Roller Rockers vs. Pushrod Lengths??

[60biscayne]

HI "W" Guys!! Has anyone ever encountered this problem? I am assembling a 65' 409 Truck block, with 11 to 1 pistons, 817 heads, had no problems going that far. I had bought a set (can't remember the brand name), no name on the box, of 1.75 roller rockers from Showcars for $199. Also, a note, we installed a set of hardened screw in studs, which, have a 5/8" hex on the bottom. I install stock 5/16" pushrods, long ones on the exhaust, and short ones on the intake, just like the book says. Everything looks symetrical at this point. With the engine at #1 firing position, I place both the intake and exhaust roller rockers on the studs, the exhaust rocker Just fits, the opening and chamfer in the bottom of the slot just misses the screw in stud hex, after adjusting it. On the intake, the aluminum rocker, the bottom edges of the slot interfere with the hex on the screw in stud, so much that the roller tip is at least 1/8" away from the valve stem end. Also, these are brand new SS Valves from Showcars, by the way. It appears to me that the easiest solution is to use longer pushrods. Is this a common problem when using roller rockers? Of course, Showcars didn't mention this when I was ordering them. THese are stock length valves, pushrods, the heads have only had a mild valve job, nothing has been drastically altered, to be contributing to this problem that I know of. Any suggestions?? Thanks;60 biscayne.

 

[oldskydog]

Which studs did you use? There are at least 3 different rocker studs out there depending on your application. I am in the process of building a 63 with 817 heads also. I have screw in studs but not the hex shouldered kind and I am using the stock rockers. I would bet that that is your problem. You could replace your studs with the non-shouldered type which should eliminate the interference. Also with roller rockers I think they recommend a longer stud. I'm certainly no expert so I'm sure some of the other guys will come up with the solution.

 

[mpris]

Just out of curiosity, you did machine down the rocker arm stud boss before installing the screw in studs? Right? What type of cam did you install? Solid roller, flat tappet, or Hydraulic roller? You most likely will have to change your push rod length, but they should not be off that much from what you had originally unless you went from a flat tappet to a roller tappet.

Poocho

 

[Ronnie Russell]

This is a common mistake. Poocho and Cecil are correct with their suggestions. Stud bosses must be shortened . 3/8 is a rule of thumb, or measure the shoulders and shorten the bosses that much. It sounds like Cecils suggestion is best, so you dont have to pull heads back off. Even then, you need to confirm your pushrod lenght is in the ballpark. Sorry for the bad news, its just part of the game.

 

[60biscayne]

Pushrod length

Good tips, Guys. First, I did not shorten the stud bosses. 2nd, I do not know what brand the screw in studs are, I bought them on Ebay, they are new, they are hard, but they do have this 5/8" hex on them, which is how I tightened them down. THis 5/8" hex, is what my rocker bottoms are hitting, but only on some, not all of them hit. It depends on where the hex ended up, radially, once the stud was tightened down. I did use blue Loktite on the threads. The cam I am using is a Comp Cam, something like a 280H, .520 lift, 230 degrees at .050. Hydraulic, flat tappet lifters. Just for grins, I tried a longer exhaust pushrod, on the intake, and this did work. But, that doesn't help me with the exhausts. I'd REALLY RATHER not jerk the heads back off. I now see showcars has .100 longer pushrods for $16 apiece, I think the price was. Stupid question: this is the 1st time i have ever installed screw in studs myself, If I use some without the hex, how do you tighten them down. All I can think of is temporarily double nutting them, to tighten them down, and then let the loctite do the rest. Sound right??? Sounds like it's either that or go with the longer pushrods. Thanks tons for the help. I'm open to any other suggestions. I want to do it right the first time! Brian.

 

[Fathead Racing]

Using longer pushrods on a flat tappet cam with roller rockers may throw the valvetrain geometry off enough that it will put side thrust on the valve to the point that you would have accelerated valve guide wear. The roller tip should roll across the valve head with equal margins with the roller centered at half lift. You may be able to get clearance by installing studs without the hex. Double nutting is the way to install, 50 ft lbs with thread locker. Usually with screw in studs you want to mill the boss and at the same time upgrade the valve seal. Just read Models post, stud with shoulder is what I was referring to, thank's Models.

http://www.compcams.com/information/Products/Pushrods/

 

[models916]

shorten it

The stud mount boss has to be reduced in height the thickness of the hex on the screw in stud. No other way around it. OR, there are screw in studs without the hex, just a shoulder. Jam nut them in place with loc-tite.

 

[models916]

MR Gasket

This should work for 3/8 stud.


http://store.summitracing.com/partdetail.asp?autofilter=1&part=MRG-1076&N=700+115&autoview=sku

 

[jim_ss409]

Lots of good advise here. I just thought I'd add that longer pushrods would probably work but they might cause other problems. The stud and valve aren't parallel, they get closer together at the top, so raising the rocker might push the roller tip too far outboard. As Fatride said it's best to have the roller tip centered on the valve. Changing over to screw in studs without the hex is probably the best bet. Another thing to consider is that when they grind a cam with more lift the lobes usually aren't any higher than the old lobes, they can't just add height because they'll stick up too high and won't fit in past the cam bushings. So they grind down base circle instead. It's usually not a problem but sometimes you need to compensate with a slightly longer pushrod. Like Ronnie says, "it's just part of the game" It sounds like that's going to be a really good engine.bang

 

[dq409]

Using longer pushrods on a flat tappet cam with roller rockers may throw the valvetrain geometry off enough that it will put side thrust on the valve to the point that you would have accelerated valve guide wear. The roller tip should roll across the valve head with equal margins with the roller centered at half lift.
http://www.compcams.com/information/Products/Pushrods/

I have to disagree with you on this on Ray,,, Even if the roller rockers are not rolling on the center they should not cause accelerated guide wear.
This would only be true with stock stamped style rockers.
A minor argument, but even then as you have said, the geomety is wrong and should be corrected.,,,dq

 

[models916]

from comp cams

this is optimal

 

[models916]

from Lunati

My last word.

 

[60biscayne]

Quick Reply

Tons of very valuable info, on this matter. I have several options, it seems. I'm definitely not going to play around with pushrod length, now that I've heard what can happen. I may first try different studs, and see how that works. It appears that the interference between the bottom of the rocker and the hex on the stud is only about .100 Max. THe hex is about twice that thick. HHHMMM. Now, I have some thinking to do. Thanks much to all whom added the advice, facts, and thumbnails. Brian-60 Biscayne.