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Discussion Starter · #1 ·
I just inherited a set of used SBC CompCam Roller Tip Rocker Arms (1.52 ratio). I can't tell if they were made for use with 3/8" or 7/16" studs or if it even matters. Are there any differences in the dimensions of the arm (i.e., such as the stud slot) or are they identical? If so, how can I tell what type of stud should be used with the set I have?
 

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My best advice, sling 'em over the fence. They're junk. Their design is exactly bass ackwards to what they should be, with a walking shoe tip and roller bearing trunnion, like the Chevy LS motor rockers. You'd be better off installing a set or stock Chevy rockers if you can't afford a nice set of roller rockers like Scorpions....
http://www.scorpionracingproducts.com/
 

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I just inherited a set of used SBC CompCam Roller Tip Rocker Arms (1.52 ratio). I can't tell if they were made for use with 3/8" or 7/16" studs or if it even matters.
This matters a lot, 7/16ths bored trunnion has a sixteenth inch of slop fit on a 3/8ths stud, A 3/8ths stud bore on the trunnion will not fit over a 3/8ths stud
Are there any differences in the dimensions of the arm (i.e., such as the stud slot) or are they identical?
That's a could be, but in general the 1.6 needs more clearance than the 1.5, you'll have to measure, that is standard practice.

iIf so, how can I tell what type of stud should be used with the set I have?
Use a 3/8ths or 7/16ths bolt or drill bit to see what passes to what is sloppy or won't pass through the trunnion stud hole. In the case of stamped or cast roller tip rockers with the half ball trunnion it will be the bore in the half ball that you need to match to the stud.
For screw in hex base studs the bottom thread is always 7/16ths USS (United States Standard) coarse thread. The top is fine threaded either 3/8ths SAE or 7/16ths SAE (Society of Automotive Engineers). Getting beyond the Gen I/II SBC things get metric, you have to be on watch for these changes in part dimensions and standards. GM pressed studs are 3/8ths SAE fine thread.

Bogie
 

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In general, the ratio you use has to do with head flow.

Find your heads on google or srweiss head flow database. Someone has flow tested them.

Take the lobe lift and multiply it by the rocker ratio to see valve lifts. Let's say lobe lift is .335, so your valve lift would be .502 with stock 1.5 ratio, and .509 with 1.52 ratio. If you used 1.6 ratio, it would be .536. Look at those lift numbers in the head flow chart. If your heads flow more above .500 and still flow more at .600, then higher rocker ratios would likely help a little by getting the valve open farther and getting to higher lift/flow points a bit sooner. My guess is that you have 1.5 rockers in there, so 1.52 roller tips likely won't make more than a 2 hp difference

There is a lot more research to do though. Higher ratio rockers get their ratio boost by moving the pushrod cup closer to the stud. On some heads, that means the pushrod will rub the hole coming through the head. You also need to look at your valve guides, valve spring, and retainer package to make sure it can accept more lift. In the case of stock Vortec heads, they can only take about .475-.480 lift before the retainers hit the guides.

As far as roller tip, you won't see much benefit from just roller tips. The reduction in friction on the nose isn't really enough to make any difference, and they add a tiny bit of weight which likely isn't a factor until higher RPMs than you'll be seeing. If you have the room, the real performance choice would be aluminum rollers, but they often don't fit under stock valve covers.

I can't speak to the quality of your specific Comp rockers as I have never used them. I either use stockers or full aluminum rollers
 

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My best advice, sling 'em over the fence. They're junk. Their design is exactly bass ackwards to what they should be, with a walking shoe tip and roller bearing trunnion, like the Chevy LS motor rockers. You'd be better off installing a set or stock Chevy rockers if you can't afford a nice set of roller rockers like Scorpions....
http://www.scorpionracingproducts.com/

I have to disagree on that. I had factory rockers on my BBC and they got eaten up and wore the tips of the exhaust valves real bad. That was with some pretty light springs. I didn't have money or room for full rollers and used the comp roller tips. If your spring pressure isn't really high, they work. Mine probably have 15K + miles on them. And for the last ??? thousand miles my springs went up to 141 seated and 394 open. I just had a cover off yesterday and all looked fine. That is above their rated specs a little bit.



One important thing with them is you should break them in. Go through a good rpm range for a couple minutes and shut it down to let them cool. Five or so times should be good. Then driving around town a while before hitting the highway. (I hadn't done that to mine and they survived) Also when I went to the higher spring rate, I used "Kool Nutz" or something like that. They do really seem to keep the ball cooler. Oh, I am slightly over the recommended spring pressure comp gives them and they are sill holding up


I forgot, I did have one go bad on the old heads but only one. The new one I put on an intake so it was cooler and all went well then with the Kool Nutz. You do not want to use a high pressure oil pump or it will shoot the oil over the top and miss the nuts and ball, unless you have drippers.


If they are used, hopefully the guy kept the balls and the matching arms together. If not, I'm not sure if new balls would be better than using the mixed up old ones?
 

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As to comp roller tip , 1.52 ratio rocker arms longevity , mine have been installed for 20 years/ 50k miles , valve springs are in the 100-300# range . they have been trouble free albeit a bit noisy . If you wish to throw some away ,I will give you my address ..LOL
 

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If you choose to use the 1.65:1 rocker arms, you should also spend another $120 and install a set of Comp Cams .080” wall chromoly push rods. The 1.65:1 rocker arms increase the side load on the push rods and that can bend the stock mild steel push rods like they were wet spaghetti.

Full roller rocker arms are needed when you have solid lifters and must restrict oil flow through to the push rods.,
 

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Discussion Starter · #8 ·
Thanks for the replies. I don't plan on using the arms. I was simply trying to find out if the arms are interchangeable with respect to the studs. In other words, are the arms designed to be used for both 3/8" studs and 7/16" studs or are they designed only to be used with one but not the other? If that is the case, how can you tell what studs work with the arms that I have?



As an aside, I have had a set (1.6 ratio) installed on a set of World Product Torquer heads with hydraulic lifters and a mild street cam. The setup has been running for the past 15 years. They are a bit noisy but have been trouble free. My plan is to eventually swap out the heads entirely with a pair of aluminum ones with full roller rockers.
 

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Thanks for the replies. I don't plan on using the arms. I was simply trying to find out if the arms are interchangeable with respect to the studs. In other words, are the arms designed to be used for both 3/8" studs and 7/16" studs or are they designed only to be used with one but not the other? If that is the case, how can you tell what studs work with the arms that I have?



As an aside, I have had a set (1.6 ratio) installed on a set of World Product Torquer heads with hydraulic lifters and a mild street cam. The setup has been running for the past 15 years. They are a bit noisy but have been trouble free. My plan is to eventually swap out the heads entirely with a pair of aluminum ones with full roller rockers.
Do you not have the pivot balls for these rockers??

The only difference for that style rocker would be the size of the stud hole through the pivot ball... Comp Cams doesn't sell the SBC cast roller tip ball pivot rocker for a 7/16" stud.
So those have to be 3/8" stud.

Only variation might be if someone special ordered them, and the pivot balls were interchangeable with the ones in BBC rockers....but I don't know if the OD of the ball pivot will interchange....I've never had a reason to check that.
 

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Most roller tip rocker arms i have seen have a pivot balls that is designed for 7/16” rocker arm studs and will not function correctly on 3/8” rocker arm studs. The pivot ball must be a slip fit on the rocker arm stud. There are roller tip rocker arms that have pivot balls for 3/8” rocker studs. The roller tip rocker arms serves no function because the roller tip does not roll across the valve stem tip. If the valves have been installed correctly, the tip of the rocker arm roller tip does not move across the valve tip. The rocker arm is always centered on the valve stem tip. Therefore the roller tip performs no function.

The pivot ball used with 7/16” rocker arms has a larger radius that the pivot balls used with 3/8” rocker arms. They will not interchange.
 

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Most roller tip rocker arms i have seen have a pivot balls that is designed for 7/16” rocker arm studs and will not function correctly on 3/8” rocker arm studs. The pivot ball must be a slip fit on the rocker arm stud. There are roller tip rocker arms that have pivot balls for 3/8” rocker studs. The roller tip rocker arms serves no function because the roller tip does not roll across the valve stem tip. If the valves have been installed correctly, the tip of the rocker arm roller tip does not move across the valve tip. The rocker arm is always centered on the valve stem tip. Therefore the roller tip performs no function.

The pivot ball used with 7/16” rocker arms has a larger radius that the pivot balls used with 3/8” rocker arms. They will not interchange.
SBC ball pivot rockers to fit 7/16" studs are virtually non-existent. They are the exception, not the rule.
Elgin is the only company currently making any, that I know of. Roller tip or stock tip with 7/16" stud hole ball pivots.

And this statement is complete baloney, quote: "If the valves have been installed correctly, the tip of the rocker arm roller tip does not move across the valve tip. The rocker arm is always centered on the valve stem tip. Therefore the roller tip performs no function".
 

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If a valve job is done correctly and the pushrods are the correct length, the rocker arm should be centered on the valve tip throughout the arc of motion.

Use some blueing on the valve tip to check the pattern left by the rocker arm. Doing that will determine the correct push rod length. Centering the rocker arm contact on the valve tip will eliminate the side load on the valve stem. Tight valve stem clearances is important if you have machined the valve guides .0012”I /.0025”E for PC style Teflon valve stem seals.

The engine builder I have used since 1970, uses K-Line smooth wall, phosphor-bronze valve guide liners, tight valve guide clearances, and PC Teflon valve stem seals....unless the customer insists on something different.
 

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If a valve job is done correctly and the pushrods are the correct length, the rocker arm should be centered on the valve tip throughout the arc of motion.

Use some blueing on the valve tip to check the pattern left by the rocker arm. Doing that will determine the correct push rod length. Centering the rocker arm contact on the valve tip will eliminate the side load on the valve stem. Tight valve stem clearances is important if you have machined the valve guides .0012”I /.0025”E for PC style Teflon valve stem seals.

The engine builder I have used since 1970, uses K-Line smooth wall, phosphor-bronze valve guide liners, tight valve guide clearances, and PC Teflon valve stem seals....unless the customer insists on something different.
If you've figured out how to make an arc into a straight line , I'd love to see how ??!
Mm
 

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I first started using tight valve stem clearances in 1971 when Kim Barr Racing prepared a pair of 1967 Pontiac 670 heads I was using on my 1966 GTO. . Kim Barr told me new Pontiac heads have .003”I/.004”E guide clearances from the factory. I have used Kim Barr Racing Engine and Dynometer Service in Garland Texas for all my engine preparation since 1971.

The loose valve stem clearances used by Pontiac was because the so-called engineers at the Pontiac Motor Division preferred to have Pontiac engines with more “upper cylinder lube” than most engines.
 

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"If a valve job is done correctly and the pushrods are the correct length, the rocker arm should be centered on the valve tip throughout the arc of motion."

WRONG, it will only be centered IF the rocker arm happens to have the exact correct pivot length needed for the particular build....and a lot of the aftermarket rockers don't.

"Use some blueing on the valve tip to check the pattern left by the rocker arm."

Well, at least that statement is correct

" Doing that will determine the correct push rod length."

WRONG againCentering the contact point does not establish correct pushrod length.

"Centering the rocker arm contact on the valve tip will eliminate the side load on the valve stem."

The biggest WRONG of the whole quote It does not eliminate side loading of the guide, which is the result of a wide sweep pattern
This "center the tip contact to find correct pushrod length" is the same incorrect method that has been floating around the hot rod community ever since some magazine writer hack printed it 40 some years ago, and it started with Harland Sharp getting it incorrect when he built the very first roller rocker arm and the rest of the industry unknowingly copied him.

It never was the right way, and never will be, if you use that method to establish pushrod length you can expect heavy guide wear, as it generates a wide sweep pattern and the sweep is what pushes the stem and side loads the guide.
 

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X2... We don't worry about exactly centering the rocker contact point on the valve stem, we use the "1/2 Lift" method of determining pushrod length... that gives the smallest contact patch...
 

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Most roller tip rocker arms i have seen have a pivot balls that is designed for 7/16” rocker arm studs and will not function correctly on 3/8” rocker arm studs. The pivot ball must be a slip fit on the rocker arm stud. There are roller tip rocker arms that have pivot balls for 3/8” rocker studs. The roller tip rocker arms serves no function because the roller tip does not roll across the valve stem tip. If the valves have been installed correctly, the tip of the rocker arm roller tip does not move across the valve tip. The rocker arm is always centered on the valve stem tip. Therefore the roller tip performs no function.

The pivot ball used with 7/16” rocker arms has a larger radius that the pivot balls used with 3/8” rocker arms. They will not interchange.
You say "the tip of the rocker arm roller tip does not move across the valve tip. The rocker arm is always centered on the valve stem tip "
Since the rocker tip travels in an arc , it cannot remain centered on the valve tip , the only reason I stay tuned is to try to correct dis- information. Pay attention .
 
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