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Chomemoly Roller Tip Rockers and Valve Spring Pressures.

Posted By: BigDaddy440

Chomemoly Roller Tip Rockers and Valve Spring Pressures. - 02/09/22 07:22 AM


Disclaimer:
This engine tech question is regarding a non-mopar engine, but could easily apply to any engine as it deals with spring pressures and matching valve train components properly.

MAIN QUESTION: How much spring pressure can a "ball / stud rocker" handle reliably without burning out?

On nearly every engine I've built over the years I've ran a true roller rocker to reduce friction, free up some power or because the spring pressures demanded it. I'm at a crossroads building a 350ci Chevy for a good friend of mine with 3/8 stud mounted rockers.
Full Trunnion Roller or a Chromemoly Roller Tip rocker?

The hydraulic roller cam isn't all that big, but it does have a fast ramp and requires stouter spring pressure to control valve operation effectively. The spring is a PAC beehive single spring that at its installed height has 145lb closed pressure and 305 open pressure at the max lift of .510" That's enough pressure that I'd never consider a factory stamped rocker to be adequate.

I'm am not questioning the performance gain of a roller tip rocker over a stamped rocker, as it's been proven to be very little, if any. Besides cost (not a factor here) the benefit in moving to a chromemoly roller tip rocker is strength (over stamped) and quieter operation (over a full roller). I'd prefer this engine to not sound like a sewing machine at low rpm as it has a fairly quiet exhaust system in place.

Back to the main question: Can a strong rocker with a ball stud design withstand 140lbs/305lbs long term? Comp Cams claims their product is intended for open spring pressures of 350lbs or less. Sounds like I have my answer, but many springs on the market with 300ish open pressures have less than 140lbs at the seat. I feel the spring pressures on this engine are very close to the limit of the ball / stud system, so I'd like to hear from others that may have experience in this area. There's plenty of stories of ball / stud rockers turning blue or "burning up" / or seizing, but more often than not, none of these people have any idea what kind of spring pressures they're running.

Input appreciated.
-Dan

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Posted By: B1MAXX

Re: Chomemoly Roller Tip Rockers and Valve Spring Pressures. - 02/09/22 12:41 PM

I used a set of those on sbc hyd roller once they turned purple in the trunnion. never failed but obviously hot. I have never used them since.To answer the question though, probably any spring pressure, I've
torn down a lot of stock chevys they all show heat in that area.Will they fail under normal conditions,no. But definitely horsepower and friction to free up.
Posted By: CSK

Re: Chomemoly Roller Tip Rockers and Valve Spring Pressures. - 02/09/22 07:33 PM

I have had many problems with that type rocker.
Posted By: Cab_Burge

Re: Chomemoly Roller Tip Rockers and Valve Spring Pressures. - 02/09/22 08:09 PM

You can do a lot more damage to the valvetrain with too little seat pressure than you can with too much twocents
I started setting my seat pressures at 140 Lbs.+ many years ago on all my flat tappet engine builds after talking to several of the cam company engineers, they said up to 175 lbs. seat pressure won't affect their hydraulic or solid lifters up
To little seat and open pressure will allow the lifter to bounce and skip on the lobes at the upper RPM shock tsk
Posted By: BigDaddy440

Re: Chomemoly Roller Tip Rockers and Valve Spring Pressures. - 02/10/22 05:26 AM


Cab,

I totally agree with everything you said and I'm confident that my spring pressures are sufficient for the camshaft especially given the RPM range of this camshaft. My concern is the spring pressures on the ball & pivot style rocker, not the lifters themselves. I do appreciate you input and wide range of engine knowledge, I read your comments here often. I'm just wanting to know if I can get away with a quieter fulcrum system at the expensive of a little power.
Posted By: BigDaddy440

Re: Chomemoly Roller Tip Rockers and Valve Spring Pressures. - 02/10/22 05:27 AM

Thank you for comments and shared experiences guys.
Posted By: Cab_Burge

Re: Chomemoly Roller Tip Rockers and Valve Spring Pressures. - 02/10/22 06:36 AM

i have no real knowledge on what works good on those type of rocker arms, sorry blush
I'm sure the open pressures are the most strain on any contact point so I wouldn't worry about raising the seat pressures some up
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