3 cars that are iron block and head in our stable not including race cars that have solid lifter camshafts and NONE of them get more gap when hot. Just the opposite is true; they get less.

 

Right! Just as piston clearance gets tighter as it gets hot. Hence the reason for clearance.

 

My understanding is that the little ticky sound is the valve lash getting taken up (when the ticky sound gets obnoxious, the lash is waaaay to big). When there is no ticky sound, there is no lash. The valve can be shut, or it can be open a poofteenth. As the engine warms, that poofteenth can get bigger. Open exhaust valves flow combusting cylinder gases past the valve and seat, which leads to the valve burning. Not so much about heat transfer to the head, more about flowing red hot gas.

Cheers,
Harv

 

It most certainly does not. Refer to the topline in my signature for the baseline explanation.

Every single thing found in an engine expands in every single direction when heat is introduced.

Cam lobes get larger. Lifters grow larger in diameter and longer. Pushrods grow larger in diameter and longer. Rocker studs grow larger in diameter and longer, but not enough to offset zero lash! Valves grow larger in diameter and longer. The block and heads get bigger, too.

Since everything on the cam side of the rockers is constrained by the presence of the camshaft, all of the expansion on the axis of action pushes towards the pushrod side of the rocker.

Since the valves are held against the seats by the valve springs, any change in valve spring length is absorbed by the spring moving the tip of the valve towards the rocker arm.

The only thing that can freely move is the valve opening.

The clearance set between the tip of the rocker and the tip of the valve is necessary to accommodate all of the expansion in the valvetrain, less any delta from dissimilar adjacent metals, and expansion of the rocker studs..

It is the default measuring point for a HAMB-era conventional OHV engine, as it is the only easily accessible place where two parallel surfaces meet.

It is not ever acceptable to have zero lash on a solid lifter equipped engine, not even when it it is at maximum operating temperature.

Zero lash with solid lifters will plow the oil off of every single friction surface, resulting in accelerated wear, and premature failure.

That is presuming that your engine lives long enough to die that soon. As has been mentioned, your exhaust valves will be hung open, and burned well before that.

Zero means zero, not zero-plus-oil. Zero-plus-oil would mean operational clearance, otherwise known as NOT ZERO!

A solid lifter equipped 261 should have its valves adjusted at full operating temperature, after driving for some time to 0.006" intake, and 0.018" exhaust.

When you are setting these clearances, you are forcing the valvetrain components together, except where you are measuring. That only happens while you are measuring.

When the engine is operating that measurement clearance is distributed across all contact points in the valvetrain: rocker arm tip to valve tip, pushrod tip to rocker arm cup (or vice versa depending on the brand), pushrod tip to lifter cup, and lifter face to cam lobe. That is four defined locations.

If you spread the exhaust 0.018" clearance across those four locations you get four contact points with clearances of just 0.0045" (114.3 microns). That is all that you get for oil between components at maximum operating temperature on your 261, on the exhaust side.

Now tell me what happens when engine components meet, with no oil in-between.

Also, as has been mentioned, if you set to zero, your exhaust valves will be held open 0.018", or so, when the engine is at operating temperature.

As has already been explained, the only way that the exhaust valve is cooled is by transferring the heat to the head, when the valve is closed. If you set zero lash, when your engine is working hardest, you will not have any exhaust valve cooling, at all.

That is the fast-track to burning them down.

Zero works with hydraulic lifters because they have springs, a check valve, and are filled with oil, which can be displaced. In other words, they are not solid. They are squishy.