Valve Spring Pressure - BBC stocker
 

My new motor 396/325hp stocker broke a valve first weekend out (had dyno time too), upon disassembly it was found that all 8 intake valves had been making light contact, of course it was one of them that broke.

My tightest ptv clearance upon assembly ( and checking again during autopsy) was .070" which should be plenty, which leads me to believe it must have been lofting the valves open due to lack of adequate spring pressure. Springs were setup to be 250# on the seat and 500# over the nose which all recommendations said should be enough. Obviously not however. Just wondering if any of you have suggestions of what we should set it up to this time. Cam is steel core, dlc coated trend lifters, pac 1325 springs and steel retainers. Fire away with any suggestions, and thank you.

Re: Valve Spring Pressure - BBC stocker
 

Can I ask what it made on the dyno and the peak RPM HP?

Re: Valve Spring Pressure - BBC stocker
 

445@5700. My dyno is known to be stingy, but it really should have made peak near 62-6300. Should have been the first clue but unfortunately it wasn't.

Re: Valve Spring Pressure - BBC stocker
 

If you indeed have 250# on the seat, and over 500# open, you have over 0.050" piston to valve clearance on the intake, and you have a valve control problem, then there is something terribly wrong. I can spin mine to over 8,000 RPM with those pressures, and a true 0.050" piston to valve clearance.

Re: Valve Spring Pressure - BBC stocker
 

Chipper, how was v-p clearance checked? Where was the contact on the piston? -Al

Re: Valve Spring Pressure - BBC stocker
 

I completely agree with Alan, but have a question. Is the camshaft you're using one you've used in the past without problems, or is it something new, perhaps with lobe profiles that are somewhat "exotic"? If the intake lobe ramp profile is too extreme, even with the kind of valve spring pressures and piston-to-valve clearance you're talking about, the lifter may not be able to stay in contact with the lobe, and you end up with an uncontrolled valvetrain. Just a thought.

Re: Valve Spring Pressure - BBC stocker
 

This is what my fear is, When I called to have cam ground I had called Chris P when he was at crane, he left while my cam was to be done and it got shuffled over to comp and ground totally different than we talked, in a more aggressive fashion. I usually check the ptv the simple way with clay, but also checked it by opening valve with checking springs and degree wheel, same result both ways.

For reference camshaft is COMP .396/.396 lift, 288/294 .006, 248/254 .050 and on the big core

Re: Valve Spring Pressure - BBC stocker
 

What "group" is that intake lobe from? They have some violent stuff that really shouldn't be in almost any engine. Your opinion may vary.

Re: Valve Spring Pressure - BBC stocker
 

Not surprised........Stock is no longer stock since 1985. I would prefer to run S/S than try to deal with these crazy cams and spring pressures of today. The pressures you are running (250/500) with .632 lift with 1.6 roller rockers is what I ran in my SS/IA 350 Camaro back in 1978 with roller lifters. Never broke a motor and ran right with Bobby Warren and Phil Hardee. Have fun !

Re: Valve Spring Pressure - BBC stocker
 

Hard to loft an intake valve on opening, it's only moved the tappet .100 or so. Now over the nose....okay, but the piston is long gone by that time. Possibly a big bounce off seat? Pushrods might change things
.

Re: Valve Spring Pressure - BBC stocker
 

Not disagreeing with what you're saying, but if the opening ramp of the intake lobe is too close to "instantly vertical" (like what roller cam guys are using these days) the lifter can actually try to dig into the lobe and create milliseconds of valve train slack (shudder), which can cause things like valve spring surge. Even the roller cam guys admit that there is only so far you can go with "snapping" the valve open and closed.

Re: Valve Spring Pressure - BBC stocker
 

Do you run with Hydrolic lifter????

How many lash you have between rochers to valves 0 or 1/4 lap

Re: Valve Spring Pressure - BBC stocker
 

Spoke to COMP today, they are claiming that the lobe is so aggressive I need to get a different spring that is going to allow me the same open pressure, but within .050” of coil bind. He claimed that the spring is most likely doing the hokey pokey since it’s about .400” from coil bind, and not designed to work there. I thought pressure was pressure, but is this something that could actually be going on and therefore causing such an issue?

Re: Valve Spring Pressure - BBC stocker
 

Probably. Horribly upset combinations can/do bounce that much. Sometimes it gets better with less spring pressure. Maybe not with this one, but it's not unusual.

Re: Valve Spring Pressure - BBC stocker
 

I think the info from Comp is accurate, but I think looking for another cam and matching springs is in order.

Re: Valve Spring Pressure - BBC stocker
 

What valves and pushrods are you using?

Re: Valve Spring Pressure - BBC stocker
 

Ferrea Competition valves (not the hollow ones as I was told they are illegal) and trend 3/8x.120 wall pushrods

Re: Valve Spring Pressure - BBC stocker
 

You answered your own question. You can't open a flat tappet with a specific diameter to the point that the lobe runs off the lifter face radius. That number is somewhat flexible depending on lifter face diameter (remember mushroom lifters?) and base circle diameter.

How far open is the valve at the point of minimal valve clearance? Is it really going to "surge" at that point in the cycle? Could it be a bounce induced from the closing cycle?

Re: Valve Spring Pressure - BBC stocker
 

Pushrods are a spring also. The rate gets altered through diameter and wall thickness.

Re: Valve Spring Pressure - BBC stocker
 

They own a Spintron, not me, but inducing spring clash is possibly a solution, probably not the most elegant....but a solution.

Re: Valve Spring Pressure - BBC stocker
 

The spring you have is to long.To have 250 on the seat your probably in at 2 in.,now subtract .400 lift your at 1.600.Coil bind is at 1.150,I can see the spring being unstable.The problem with the 325/396 is you only have.398 lift,so you have to find a short spring that would put you .50-.100 from CB.That would make it more stable.CC should have a spring that would work in those parameters.If you find one I would put it on the dyno and see if the rpm and HP go up.On your initial pulls your down quite a bit both ways.If it's still down after the change, give Bullet a call and see what they recommend for a cam.The good thing here is you didn't have the Shubeck's in it.. gsa612

Re: Valve Spring Pressure - BBC stocker
 

Correct. Same as the springs, sometimes more is actually worse. You can't know either way until you measure.

Re: Valve Spring Pressure - BBC stocker
 

Hollow stems are not illegal. According to Wesley Roberson,anyway, I've been running them ever since he told me they were legal about 8 years ago.


Your pushrods are a problem at the spring pressures you need. I suggest Trend 7/16" x 0.165" wall.


The intake is only going to hit between about 10-15 degrees BTDC and about 10-15 ATDC. After that, the piston is way out of the way.


I do not use clay to check. I check as run, complete the springs. Manley makes a tool to open the valve using the rocker arm. Check every 2 degrees between 25 degrees BTDC and 25 degrees ATDC. Your piston to valve clearance, as run, should be equal to or greater than your TOTAL piston to deck clearance. On the exhaust, you need 0.075", checked the same way.



I use the Comp 26115 spring, with the corresponding retainer and keeper.


My setup is good to over 8,000 RPM with the latest and fastest lobes Billy Godbold has designed for a big block at Comp. However, be aware that I'm using rectangle port cams, the lobes may be different. I have seen people run into trouble with the oval port stuff because it was designed for lower RPM. My stuff was all developed with the help of Billy and Tim Cole, who also did stuff for Wikle, Greene, and others. You need to talk to Billy, or at least talk to Dave McCarver and have him talk to Billy for you.

Re: Valve Spring Pressure - BBC stocker
 

Why didn’t they tell u that to behind with? To bad Tim Cole isn’t there anymore.

Re: Valve Spring Pressure - BBC stocker
 

[QUOTE=Chipper Chapman;566240]My new motor 396/325hp stocker broke a valve first weekend out (had dyno time too), upon disassembly it was found that all 8 intake valves had been making light contact, of course it was one of them that broke.

My tightest ptv clearance upon assembly ( and checking again during autopsy) was .070" which should be plenty, which leads me to believe it must have been lofting the valves open due to lack of adequate spring pressure. Springs were setup to be 250# on the seat and 500# over the nose which all recommendations said should be enough. Obviously not however. Just wondering if any of you have suggestions of what we should set it up to this time. Cam is steel core, dlc coated trend lifters, pac 1325 springs and steel retainers. Fire away with any suggestions, and thank you
who told you needed 250 on the seat? I have ran several 396/454 oval port engines with no way near that much seat or open pressure. I wou call pac and get the correct spring.

Re: Valve Spring Pressure - BBC stocker
 

[/QUOTE]I do not use clay to check. I check as run, complete the springs. Manley makes a tool to open the valve using the rocker arm. Check every 2 degrees between 25 degrees BTDC and 25 degrees ATDC. Your piston to valve clearance, as run, should be equal to or greater than your TOTAL piston to deck clearance. On the exhaust, you need 0.075", checked the same way.
Alan,
I know many people use this method for checking ptvc, but when you open the valve using the rocker arm to find the clearance you basically take all of the load off of the pushrod and lifter which doesn't account for any pushrod flex. Seems to defeat the purpose of checking the clearance in an as run situation. I do realize that the larger diameter and thicker wall pushrods would have minimal flex. Just a thought.

Re: Valve Spring Pressure - BBC stocker
 

There ya go!! ^^^^^^^
I did not know anybody used modeling clay these days.

Re: Valve Spring Pressure - BBC stocker
 

Well, by ignoring the pushrod flex, you actually end up being conservative on your clearance. If the pushrod flex reduces lift,then you actually have more clearance.


Also, you zero the dial indicator BEFORE taking each measurement, so the measurement is taken from the point of the pushrod being loaded.

Re: Valve Spring Pressure - BBC stocker
 

More the reason for stiff pushrods

Re: Valve Spring Pressure - BBC stocker
 

Keep the cam and get the right springs and pushrods.
Want to Place bets on the Peak's going higher?
The RPM peak should have told you it was unstable.
BTW check PSI for a spring, too.
I've had some good results with their springs lately.

Re: Valve Spring Pressure - BBC stocker
 

Your guides are tight when you put heat in the thing. Mic your stems then ream guides with a reamer .0025-.003.

Re: Valve Spring Pressure - BBC stocker
 

Just my 2 cents, based on personal experience.
I too, have been victim of this very same issue... difference being, I didn't learn after the first time it happened. Took two more incidents... which is why I haven't been on a track for almost 6 years.
in short
After providing my lobe number to my Comp Cams rep... his response:
"YOU CAN'T REV THAT LOBE" !
me:
"THAT'S WHAT I'VE BEEN TRYING TO TELL YOU" !

Yes, there ARE lobes that can't be controlled at RPM... "torque lobes", as they were described to me.

Re: Valve Spring Pressure - BBC stocker
 

I remember trying to work with you on that.


And that was my first thought on this thread.

Re: Valve Spring Pressure - BBC stocker
 

Yes, Alan... and you definitely DID help !
I went with spring specs you recommended, and actually designed my own intake lobe variation of what I had.
All good now, and seems to run better than it ever did.