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BBC Rocker Studs

General engine tech -- Drag Racing to Circle Track

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Bishop540
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BBC Rocker Studs

Post by Bishop540 » Mon Nov 04, 2019 2:25 pm

Changing my old PRW 1.8/1.7 stainless roller rockers after 1300 miles because they are wearing out and effecting my lash. The 1.8's are wearing the fastest. I am going down to a 1.7/1.7 ratio, since that is what my cam was designed for (Lunati 502A5LUN). I hear AFR has a roller rocker design made by Harland Sharp (2 different part#'s. 1 for intake and 1 for exhaust). It helps with the intake geometry problem that my 325cc AFR heads have, and I experienced when building this 540 BBC. I bought 2 rockers from HS so I could mock it up, and with my same pushrods they were close to a good center-sweep pattern on the valve tip. I have ordered new pushrods so the Midlift will be perfect -1 longer and 1 shorter. They were off about .050. Since I will need a longer pushrod on the intake (if I use the AFR 6043 rockers) it is getting real close to only having about 5-6 turns of the thread on the stud. My questions:

1) Is it ok to run the rockers on only the threaded part of the stud? This is something new that I heard this weekend. I have always done it that way but I have more spring pressure on this engine -250 seat, 600 open.

2) And how many threads on my 7/16 stud is safe with my 250/600 spring pressure and 6500 rpm redline -street engine? In the past I went with 8-9 turns minimum.

3) If I order the longer stud for the intake only (ARP 135-7202), the rocker will ride on the smooth shank and have plenty of thread-turns. But the exhaust is fine as-is and has plenty of thread-turns now, but it will ride on the threads instead of the smooth shank. Is that ok?

Thanks, as always!
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Eric

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Re: BBC Rocker Studs

Post by prairiehotrodder » Mon Nov 04, 2019 2:39 pm

what length pushrods are you using ? I've run the comp gold rockers for years with the AFR 325 and then the AFR 335 head. My current cam is .765/.731 lift so its fairly healthy. I also use the AFR stud girdle.

Last season i ran scorpion 1.8 race rockers on the intake valves with no problems.
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Bishop540
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Re: BBC Rocker Studs

Post by Bishop540 » Mon Nov 04, 2019 2:51 pm

prairiehotrodder wrote:
Mon Nov 04, 2019 2:39 pm
what length pushrods are you using ? I've run the comp gold rockers for years with the AFR 325 and then the AFR 335 head. My current cam is .765/.731 lift so its fairly healthy. I also use the AFR stud girdle.

Last season i ran scorpion 1.8 race rockers on the intake valves with no problems.
The sweep you see in the picture is my old pushrods with the new AFR rocker mock-up. They are 8.70/9.45. I had no milling on my new Dart block or AFR heads, and .027 Cometic head gasket -since my piston was .015 in the hole.

If I use the AFR rockers I will need 8.75/9.55 to get the good geometry.
Eric

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Re: BBC Rocker Studs

Post by Bishop540 » Mon Nov 04, 2019 2:56 pm

The first picture is the difference in my old PRW 1.8's and the new AFR 1.7's. I already have a problem with the new AFR rockers not fitting under my stock-like valve cover. And that was only with 2 of them installed!!!!
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Eric

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Re: BBC Rocker Studs

Post by prairiehotrodder » Mon Nov 04, 2019 3:40 pm

mine are 8.55 / 9.5. My block has been milled to get .005 deck clearance and i'm using a .039 gasket. Are you married to short valve covers ? I think the stud girdle will probably help your situation
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shoedoos
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Re: BBC Rocker Studs

Post by shoedoos » Mon Nov 04, 2019 3:45 pm

Me personally? I would not run pivot on the threaded section....

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Re: BBC Rocker Studs

Post by shoedoos » Mon Nov 04, 2019 3:47 pm

have you investigated the Miller Mid-lift rockers?

Bishop540
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Re: BBC Rocker Studs

Post by Bishop540 » Mon Nov 04, 2019 3:48 pm

prairiehotrodder wrote:
Mon Nov 04, 2019 3:40 pm
mine are 8.55 / 9.5. My block has been milled to get .005 deck clearance and i'm using a .039 gasket. Are you married to short valve covers ? I think the stud girdle will probably help your situation
My redline is 6500. If I am going to need a girdle then I am stopping here and going with shaft rockers. But I feel that is overkill for my street engine. But it would help I'm sure. Thanks!
Eric

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Re: BBC Rocker Studs

Post by ProPower engines » Tue Nov 05, 2019 1:34 am

Bishop540 wrote:
Mon Nov 04, 2019 2:25 pm
Changing my old PRW 1.8/1.7 stainless roller rockers after 1300 miles because they are wearing out and effecting my lash. The 1.8's are wearing the fastest. I am going down to a 1.7/1.7 ratio, since that is what my cam was designed for (Lunati 502A5LUN). I hear AFR has a roller rocker design made by Harland Sharp (2 different part#'s. 1 for intake and 1 for exhaust). It helps with the intake geometry problem that my 325cc AFR heads have, and I experienced when building this 540 BBC. I bought 2 rockers from HS so I could mock it up, and with my same pushrods they were close to a good center-sweep pattern on the valve tip. I have ordered new pushrods so the Midlift will be perfect -1 longer and 1 shorter. They were off about .050. Since I will need a longer pushrod on the intake (if I use the AFR 6043 rockers) it is getting real close to only having about 5-6 turns of the thread on the stud. My questions:

1) Is it ok to run the rockers on only the threaded part of the stud? This is something new that I heard this weekend. I have always done it that way but I have more spring pressure on this engine -250 seat, 600 open.

2) And how many threads on my 7/16 stud is safe with my 250/600 spring pressure and 6500 rpm redline -street engine? In the past I went with 8-9 turns minimum.

3) If I order the longer stud for the intake only (ARP 135-7202), the rocker will ride on the smooth shank and have plenty of thread-turns. But the exhaust is fine as-is and has plenty of thread-turns now, but it will ride on the threads instead of the smooth shank. Is that ok?

Thanks, as always!
If you run the rocker on the shank of the stud rather then the threaded area it may solve the tip alignment issue on the exhaust valve pictured.
Real Race Cars Don't Have Doors

Bishop540
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Re: BBC Rocker Studs

Post by Bishop540 » Wed Nov 06, 2019 9:23 am

ok. Maybe I shouldn't have given all those details and simply just asked:

1) Is it ok to run the rockers on only the threaded part of the stud?

2) And how many threads on my 7/16 stud is safe?

Thanks.
Eric

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Re: BBC Rocker Studs

Post by bobmc » Wed Nov 06, 2019 10:26 am

first I would not run 250# spring pressure on stud rockers on the street. only one way to know if it will work-try it. one thread on the stud is .050" so 10 turns on the nut is half inch-the least I would use, the higher on the stud the rocker pivot is the higher the bending force on the stud, you can put washers under the stud to raise the shank portion

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Re: BBC Rocker Studs

Post by Cobra720 » Thu Nov 07, 2019 5:26 am

I would not run the rocker on the threads, buy the correct rocker stud to get the rocker on the shank.
I would not put washers under the stud as this would weaken the engagement into the head.
250lbs. seat pressure 600lbs. nose on a stud for street use and once and a while strip is ok, I just use a good girdle. Never had a problem. I run 230/550
I would engage the thread by at least the dia. of the stud

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Re: BBC Rocker Studs

Post by 70MC » Thu Nov 07, 2019 7:16 am

In my early days of running a sbc solid roller my thread engagement into the poly lock was about 5 threads and one broke right at the 5th thread, they were 7/16 studs. I replaced all the studs and never happened again.
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Re: BBC Rocker Studs

Post by tenxal » Thu Nov 07, 2019 8:17 am

Bishop540 wrote:
Wed Nov 06, 2019 9:23 am
ok. Maybe I shouldn't have given all those details and simply just asked:

1) Is it ok to run the rockers on only the threaded part of the stud?

2) And how many threads on my 7/16 stud is safe?

Thanks.
1: Not preferred but it will work. For a few bucks, get the longer shank studs.
2: The diameter of the stud is a good minimum.

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Re: BBC Rocker Studs

Post by Bishop540 » Tue Nov 12, 2019 11:40 pm

So I have tried several different rockers to see which ones would give the best centered sweep and lift. Crower 1.7's were about .020 less lift than the others, so they are out. Comp stainless and the AFR's are seeing the best lift. All but the AFR exhaust (used on the intake) give their best lift, but comes at the expense of the roller being too outbound the center third (the AFR intake rocker's best lift is exactly the same as the exhaust but when max lift is achieved, the rocker is too far inbound -the roller tip is purposely moved in by Harland Sharp to help with the weird AFR intake valve stud position). The Comps keep needing longer pushrods for best lift and the AFR's need shorter. As it stands the AFR exhaust rocker also gives more thread count and a centered sweep, so they are first on my list. I'm just concerned that both are way off their initial Midlift geometry that I measured at first. And when I rotate the engine to half lift it is nowhere near the perfect 90 degree angle to the valve but still gives the best lift. The perfect 90 degree will happen OVER half lift.

So is this normal to give best lift outside the "perfect midlift geometry"?
Eric

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