Technical Zero valve lash for solid lifters?

Does anyone here remember that we are talking about the valve lash on a Chevrolet 261?

 

The lash specs are factored into the valve timing for the cam, altering the lash changes the valve timing. This can be a useful tuning tool if used properly but in no way can you eliminate valve lash completely on a solid lifter cam and expect it to live or perform properly.

 

I cannot remember the last time that I saw a cam card that did not have a lash specification for a solid lifter cam.

For everything not aftermarket, the OEM has a spec. I can vouch for the designers when I say that they did not guess.

For the masses, with HAMB era (or acceptable) engines, there will not be too much call for tuning at the depth of that of valve lash.

For race folks that might be another story, but that's another story.

 

Now you got me curious. Using valve lash as a tuning tool to change valve timing sounds like a slippery slope, as it also plays with lift. I would have thought an adjustable cam gear or stepped woodruff keys would have been a more predictable way to modify valve timing. Do you have an example of where lash has really been used as a valve timing tuning tool?

Not trying to be offensive, but damn curious. I've spent the last few weeks thinking through how to change the valve timing on GM Holden's "grey" motor (I6 similar to a Stovebolt Chev, '48-63) and playing with lash had not been on my radar. For the curious, research results here: http://www.fbekholden.com/forum/viewtopic.php?f=25&t=24246

Cheers,
Harv

 

Interesting read Harv.
There are a lot of "dial-in" cam gears out there for V8, but unfortunately non for 235/261 as far as I know - let alone the grey motor. Probably too much of a niche market to make it profitable.

Frank

 

Yeah sure, but a high zoot 6 with headers or split manifolds might sound like a 2 stroke at full tilt! Just sayin...

 

My sincere apology. I was not trying to offend anyone just a bad joke I guess. I don’t agree with the findings but it was poor taste on my end to express it that way.

 

No Worries!! My come back was not funny either!!!! Pete

 

It is a pretty much a race only fine tuning tool. For example, the Chevrolet .030-.030 Duntov cam that lashes @.030 int. and exh. could be advanced slightly by closing the lash say to .024 exh and to .020 intake this would also increase the valve lift by the same amount. There are a lot of factors but depending on the set up you could possibly gain some low end torque. Tighter lash cam specs would leave you less to play with of course. A dyno would be needed to really check results accurately but back in the Super Stock days this method was used frequently on solid lifter engines.

 

Cool - thankyou.

Cheers,
Harv

 

Back in the 70's when hot rodding a 2 stroke motorcycle engine one would "stuff the crankcase." For those unaware, the crankcase actually has the intake mixture flowing through it. There are no poppet valves like a 4 stroke, but fuel and exhaust enter through ports and a rotary valve or reed valve. By reducing the volume of the crankcase, using Devcon epoxy, ie. stuffing, you would speed up the intake flow and gain power.

 

Rocky Mountain Hummingbird? The Green Leaker?

 

AKA Screamin Jimmy!

 

My last stray, but no promises. I actually removed and reshaped a lot of area on another one. I didn't do the Devcon thing which was for shaping not stuffing. The increased volume was a massive improvement, but I was turning 8800 at peak, engagement was about 4500, 5000, 3 cylinders.

I love these theory threads. So many "scenic routes" to take.

 

closer on topic..I built a GMC 302 inline 6 about 20 years ago...I sent a NOS cam to the late Lazer Cams..This was a street engine so not too radical...Due to the limitations of a non welded stock cam regrind it was ground using a tight lash short track grind.About 215 degrees duration at .050 lift and .440 lift at the valve......Recomended by Lazer was .005 hot lash ,intake and exhaust...more area under the curve as they say. The engine made excellent power for what it was...I sold the truck to Larokee on this site, he ran it for about 80,000 miles before tearing it down for a leaking head gasket, the cam was still in nice shape..
I messed around with tightening lash on a 261 Chevy with an old Howard M4F grind...the engine ran worse....

 

First, let me say I agree with Bob........


Questions........ When you are setting lash, it is done so on the base of the lobe where there is no lift. I can see that increasing or reducing the gap between the lifter and the base will change timing and lift somewhat, but as far as wear goes.......once the lifter is off the base or has no spring pressure pushing it, why would it matter if the lifter was .001 or .010 . The greater the gap, the more room for "slapping" the cam upon return. Also, where is the gap actually located in the valvetrain components? Is it a little at each component or all of it right at the lifter to lobe interface? What ever slack exists, it must be taken up as the cam rotates and the cams lifting ramp comes into play.
Also, if the lifter does not have any play..........but simply touches the base of the cam, the spring pressure against the lifter would be very minimal. How much pressure would .0075 (.005 lash x 1.5 rocker ratio) of spring compression be putting on the camshaft. Why would that be a problem when at full open spring compression the cam does not suffer?
What does a hydraulic lifter do? It keeps the lifter against the camshaft lobe 100% of the time, so it must be exerting some pressure all the time. My point simply is that setting lash with a feeler gage is a good starting point, but results are going to vary from engine to engine and replacement part to replacement part. As long as there is minimal pressure and no slack at normal to slightly elevated operating temperatures, I think the way Bob proposed is a good way. Now if you live in Arizona or Alaska, your results are going to vary when using a feeler gage, but if you are adjusting the engine components themselves, that seems like the best approach to me.

 

I think the issue with solid lifters run at true zero lash is that it leaves no room for error or, after enough running miles, things like a bit of valve seat recession. Or maybe the occasional times when your engine temps creep up above their normal range. Think of long periods idling in heavy, summer traffic. Maybe with the A/C on. Hauling a load in the back of a truck or trailer. Or pulling a long grade for an extended period of time.

For the types of engines usually discussed here that spend most of their time on the street and not on the track, the presence of lash allows for safe operation during those occasional "what-if" conditions. Setting solid lifters by ear probably works more often than not because they are not running at true zero lash. But they may be running at less than ideal or recommended lash. Which means there's less of a "cushion" to protect the valves, especially exhaust valves, under the extreme conditions mentioned above.

A hydraulic lifter in good working condition senses these changes and adjusts to compensate and maintain a minimum pressure on the valve train at zero lift. A solid lifter does not have this ability to "fine tune" itself in this manner.

 

Here is the answer I got from a cam designer:

"There is an opening lash ramp coming off the base circle, and a closing lash ramp going back down to the base circle.

Both of these ramps are a given height from the base circle.
You take the lash ramp height and multiply it by the rocker ratio, and that's the Hot Lash you see on the cam card.

If you run a Hot Lash that is not what the cam lobe profiles are designed for, the cam will not run the way it was designed to run. Performance and/or Reliability will suffer."

Regarding setting the lash on a running engine - I wonder what happens to your feeler gage when you do that. From my gut feeling, it's like using your caliper as a can opener.

Frank

 

It helps if you can use a single feeler gauge blade of the correct thickness. Say if you need .018" but don't have one, try two thicker blades like a .010" combined with a .008". Fight the urge to use a .016" and a .002", unless you don't mind hammering up the .002" feeler.

 

Just a thought. When I was taught how to adjust the valves on a small block Chevy many decades ago on a new cam or complete engine, the mechanic said set them all cold to the cam card spec. It's close enough to start and warm up the engine. Once at operating temperature, set #1 & #2 to the proper hot spec. Now walk away until it's back to ambient temperature , usually the next day.

Now check #1 & #2 cold and see what the cold set clearance is. Set all the rest to that cold clearance Clarence, and good to go. If you're the retentive type, get the engine up to operating temperature after this and check all 16. I did once, and found about a thousandth variance. I have used that procedure ever since, regardless of flat or roller lifters, and never experienced problems. Well not from that. Had a roller lifter pair break the tie bar once. And the rollers both decided to turn sideways. That will wipe the lobes quick!

 

Back when I had a 58 Chevy with a 348 that had hydraulic lifters , I set them at .003" hot . that engine turned 6500 rpm and won many street races .

 

So curious, you set them cold at the hot lash spec, then got engine warmed up and set hot lash.
When you set hot lash was there more or less clearance? Or maybe another way to ask when you rechecked the cold after the hot adjustment, was there more or less clearance than the initial cold setting?

 

No. He said hot 1st. Then check out cold. Set to cold. I.E., if hot is .025, and then cold is .018 set em all at .018 cold.

 

I read it as “set the cold to the hot lash card spec”. Then warm engine up, set them again, then walk away a day, recheck cold.

 

He does not specify if the cam card spec is for hot or cold. Most cards are just cold...some have both so...?

 

The 261 rocker arms may be worn at contact point on valve tip, so can't read/feel real clearance. True for any engine except Crosley

 

The cams usually specified hot lash in those days (long ago, in a far away barn...), and usually the lash for the roller cams I used in my dirt days were 0.018 give or take a couple of thousandths. So warm the engine, set hot lash to the cam card spec hot, and the rest as described above. If they had a cold lash, I don't remember. Last engine was about 18 years ago, an older 400 cid all aluminum sprint car engine. Rodec 350 plus block and Brodix Gaerte -12 heads (huge ports). Comp Cams roller with rev kit, and shaft rockers. Over time and 3 rebuilds with different combinations, I did it the same way. It always worked for me...

That's my story and I'm sticking to it!

 

We found out the white horses we had ate more than the black horses so we sold all the white horses. We tried every reason to figure why the white horses ate more than the black horses. The only thing we could figure was maybe because we had more of the white horses.

 

My Dad use to tune the race car with lash, spark plug heat ranges, and obviously carb jetting.

He figured out cam was twisting at speed, back cyl were 2 deg, behind front cyl. They had a cam ground, with 2 deg twist from front to back. They re set the record many times, and were never beaten in 1975. We ran Harland Sharp experimental 1.7 ratio shaft rockers on a sbc.... I called HS, they sent me the vintage flyer on the rockers, look like T&D today.

Yes racers back in the day would adj lash for tuning, tighter or loose, many classes had lift rules, head port rules, every 5hp was an edge. When you dont have a dyno, the track is it....

 

Let me rephrase my question based on your first reply.
You said the mechanic told you to set them cold to the cam card spec.
Then you got the engine warmed up and set hot lash.
Then you let it sit until the next day, checked cold lash on 1 and 2, then set the rest to that cold setting.
Is that correct? If so, my question is from the initial cold setting to fire the engine vs the second cold “check” after setting the valves hot, was the second check cold looser or tighter than the initial setting?

Or another way to ask. If say you set them initially cold at .018, when hot, did you have to tighten them up or loosen them up to get back to .018?

Im just asking based on the video, differences I’d guess were you were running cast iron heads v Al heads.

Really looking for real world experience with non aluminum heads/parts.
Thanks!