Technical roller cam valve lash

The cam is a Chet Herbert solid roller bought in 1968 and in the 327 in my avatar. Long story but while in storage termites ate the paperwork that came with the cam. I assembled the engine about 4 years ago and Chet had already passed. I know there are people out there running these cams or have in the past . I would love to find out the recommended valve lash. advertised lift :.500 , duration 300 deg. I never had the .050" duration. IIRC the cam was a circle track grind and the same grind for a different engine might have the same lash settings. I called Doug Herbert cams and they had no idea.
This is a real Hail Mary but I appreciate any help you can give.

 

I bit loose is better than tight . I have not one idea on your cam . I would guess at .012 intake and .022 exhaust . I did have a flat tappet GM cam years ago that was set at .030. And 030. . I know this isn’t much help , but just a little fat to chew .

 

.030 .030 used to be the old standard
Then I have seen some at .026,,,then .022. Then. .018,,,,then .016.
Start safe,,,and then move tighter

But,,,seems like the older grinds used more clearance .
Since this is an old ground cam,,,,makes since to me.

It is an old solid roller,,,you could easily tighten it and not hurt anything,,,,in fact,,,less clearance would probably be a little easier on the rollers.
Good luck.

Tommy

 

Lash has to have something to do with the clearance ramps ground on a cam.
If you compare the ‘097 Duntov with it’s .012/.018 lash and the later .030/.030 375 horse cam the .030/.030 has an advertised duration that is very long, but it loses a lot at .050 lift, in comparison more than the ‘097.
You might try taking a degree wheel and a dial indicator and check the degrees in the ramps to .010 lobe lift and then compare to a stock Chevy solid cam.
But the unknown is this- does a roller cam use different ramps?
So I wonder- short ramps, less lash?
How about it @squirrel, any thoughts?

 

I don't know, I've not gotten into that.

 

From my checking after the initial readjustment, the intake change cold to hot is .002/.003" and the exhaust about double that. That seems reasonable to me. I'm checking the cold settings now. Exh is running .026 cold and int. .020 cold.

 

Since I'm planning on driving the car, I would not like the rollers dancing around and I hadn't considered that. I'm going to take the int. to .018 cold and exh. to .024 cold and see how that works.

 

When I was assembling the engine,degreeing the cam, I tried to get a duration number at .050". It was very touchy. 2 deg on the wheel was .002/.004 on the indicator ( measuring on the lifter). I didn't think of comparing a non roller cam. My guess is a roller has to use faster ramps in order to get to the profile.

 

You're thinking right and there's some good points here. The only thing I'd add is where each one is at 50% lift. The lash setting that gets you closest to the center of the valve stem at 50% lift is the setting that will keep things stable and safe. The whole gig is gonna tighten up hot and be what metals are when up to temp, but what's going on mechanically is the goal, the actual operational dynamics are the key. I'm assuming that you've already sorted out push rod lengths to get you there and the final detail will be the lash. Break out the Prussian Blue...

 

Aluminum heads or iron? Probably wont much difference as your starting from scratch anyways.
Aluminum heads generally require you tighten the lash up .006 cold.

 

Thinking about the .050 numbers I found while degreeing, I might have slower ramps than current cams. I found around 236 deg int. @.050 and 242 exh.@ .050. which indicates a longer (slower) ramp to me. Maybe I can squeeze the lash down some more.
Thanks to everyone for your comments.

 

.018-.024 wont be bad,,,sounds like a good safe benchmark.
Who knows,,,you might be right on the money,,,,?

Tommy

 

When I checked for pushrod length, I used zero lash. The intakes are dead center and the exhausts are a little on the high side. Past center toward the outside of the head. That halfway up thing makes sense. I wish I would have thought of it.

 

Iron heads

 

I am most concerned about holding the valves off their seats and therefore burning the valves. A little at a time I guess.

 

This is an extremely useful little tool in checking pushrod lengths for a SBC.
Very accurate,,,for a street engine.

Tommy

 

Too little lash could hold the intakes open and/or burn the exhausts. Too much will be hard on the valve train, you can miss the ramps altogether.

 

If you have the lash set to a big number (.030) a longer ramp will be less harsh on the valvetrain components than a short ramp and big lash. A little tighter lash on a long ramp will just give you a bit more lift and duration.

 

Does that tool show the if it's sliding on the stem or?

 

Budget -

The tool...doesn't move..!
It slides down the stud, it stops on the stem...that's it. Adjust the push rod to touch the plastic...done.

Mike

 

I see, thanks.

 

This may seem obvious, but contact Herbert Cams. A lot of times they still have the grind info or could tell you a ballpark on how they usually design their cams.

 

Roothawg in the OP's first post he noted that Chet Herbert is deceased and Doug Herbert said he knew nothing about those old cams his dad ground. Did you read the posts?

 

That's not traditional!

 

Looking at this web page

https://www.herbertcams.com/chevrolet-sb-v8-1/

Solid roller cams somewhat like you measured yours, looks like .022 to .024 lash would be close.

Look at the page and see if you agree.

Phil

 

Nope, I missed it. My bad. I skimmed it. When I called Engle a few years ago, the guy helping me didn't know anything about my particular cam, but they had a basic philosophy that they followed. He wasn't even alive when they ground it.

I figured they might have something like that , they would be willing to share.

 

Thanks guys; there are a lot of good thoughts. I set the valves like I posted ( cold .018I, and .024E ) . Now I'm going to run a compression check and maybe a leakdown. Mostly, I'm curious after about 600 miles and it's supposed to rain tommorrow.

 

My old shop teacher was a firm believer in setting valves with a vacuum gauge,adj to the highest vacuum reading,just like setting the timing.

 

Manifold vacuum will definitely drop off at some definite point if lash settings are too tight.

 

I was in So Cal in 1983 or 1984 and decided to drop in on Chet since he did all my stock car cheater cams. I did not know he was wheel chair bound, a great guy to talk with. He showed me around the shop too.