Any suggestions for stock-ish cams that can use springs installed at or below 1.76 installed height or even as much as 1.80 with .05 valve locks? I really didn't want to have to do machine work on these heads or buy new ones just yet. Lunati, Howards, Crane & Comp all seem to recommend springs w/ at least 1.875" installed height even for their most most mild cams. Had no idea it was going to be this difficult to get a replacement cam for what seems to be a very common big block head w/o machine work. The car mags make it sound so easy to swap cams...

Hi Mike, you have other issues, that hgt will not work on a BBC, period.

Thanks, Gary in N.Y.

P.S. If you should try to do a "quick-fix", it WILL come back later to bite you. Fix it with the correct method! Find out WHY it's too short!

 

OK thanks Gary, I guess I will need to bite the bullet and do it the right way from the get go. Before i started, I had envisioned building the motor up a little bit at a time, but it's obvious to me now that it just doesn't work that way, at least in my experience. One thing leads to another which leads to another and so on.

 

Mike,
How are you measuring it ? Not sure if I have ever seen those heads with that short installed hgt. They dint have rotators under the springs do they ?

 

Using the valve spring height micrometer from Comp cams , the one that fits in the pocket under the spring retainer. I measured the first intake valve several times to make sure I wasn't mistaking an "8" for a "7". To be extra sure I took it out and measured the resulting height with a digital caliper. Definitely 1.75" & change. The exhaust side is even worse with the rotators in place.

 

If your 781 heads are newer than than 1974, and yours are, you will have to machine the intake valve pockets, the exhaust is no problem you just have to have the right roto coil replacement.

 

I figured I might as well get bigger valves, 2.19 and 1.88 if I was going to haul these to the machine shop anyway. I was hoping ones with .1 longer stems would solve the problem

 

I have used dial calipers to measure height for many years.
Do you have dial calipers to compare your height mic to??
I actually cut a nail many years ago and polished the ends flat and made it 1.800" for a quick reference.

More than 1 way to get the measurement..But i would check your measurement against another measuring tool.

If you do not have another tool a parts store usually has one behind the counter..You could adjust the tool you have and take it there and measure it with their dial calipers.. just to see if it is correct.

 

Yes, it did finally occur to me to check the mic height against a digital caliper exactly as you're suggesting. I'm convinced the measurement is correct at this point.

 

Mike,
Are you measuring with stock retainers ? I am pretty sure that the Comp retainers give you some extra height also. If you are going with anything much larger than a stock cam you are probably going to have to cut the guides down too so you might end up at the machine shop either way.

 

I have the locks that have + .05 , which would bring me up to 1.8 but id still be short .075 since they call for 1.875. I could try with the new retainers to see if i get more height , but that seems like a big difference to make up. The Crane Cams online catalog showed the matching springs installed height at 1.8 which was one of my reasons for picking the cam i have now. Its only until i looked at the instruction sheet that came with the new springs that i found out they want 1.875.

 

Mike,
One more possibility is to just put a stock cam back in it ? They are pretty cheap and you wont have to mess with anything at all.

 

I have my eye on this one
http://howardscams.com/i-24079206-howards-cams-cl127641-14-american-muscle-1965-1996-chevrolet-396-502-mark-iv-hydraulic-flat-tappet-1000-to-4500-camshaft-lifter-kit.html
Its the only one in their catalog that seems to be ok for stock springs. lift is .412 /.412/ not sure what stock was.

One problem is i can no longer use the stock springs (or so i read) because i mixed up the order taking them off thinking I was going to replace them anyway. If that's true, and they have to go back into the valves they came from, then i need to get new springs either way. If i can find springs close to stock specs and use this cam , then maybe its not such a bad thing after all. Ill have to return the cam and springs i have now of course. I have to talk to my machine shop guy anyway where I'm having the block bored, cleaned and magna-fluxed. Ill see how much he wants to do the valves. If i can trust him to do a good job and its a decent price, might just do that.

 

Here is what is important.. Not so much the installed height.

The seat and open pressures are important..The clearance you have between the retainer and the valve guid or retainer to valve guide seal if you have seals on the guides.

You run a .520" lift cam you need at least .520" clearance before the retainer hits the seal. .020" more would be a nice minimum.

You do not want the coils on the springs to stack together tight...Say that you open the valve .520" and the spring coils are stacked at .500" you will bend pushrods or pop the keepers etc.

You need to measure those clearances.. and see just what kind of lift you can get by with.

If you plan to rev it to 7000 rpm you need more seat pressure than if you keep it at 5000 rpm.

That is not always true though... depending on the cam profile you can get by with minimal seat pressure.

425HP 396 for instance I want to say super stock class spec called for 95 pounds of seat pressure for that cam.

Now the 280H comp magnum I ran 121 seat pressure with 219-188 valves and it was not enough to keep it out of valve float past 6600rpm.

So many variables to consider when swapping a cam.
Don't get hung up on installed height.. if all the pressures and clearances work.

I like to keep open pressures below 340..I ran 135 seat -345 open on a solid flat tappet with howards direct lube lifters and that cam/ lifters and heads lasted through 2 short blocks and is still perfect.

I was iffy on the 345 open.. some others may chime in and give some pressures to go by ..seat pressure is not the killer ..the seat side don't wear out..That is my thinking.

But lifters need to spin foremost.
And there is a certain amount of clearance you need between the spring coils at max lift. Some are running that clearance tight now days.. but that is usually for max rpm kind of deal.

 

I have a few friends that stuck in the comp cams 268H in their mid to late 70's 454's and never changed springs.. pull really good to 5500 rpm.
I even had one buddy stick the 292H in his 350 with stock springs ..55 seat pressure.. he thought it was fast.
It was a turd that petered out at 5500. I talked him into a 268H and it went much quicker.

So the recommended height is more of a guideline than an absolute rule that way you don't get binding or hit the tops of the guides when the valve opens. If so, that makes sense because they recommend the same springs for a bunch if different cams all with different lifts. I actually have right now a Crane cams 272 h which has .515/.515 lift

 

I have a few friends that stuck in the comp cams 268H in their mid to late 70's 454's and never changed springs.. pull really good to 5500 rpm.
I even had one buddy stick the 292H in his 350 with stock springs ..55 seat pressure.. he thought it was fast.
It was a turd that petered out at 5500. I talked him into a 268H and it went much quicker.

 

you real sure there's no kind of spacer in the spring pockets? I've never seen a 781 or any other BB head with that short installed height. Maybe the valves short? some rebuilder deal?

 

i don't have any history on these heads,the car itself appears to have been used for racing in some capacity, but the cam appears original since i'm able to make out GM 28 casting #, and the motor's internals are definitively original so I've always assumed that this engine was just swapped in as is from a 78' suburban when the original 396 blew up or whatever fate it had years ago. Its obvious the guy didn't want to spend a lot of money, so i see any kind of machine work being unlikely.
No spacers though except for the .015 washer thats meant to protect the spring pocket.

 

You got it Mike.. starting to sink in on how this stuff is supposed to work.


Would be nice if you could take a picture of the head where the springs seat and post it.
I would like to see as I bet Tom would also.. seems something is not playing nice.

Could you measure an over all length of the valve.

You know something else there are Plus + and minus - .050" keepers and retainers.

could be someone was upping the spring pressures with what he had on hand.. being a bit new at this you will learn of all kinds of oddities or odd tweaks people do.

 

Pics attached . The intake valve is around 5.22, shows 5.19 in the pic it but was difficult to keep it straight while taking the shot. ... Last shot is the valve keepers i bought with .05 added height. the height is actually 1.76(shows 1.758) with the pocket shim & 1.775 w/o it in.

 

Mike there in the picture #2 the gold collored thing in the intake pocket... take it or them out.. those are shims to shorten spring height.
Picture 3 the exhaust rotator is still in the exhaust spring pocket.. take it out.
Measure again with that stuff out.

 

so with the gold washer out, intake is 1.775" thereabouts, with the rotator out, exhaust is 2.055"


Just to add, if i put in the .05 valve locks im up to 1.791, but... only if i use the old retainer. If i use the new retainer with the new .05 locks i'm back to square one with 1.75ish. Go figure.

 

The springs are crane cams #99839, and the instructions show 1.875 installed height with a max lift of.580. If my max lift is only .515, that gives me .065" of leeway. Subtracting .065 from 1.875 you get 1.81 (1.875 - .065). So 1.81 would be my minimum target, at least on paper, right? Just want to make sure i'm understanding correctly.

 

Pretty sure I see the problem. Your height mic measures off the top of the tool. I see a gap from top of mic to bottom of retainer. The bottom of the retainer must be interfering with the ID of the tool which is not allowing the mic to turn up to the bottom of the retainer where the top of the spring is suppose to fit.

Trim down a piece of straight wire to fit between the retainer and spring seat and then measure with some dial calipers.

 

Yep looks funky alright.


crane 99839 that i looked up Crane Cams 99839-16, Crane Cams Single Valve Springs | Crane Cams

They have 121 LBS @1 .800 coil bind at 1.130" and spring rate of 354 LBS ( that means for 1" compression it will exhibit 354 LBS) ..298 LBS @ 1.300"

Now if you install them at 1.875" you will have 94.45 LBS open them to .51." you will have 276 LBS open.
And you will have only compressed them to 1.36" and you will have .230" before coil bind..
Install at 1.775" You will have 35.4 more LBS (or 129.85 seat. and 333.4 open) and coil bind clearance of .130" if all my math is right.

That last is a little more than you need for that 272H I would think.

 

Turn the mic upside down and remeasure.

 

do your valve spring retainers have some of seal umbrella hanging off the bottom?

 

Hi Mike, one more time, go back to "square-one", lay an intake and an exhaust valve in one head and measure from where BOTH springs rest to the very TOPS of the valves (not the lock grooves, the very tips).

Come back and put those numbers/measurements up here. You can use a conventional old-school ruler, we need a nominal (close) number only here.

Do NOT leave the exhaust rotators OR any present shims in there while measuring, toss them in the dumpster immediately, in your case here the rotators are useless!

Thanks, Gary in N.Y.

P.S. When you toss the roto-caps in the dumpster (if it was me) I would toss that hgt mike along with them. Just my opinion on that, those things are a pain in the butt to use, have never even owned one here)

 

1.866 using the mic turned upside down and 1.848 using a piece of plastic cut to size as best i could get it. Exhaust - 2.153 (no rotator)
:smile2:
Cant thank you guys enough..

 

I think Comp makes a rotator cup eliminator shim, it's .300 thick, to take the place of the rotator. That would put your exhaust right with the intake. 1.85-1.86 will work fine.

 

Correct info here, Comp's #4779-8, fills in the where the OEM rotators go.

Also Mike, again, what is the hgt of the valves from the spring seats to the tips of the stems? On the exhaust it would be from the rotator register. They should be the same measurements, intake and exhaust?

Thanks, Gary in N.Y.

P.S. When working with these we place any necessary shims (to correct the pressure) below these "eliminators".

 

From the int spring seat to the tip of the int valve=2.125"
From the exh spring seat to the tip of the exh valve=2.125" (eliminator's in place) This IS where you should be at the end.

1.966 intake
1.997 exhaust

BTW i think that on the instruction sheet that came with the crane cams springs i have, the 1.875" is a misprint. The copy on their website has the same springs for 396-454 pre-1980 showing as 1.80 height. 1.80 also shows on summit website and the crane cams catalog as well.
crane cams 99839-16
Installed Height (in): 1.800 in.
Seat Pressure at Installed Height (lbs): 121 lbs.
Open Height (in): 1.300 in.
Open Pressure (lbs): 298 lbs.