This question was originally asked on digital corvettes.


This is the first time I have ever had solids in a car. I was wondering how you guys adjust your valve lash. How tight do you snug them down on the feeler gauge. I snugged them down on the gauge so it took a good tug to get the gauge out then tightened the lock down then the nut and pulled the gauge out.


My response after a number of other posts
I like to set mine on the tight side. It does increase lift by running them tighter . Running them looser decreases lift and cuts down on duration. How does that help top end.
Tighten them up, not loosen.
Also the suggested setting is only a guide. You can go up to .010 tigher then the card says.
I set mine at around .020 in the spring and back them off at winter storage.
I have a card that tells you which valves to set to TDC and BDC.
I set the valve so the .020 feel gage is snug and takes a little effort to pull it out.
Remember tighten to increase lift and duration, loose if you like the noise and want to increase bottom end.




I learned something new. You can float the valves to gain lift and duration.
moore_rb set me straight



My opinions:

1) Grumpy sets his solid lifters the way I have since I was 16 (21 years ago).

2) Grumpy, robconnor's engine builder, and c5D are correct. Setting your valve lash toward the looser end of the spec means more top end power.

Here's why I disagree with you, Norval. You're thinking purely from a static, geometric point of view, and as such, you are equating tighter valve lash with greater lift. This is absolutely the case at low rpms where the lifter is held to the cam lobe by the pressure of the valve spring, but there are MANY other considerations besides geometry to take into account as RPM's increase, not the least of which is friction. Running tighter lash increases the coefficient of friction between the rocker and valve stem on a logarithmic scale as RPM increases. Since friction is the primary cause of parasitic drag, it stands to reason that the parasitic drag, and production of heat, must also increase exponentially as as RPM's increase. Tighter valve lash has a negative effect on friction as RPM's rise.

Also contrary to what your geometric reasoning suggests to you, a solid lifter does not "ride" the cam lobe with consistent pressure applied to it by the valve spring at higher RPM's- there is another dynamic involved. At high RPM, as the cam lobe runs the lifter up the opening ramp and over the top, the mass of the lifter and the pushrod are accelerated, and actually forced off the top of the cam lobe by their own inertia, thereby compressing the valve spring even more and increasing the maximum valve lift.

Looser valve lash settings accentuate this dynamic, tighter valve lash settings attenuate it...

The last thing you aren't taking into account is the phase angle between the topover point of the cam lobe and the point at which the valve spring actually begins unloading tension and closing the valve. Valve spring rates do not increase with RPM, therefore the time required to close the valve is constant regardless of RPM, but as RPM's increase, so does the width of the time delay between the point that the lifter reaches the top of the cam lobe and the point that the valve spring begins unloading. This is due to the inertial lift factor explained above. This dynamically increasing time delay actually holds the valve open at maximum lift for greater periods of time as RPM's increase in a solid lifter engine: the net effect is an increase in duration as RPM's rise. Again, this principle is enhanced by looser valve lash settings, not tighter...

All this is, of course, a matter of dynamic physics, and nothing personal. If you still choose not to believe what you read here, then I encourage you to either run your own tests on a dyno, or seek out some professional racers who have. All the experimental data necessary to support our claims is out ther


I just learned something new and thought I would share it

 

I dont see how valve float is going to gain you any hp. The dynos I have seen with valve float showed significant drops in hp, and a very erratic curve where ever float occured.

 

Talk about the hairy edge....there is so damn much fuzz I can't tell where the things ends and begins.....

how much is all this worth?? in hp, please....I"d be surprised if it's .5% of total power, if that...wonder if it's repeatable on a dyno??

GENE

 

The things he mentioned are true and correct. As far as percentages it is a small amount for you or I but not to someone that is heavy into the race game. You try and get every ounce of HP you can get. Other than just parts that you pick there are a bunch of tiny odds and ends they do to make a little more HP that may only add up to about 25hp or so.

I will add just a couple of little ones. One is you can back cut the valves which is easy for anyone to do at home with a drill press. You can take the intake valve and make sure you use a lapping compound or even a marker so you can rotate the valve in the head and the valve will show the contact point to the seat. Then you just take the valve chuck it up in a drill press and use a fine file and round from just behind the contact area to the back of the valve to make a smooth transistion for the fuel and air to pass and just barely touch up the edge of the face of the valve so you can reduce hot spots. On the exhaust you would just round off the edge of the valve of the face to make it easier for the exhaust to go around the valve and out of the engine. This will add maybe 5 to 8 hp alone.

And to make a little more hp and not have to use straight expensive synthetic oil. You can use lets say 5 quorts of your favorite dino oil and just 1 of synthetic and you will gain about 5hp.

 

lostpatrolman valve float was probably a bad way to describe what he was trying to say. I know what you are thinking. Valve float is when the valve is uncontrolled and in a sense making a ski jump and the valve spring is unable to control the action of the valve.

What he was saying is that if you leave a little more clearance it does not put as much stress on the valve train and things move a bit easier at high rpm and allows to make more hp easier. You can change a little bit of how an engine will run by how you set your valve lash. But for a street application I do not think you would notice. So really I feel that you should set your valves as the cam company describes.

 

You never want to float your valves ,period. Loss of spring pressure and instantly bent valves or worse,especially at high rpm racing engines, hell you dont even like getting in the rev limiter.I would adjust your valves loose on a cold engine with iron heads, they will get tighter where alum heads will get looser.

 

I think this guy is full of it. Any time the lifter is not in contact with the cam lobe you lose control of the valve, period. I don't like this even on a race engine.

BigBlockk

Later.....

 

I think they are talking about the launcher series solid cams from compcams.

http://www.compcams.com/information/...ID=-1997070293

 

He didn't go into the details of when you adjust the lifters too loose how impact (rate of change of momentum) from a lifter actually leaving the cam lobe and returning to contact with the cam quadruples the effective force (and thus friction) between lifter and cam at that particular moment and creates an extra amount of lateral (shear) force on the lifter along with friction between the lifter and lifter well which slows the lifter from closing and may result in the valve coming in contact with the piston...this of course is bad.

You want the lifter to always be in contact with the cam lobe...the entire valvetrain must be kept under compression...that's what the spring is there for. The goal of course is to minimize the amount of force (and friction) between the lifter and cam lobe. The minimum at low RPMs is located when the lifter begins it's fall on the backside of the cam lobe...while at high RPMs the minimum is just after the front crown of the lobe due to the momentum of the lifter...again...you don't want the lifter to leave the surface of the cam lobe...only reduce the force between them.

OK...theory out of the way. Well...except to point out that the "gap" measured with the feeler gage when the engine is cold will become zero when the engine heats up due to expansion of the lifter and push rod. Essentially, at operating temperature the lifter is always in contact with the cam lobe.

Now the application. Since we know that at low RPMs the only factor is the valve spring force, then our only concern is making sure that the spring has the right specifications...and it makes very good sense to consider the momentum of the lifter as well as the momentum of the springs own movement when designing the spring specs...for higher RPMs. When in doubt do the math. If you don't do the math, then follow the manufacturer's specs since (hopefully) the manufacturer hired someone to do the math for them.

He was right about at least one thing...it's a lot more complicated than just changing the gap. It really boils down to the spring spec...each spring will have a force equation which includes time, distance, force, etc. that must meet the requirements of keeping the lifter in contact with the cam lobe at all times and most importantly just after the crown of the cam lobe and just after the falling edge of the cam lobe. If you inspect a cam lobe and see some signs of severe wear on the fall of the cam lobe including what appears to be burn marks then the spring or adjustment is too loose. If you see signs of severe wear on the rise of the cam lobe then the spring is too firm or adjustment is too tight. An ideal inspection will reveal even wear throughout the cam lobe surface...there will still be more wear on the rising edge of the cam, but normal wear...there should not be any scoring, pitting, signs of friction burns, etc.

Hope this isn't too deep. The point I am making is that the "gap" is just the amount of expansion of the lifter and pushrod, and if you want to get more topend or bottomend out of the engine, then it's much wiser to change the spring spec...this is normally done by adding shims to increase the force/distance or removing shims to decrease the force/distance. There's some more math that can go into harmonics or chaos theory which cause the specs to include a range of values...which is why there are two springs in our valve train. The system isn't perfect, but don't try to bubba the job of setting valve lash thinking that you are altering the "design" of the engines performance.

 

The system isn't perfect, but don't try to bubba the job of setting valve lash thinking that you are altering the "design" of the engines performance.
Cam co's. recommend their own lash setting for a reason. With all the high tech equiptment available for R&D it won't magically run harder by changing things. Running too much lash just beats the crap out of valvetrain parts.
If it runs better with more lash you may be in need of a smaller cam.

 

On circle track cars, we vary the lash. If we want more power coming out of turns, we run a tighter lash. But, if we want more further down the straight we loosen the lash. There are also "tight-lash cams" ... the cam itself is ground to be run with a tighter lash than typical ... where lash for "tight-lash cams" might be about 0.012"-0.016" ... in contrast, "typical cams" might be about 0.025". Heck, ... maybe someone else (not me) would jump in & discuss "4-7 swap cams".

 

I adjusted mine a little loose...with the 427/435 cam, I found out that when the adjustment was tighter, the motor didn't rev as high, and was straining to go past 6500. Looser adjustment, no problem going past 7000 K.

 

Wow GDaina, I wish my engine would rev to 7000K rpm !!! You have one crazy engine.

 

It's been my experience that the opposite is true. But that's just me. This is not an arguement or saying somebody is wrong.

Logic says that a solid cam with a nominal lash of .024 will gain lift and .050 duration if you sent the lash tighter to .016 Your only talking .008 more lift so the change is very marginal.

I had an every day 8000 rpm motor. That actually had too radical of cam for it's ci. I found that idle quality increased as the lash number got bigger. So taking lift and duration out of it changed it for the better. I've seen dyno runs that agree with my statements. But it's such a minor change that your better off adjusting the cam timing 2-4 degrees and then you really will see your power curve fluctuate 500 rpm up or down

 

Saw a recent article in Hot Rod(?) about launching the valves to gain a little lift on top end. Evidently Comp Cams has actually manufactured some cams now to take advantage of this old technique...

 

Absolutely correct, had the same experience with my 365 HP 327 65 Vette. Ran best when they were all adjusted the same to GM specs and sounded like a sewing machine. Easy to do with a P&G Valve Gapper. No fuss, no mess to almost "0" tolerance.

 

Solid lifter cam will do that...the current engine goes to 7K, no strain....l....

 

YOu and I have the same cam I believe. The 288R from comp. I am not that pleased with the cam. I just have so much money in it I don't want to dump it.. The cam before this was a crane flat tappet and it pulled alot harder in the top end.

I set my valves around .020 and you don't hear them at all. I do set them with the motor turned off and go through the 180 degree, set certain valves, move another 180 and set more.
I have the stud girdle so it gets complicated.

 

Yes we do


Why the girdle? The lift is not that radical and the spring pressure isn't that high.

I adjust the valves using both methods, using the 180 degree and other times adjusting by the valves opening and closing method. I keep it little loose, rather than have a lot of drag on the feeler, I have a slight drag.

The only performance car I've owned that had hydraulics was my 67 GTO, the other, 57 Chevy, 283 bored to 301 had the 12-18 Duntov and later the 30-30.

I like the 288 AR, though I have nothing to compare it to except the stock 435 hp cam, and the difference is night and day. The 427 would rev to 7k without a problem with the stock cam. Same with the roller. Most people look at me cross eyed and ask how is that possible with a long stroke (4.25"). Internally balanced crank. What I should have done, put the shorter stroke (3.76") in the 502 block...big bore, short stroke...talk about quick revs....

 

I run the girdle because I don't want to take chances. At one time I was turning 7500 regularly with the nitrous motor and for about $300 I wanted the best.
I have had 7 different cams over the years in the motor and found the crane flat tappet the best. I could dig up the part number. I hated to even shift at 7500.
I went roller thinking I was stepping up but was very dissappointed after spending about $1300 CDN

My old flat tappet had more from 3000 to whatever you wanted to go.

I found that on a routine tear down that I was seizing 3 wrist pins so from then on I went full floaters.